Fish Nutrition and Feed Technology (2+1)

Unit 11 - Different forms of feed

11.2. Feeds based on life-cycle of fish

Feeds can be classified based on the stage of the life cycle at which they are targeted.

Starter feeds
Starter feeds are given as first feeds to feed the fry or larvae, when their yolk is exhausted or about to be exhausted. The transformation from an endogenous to an exogenous food supply is critical and thus starter feeds should be nutritionally complete, easily digestible, and with appropriate particle size. Starter feeds are generally in the form of fine crumbles or flakes. However, in the case of shrimps starter feeds are given to post larvae up to 0.5 g size juveniles.

Fry feeds
Fry is the term used for the unmetamorphosed young stage in the life cycle of fish. Fry feeds generally contain higher levels of protein because the protein and energy requirements are high in the early stages of life because the highest relative weight gain is achieved in the fry stages. Fry feeds are generally in the form of flakes or crumbles.

Fingerling feeds
The fingerling stage is defined as metamorphosed younger stage of fish to a growth of about 10-20g. Fingerling feeds vary from crumbles to pellets depending on the species to be cultured and their size. Fingerling diets tend to contain less protein and energy than fry and starter diets.

Grow-out feeds
The weight increase in fish during this grow-out stage is at a uniform rate, decreasing slightly as the fish increases in weight. Thus the nutritional requirement during this stage is rather uniform. It is important to ensure that the protein that the protein in the feed is used mainly for growth and not for metabolic activity. The biomass increments are considerable and also the quantity of feed administered is high. Thus, during this stage cost-saving feeds are essential. Generally pellet form of the feed is employed during grow-out stages.

Broodstock feeds
Adequate nutrition has an important role to play in the reproductive success of fishes. A number of aspects of reproduction like the time of first maturity, number of eggs produced (fecundity). egg size and egg quality as measured by chemical composition, hatchability and larval survival can be affected by nutritional status.

It has been shown that essential fatty acids, vitamins (A, E and C), trace minerals and carotenoids can affect fecundity, egg quality, hatchability and larval quality. Nutritional requirements of broodstock can further differ depending upon the phase of reproductive period.

Formulation of complete diets should, therefore, take into account the stage-specific, as well as species-specific nutritional requirements of the broodstock. Nutritionists and the feed industry should also consider the options for developing three types of broodstock diets:

• conditioning diet
• reproduction diet
• recovery/maintenance diet

The broodstock conditioning diet should be formulated as an optimized growout diet to meet the full nutritional requirements of the species from commercial to broodstock size. The reproduction diet used before or during spawning should meet the needs for maximal reproductive performance (spawning success and fecundity), gamete quality, and transfer of nutrients and biologically active substances to offspring. The recovery/maintenance diet should assist recovery from reproductive exhaustion and reconditioning for the next reproductive cycle.