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Genetic improvement of cultured marine finfish: case studies
Knibb, W.; Gorshkova, G.; Gorshkova, S. (1998). Genetic improvement of cultured marine finfish: case studies, in: De Silva, S.S. Tropical mariculture. pp. 111-149
In: De Silva, S.S. (1998). Tropical mariculture. Academic Press: San Diego. ISBN 0-12-210845-0. 487 pp., more

Available in  Authors 
    VLIZ: Aquaculture [7213]

Keyword
    Marine

Authors  Top 
  • Knibb, W.
  • Gorshkova, G.
  • Gorshkova, S.

Abstract
    In sharp contrast to land agriculture, tropical and marine fish mariculture benefit little from genetically improved strains. Obviously, the short history of fish mariculture provided little opportunity for selection gains. Also, husbandry and reproduction technologies remain unreliable for most captive marine fish, and greatly impede genetic research and application (see Gjedrem, 1985; Colombo et al., 1996). To date, the few attempts to conduct genetic improvement in cultured marine fish were restricted mostly to species within the Sparidae, Moronidae and Pleuronectidae where some control over husbandry and reproduction existed. This information may guide future attempts genetically to improve tropical and other marine fish, including the mullets, groupers, tunas, etc. Between-strain differences for performance in culture were detected for Sparidae, even though few strains were tested. This finding should encourage further strain assessment for marine fish. Also, future programmes should assess possible genotype x environment interactions (whether different strains are required for different environments), and the importance of competitive and magnification effects (for strain comparisons in communal rearing conditions). Reproductive constraints dictate present choices of within-strain selection methods. Mass selection, rather than family selection, was technically possible for the group spawning S. aurata, and usually resulted in genetic gain for growth. Contingent upon advances in husbandry and reproductive technologies, future possibilities for within-strain selection include: - selection for traits other than growth, including carcass quality/composition and disease resistance (Chevassus & Dorson, 1990); - selection for several traits simultaneously, and for overall economic value using index selection and additional performance information from relatives (Falconer, 1981);- use of precise methods to quantify selection criteria, including molecular assays for disease incidence (Knibb et al., 1993); - use of variable DNA markers to permit pedigree analyses (even from mass matings), and to detect linkage groups of economic importance (Magoulas et al., 1995); - reduction of generation intervals (through induction of precocious sexual maturation with hormonal therapy) in order to accelerate rate of genetic gain;- selection of fish grown under full commercial production conditions to optimize commercial gain. Many new interspecific marine fish hybrids were created, but information on their performance in commercial culture is scarce. Presently, only the striped bass hybrid is popular with farmers. Some intergeneric Sparidae hybrids had vestigial gonads that also were sterile, but hybrids failed to show growth acceleration. Sterile hybrids might be of commercial interest when production of fertile fish is restricted for ecological reasons. As for freshwater interspecific hybrids, the commercial prospects for each new marine hybrid appear remote. Similarly, various marine triploids and hybrid triploids were produced, but little information exists regarding their commercial performance, and few (if any) are used by farmers. Again, some have small and sterile gonads (especially hybrid triploids) with little or even contrary indication for somatic growth acceleration. A similar conclusion was reached for triploid C. carpio (Cherfas et al., 1994, 1995). Even so, ecological issues might sustain future research on sterile and triploid marine fish, and methods to produce them (e.g. using tetraploid x diploid crosses). Reviewing together the various combinations of marine fish hybrids, triploid hybrids, and triploids, it seems gonadal sterility and genetic sterility does not translate simply into superior somatic growth (also see Kerby et al., 1995). Logically, other factors, the most obvious being the overall hybrid or triploid genome, are associated with overall growth. Of the new species under consideration for culture, those which exhibit exceptionally large GSI values during reproduction may be more attractive candidates for triploidy and hybridization experiments. All female or all male (monosex) marine fish produced with administration of steroids. However, genetic procedures for monosex production without steroid treatment were not developed. Genetic engineering in marine fish remains in its infancy and is unlikely to progress without validated and efficient gene integration methods.

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