An all female fish (freshwater) species called the Amazon molly that inhabits rivers and creeks along the Texas-Mexico border is living proof that sexual reproduction may be vastly over-rated according to WASHINGTON (Reuters).
Meanwhile, Female fish can breed a new species if they aren’t choosy about who is Mr. Right. Fish will mate with a species outside their own if the male’s coloring is attractive enough or if the female can’t see him properly, according to new research. Such ‘mistakes’ in mate choice can lead to the evolution of new species, an international team of scientists found after they analyzed the DNA of more than 400 cichlid fish.
In many animal species, females are expected to choose mates according to criteria that are relevant to their own fitness. Direct benefits obtained from adaptive mate choice include material resources provided by the male, as well as brood care and protection, which can increase the female’s present and lifetime fecundity. Indirect benefits for the female are derived from high fitness of her offspring, to which the male contributes genes and parental investment.
Trade-offs between direct and indirect benefits have been identified in several species, but positive correlations are also possible, for example, if the genetic quality of a male also benefits a female mate directly. If males require certain resources such as territories or nest sites for mating, male–male competition can narrow the pool of candidate mates to competitive individuals and thus can facilitate female choice.
One prerequisite of intensive fish culture technology is to have healthy fish seed in the required amount available. This can be realized only with preliminary propagation planning. Besides natural and semi-artificial propagation, artificial propagation carried out in a well-equipped hatchery is the up-to-date way in which the necessary quantity of fry can be produced.
1.1 Culture and Management of Brood Stock
A basic precondition of fish propagation is to have sexually mature male and female fish producing milt and eggs. Breeders of fish species which cannot be cultured or kept domestically, are collected before spawning from rivers or lakes, their milt or eggs are stripped and then they are released again. These species are sturgeons (mullets) mugils (Mugilidae), and salmonids (Salmonidae).
The brood stock of cultured fish species are sorted out with aimed selection and cultured in fish ponds up to sexual maturity. The males and females of breeders are cultured in the same fish pond while they are young. Then, when sexually mature they are selected and cultured in separate fish ponds.
1.2 Environmental Conditions for Culturing Breeders
When culturing breeders, the following environmental conditions should be ensured considering the specific demands of the respective species: – suitable water and pond
– feed light/photoperiod
During culturing of breeders, the water quality should meet the same requirement as during routine fish culture.
For species with preference for still water (e.g. cyprinids, catfish, tilapia) earthen or concrete-walled fish ponds should be constructed. For rheophyl species (e.g. trout) flow-through systems, canals, or tanks with circulating water should be provided.
The temperature, as an environmental factor, has an important role in fish culture. Fish are a polikilotherm animal, which means that their body temperature follows the surrounding temperature, but in case of increased muscular work and metabolism it can be somewhat higher.
Fish can be warm water or cold water species
Cold water fish are salmonids and trout. Their optimal temperature range is 10-16°C and their oxygen demand is high.
Warmwater fish are the cyprinids like common carp, Chinese carp, Indian carps and from other families the tilapia, milkfish, mullet and the American catfish. Their optimal temperature range is 18-26°C.
There are some species “in-between”, they reproduce in cold water, but later can live in warm waters too. Such are pike and pike-perch. The development can be greatly influenced by water temperature. Feeding at low temperature can be normal, but the conversion of the feed, and consequently the growth, especially sexual maturation can be considerably slower. The duration of sexual maturation also depends, first of all, on the environmental temperature, with most fish species, thus there is a characteristic total temperature value for each species which is necessary for gametogenesis.
In the case of carp, from hatching to the first reproduction, 10-12 000 degree days of heat is necessary. This quantity of heat under a tropical climate is ensured in l-l.5 years while in Middle Europe in 3.5-4 years.
1 600-2 000 degree days is necessary in the proper temperature range for the oogenesis of matured carps between two propagations. If the temperature is lower than that, considering the days with temperature higher than 17°C only, it is 2 500-2 700 degree days. The minimum temperature which is necessary for propagation of carps is 17°C, below this value the gametogenesis is very slow.
Optimal oxygen content of water is very important especially in active cytogenetic processes. Development of gametes and complete conversion of feed are all oxygen consuming processes. In case of oxygen deficiency the gematogenesis slows down, development is inhibited and if it is prolonged the resorption of gametes starts. Therefore, the proper oxygen supply is a crucial point of brood stock culture.
Feeding of breeders, especially in the nutriment accumulating phase of oogenesis requires feed of specific composition. Amino acids, carbohydrates, fats, vitamins, and minerals are available for the fish via natural feeding. But at high stocking density under controlled culturing conditions these must be provided through artificial feed. It is also important that the breeders can get the type of feed characteristic of their species, i.e. herbivorous fish should get nutriment of plant origin, and carnivorous should get nutriment of animal origin.
Light/photoperiod has a significant role in the reproductive processes of several fish species.
Stress factors, and the sensitivity of the cultured breeders to these factors also should be kept in mind. Handling, transportation, enclosure which all differ from their normal lives, are stress inducing factors, and may affect their condition.
This may hinder the last phase of maturation and ovulation. Therefore, conditions should be established for the breeders where all these stress factors can be minimized. – Stocking density must be optimal, thus ensuring a supply of natural food; – Water supply, flow rate, temperature and oxygen content should meet the requirements of the fish; – Breeders during spawning are kept in smaller size fish ponds or concrete tanks.
Their filling or draining should be efficient since the fish must be caught very often; – Breeders can be transported in tanks only, maintaining the proper oxygen content by spraying liquid oxygen; – case of timid fish (e.g. Chinese carps) sedatives can be added to the water; – When handling is necessary, the seine can be applied.
Manual transportation of fish needs skill, so well-trained fishermen should do it. If the breeder with eggs is dropped it may lose the eggs, the ovary inflames and in most cases the fish dies.
The Artificial Propagation of Cultivated Fish Species
2.1 Common carp
|Species:||Common carp (Cyprinus carpio L.)|
|Origin:||China, South Asia, Europe|
|Natural habitat:||Rivers, lakes, fish ponds|
|Feeding and nutrition:||Zooplankton, water insects and their larvae, bottom inhabiting organisms, grains and granular and pellet foods|
Weight, at age intervals: (Europe only)
|1||20 – 100|
|2||200 – 500|
|3||800 – 2 500|
|4||3 000 – 4 000|
|5||4 000 – 5 000|
In a natural environment, the fish spawn in groups, in lakes and slow moving rivers, at a water temperature of 18 to 22°C. The egg attaches itself to vegetation and hatches within three days. In extensive cultivation they are spawned in small ponds. Methods of modern artificial propagation were developed by Woynárovich (Hungary).
