Methods of Fish Hormone Administration

April 13, 2023 Agric4Profits

There are several variations in fish hormone administration methods. Each method may have some justification, but may not be universally applicable. The technique is adopted generally dependent on the species of the fish, local conditions and working methods developed by the local scientist and techniques.

However, none can be proclaimed as the only definitive technique. As a rule, the females generally require higher doses of hormones than males, with split doses producing better results than a single large dose.

Methods of Fish Hormone Administration

The different methods of fish hormone administration, as generally practiced, are detailed below;

1. Single injection method

The calculated 100% dose is, also called the knock-out dose, is given in a single injection. It will be successful if only the female fish is fully ready for spawning as those that are captured in their spawning ground or those in spawning migration.

Suitably fed fishes achieve this condition during the second half of the breeding season. In majority of fish species, males are better prepared for spawning than females, and therefore a single dose suffices.

If the hormone administered to them amounts to an overdose, or is not synchronized with the gonadal maturation of the female, it may result in wild discharge of milt before the females are ready.

2. Preparatory and Decisive those Method

The preparatory dose (which is 10% of the decisive dose) advances the gonad development up to the pre-ovulation stage. It is generally given about 18-24 hours prior to the decisive dose (100% of the calculated dose.

This is a generally successful sequence of hormone administration in the temperate and subtropical regions. This method also holds for nervous and difficult-to-handle fish. Sometimes the interval between preparatory and decisive doses can be shorter than that indicated above.

About 14-18 hours suffice during the latter half of the spawning season given that the water temperature is higher than normal spawning temperature.

If the female are less than 1 kg in weight and are in ripe condition for hormone treatment, an interval of only 6 hours is sufficient.

One Preparatory and Two Decisive Doses

In tropical regions, where metabolism in fish is more rapid, the decisive dose is given in two equal instalments or two instalments of 40% and 60% within intervals of 6-8 hours between them. A preparatory dose of (5-10%) should precede the first decisive dose by 18-24 hours.

Several Preparatory and Two Decisive Doses

It is employed in cases of fish where the eggs are already in the dormant stage but the ovary has not yet descended into the lower part of the body cavity. In such cases, a series of several preparatory are required before the decisive dose can be successful

Distributed doses method: In this method the injections are given in many doses and the time span between the doses is generally short about6-8hrs. The sequence and quantity of doses may vary as follows:

50 & 50% with an interval of 6 – 8 hours.

40 & 60% with an interval of 6 – 8 hours.

10, 30 % and 60% with an interval of 6 hours each.

33¹/3, 33¹/3 & 33¹/3% with an interval of 6 hours.

20, 30 and 50 % with intervals of 6 hours each.

These sequences have proved very successful in the cases of tropical fishes and those spawning confined waters.

There is usually 24 hours between doses when the decisive dose is given in two or three parts. The time lapse between injections should not be more than 6 – 8 hours.

As a rule, the males are only given one dose of hormones but usually at the time when the females are given the last decisive dose.

It is important that males are not administered the hormones earlier; that may result inducing the sperm before the females are ready to ovulate. The recommended single decisive dose for male is 0.5 gland (1.0 – 1.5 mg)/kg of body weight regardless of their length.

A little excess hormones in the decisive dose does not harm the fish, therefore, fishermen are advised to increase the required dosage by 1.0 – 1.5g to be on the safe side.

As a rule, the female generally require higher doses of hormones than the males, with split doses producing better results than a single large dose. It has been found that more hormones are needed for ovulation when the ovary is bulky. The bulkiness of the ovary can be expressed by them.

Read Also : Methods of Induced Spawning In Fish

Preparation of Pituitary Gland Solution

Based on the weight, number and sex of the breeders, the dose is determined after which the requisite number or quantity of pituitary gland is counted or weighed. If the glands are not already in pulverized condition, they are thoroughly pulverized in a small porcelain mortar or a homogenizer.

The mortal has to be totally dry, as otherwise the gland would become pasty while pulverizing and would not easily dissolve. A measured quantity of solvent is then added immediately.

The solvent is usually measured in a graduated syringe. It is necessary to ensure thorough mixing of the solvent and the hypophysis powder. About 10-30 minutes would be required to dissolve the hormone.

