Fish Hatchery Management - fisheries & aquaculture

HAI'CHERY OPL,RATIONS 7 5Warmwater Fish Rearing DensitiesChannel catfish have been reared at densities of up to eight pounds Per cubicfoot of water. Stocking density and water turnover both had substantialeffects on growth and food conversion. Reduced growth due to the increasein stocking density was largely compensated by increased water exchange,and growth rate data indicated that production of over 20 pounds per cubicfoot of water was possible in a 365-day period. High-density culture ofcatfish in tanks or raceways can be economical if suitable environmentalconditions and temperatures are maintained'Fish weight gain, food utilization, and survival may decrease as fish densityincreases, but faster water exchanges (inflow) will benefit high stockingdensities. The best stocking densities and water exchange rates will takeinto consideration the various growth parameters as they affect theeconomics of culturing channel catfish. Stocking densities between five andl0 fish per cubic foot have been suggested as feasible and production canbe increased to higher densities by increasing the oxygen content withaeration, if low oxygen concentration is the limiting factor.Acceptable stocking densities for warmwater fish are related to the typeof culture employed (intensive or extensive) and the species cultured. Theappropriate density is influenced by such factors as desired growth rate,carrying capacity of the rearing facility, and environmental conditions.Most warmwater fish, other than catfish, normally are cultured extensively.The following paragraphs cover representative species of the major groupsof commonly cultured warmwater and coolwater fishes. Stocking rates forrelated species can be estimated from these examples.LARGEMOUTH BASSProduction methods used for largemouth bass are designed to supply 2-inch fingerlings.Fry are stocked in prepared rearing ponds at rates varying from 50'000to 75,000 per acre. If a fingerling size larger than 2 inches is desired, thenumber of fry should be reduced. Normal production of small bass rangesfrom 30 to 150 pounds per acre depending on the size fish reared' the productivityof the rearing pond, and the extent to which natural food hasbeen consumed and depleted.The length of time required for the transferred fry to grow to a harvestablesize depends mainly upon the prevailing water temPerature and theavailable food supply. Normally, it is 20 30 days in southeastern UnitedStates at a temperature range of 65-75'F.A survival rate of 75 to 90'fl isacceptable. A higher survival suggests that the number of fry stocked wasestimated inaccurately. Less tharr 7 5ol: survival indicates a need for