2.1.2 Economic characterization
– Rapid growth
– High degree of fecundity
– High meat quality, though containing intermuscular bone
– Very suitable to warmwater polyculture Good sport fish.
2.1.3 Artificial propagation
Rearing and keeping of the brood stock: the young brood stock is selected from the offspring of parents of known quality.
The selection criteria are: – Rapid growth
– Good viability
– High food conversion rate
– Low fat content
– Resistance to disease.
The brood stock is reared in individual ponds, segregating male and female. The stocking density of the rearing ponds is 500 to 1 000 adults per hectare.
Feed is an artificial pellet, containing 20 to 25 percent of protein, of which 15 to 18 percent is animal protein; fats 3 to 4 percent; vitamin premix 2 percent; mineral pre-mix 1 percent. Vitamins A and E are critical. For two months prior to propagation the daily feed should contain 5 to 10 percent of raw ground meat or hard boiled eggs. Feed quantity is 2 to 5 percent of body weight, per day.
Sexually mature fish measure 35 to 70 cm and weigh 2 500 to 10 000 g.
The fish achieve sexual maturity in Europe: female 3 to 4 years, male 2 to 3 years. In tropical climates: female 1 to 2 years, male 1 year.
The female has a large belly. The male, if lightly squeezed around the belly will emit white milt.
Handling of the spawners: – The spawners should be moved into the hatchery one day prior to propagation; – The spawners should be transported in containers made of inorganic, non metallic materials; – The male and female spawners should continue to be segregated in the hatchery, in plastic or concrete tanks; – Space requirement is 0.5 to 1m2/adult; – Tanks should be 5 to 10 m2, 1 to 1.2 m deep; – Water quantity required is 4 to 6 litres, per fish, per minute; – Oxygen content of the water should be 6 to 8 mg/l; – Water temperature should be 20 to 22°C; – Prior to handling, the fish may be tranquilized; – The tranquilizer recommended is MS 222 (Sandoz), in a 1:10 000 dilution; – After 5 to 10 minutes in the above solution, the fish should be moved into fresh water of high oxygen content, otherwise they will perish.
Hypophysation: – To induce ovulation in the female and milt production in the male, hormone of the carp’s pituitary gland is used; – The dosage used in the hypophysation of the female is 4 to 4.5 mg per kg of body weight; – The dosage for the male is 3 mg per kg of body weight; – The dried pituitary gland is pulverized and dissolved in a 0.65 percent solution of salt (NaCl); – 2 ml salt solution per fish is used; – The hypophysation of the female should be done in two stages; – Ten percent of the dosage is given 24 hours before the removal of eggs; – 90 percent of the dosage is given 12 to 14 hours prior to the removal of eggs, if the water temperature is 21 to 22°C (240-260 degree hours); – The injection is done with a fine needle, into the muscle of the back; – Prior to withdrawal of the needle, the locus of the injection is lightly massaged, in order to avoid leakage of the solution injected; – Concurrent with the second injection, the opening of the oviduct is sewn up to prevent the loss of mature eggs during the period of ovulation; – The suture is done with surgical implements; – The male is to be injected 24 hours prior to the desired time of milt discharge; – It is imperative that the fish in the hatchery have absolutely quiet surroundings.
The removal of eggs and milt, fertilization – One hour prior to removal of the eggs, one or two males are placed among the females; – At the onset of ovulation, the male and female fish will swim along side one another, flapping forcefully; – One half hour should elapse to assure that the full quantity of eggs will have detached itself from the walls of the ovary; – After this time, the female fish are tranquilized; – The sutures are removed from the opening of the oviduct; – The belly of the fish should be wiped dry with a cloth, to prevent wetting the eggs which will rapidly lose their fertility if mixed with water; – The eggs are released into 2 litre plastic dishes; if necessary, light pressure may be applied to the belly to make the roe flow out; – The milt is pressed out of the male with light pressure into test tubes; – The eggs should be fertilized immediately upon their removal from the female; – Ten to twenty ml milt is used to one litre of eggs; – Each batch of eggs should be fertilized with milt from no less than three males, since the sperm of any male may occasionally be inactive; – The eggs and milt are thoroughly mixed (without the addition of any water), so that all eggs are reached by the milt; – The mixing should be done with a plastic spoon; – Fertilization is promoted by the use of a fertilizing solution; – The ingredients of the solution are: water, 1 litre
salt, 4 grams
urea, 3 grams (CO/NH2/2) – Temperature of the solution should be 20 to 22°C; – The fertilizing solution has a two-fold effect, it prevents the adhesion of the eggs and it activates the sperm; – 100 ml of the solution is added to 1 litre of roe and immediately mixed with it; – The mixing action should be continuous; – At two minute intervals, another 100 ml of the solution is added to the mixture; – After ten minutes, the fertilizing solution is poured off; – Fresh fertilizing solution is added, 2 litre solution to 1 litre of eggs; – The eggs, together with the fertilizing solution, are then poured into a plastic container of 15 to 20 litre capacity; – The eggs will swell to 4 to 5 times their original volume within one hour; – For one hour, the fertilizing solution should be exchanged at ten minute intervals, in order to continue to dissolve and remove the adhesive of the eggs; – Mixing should be done intermittently and gently whether manually or mechanically; – After one hour of the above process the eggs should be treated with a tannic acid solution, in order to dissolve the adhesives coagulated during the previous treatment and still present on the surface of the eggs; – The tannic solution consists of 1.5 gram tannin dissolved in 1 litre water; – Treatment with the tannic solution is preceded by pouring off the fertilizing solution; – One to two litres of tannic solution is added to the eggs and immediately mixed in; – After ten seconds, water is added to dilute the tannic solution; – The solution is then immediately poured off; – The eggs should then be rinsed 3 or 4 times with ample quantities of water; – After rinsing the eggs are placed in hatching jars.
