Food Organisms and Feeding Habits of Fish

April 13, 2023 Agric4Profits

The richness and variety of various aquatic habitats provide a wide range of possible food organisms and feeding habits of fishes. These originate either from within the aquatic ecosystem itself (authochthonous food sources) or from outside (allochthonous food sources).

Food Organisms of Fish

Classification of food items of fish based on their origin, fish food can have the following subdivisions:

1. Autochthonous food

These are food found within the aquatic community. They include the following groups:

a. Plankton community: Planktons are floating micro-organisms of both plants (phytoplankton) and animals (zooplankton) which do not exhibit any significant movement of their own and so they are carried by water movement.

Phytoplankton includes blue-green algae, green algae, diatoms, eugleniods and dinoflagellates. Zooplankton include, some protozoans, crustaceans such as copepods, cladocerans, ostracods, larval decapods, rotifers, molluscs larvae, fish larvae and eggs

b. Benthic community: This is made up of organisms associated with the substratum, including various benthos, such as some protozoan, decapods crustaceans, mollusks , annelids, aquatic insect larvae, aquatic arachnids, echinoderms etc. as well as decomposing organic (plant and animal) remains.

c. Plant community: This is made up of higher plants mainly aquatic weeds including submerged, floating or emergent vegetation.

d. Neuston community: This includes surface living insects and larvae at air/water interface.

e. Fish community: This includes small –sized fishes, particularly juveniles, as well as fish larvae and eggs.

f. Other vertebrates: These are mainly amphibians particularly their eggs and larvae.

2. Allochthonous food

These are food from outside the aquatic habitat consisting of terrestrial organisms which include the following:

Higher plant: These are largely leaves, roots, flowers, fruits, seeds and branches of terrestrial plants growing near the water. Most of these parts drop into the water, and the fishes feed on them.

Animals: These are mainly terrestrial insects, arachnids, worms etc. washed into the water from land.

Fishes make use of the available fauna and flora in their habitat as food. Based on the quantity of the various food items consumed and the frequency with which they are consumed, food items of fishes can be classified into the following groups:

Main/Major or Basic food: This is the food which the particular fish usually consume. It comprises the main part of the stomach content. For instance, phytoplankton and detritus are the major food items of adults’ tilapia while that of the African pike Hepsetusodoe is fish.

Secondary or Supplementary food: This food is frequently found in the stomach of the particular fish but in relatively smaller amount .This fish uses this food to augment its main food. Zooplanktons are supplementary food of adult tilapia.

Incidental food: This is the food that the fish rarely eats.

Obligatory food: This is the food which the fish consumes in the absence of its basic food

Feeding Habits of Fish

According to their food and mode of feeding, fishes can be broadly classified as planktivores (plankton feeders), herbivores, predators, omnivores and detritivores.

1. Planktivores or Plankton feeders

These are fishes that feed mainly on plankton. There are two groups of planktivores: those that feed on phytoplankton are mostly are phytophagous and in the inland waters, this group is dominated mostly by tilapias.

Food Organisms and Feeding Habits of Fish

Such tilapias include; Oreochromisniloticus, Sarotherodongalilaeus and Sarotherodonmelanotheron. Other phytophagous species include mullets (Mugil and Liza species) and upside-down catfish (Synodontis species).

The other group of planktivores are those that feed mainly on zooplankton and they include the glass catfish (Parailia (= Phsailia) pellcida} and silver catfish (Chrysichthysfilamentosus).

The sardines (Ethmalosailisha and Pellonula species) and sardinellas species0 as well as the silversides (Aletes and Brycinus spp.) have a mixed diet of both phyto- and zooplankton.

Herbivores: These are the fishes that feed predominantly on higher plant materials including vegetable matter. Herbivore includes tilapia like T.zilli and T.mariae. Another group of herbivores is composed of the grass eaters (Distichodus spp.). The upside-down catfishes are also herbivore.

Predators: There are two groups of predators. Those that feed mainly on fish are piscivores (such as barracuda, snake head, atlantic tarpon) and those that feed on mainly on animals other than fish( such as insects, crabs, shrimps/prawns, worms, gastropods etc.) are non- piscivores e.g. tongue sole, the silver catfish, croakers.

Some predators have mixed diets. The African Lady fish, Elopslacertafeeds mostly on fish and prawn in the brackish water and on fish and insects in the fresh water environment .Only few predatory species have bottom deposits in their diets and this is found among non-piscivorous predator.

Omnivores: These are species that feed mainly on both plant and animal materials. The mud catfish (clarias) are mainly omnivores with diets ranging from algae, vegetable matter, crustaceans, insects, mollusks and fish.

Dettritivores: These are fishes that feed mainly on detritus or organic debris. Often detritivory is an overlap with other feeding habits. For instance, all tilapias and mullets include detritus in their diet, indicative of benthic feeding habits, and are thus also detritivores. So also are the snout fishes, the grass eaters, moon fish (citharinus spp), African carb (Labeo and Barbus).

In general, the great diversity of food items encountered in the different species is an indicative of the fact that fish of fishes differ with species and also with different habitats.

