SELECTION, HYBRIDIZATION AND GENOME MANIPULATION IN SILUROIDEI

Selection, hybridization, and genome manipulation in the Siluroidei is reviewed. Selection topics include strain evaluation, qualitative tra its, quantitative traits, mass selection, family selection, inbreeding , and crossbreeding. Hybridization is discussed with reference to cult ure traits. Genome manipulation technologies - sex reversal, gynogenes is, androgenesis, polyploidization, add gene transfer - are considered with application to genetic improvement of Siluroidei. Strains of ict alurid catfish vary significantly for traits such as growth, disease r esistance, harvestability, reproduction, body conformation and carcass yield. Growth of domestic strains can be 250% greater than that of wi ld strains. Strain differences have also been identified for clariid, bagrid, and silurid catfishes. Mass selection has increased growth rat e by up to 30%. Heritability estimates predict a response to selection for the traits of disease resistance and tolerance to low oxygen leve ls. Crossbreeding strains of Ictalurus punctatus have improved growth, disease resistance and reproductive performance. Two generations of i nbreeding depressed body weight of I. punctatus as much as 30%, and ca n reduce viability and reproductive performance. Hybridization of I. p unctatus X I. furcatus has resulted in a 20% increase in growth. Trait s for tolerance to oxygen deficit, feed conversion, disease resistance , harvestability, and carcass yield were also improved. Interspecific, intergeneric, and interfamilial hybrids have been made with clariid f ishes; heterotic growth was indicated. Hybridization has also been use d to combine desirable traits of parental species. Sex reversal of I. punctatus using estrogen treatment followed by progeny testing can res ult in monosex, all-male populations. Gynogenesis and androgenesis are approaches to production of inbred lines of catfish, but thus far hav e limited application in aquaculture. Polyploidization has been applie d in several ictalurid, silurid, and clariid fishes, but predicted imp rovements in performance have not been realized. Gene transfer has bee n accomplished in I. punctatus and Clarias gariepinus using microinjec tion and electroporation; the foreign genes have been expressed and in herited. Transgenic I. punctatus containing salmonid growth hormone ge nes grew 20-40% faster than controls.