Fish Hatchery Management - fisheries & aquaculture

148 FISH HATCHERY MANAGEMEN'I(1) Avoid inbreeding, which includes father-daughter, mother-son andbrother-sister mating. Current practice is to keep the same broodstock 4 tol0 years, with replacement broodstock coming from progeny produced onthe farm. Furthermore, a beginning producer may have unknowinglystarted a broodstock with full brothers and sisters having a narrow geneticbase. Catfish should be marked in some manner to identify broodstock forpen mating to avoid inbreeding. The stocks can be clearly identified byheat branding, applied when water temperature is 72"F or above, so thathealing proceeds rapidly.(2) Enrich bloodlines through the addition of unrelated stock. This canbe effective in correcting deterioration in quality of broodstock common toinbreeding. The need to enrich bloodlines might be suspected if a highpercentage of deformed progeny, low hatchability of eggs, low survival offry, or poor growth becomes evident.(3) Crossbreed unrelated stocks. Stocks orginating from different riversystems and commercial sources are usually quite diverse, and may combinewith resulting hybrid vigor, especially in growth and disease resistance.(,t) Select broodstock carefully; as males grow faster than females inchannel catfish, blue catfish, and white catfish, rigorous selection by gradingin ponds probably will result in practically all males. More properly, arandom sample should be taken at the first selection at 6 months of age,with selection for growth and broodstock occurring at 18-24 months ofage. Select equal numbers of males and females.HYBRIDIZA'IION AN D CROSSBRF]T]DINGHybridization between species of fish and crossbreeding between strains ofthe same species have resulted in growth increases as great as 100%, improvedfood conversions, increased disease resistance, and tolerance to environmentalstresses. These improvements are the result of hybrid vigortheability of hybrids or strain crosses to exceed the parents in performance.Most interspecific hybrids are sterile. Those that are fertile often producehighly variable offspring and are not useful as broodstock themselves. Hybridscan be released from the hatchery if they cause no ecological problemsin the wild.Several species of trout have been successfully crossed, the more notablebeing the splake, a cross between brook and lake trout.Hybridization of the chain pickerel and northern pike in a study in Ohiodid not produce hybrid vigor and the resulting offspring grew at an intermediaterate to the parents. A cross between northern pike males andmuskellunge females has yielded the very successful tiger muskie.