Fish Hatchery Management - fisheries & aquaculture

NU f RIIIUN AND FI,EIJINC2I3their food, but gulp it down intact. Pharyngeal teeth are used by somespecies to grind feed.The giryard serves as a grinding mechanism in some species of fish.The stomach is for feed storage and preliminary digestion of protein. Verylittle absorption occurs in the stomach.The finger-like pyloric ceca at the junction of the stomach and small intestinesare a primary source of digestive juices.The small intestine is the major site of digestion and receives the digestivejuices secreted by the liver, pancreas, pyloric ceca, and intestinal walls.The absorption of the nutrients occurs in this area.Some water absorption occurs in the large intestine, but its primary functionis to serve as a reservoir of undigested materials before expulsion as feces.Oxl,gen and Water RequirementsOxygen and water normally are not considered as nutrients, but they arethe most important components in the life-supporting processes.All vital processes require energy, which is obtained from the oxidationof various chemicals in the body. The utilization of oxygen and resultingproduction of carbon dioxide by the tissues is the principal mechanism forthe liberation of energy. Oxygen consumption by a fish is altered by size,feed, stress, water temperature, and activity. The oxygen requirement perunit of weight decreases as fish size increases. High-nutrient feeds, density,stress, elevated water temperatures, and increased activity all increase oxygenrequirements of fish. As a consequence, adequate oxygen must be suppliedto assure efficient utilization of the feed and optimal growth.Water is involved in many reactions in animal systems either as a reactantor end product. Seventy-five percent of the gain in weight during fishgrowth is water. Water that is not provided in the feed itself must be takenfrom the environment. Because water always diffuses from the area ofweakest ionic concentration to the strongest, water readily diffuses throughthe gills and digestive tract into freshwater fish. In saltwater fish, the bloodion concentration is weaker than that of marine water, so that the fish loseswater to the environment. This forces the fish to drink the water and excretethe minerals in order to fulfill their requirements.A nutritionally balanced feed must contain the required nutrients in theproper proportion. If a single essential nutrient is deficient, it will affectthe efficient utilization of the other nutrients. In severe cases, nutrient deficienciescan develop, affecting different physiological systems and producinga variety of deficiency signs (Appendix F). Because all essential nutrientsare required to maintain the health of fish, there is no logic to rankingthem in terms of importance. However, deficiencies of certain nutrientshave more severe effects than of others. This is exemplified bv a low level