Hatching: – Water temperature during hatching should be 20 to 22°C; – One litre of hatching jar volume is needed for each 20 000 eggs; – The volume of 20 000 swollen eggs is 200 ml; – The eggs are a risky process, since the segmentation of the ovum is already started and strong jolting will destroy it; – The eggs are placed in the water-filled hatching jar with the aid of a funnel, which is equipped with a length of hose, to assure that they will exit from it under water; – In the first ten hours, the hatching jar is to have a moderate flow of water: assuming a 10 litre jar, the rate would be 0.8 to 1 l/min; – After ten hours, the flow should be increased, since the oxygen need of the ova is on the rise, to a rate of 1.5 to 2.5 l/min; – The eggs will be drifting loosely on the bottom of the hatching jar; – Four to five hours prior to hatching, the embryos’ need of oxygen is considerable, therefore, the flow rate should be increased to 2.5 to 3 l/min.; – On the second day of the hatching process, the eggs should be treated with malachite green to prevent the generation of fungus; – Malachite green is added to the water in the hatching jar in a quantity to give a 1:200 000 solution; – Let the solution stand for 5 minutes; – After 5 minutes, the water flow is restored and the malachite solution will thereby be slowly washed out; – Hatching of the larvae may be expected on the third day; – After the first few larvae have hatched, the process should be artificially accelerated; – This is accomplished by shutting off the flow of water for 10 minutes. The lack of oxygen agitates the embryos, and due to their movements the shell will split; – After 10 minutes, the water flow is restored and hatching will start on a large scale; – The hatched larvae are transferred, together with the water, into larvae containers.
Maintenance of the larvae: – The implements used in the maintenance of larvae may be any one of the following: 1. Cylindrical containers, conical at the lower end, of 50 to 150 litre capacity, of glass, plastic or fibreglass, 2. Circular flow raceways of concrete or plastic, 3. Cages made of nylon cloth (screen). 1. Cylinders – In the containers 2 000 larvae per litre of water can be maintained; – Water should enter at the bottom and flow out at the top of the container; – The area of the overflow screen should be 10 cm2/litre of capacity; – The flow rate should be such that the larvae are kept in suspension but not washed onto the overflow screen; – The screen should be cleaned at intervals, as it will be stopped up with remains of shells; – The larvae are kept in these containers only until their first intake of feed (3 to 4 days), after which they are transferred to rearing ponds; – The above process is the most up-to-date and most hygienic method of keeping the larvae. 2. Raceways – The raceways, of plastic or concrete, should be of 1 to 2 m3 capacity, the depth being 60 to 80 cm; – Water enters the raceway through perforated tubes placed vertically at two opposite sides, to assure a circular flow; – The rate of flow should be such that it produces a constant slow motion of the water; – The overflow tube is placed in the centre, vertically; – The overflow screen, of nylon, should have 0.8 mm openings; – Surface area of the screen should be 8 to 10 cm2/litre of flow; – The oxygen content of the water is increased by surface spraying; – The raceway should be stocked at the rate of 1 000 hatchlings per litre of water; – The advantage of this method is that the larvae can be kept for several days beyond the first feeding, if suitable nourishment can be assured. 3. Cages – Size: 70×40×30 cm; – Frame: aluminium or plastic tubing; – Screening: of nylon, 0.8 mm opening; – The cages are kept in plastic or concrete tanks; – An upward flow of water through the cages is needed which keeps the larvae in motion; – This is effected by laying tubing, perforated at the top, on the tank bottom; – The bottom of the cage should be cleaned the day after hatching to remove shells and unhatched larvae, which will start to decompose thus causing oxygen deficiency; – The bottom and sides of the cage should be cleaned with a brush from the outside at 6-hour intervals in order to assure free passage of water into the cage; – The rate of flow in the tanks should be 4 to 5 l/min/cage; – To increase the oxygen content of the water, a fine surface spraying should be used.
Feeding and transportation of the brood: – The mouth and gills of the carp larva develop in 3 to 4 days; – The carp’s larval stage ends with the first intake of food, at this point it becomes fry; – At this stage the yolk sac will have been largely absorbed; – At this point the hatchlings will rise to the surface of the water, fill the swimming bladders with air and begin to swim horizontally; – At this time the first feeding is given; – The feed is yolk of hard boiled egg (hen’s or duck’s egg) mixed in a blender with water; – 100 ml water per one yolk is used; – One to two ml per 100 000 fish is given at 2-hour intervals; – As soon as the hatchlings begin to feed, they should be transferred to ponds; – The 4-day old feeding fry are transported in plastic bags containing water and oxygen; – In 20 litres water plus 30 litres oxygen, at 20°C water temperature, 100 000 brood may be kept up to 5 hours; at 15°C, 200 000 brood may be kept up to 5 hours; – If chilled for transport, the temperature of brood and water should be lowered gradually; – The plastic bags, when filled, should be as firm as well filled balloons; – The bags must be well tied, to prevent escape of the oxygen; – To avoid rupture, the bags should be placed in cardboard boxes; – The 4-day old larva measure 6 to 7 mm in length.
Biological and technical data: – The sexually mature fish measure 35 to 70 cm, and weigh 2 500 to 10 000 g; – The period of propagation in Europe is May through July; – Optimum water temperature is 20 to 22°C; – Optimum male to female sex ratio is 1:1; – 70 to 80 percent of the females subjected to hypophysation may be expected to produce eggs; – Quantity of eggs per female will vary from 200 000 to 1 500 000; – Quantity of eggs by body weight of female is 100 000 to 200 000/kg; – Quantity of eggs by weight is 500 to 1 000 g dry; – Milt production is 10 to 20 ml per male; – Fertilization of 1 000 g of eggs requires 10 to 15 ml milt; – Dry size of the egg is 1.0 to 1.5 mm diameter, in the swollen state 2.0 to 2.5 mm; – Count of dry eggs per kg is 700 000 to 1 000 000; – Count of swollen eggs per litre is 80 000 to 120 000; – Quantity of eggs to be placed in a 10 litre hatching jar: 150 to 250 g dry, or 1.5 to 2.5 litre swollen eggs; – Fertility rate of the eggs is 80 to 95 percent; – Time required for hatching in the hatching jar is 3.0 to 3.5 days (60 to 70 degree days); – Successful hatching of 90 to 95 percent of the fertile eggs may be expected; – Time span of the larval stage is 3 to 4 days (60 to 70 degree days); – Survival rate of the hatched larvae to the first feeding is 90 to 95 percent; – 1 kg of dry eggs will produce 600 000 to 800 000 four-day old brood: – Larva containers are stocked at the rate of 2 000 larvae/litre; – Four-day old fry measure 6 to 7 mm in length; – First feeding will occur within 3 to 4 days of hatching; – Size of the fish feed should be 50 to 150 micron; – Area of the rearing pond is 500 to 10 000 m2; – Density of stocking should be 200 to 500 per m2; – Transportation of the four-day old fry: in 20 litres water plus 30 litres oxygen, at 20°C water temperature, 100 000 fry may be kept up to 5 hours; at 15°C 200 000 fry may be kept up to 5 hours.
