2.3 Biodiversity and Genetics

Bartley, D.

Figure 2.3.1
Although genetic improvement of common carp probably started several thousand years ago, the application of genetic principles to most aquaculture species is a relatively recent phenomenon. Thus, the majority of farm-raised aquatic animals and plants are very similar to their wild forms. Genetic improvement programmes are beginning to be applied to more and more aquatic species, but when compared to the levels of domestication in livestock and crops, the aquatic sector is still far behind. The number of farmed taxa for which data are reported to FAO has increased for all major groups since 1984: 34% for fishes, 29% for crustaceans, and 31% for molluscs (Garibaldi, 1996) ( Figure 2.3.1). As domestication extends to more and more species, so will the application of genetic improvement technologies.

Documentation and characterization of the biodiversity of aquatic organisms are vital first steps towards its sustainable use and conservation (Bartley and Welcomme, 1996). Although the number of farmed species reported to FAO is increasing, there is a vast amount of information on genetically differentiated strains, races, varieties and genetically improved species that is not well reported. Such information may not be used effectively to improve aquaculture production. For example, almost none of the hybrids used in aquaculture have been reported as such in national statistics (Bartley et al., in press). In order to assist with documentation, the International Center for Living Aquatic Resources Management, in collaboration with FAO and others, is distributing a relational database on CD-ROM, FishBase, that contains information on many aspects of aquatic biodiversity, including introduced species, fish health, distribution maps, strain registry, genetics and aquaculture (Froese and Pauly, 1996).

A small percentage of aquaculture production now comes from genetically improved species (Gjedrem, 1997). (This refers to directed genetic improvement and not simply to the domestication process). Therefore, there is tremendous scope to increase productivity by applying techniques of genetic improvement, such as selective breeding, chromosome manipulation, hybridization, production of mono-sex groups, and gene transfer.

Figure 2.3.2

Selective breeding programmes represent a long-term genetic improvement strategy and are the best means to use fully the genetic resources of aquatic species. However, short-term strategies are also being applied for immediate increase in production. Hybridization between cachama (Colossoma macropomum) and morocoto (Piaractus brachypoma) accounts for perhaps 80% of the aquaculture of these species in Venezuela. Manipulation of the sex of tilapia broodstock through hormone-induced sex reversal and subsequent breeding can be used to produce predominately male tilapia which then allows tilapia breeders to take advantage of the better growth rates of male tilapia and reduces unwanted reproduction. This technology is being developed and tested in the Philippines as part of a Department for International Development (UK) project with Central Luzon State University (Mair et al., 1995) for commercial application.

Another technique receiving current attention is the transfer of genes between species, or the addition of copies of a species’ own gene to improve production. Transgenic common carp, catfish, coho salmon and tilapia have been produced and are being tested for commercial use. Transgenic Atlantic salmon are now being marketed to the industry (Entis, 1997). These transgenic fish demonstrate increased growth and have the potential to increase aquaculture production substantially.

However, there are numerous concerns that must be overcome before full commercial application. Testing of transgenic salmon in Scotland was opposed by several public groups. Expressed concerns were that: i)transgenic fishes may escape into the wild and disrupt natural populations; ii) the "transgene" could be passed on to wild relatives; iii) consumers would not accept genetically modified organisms; iv) the transgene could cause human health problems if it produced an allergic response where no response was produced by the non-transgenic organism; v) animal welfare may be compromised by the addition of the transgene; and vi) genetic engineering is morally and ethically wrong. In response to these concerns, many researchers and developers are abiding by performance standards such as those produced by the US Department of Agriculture (ABRAC, 1995), and by international agreements, such as the Convention on Biological Diversity and the FAO Code of Conduct for Responsible Fisheries.

The Convention on Biological Diversity has recently designated aquaculture, especially coastal aquaculture, and agrobiodiversity, which includes biological diversity and genetic resources used in or of potential use to aquaculture, as priority areas for action. These international mechanisms acknowledge the value of genetic diversity to both natural ecosystems and aquaculture production systems. Nearly all genetics technologies and breeding programmes rely on genetic diversity as the raw material for improving farmed species. Technical guidelines have been produced to help implement the section of the FAO Code of Conduct for Responsible Fisheries that deals with aquaculture and the use and protection of aquatic biological diversity.

Many genetic techniques have been refined to a point where they are becoming practical for commercial aquaculture and are now being combined to improve production and to address biosafety concerns. For example, transgenic Atlantic salmon are made triploid to reduce the chance of them breeding if they escape. (Entis, 1997). Hybrid Pacific salmon do not perform well in culture, but hybridization combined with triploidization has been shown to provide better sterility, improved growth, and better disease resistance for many species (see general review in Bartley, in press).

