TYPES OF FEEDS
Two types of diets are in use to nourish fish in aquaculture. Diets designed to add nutrients to food obtained from the pond or aquarium environment are called supplemental feeds. Feeds for intensively reared fishes that do not get nutrients supplied from the environment are called complete feeds. Complete feed formulas are based on the nutrient requirements of fishes, availability of the essential components, and digestibility of the ingredients used to prepare them. Various stages of fish require various sizes of feeds, thus, according to size, feeds are classified as: (1) larval feeds, (2) starter feeds, (3) grower feeds,(4) finisher feeds, (5) broodstock feeds, and (6) maintenance diets.
Supplemental or complete feeds may be prepared in moist, semi-moist or dry form. The type of ingredients used to prepare fish diets determines the type of diet. Moist rations are prepared from ingredients with high moisture content such as raw fish, meat products, wet vegetable products and similar ingredi-ents. The moisture content of most moist rations is 70%. Semi-moist rations are prepared from dry products (dried fish products, cereal grains and other dry animal and vegetable products) that are added to ingredients with high mois-ture content. The final moisture content of semi-moist diets is approximately 35%. Dry rations are prepared from dry animal and vegetable products with a final moisture content of about 10%.
Larval fish must ingest and digest feed particles, and then absorb and utilize the released nutrients. Most research has focused on larval feed ingestion. Only now are researchers beginning to look at digestion, absorption, and utilization. It has been suggested that live food is needed because the prey contains diges-tive enzymes which help the larvae in digestion. They also contain relatively high levels of free amino acids that the larvae can easily absorb.
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