2.2 Chinese Herbivorous Fishes
|Silver Carp (Hypophthalmichthys molitrix Val.)(SC)|
|Bighead Carp(Aristichthys nobilis)|
|Grass Carp (Ctenopharyngodon idella Val.) (GC)|
|Natural habitat:||Large rivers, warm water, lakes, fish ponds|
|Feeding and nutrition:|
|Silver Carp (SC)||phytoplankton diet|
|Bighead Carp (BC)||zooplankton diet|
|Grass Carp (GC)||aquatic macrophyte diet|
Size at ages in grams
|1||10 – 15||15 – 30||10 – 20|
|2||100 – 200||150 – 300||150 – 250|
|3||500 – 800||800 – 1 500||800 – 1 500|
|4||1 500 – 2 000||3 000 – 4 000||2 500 – 3 000|
|5||3 000 – 4 000||5 000 – 6 000||4 500 – 5 000|
|6||4 500 – 5 000||7 000 – 8 000||6 000 – 7 000|
– In slowly flowing warm rivers they spawn in groups;
– In cultured conditions, spawning occurs only artificially;
– Spawning temperature, 22-26°C;
– The eggs are pelagic.
2.2.2 Economic characterization
– Good quality of meat;
– Good sport fishing (GC)
– In polyculture they utilize the primary and secondary production of the water directly;
– GC controls the macrophytes in lakes and channels.
2.2.3 Artificial propagation
– Keep the stock material in a special pond; – Stocking rate per hectare (ha)
|Cc||100||(common carp or any kind of bottom cultivator and artificially fed fish)|
Age by spawning in years
2.2.4 Sexual differentiation
The first hard rays of the pectoral fins of the male are sharp while those of the female are smooth.
2.2.5 Handling of spawners
– The following tranquilizers have been used successfully to prevent active moving and jumping.
|MS 222 (Sandoz)x||1 to 10 000 – 1 to 40 000|
|Quinaldinexx||1 to 100 000|
x MS 222 can be obtained from: Sandoz Ltd. CH-4002 Basle, Switzerland
xx Quinaldine (2-methyl-quinoline) in pharmacy. – After 5 to 10 minutes of rest, put the fish into the fresh water to be refreshed;
– Move the spawning fish carefully by using plastic stretchers.
– For the induced ovulation of the eggs and milt we use the pituitary gland of carp dissolved in 0.65% NaCl solution; – Calculate the dose of dry hypophysis on the basis of a maximum outline of the body, by females, circumference:
|below 50 cm||4 mg/kg|
|50 – 60 cm||4.5 mg/kg|
|over 60 cm||5 mg/kg|
– The dose of the males is 2 mg/kg.
Time of injection – Female dosage – the first dose, which is 10% of the total, is injected 24 hours before spawning. The second dose, which is 90% of the total, is injected 9 to 11 hours before spawning or 200-220 degree hours. – Male dosage – the total doses are given 24 hours before spawning.
2.2.7 Keeping injected fish in the hatchery
– The injected females and males are together in a plastic or concrete raceway;
– The size of raceway: 20-50 square metres, 1 to 1.5 metres deep;
– Necessary surface: 1.5 square metres per fish;
– Running water: 4 to 6 litres per minute per fish;
– Water temperature: 22 to 26°C;
– Ovulation period: 9 to 11 hours after the second injection, or 200 to 220 degree hours.
Important: Room must be kept quiet.
2.2.8 Procurement of eggs and milt
– At spawning time, we narcotize the fish;
– Collect the eggs in a plastic dish and the milt in a glass test tube.
2.2.9 Fertilization of eggs
Important: After taking the eggs, fertilize immediately. – 1 litre of eggs per 10 ml of milt;
– Mix the eggs and milt together carefully in dry conditions (not with water);
– Mix continuously, but carefully, 1 litre eggs and milt mixture and 0.1 litre pure pond water;
– Two minutes later, add an additional 0.1 litre water and mix;
– After 5 minutes rinse the eggs several times with water;
– Ten minutes later, after fertilization, put the eggs into a spawning jar.
2.2.10 The ripening, attending and hatching of the eggs
– For a 1-litre spawning jar, use 5 mls dry eggs; – The measurement of hatching glasses are 8 to 10 litres or 50 litres, transparent plastic or glass; – The water requirement of 10-litre size spawning jars during the first 10 hours is 0.2 to 0.3 litres per minute, after 10 hours – 0.5 to 0.8 litres per minute, and during the hatching period – 1 to 1.2 litres per minute; – The swelling of the eggs will be complete after 1 to 2 hours; – The diameter of the swelled eggs is 4 to 5 mm; – If the eggs hatch out before the predicted time, and the fry are premature because of bacteria, we use formalin in the water, 1 to 5 000 or 1 to 10 000 every 5 hours; – Hatching occurs 24 to 32 hours after fertilization if the water temperature is 22 to 26°C.
2.2.11 Keeping the larvae
– After hatching, the larvae leave the spawning jars and are collected; – The collectors used most commonly are large Zuger glasses (50 – 200 litres glass or plastic) or raceways 1-2 cubic metres in size, plastic or concrete – The screen of the overflow should have a 0.8 – 0.9 mm mesh nylon filter; – Security filter surface – 10 square cm per litre; – Stocking density in the larva rearing tanks should be 1 000 per litre; – Keep continuously running water in the rearing tanks; – Keep larvae in the tanks for four to five days; – During this time, the mouth and gill are developed and the larva fills up swimming bladder with air; – At this stage, the larvae can be fed boiled egg yolk suspended in the water Use a dose of 1 ml per 100 000 fish per two-hour period; – If the larvae are able to eat, put them in the rearing pond.
