The application of gene manipulation to aquaculture

Abstract

Both finfish and shellfish are very suitable types of animals to use in terms of the introduction of novel genes into their genomes (transgenic induction). Genetic manipulations involving gynogenesis, androgenesis, triploidy, and sex reversal are already established, and future applications of DNA manipulations may well include population studies by DNA analysis and genetic tagging prior to release. Methods for the production of transgenic fish are considered and success to date with rainbow trout, Atlantic salmon, tilapia, channel catfish, medaka, zebrafish, goldfish, carp and loach is discussed. Transgenic induction techniques normally involve injection of cloned copies of the appropriate gene into the cytoplasm of the fertilized egg by microinjection. Ways of assaying for integration, expression and germ line transmission are reviewed. Candidate genes for transgenic induction in fish include those coding for somatotropin (growth hormone), somatotropin release factor, metallothionein, ‘antifreeze’ proteins, crystallin, esterases, and disease resistance factors (when available); useful promoter sequences include metallothionein, heat shock and those of other tissue-specific genes. The use of genes and promoters from piscine rather than mammalian sources will probably be advantageous both for effective expression and the market image of the product. Transgenic fish are also considered as potential expression systems for pharmaceutical products, and problems of containment and planned release are discussed.