Wherein fishes are purely predatory in one habitat, such species have been known to include plant materials in their diets in another habitat. This justifies the assertion that when a fish is feeding, it is the most available food item that it mostly feeds on.

Factor Influencing Food and Feeding Habits of Fishes

1. Size: Different sizes of some fishes have different food habits. This could be as a result of competition or preference. For example, the fry of Heterotis niloticus are planktophagous while their adults are omnivorous.

Most juveniles tilapias are omnivorous, while their adults are herbivorous/detritus feeders. Fingerlings of mud catfish, Heterobranchus bidorsalis are plankton feeders and they switch to a predatory feeding mainly on fish and prawn as they grow into adults

2. Sex: Food habits also vary with sex. Spawning female fish may change depth or location in water. This affects the food available to the fish. Some females even go without food during spawning.

3. Season: Seasonal distribution and abundance of preys and plankton also control the rate at which they are consumed as food. It is generally known that fishes make use of the most available items depending on season.

4. Temperature: Temperature regulates the spatial distribution of most of various fish species as well as most food items. This affects the food habits of the fishes. Fishes generally eat more and digest food faster at higher water temperatures. However, each species has its own suitable temperature range.

5. Habitats/Locality: Food habits of fishes differ with habitats and locality. The occurrence and abundance of different food items in different habitats affects the food habits of fishes therein.

For instance, the major fish preys of African pike in Lekki lagoon, Lagos, Upper Ogun River and Ado-Ekiti Reservoir , Ekiti are tilapias and cyprinids (Barbus) while in River Sokoto and Epe Lagoon, Lagos, the major preys are sardines (Pellonula), silversides (Aletes and Brycinus) and juvenile African Lady fish (Elops)

6. Competition: Food habits of fishes could also be influenced by competitor species. Food habits may change to avoid or minimize competition, and this diversification makes for a fair sharing of the available food items.

Overlaps if feeding habits of some species in the same habitat is an attempt to reduce competition for food. There is often an overlap between planktophagous or herbivorous and deposit feed amongst many tilapias in habitats where they are found.

7. Preference/Selectivity: Preference for a particular food over the other (i.e. selectivity) also influences food habits. Although, different food items occur abundantly at a particular time, some fishes show preference in their selection of particular food items.

For instance, tilapias actively select phytoplankton as food, while zooplanktons are passively selected.

8. Time of Day: The food of fish could differ with time of day; this is mainly linked to the time the food is available and when fish is feeding. Feeding could be in the day or at night. For many species, peak period of feeding corresponds to peak period of availability of their food.

Peak period of feeding of the tilapias. Oreochromis and Sarotherodon inhabiting Awba Reservoir in Ibadan, is from 1300-1500hrs. This is likely due to high primary productivity during this period; hence increase in abundance of phytoplankton, a major food of these species.

9. Shape and Nature of the Feeding Apparatus/Gut: The shape of the mouth, teeth, stomach and intestines the food and feeding habits of the fishes to a large extent.

For example, predatory fishes e.g. Nile perch (Latesniloticus)African pike (Hepsetusodoe) and barracuda (Spyraena) have large protusible mouth armed with powerful teeth to capture or seize large prey such as fish which form the bulk of their food.

Their stomachs are larger and their intestines short. Herbivorous and phytophagous fishes, such as tilapias lack powerful teeth.

Their teeth are small and they are arranged in many rows on the upper and lower pharyngeal bones, to form grinding surfaces used to crush the hard wall of their plant food. Their intestines are long typical of herbivorous species.

Other phytophagous species like mullets (Mugil and Liza sp.) have their stomach modified to form a gizzard used to crush the food. Similarly, benthophagous/omnivorous species like the African bony-tongue, Heterotisniloticushas a gizzard stomach for crushing the shells and exoskeletons of bivalves, snails and insects as well as the walls of higher plant materials, which constitute significant parts of its food.

In summary,like all organisms, fishes require an energy source to fuel their body machinery and processes, including growth, metabolism, and reproduction.

Different fishes have evolved feeding structure and mechanisms that allow them to exploit a vast array of plant and animal food sources, ranging from the indiscriminate filtering of a large ram-feeding planktivore to the precision biting of a manipulating carnivore.

Similarly fish guts incorporate numerous adaptations for the efficient breakdown and absorption of essential nutrients, including appropriate enzymes and absorptive surface areas. Finally, nitrogenous wastes must be excreted, principally as ammonia (or urea in strongly alkaline environments).

A complete study on the food and feeding habits of a fish species would not only investigate the dietary composition, their quantity and selectivity but would also involve an examination of the functional morphology and physiology of the alimentary system as well as the fauna and flora of the environment, particularly, those that are food for fish to reveal their interrelationship with each other and the fish species.

Fish Food, based on their origin, could be authochthonous and allochthonous; and the feeding habits of fish could be planktivorous, herbivorous, predatory, omnivore and detrivores. Size, sex, season, temperature, habitat/locality, competition.

Preference/selectivity time of the day and the shape/nature of feeding apparatus/gut are some of the factors influencing food and feeding habits of fishes.