2.2.12 Biological and technological data spawning ages in years
– The size of mature fish
|SC||40 – 60||3 – 4|
|BC||70 – 80||8 – 10|
|GC||60 – 70||5 – 6|
– The reproduction season is May to July when temperatures are 20 – 26°C;
– The sex ratio by propagation is female:male = 1: 1;
– Expected percentage of spawners which produce eggs after hypophysation is 70-90%;
– Number of eggs produced is 60 000 – 80 000 per kg of body weight;
– Weight and number of eggs obtained from one female:
|Weight in grams||No. of eggs|
|SC||700 – 800||200 000 – 1 500 000|
|BC||800 – 1 300||200 000 – 1 200 000|
|GC||500 – 1 000||200 000 – 1 500 000|
– Quantity of sperm obtained from one male after hypophysation is 10 – 20 ml;
– The necessary ratio of milt to eggs is 10 ml milt per 1 000 g dry eggs;
– The diameter of eggs, mm
|SC||0.7 – 1.0||3.7 – 5.3|
|BC||1.0 – 1.1||3.7 – 5.3|
|GC||0.9 – 1.2||3.7 – 5.3|
– The number of dry eggs per litre is:
|SC||900 000 – 1 100 000|
|BC||600 000 – 800 000|
|GC||800 000 – 900 000|
– The number of swelled eggs per litre is:
|SC||18 000 – 22 000|
|BC||12 000 – 16 000|
|GC||16 000 – 18 000|
– Stocking density of spawning jars:
|dry eggs||5 g/l|
|swollen eggs||0.25 g/l|
– Fecundity of eggs: 75 – 95 %;
– Development of eggs in spawning jar: 24-36 hours at 20-25°C;
– Hatching ratio of the fertilized eggs: 80-90%;
– The time span from hatching to first feeding of larvae: 3-4 days, 60-70 degree days;
– Expected production for four days: 400 000 – 600 000 larvae from 1 kg dry eggs;
– The larvae begin to eat when they reach a size of 6-7 mm;
– The measurement of first food: 50-300 m;
– The time of first feeding after hatching: 3-4 days.
2.3 European Catfish
|Species:||European catfish (Sheatfish, Silurus glanis L.)|
|Origin:||a typically European species|
|Natural habitat:||Rivers, lakes, artificial ponds|
|Feeding:||carnivorous predator, will also eat carrion. Well suited to artificial feeds|
Weight, at age intervals:
|1||20 – 100|
|2||200 – 400|
|3||500 – 2 000|
|4||3 000 – 4 000|
|5||5 000 – 6 000|
|6||7 000 – 10 000|
In natural circumstances the fish uncover the roots of aquatic vegetation, depositing the eggs among these roots. The eggs cohere into a lump. After hatching, the larvae remain hidden here. Six to eight days later, the fry emerge swimming and depart in search of food.
In rearing ponds, they spawn on “artificial nests”, which are then removed to the hatchery. May be artificially propagated in hatcheries.
Required temperature for reproduction: 22 – 24°C.
2.3.2 Economic characterization
– Rapid growth;
– Good quality meat, with no intramuscular bone;
– Eats undesirable small fish;
– Good sport fish;
– Well suited to polyculture.
2.3.3 Artificial propagation
– The brood stock is kept in individual ponds of their own; – Space requirement is 1-2 m2/fish; – The fish is small, inhabiting the same ponds; – The ponds must always contain prey amounting to 20 to 30 percent of the brood stock in weight; – The brood stock must be disinfected at six-month intervals as protection against parasites; – Sexually mature fish weigh 3 000 to 15 000 g; – Age at which sexual maturity is achieved: male 3 to 4 years, female 4 to 5 years; – One month before propagation, the males and females should be separated and placed in segregated ponds.
Distinguishing sexual characteristics: – The frontal portion of the head, about the mouth, is angular in the male, while rotund in the female;
– The genital papilla of the male is pointed, that of the female blunt and rounded.
Hypophysation: – As a reaction to the hormone, the catfish become extremely irritable and will bite one another; to prevent this, the mouth is sewn shut with a single stitch, using a sturdy, straight needle; – To induce ovulation of both egg and milt, hypophysation (with carp’s pituitaty gland) is used; – The dry, pulverized pituitary gland is dissolved in a 0.65 percent saline solution; – 2 ml/fish is used of the solution; – The hypophysis dosage required to induce ovulation is 4 to 5 mg/kg of body weight for the female, 3 to 4 mg/kg of body weight for the male; – Hypophysation should be done 24 hours prior to the removal of eggs/milt, at water temperature of 22 to 24°C (200-220 degree hours); – After the injection, the brood stock is kept in tanks in the hatchery, segregating males and females; – Constant water flow and high oxygen content, with the addition of air or oxygen, should be maintained in the tanks; – The tanks should be covered, since the fish will be calmer in the dark.
The removal of eggs and milt, fertilization: – From hypophysation to ovulation 220 degree hours are required. Hourly temperature readings are taken in the tank housing the females, when 220 degree hours is achieved, ovulation can be expected; – At this point both females and males are tranquilized; – The tranquilizer used is MS222, in a 1:10 000 concentration; – The belly of the female should be wiped dry using a cloth to avoid wetting the eggs; – Using slight pressure, the eggs are easily expressed and collected into plastic dishes of 1 to 2 litre capacity; – If hatching jars of 10 litre capacity are to be used, 100 to 200 g of eggs should be collected into each dish, this being the quantity to be placed into the hatching jars; – 1 000 g of eggs (dry) require 10 to 20 ml of milt; – The eggs and milt are mixed dry, then 20 to 30 ml of water is added; – The eggs and water solution should be mixed for five minutes in the dish before placement into the hatching jars; – The eggs should be poured into the hatching jar while the jar is being rotated in such a fashion that the eggs floating in the solution will deposit themselves in a fairly uniform layer onto the interior surface of the jar and adhere thereto; – No more than one or two layers should be thus adhered, since deeper layering would cause oxygen deprivation, resulting in the demise of large quantities of eggs; – The eggs are 4 to 5 mm in diameter; – After placement of the eggs, the jars are put on their racks, and water flow is established.