The tissue residue can be removed from the solution by using a centrifuge or by simply allowing the residue to settle down and then sucking the clear supernatant solution with a syringe.

The solvent is first prepared by dissolving 7g of common salt, free of iodine, in 1l of boiled and already cooled drinking water. There is no need to use distilled water. The solvent can be stored for long periods in sealed bottles.

The solvent used for GTH is 0.9% NaCl (physiological common salt). 1ml solvent is used for the preparatory injection regardless of the dosage (ranging from 0.25-1 gland).

The quantity of solvent for the decisive dose is calculated at the rate of 0.5ml for each gland (2.5-3.0 mg) but the maximum amount of solvent should not exceed 5ml.

It is not advisable to use too little solvent because the loss of solvent would mean the loss of considerable quantity of hormones neither is it advisable to use much solvent because the administration of a large volume of solution would pose a difficult problem. In general, the quantity of solvents should be between 1-5ml.

Choice of Body Part to Inject

The most commonly adopted procedure is to inject the hormone into the dorsal muscles above the lateral line and below the anterior part of the dorsal. In Indian, fishes are generally injected at the dorsal part of the caudal peduncle (also intramuscularly).

This procedure appears to be best for sensitive fishes. In some fishes, the injection are administered into the body cavity (from under the pectoral or pelvic fins) i.e. intraperitonial administration. This method generally yields poor results.

Limitation of Hypophysation

Like other technique, this technique too has its limitations. Some of the sensitive fish such as pike-perch cannot tolerate the treatment, while other may ovulate only irregularly.

Then again, the breeders whose ovaries have not yet reached breeders whose ovaries have not reached the appropriate ripe stage will fail to response to hypophysation.

It is a fundamental that hypophysation is only effective when the eggs in the ovaries have reached the resting or dormant phase after completion of vitellogenesis. The eggs are then materially ready for further development to be triggered by gonadotropin(s)

Environmental Conditions for Culturing Breeders

When culturing breeders, the following environmental conditions should be ensured considering the specifics demands of the respective species:

Suitable water and pond.

Temperature.

Oxygen.

Feed light and 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, and tilapia) earthen or concrete walled fish ponds should be constructed. For rheophyl species (e.g. trout) flow-through systems, canal, or tanks with circulating water should be provided.

The temperature as an environmental factor, has an important role in fish breeding. Fish are poikilothermic 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.

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.

Optimal oxygen content of water is very important especially inactive cytogenetic processes. Development of gametes and complete conversion of feeds are all oxygen consuming processes.

In case of oxygen deficiency, the gametogenesis slows down; development is inhibited and if it is prolongs the resorption of gametes start. Therefore, proper oxygen supply is a crucial point of brood stock culture.

Feeding of the brooders, especially in the nutrient accumulating phase of oogenesis requires feed of specific composition. Amino acids, carbohydrate, 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 feeds.

It is also important that the breeders can get the type of feed characteristic of their species i.e. herbivorous fish should get nutrient 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 factor should also be kept in mind.

Handling, transportation, enclosure which all differs 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.

In summary, artificial propagation involves human intervention in the process of natural propagation and has the advantages of;

(a) Better rates of fertilization and hatching,

(b) Protection against enemies and unfavorable environmental conditions and

The different methods of fish hormone administration, as generally practiced include single injection method, a preparatory and decisive dose, one preparatory and two decisive doses, several preparatory and two decisive doses and the distributed doses.

Based on the weight, number and sex of the breeders, the dose is determined after which the requisite number or quantity of pituitary gland is counted or weighed; the solvent used for GTH is 0.9% NaCl (physiological common salt). 1ml solvent is used for the preparatory injection regardless of the dosage (ranging from 0.25-1 gland).

The most commonly adopted procedure is to inject the fish hormone into the dorsal muscles above the lateral line and below the anterior part of the dorsal. When culturing breeders, the following environmental conditions should be ensured considering the specifics demands of the respective species:

Suitable water and pond;

Temperature;

Oxygen;

Feed light and photoperiod.

Induced breeding basically involves the induction of final oocyte maturation and spermiation in male and female fish respectively, followed by stripping and artificial fertilization or natural spawning; the former being preferable for complete control of fertilization.