Fish Hatchery Management - fisheries & aquaculture

NUTRITION AND FEEDINC2t9creased. In trout, the accumulation of blood glucose follows the same patternas that in diabetic humans.No absolute carbohydrate requirements have been established for fish.Trout nutritionists have placed maximum digestible carbohydrate valuesfor feeds at 12-20%. Digestible carbohydrate values are determined bymultiplying the total amount of carbohydrate in the feed by the digestibilityof the carbohydrates. Digestibility values of various carbohydrates are:simple sugars, 100%; complex sugars, 90%; cooked starch, 60%; raw starch,30%: fiber. 0%.Digestible carbohydrate levels over 20% in trout feeds will cause an accumulationof glycogen in liver, a fatty infiltrated liver, fatty infiltratedkidneys, and excess fat deposition, all of which are detrimental to thehealth of the fish.Levels of carbohydrates up to 20(/o can be tolerated in trout feeds in55 65"F water. These same feeds fed in water below 50'F will cause excessivestorage of glycogen in the liver and can result in death. Carbohydratesshould, therefore, be limited in trout feeds. However, there are definitebeneficial effects from the carbohydrate portion of the feed. It can supplyup to 20()t of the available calories in a feed, thus sparing the protein. Theenergy from carbohydrates available to mammals is 4 kilocalories per gram,whereas the value for trout is only 1.6 kcal/g, a 40%r relative efficiency.Most trout feeds do not contain excessive amounts of digestible carbohydrate.A balance between plant and animal components in the feeds generallywill assure a satisfactory level of digestible carbohydrate. The majorsources of carbohydrate in trout feeds are plant foodstuffs, including soybeanoil meal, cereal grains, flour by-products, and cottonseed meal. Mostanimal concentrates such as meat meals, fish meals, tankage, and bloodmeals, are low in carbohydrate (less than 1.0%). The high percentages ofmilk sugar in dried skim milk, dried buttermilk, and dried whey may causean increase in blood sugar and an accumulation of glycogen in the liver iffed at levels greater than l0% of the feed.Pacific salmon have been reported to tolerate total dietary carbohydratelevels as high as 48%, with no losses or liver pathology. The digestible carbohydratevalue would be lower, depending on the forms of the carbohydrate.CARBOHYDRATES IN CATFISH I'E[,DSDietary carbohydrates are utilized by catfish, but only limited informationis available on their digestibility and metabolism. Channel catfish utilizestarches for growth more readily than sugars. In feeds containing adequateprotein, fish weight increases with the level of starch, but remains essentiallythe same regardless of the amounts of sugar in the feed. Liver abnormalities,poor growth, and high mortality observed in salmonids due to highlevels of dietary carbohydrates have not been found in catfish.