Hatching: – An uninterrupted water flow, of 1.5 to 2 litres/minute should be maintained in the hatching jars; – To prevent the generation of fungus, the eggs are rinsed once or twice daily with a 1:200 000 solution of malachite green for five minutes; – Hatching may be expected on the third day, if the water temperature is 22 to 24°C, 50 to 60 degree days being required for the complete development of the embryo; – The hatched larvae should be drained from the hatching jars with the aid of a rubber tube and placed into holding cages; – The larvae are yellow in colour and are 8 to 9 mm in length.
Keeping of the larvae: – The larvae are kept in cages of 0.8 to 0.9 mm nylon mesh, the dimensions of the cage being 70 × 40 × 30 cm; – The cages should be stocked at the rate of 300 to 400 larvae per litre; – The cages are placed in tanks with flowing water; – Water temperature should be 22 to 24°C; – The larvae will begin feeding on the fourth day; – The first pigmentation spots appear on them about this time; – The first feed given the larvae is zooplankton or finely chopped tubifex (mud inhabiting worms).
Biological and technical data: – Age at sexual maturity: male – 3 to 4 years, female – 4 to 5 years; – Sexually mature fish measure 50 to 70 cm; – The spawning season is May to June; – Water temperature required for spawning: 22 to 24°C; – Optimum male to female sex ratio is 2:1 for artificial propagation; – The effectiveness of hypophysation of the female is 80 to 90 percent; – Quantity of eggs per female: 40 000 to 120 000 or 200 to 600 g dry weight; – Quantity of eggs by body weight of the female: 20 000-30 000/kg; – Quantity of milt per male, with hypophysation: 5 to 10 ml; – Fertilization of 1 000 g of eggs requires 10 to 20 ml of milt; – Dry size of eggs: 1.5 to 2.0 mm, swollen: 4 to 5 mm; – Count of dry eggs per kg: 180 000 to 220 000; – Count of swollen eggs per litre: 30 000 to 50 000; – Stocking density of hatching jars: dry eggs, 20 mg/l, swollen eggs, 100 ml/l; – Fertility rate of the eggs is 70 to 90 percent; – Time required for hatching in hatching jars: 2.5 to 3 days (50 to 60 degree days); – Hatching ratio of fertile eggs is 70 to 80 percent; – Time span of the larval stage is 4 to 5 days (70 to 100 degree days); – Survival rate of the larvae (to the first feeding) is 60 to 80 percent; – Size of fry at first feeding: 9 to 10 mm; – Size of the first feed is 200 to 500 micron; – First feeding will occur 4 to 5 days after hatching; – Raceways used are of 100 to 200 litre capacity; – Stocking density of the raceways is 50 to 100 fry/litre; – Rearing period in the raceway: 15 to 20 days; – Optimum rearing temperature: 24°C; – Size of the 15 to 20 day old fry: 20 to 30 mm; – Size of feed at 15 to 20 days: 1 to 2 mm; – Survival rate of the fry through the rearing period: 90 to 95 percent; – Number of fry surviving at 15 to 20 days, from 1 kg (dry) eggs is 70 000 to 80 000.
2.4 Pike Perch
|Species:||Pike perch (Stizostedion lucioperca L.)|
|Habitat:||Prefers oxygen rich waters. It lives in rivers, lakes, reservoirs and fish ponds|
|Feeding:||It is a carnivorous predator, feeding mainly on small fish|
Weight at age intervals:
|1||10 – 20|
|2||100 – 200|
|3||400 – 700|
|4||800 – 1 200|
In its natural environment, it uncovers the roots of aquatic vegetation, depositing the ova among them. The male then fertilizes the eggs. It spawns in pairs, and guards the ova until they hatch. Temperature at spawning: 14°C.
2.4.2 Economic characterization
Its meat is outstanding, and contains no intramuscular bone. – Good sport fish; – In polyculture, it consumes small fish of no value; – It does not withstand well the handling necessary in harvesting and transportation, thus requiring extraordinarily careful treatment.
Care of the brood stock: – In the autumn the brood stock is harvested from natural waters or fish ponds;
– The stock is placed in wintering ponds without segregation by sex;
– Wintering space requirement is 3 to 4 m2 per fish;
– Small fish, at the rate of 20 to 30% of the brood stock by weight, are placed in the pond;
– Continuous water circulation must be ensured in the wintering ponds.
2.4.4 Sexual differentiation
– The female’s belly is full, rounded and its general area is white in color;
– The male’s belly is flatter, its area gray.
2.4.5 Spawning in fish ponds
The spawning pond should be small in area (500 to 1 000 m2), and 1.5 to 1.8 m deep, – The bottom must not be very muddy; – Spawning nests are prepared for the fish, made either of willow roots (Salix), or of a special artificial fibre “spawning rug”; – The nest is square, of 50 cm dimension; – The spawning nest is placed on the bottom and secured; – Females and males are placed in the spawning pond in equal number; – Each pair requires 30 to 50 m2 area.
– Hypophysation is carried out before placing the brood stock in the spawning ponds; – The pulverized hypophysis of carp should be administered in 1 ml of a 0.65% salt solution; – Hypophysis dosage by body weight is 2.5 mg/kg for the female, 2 mg/kg for the male; – Three days after placing the spawners in the pond, the nests are examined, and those containing ova are transferred to the hatchery; – During the transfer – if over a short distance – the nests are covered with wet rags to prevent their drying by wind.
– The ova in their nests are ripened by sprinkling with water, the method developed by Woynárovich (Hungary); – The nests are placed vertically on racks over troughs of concrete or fibreglass; – Above the racks sprinklers are deployed, which produce a fine spray on the nests; – Water temperature should be 12°C, ambient temperature 16-18°C thus the ova are ripened at 15-16°C; – Incubation requires 110 degree days (6-7 days); – To prevent the generation of fungus, malachite green should be used in a 1:100 000 solution; – The nets are immersed in the solution for 6-8 minutes, rinsed and replaced on the rack; – If required, the treatment is repeated each day; – When the ova are assumed to be ready to hatch, a few of them are placed in a glass containing water of 15-16°C temperature. If these hatch readily, the nests are placed in hatching tanks; – The hatched larvae have no pigmentation and are extremely sensitive to light; – The hatching tanks are therefore covered to keep the larvae in the dark; – The tanks must have a continuous flow through of oxygen rich water; – Water temperature should be 12-14°C; – First feeding will take place at 6 to 8 days; – First feed is zooplankton, measuring 50 to 100 micron; – The feeding fry are transferred to fish ponds, which contain ample food supplies.
