Selection, hybridization and genome manipulation in Siluroidei

Abstract

Resume Selection, hybridization, and gcnome manipulation in the Siluroidei is reviewed. Selection topics include strain evaluation, qualitative traits, quantitative traits, mass selection, farnily selection, inbreeding, and crossbreeding. Hybridization is discussed with reference to culture traits. Genome manipulation technologies - sex reversal, gynogenesis, androgenesis, polyploidization, and gene transfer - are considered with application to genctic improvernent of Siluroidei. Strains of ictalurid catfish Vary significantly for traits such as growth, disease resistance, harvestahility, reproduction, body conformation and carcass yield. Growth of domestic strains can be 250% greater than that of wild strains. Strain differences have also been identified for clariid, bagrid, and silurid catfishes. Mass selection has increascd growth rate by up to 30%. Heritability estimates predict a rcsponse to selection for the traits of diseasc resistance and tolcrance to low oxygen Icvels. Crossbreeding strains of Ictalurus punctatus have improved growth, diseasc resistance and reproductive performance. Two generations of inbreeding depresscd body weight of I. punctatus as much as 30%. and can reducc viability and reproductive performance. Hybridization of I. punctatus X I. furcatus has resulted in a 20% increase in growth. Traits for tolerance to oxygen deficit, feed conversion, disease resistance, harvestability, and carcass yicld were also irnproved. Interspecific, intergeneric, and intcrfamilial hyhrids have bccn made with clariid fishes; heterotic growth was indicated. Hybridization has also been used to combine desirable traits of parental species. Sex reversal of I. punctatus using estrogen treatment followcd by progeny testing can result in monosex, all-male populations. Gynogenesis and androgenesis are approaches to production of inbred lines of catfish, but thus far have limited application in aquaculture. Polyploidization has been applied in several ictalurid, silurid, and clariid fishes, but predicted improvements in performance have not been realized. Gene transfer has been accomplished in I. punctatus and Clarias gariepinus using microinjection and electroporation; the foreign genes have been expressed and inherited. Transgenic I. punctatus containing salmonid growth hormone genes grew 20-40% faster than controls.