Larvae of a stomachless carp hatch very small (weight 1.0 to 1.5 mg, length 5.0 to 5.5 mg) with a large yolk and pass stages of yolk and combined feeding rapidly, within several days. The combined feeding stage takes 3 to 5 days depending on the water temperature. Formation of digestive system within the following 10 days is mostly based on exogenic nutrition.
At earlier stages, only intestinal peptidases. When a fish gains weight of 30 to 50 mg, pancreas joins the work of digestive system; rapid trypsin increase is a response to food intake; conditions for effective protein digestion are formed. At this point, the larvae start taking up artificial protein rich feed and grow fast.
At earlier stages of feeding, amilase activity is notable due to the larvae's active consumption of phyto- and animal plankton. Thus, natural food contains highly digestible proteins, fat and bioactive substances.
Salmonid fishes (donaldson trout) have the most developed digestive system by the beginning of feeding. By this time, they weigh 80 to 120 mg and reach the length of 17 to 22 mm or more.
An important feature of the salmonid by the beginning of the feeding is formed digestive glands in the stomach wall which already function and produce acid environment and pepsin for the stomach. Protein digestion may already take place in the stomach, which is usual for older ages, facilitating its further intestinal destruction. Main protein breakdown into small peptides, their final hydrolysis and absorption take place in the mid-gut and end-gut affected by alkali enzymes produced by pancreas.
Thus, by the beginning of feeding, the salmonid have all digestive elements functioning usual for mature animals. This is followed by significant increase in all enzymes' activity in trout which is greatly dependent on the type of feed.
Sturgeon digestion is similar to that of the fish having a stomach.
Focus of endogenic enzymes, i. e. breakdown of peptide bonds, is general for all the species of fish and there are no enzymes which could break down cellulose, lignin, pectin, phytine and many other complex organic substances.
Possible issues:
- Energy deficit.
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Disproportion of essential amino acids.
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Deficit of own digestive enzymes.
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Low digestibility of feeds.
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High content of antinutrients.
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Low growth rate.
- Low survivability.
- Ferment ООО