2.4.8 Biological and technical data
– Age of sexual maturity, female: 3-4 years; male: 2-3 years
– Length of broodfish: 30-50 cm
– Weight of broodfish: 500-3 000 g
– Optimum water temperature: 10-14°C
– Sex ratio male to female: 1:1
– Quantity of ova produced by the female is 150 000 – 200 000 per kg of body weight;
– The diameter of dry eggs is 0.5 – 0.8 mm;
– The diameter of swollen eggs is 1 – 1.5 mm;
– Incubation period: 6-7 days, 110 degree days
– Hatching rate: 90-95%;
– Size of the larva: 4-5 mm;
– Size of first feeding fry: 6-8 mm.
|Species:||Pike (Esox lucius L.)|
|Geographical distribution:||Europe, Asia, North America|
|Natural habitat:||Rivers, lakes, backwaters and artificial fish ponds. It prefers the edges, with vegetative growth of slow or stationary waters|
|Feeding:||The pike is a carnivorous predator, feeding on fish aquatic mammals, water fowl and vermin. It possesses a large appetite, if ample food is available it grows rapidly.|
Weight at age intervals:
|1||15 – 25|
|2||150 – 250|
|3||500 – 1 500|
|4||2 000 – 3 000|
In a natural environment, it spawns in the shallow waters near the shoreline of lakes, slow moving rivers, and dead waters. The ova adhere to the underwater vegetation and will hatch there in 15 to 18 days. The pike does not guard or tend its eggs. The larvae suspend themselves from the vegetation and stay thus until the resorption of the yolk sac in 8 to 15 days. The first feed consumed by the feeding fry is zooplankton.
In cultivation, the pike may be placed in fish ponds for spawning or propagated artificially in hatcheries. The spawning temperature is 5 to 12°C. Sexual maturity is attained at 3 to 4 years by the female, 2 to 3 years by the male.
2.5.2 Economic characterization
– The species is suited primarily to the stocking of natural waters;
– It is an excellent sport fish;
– It’s meat is of good quality;
– In fish ponds it will eliminate undesirable small fish which may be brought in with the water supply.
2.5.3 Artificial propagation
– A proven method is the collection of the ripe fish in the spawning season from natural waters. The collection is done using fyke nets. The ripe ova is already flowing from the female. It is fertilized and then taken to the hatchery and placed in hatching jars. The mature fish kept in ponds or backwaters are collected in the autumn and placed in wintering ponds; – Feeding is necessary in the wintering ponds. This consists of placing small fish in the pond, at the rate of 20 to 30 percent, by weight, of the pike. The space requirement of the brood stock in the wintering pond is 2 m2 per fish; – The pond should have a continuous flow-through of oxygen rich water; – Size and weight at sexual maturity:
|Female:||30 to 40 cm,||500 to 2 500 g|
|Male:||25 to 30 cm,||350 to 2 000 g|
– Water temperatures required for propagation: in wintering ponds 6 to 8°C, in hatcheries 10 to 14°C.
2.5.4 Sexual differentiation
– The pike does not demonstrate a marked dimorphism. The female, in the spawning season, will have a fuller belly than the male. The male will emit white milt if pressed lightly. Occasionally the males have vivid yellow spots.
– For the artificial induction of the production of ova and sperm in pike, hormone of the carp’s hypophysis is employed; – Prior to hypophysation, the brood stock is collected from the wintering ponds. After hypophysation, the fish are kept in tanks or small ponds until the removal of ova and sperm from them; – Dosage;
|for the female,||3 mg/kg of body weight|
|for the male,||2 mg/kg of body weight;|
– The hypophysis is dissolved in a 0.65 percent salt solution. Two ml salt solution per fish is used. The hypophysis is injected 72 hours prior to the removal of ova and sperm. The water temperature is maintained at 10°C; – After hypophysation, the males and females are placed in separate tanks; – Each fish is provided with 0.5 m3 of water in the tank. Water circulation required is 2 litres/min/fish. Saturation of the water with oxygen must be maintained; – The fish should not be fed while in the tanks. Tranquilization is not employed.
The removal of ova and sperm, fertilization; – 72 hours after hypophysation, the tanks’ water level is lowered and the fish are picked up by hand, one by one. With slight pressure, the ripe ova are easily made to flow out; – The ova are collected in plastic dishes; – Sperm will emerge from the male with slight pressure on the belly. The sperm is collected with pipettes; – Care must be taken that neither ova nor sperm come into contact with water; – Ova and sperm are thoroughly mixed, without the addition of water, so that each ovum will be reached by the sperm. 8 to 10 ml sperm is used to each 1 000 g of eggs. Each batch of eggs is fertilized with sperm from no less than 3 males to assure successful fertilization; – A fertilizing solution is used in the process of fertilization. The composition of the solution is:
– To 1 000 g ova, 150 to 200 ml fertilizing solution is added, with continuous stirring, using a plastic spoon; – After two minutes, a further 200 ml fertilizing solution is added and the stirring action continued; – After five minutes, the solution is carefully poured off, then fresh solution added in a volume that is three times that of the ova; – This is stirred for ten minutes, then the solution is poured off; – Fresh water is poured on the ova, in which it will be soaked for 45 minutes; – The water is exchanged at ten minute intervals, with a cautious stirring at five minute intervals; – The rinsed ova may be transported without loss for two to three hours, in a 1:2 mixture of ova to water.
– The ova are placed in hatching jars; – In a 10 litre capacity hatching jar, 1.5 to 2.0 litre ova may be placed. The ova will become somewhat lumpy in the jar, but this is of no consequence; – The ova are sensitive to water turbulence for the first 48 hours, therefore, the water flow in the hatching jar is held to 0.5 l/min; – After 48 hours, the flow is increased to 2.0 to 2.5 litre/minute. At this time the lumps are separated to prevent adhesion with careful stirring; – The water temperature in the jar should be 6 to 8°C during the first two days, then gradually increased to achieve 12 to 14°C on the fourth day. The water temperature should not be raised above 14°C, since this would incapacitate the hatching larvae; – To prevent the generation of fungus, the ova must be disinfected each day, beginning with the third day after placement in the hatching jar. The disinfectant to be employed is malachite green, in a concentration of 5 ppm, the duration of the treatment is five minutes; – The infertile ova, which are lighter in colour will rise to the top and may be siphoned off through a rubber tube; – Incubation requires 130 to 150 degree days, depending on water temperature, the time required may vary from 8 to 15 days; – Upon hatching of the first few larvae, the ova are transferred through rubber tubes, into large plastic dishes; – The dishes contain warm water, of 15 to 17ºC, in which the larvae hatch within 10 to 15 minutes.
Maintenance and transportation of the larvae: – The larvae are placed in pens; – The larva pens are 70×40×30 cm in size, and are made of 1 mm nylon mesh; – The pens are kept in concrete or fibreglass tanks with flow-through circulation; – The pens are stocked at the rate of 150 to 200 larvae per litre; – Soon after being placed in the pen, the larvae will suspend themselves from the walls of the pen and remain in place for 5 to 6 days. They should not be disturbed during this time, since they will have difficulty in repeatedly reattaching themselves. The bottom of the pen is carefully cleaned of shells, the detritus being siphoned off through a rubber tube; – Water temperature is kept at 10 to 12°C; – Time span of the larval stage is 8 to 10 days; – The swim up fry is transferred to fish ponds. The fry is transported in polyethylene bags; – At 10°C, 100 000 fry may be kept in 20 litre water plus 20 litre oxygen for 2 to 4 hours; – The size of the swim up fry is 8 to 10 mm.
2.5.7 Biological and technical data
– Age of sexual maturity, female 3-4 years, male 2-3 years;
– Length of broodfish: 30-80 cm
– Weight of broodfish: 500-5 000 g
– Optimum water temperature: 6 – 12°C
– Sex ratio male to female: 2:1
– First hormone treatment of females: 2-3 mg/kg
– Second hormone treatment of females: 5-7 mg/kg
– Time between the two treatments: 24 hours
– Time between the second treatment and ovulation: 550-750 degree hours
– Hormone treatment of males; 3 mg/kg
– Effectiveness of hormone treatment of the females: 70-80%
– Quantity of eggs per female, dry weight: 200-800 g
– Quantity of milt per male; 2-5 ml
– Quantity of milt for fertilizing 1 kg of dry eggs; 4-8 ml
– Fertility rate of eggs: 40-60%
– Size of dry eggs: 2 mm
– Size of swollen eggs; 3 mm
– Count of dry eggs per kg: 180 000 – 200 000
– Count of swollen eggs per litre: 50 000 – 80 000
– Quantity of swollen eggs in 10 litre hatching jar: 1.5 – 2.5 1
– Water flow in hatching jar; 0.5 – 2.5 l/min
– Time required for hatching: 120 degree days
– Hatching rate: 80-90%
– Time of the larval stage: 100-120 degree days
– Stocking density of larvae container: 150 – 200 larva/litre
– Number of first-feeding fry from 1 kg of dry eggs: 50 000 – 100 000
– Size of fry at first feeding; 11 – 14 mm
2.6 Semi-Artificial Propagation of Indian Carps
|Species:||Catla catla (Hamilton)||(Catla)|
|Labeo rohita (Hamilton)||(Rohu)|
|Cirrhinus mrigala (Hamilton)||(Mrigal)|
|Origin:||India, Pakistan, Bangladesh, Burma|
|Natural habitat:||Rivers, lakes, fish ponds|
|Feeding:||Catla catla – zooplankton, phytoplankton in surface strata,|
|Labeo rohita – zooplankton, along the whole water column,|
|Cirrhinus mrigala – omnivorous bottom feeder.|
Age dependent size of fish
– Spawning in rivers during monsoon rains;
– Spawning can be induced semi-artificially;
– Optimal temperature of spawning is 26-31°C;
– Eggs are floating, not sticky.
2.6.2 Economic features
– Applicable in intensive polyculture technologies;
– Meat is tasty, important food.
2.6.3 Way of distinguishing male or female spawners
– The belly of female is swollen, genital organ is red;
– Upon light pressure the male produces white milky drops;
– The hard ray of pectoral fin is rough with the male, and smooth with the female.
2.6.4 Age of fish at first propagation
– Carp pituitary gland is used dried in acetone – Female spawners:
|1st injection||2, 3 mg/kg,||10 – 12 hours before ovulation;|
|2nd injection||5, 8 mg/kg,||4 – 6 hours before ovulation;|
– Hypophysation of males: 2-3 mg/kg, 4-6 hours before stripping the milt; – Hypophysation is performed with powdered pituitary gland, injected in 0.65% NaCl solution, calculating 2 ml/fish.
2.6.6 Keeping of spawners and spawning
– The injected males and females are transferred to a breeding hapa in a fish pond or tank with slow water flowing; – Spawning is generally 4-6 hours after the 2nd injection; – After spawning the parents are taken out .
2.6.7 Hatching of the seed
– The fertile eggs in the hapa hatch 15-18 hours after spawning; – 12-14 hours after spawning – when the embryo starts moving in the egg – the eggs are collected and transferred from the hapa to the hatching glass (Zuger glass); – The hatched larva slips from the breeding hapa to the outer narrow-meshed rearing hapa.
2.6.8 Rearing of larva
– The larva starts feeding 4-5 days after hatching;
– The fry at this stage is stocked in nursery ponds.
2.6.9 Biological and technical figures
– Age of sexual maturity. Female: 2-3 years, male: 1-2 years
– Length of broodfish: 40-80 cm
– Weight of broodfish: 200-6 000 g
– Optimum water temperature: 24-31°C
– Sex ratio male to female: 1:2
– Effectiveness of hormone treatment of the female: 60-80%
– Quantity of eggs per female, dry weight: 200-2 000 g
– Fertility rate of the eggs: 30-40%
– Size of dry eggs: 1-1.5 mm
– Size of swollen eggs: 4-6 mm
– Count of dry eggs per kg: 700 000-1 000 000
– Count of swollen eggs per litre: 15 000-25 000
– Time required for hatching: 15-18 hours, 20-22 degree days
– Size of fry at first feeding: 6-7 mm.