Modern molecular techniques now allow analysis of an organism’s DNA, such that family relationships and pedigrees can often be established and the genetic stock structure of natural populations can be determined. The use of DNA probes, specifically micro-satellite DNA probes, to identify families and establish pedigrees of farmed animals may greatly facilitate selective breeding programmes where physical tagging is impractical. Micro-satellite probes are being used to map the genomes of commercially important aquaculture species such as Atlantic salmon, carp, catfish, rainbow trout, brown trout, and oysters (e.g. Danzmann et al., 1997; Lie et al., 1997). The mapping effort, which involves collaborative research among several laboratories, countries, and the European Union, will also help identify genetic markers for traits that are of interest to aquaculture. DNA probes are also being used to identify minute quantities of such pathogens as shrimp viruses, thus helping to ensure that an organism is free of a specific pathogen (Wongteerasupaya et al., 1996; see also Section 2.2 Fish Health and Quarantine). Most of this work is in the research and development phase at present, but may provide benefits to the industry and to managers of natural aquatic populations in the near future.

Figure 2.3.3
Aquaculture is a rapidly growing sector with production steadily increasing at about 10% per year (see Section 1.1 Status of Global Production and Production Trends). However, the price of aquaculture products decreases as markets become satiated. For example, the 1995 value per tonne of production from Norway, which is primarily Atlantic salmon, was 29% lower than the 1984 value ( Figure 2.3.3). When these figures are adjusted for inflation, the decrease in price is even greater. Genetic improvement programmes were initially developed to increase production. Now one goal of genetic improvement programmes is to increase the value of the farmed product. Additional characters such as flesh quality, body shape and colouration, that are related to the economic quality of the product are being incorporated into genetic improvement programmes. A selective breeding project on red tilapia in Venezuela will try to improve skin colouration because of the higher market value of red tilapia (FAO unpublished report); the hybrid between the Thai and African catfish is popular because of its flesh quality.

There are still controversial issues that must be addressed in relation to biological diversity in aquaculture, such as the use of introduced species and genetically improved species. Genetic changes in aquaculture species as a result of selective breeding,hybridization, chromosome manipulation, and gene transfer complicate the regulatory structure meant to control the use and movement of such organisms and even the definition of the terms alien, exotic, and species (Pullin and Bartley, 1996). There is a trend toward more regulatory oversight and restrictions on the use of transgenic organisms because this technology is perceived as having a greater risk than other forms of genetic improvement (see above). Although certain technologies, such as gene transfer, may have more uncertainty associated with their use, it is the product of the technology that should be evaluated as to its risk and not the technology per se; that is, the change in an organism’s phenotype and not the method used to impart that change should be examined (Pullin and Bartley, 1996). Uncertainties must be addressed through extensive testing, and evaluation and a precautionary approach should be adopted as part of the regulatory oversight. Codes of practice and guidelines for the responsible use of introduced species and genetically modified organisms (e.g. Bartley et al., 1996) and for the application of the precautionary approach to species introductions (FAO, 1996) have been produced to assist in this area.

ABRAC. 1995. Performance Standards for Safely Conducting Research with Genetically Modified Fish and Shellfish. U.S. Department of Agriculture, Agriculture Biotechnology Research Advisory Committee (ABRAC), Working Group on Aquatic Biotechnology. Document No 95-01.

Bartley, D.M. (In press). Genetics and breeding in aquaculture: status and trends. Presented to the Seminar on Genetics and Breeding of Mediterranean Aquaculture Species. Network on Technology of Aquaculture in the Mediterranean, Zaragosa, Spain, 28-30 April 1997. Zaragosa, International Center for Advanced Mediterranean Agronomic Studies, and Rome, FAO.

Bartley, D.M. and R.L. Welcomme. 1996. Goals and activities of FAO in relation to fish genetic resources, p. 6-8. In R.S.V. Pullin and C.M.V Casal (eds). Consultation on Fish Genetic Resources. International Center for Living Aquatic Resources Management and CGIAR System-wide Genetic Resources Programme, 11 - 13 December 1995, Rome, Italy.

Bartley, D.M., R. Subasinghe and D. Coates. 1996. Framework for the responsible use of introduced species. EIFAC/XIX/96/inf. 8. Report of the 19th Session of the European Inland Fisheries Advisory Commission, Dublin, Ireland.

Bartley, D.M., K. Rana and A.J. Immink. (In press). The use of inter-species hybrids in aquaculture and their reporting to FAO. FAO Aquaculture Newsletter. Rome, FAO.

Danzmann, R.G., T.R. Jackson, M.M. Ferguson and P.E. Ihssen. 1997. The identification of multiple QTL influencing temperature tolerance in rainbow trout and their phenotypic effects and genomic backgrounds. Abstract and presentation to the Sixth International Symposium on Genetics and Aquaculture, 24-28 June 1997, Stirling, Scotland.

Dunham, R. A. 1995. The contribution of genetically improved aquatic organisms to gGlobal food security. Thematic paper presented at the Japan/FAO International Conference on Sustainable Contribution of Fisheries to Food Security, 4 - 9 December 1995, Kyoto, Japan.

Entis, E. 1997. Aquabiotech: a blue revolution? World Aquaculture 28: 12 - 15.

FAO. 1996. Precautionary approach to fisheries. Parts 1 and 2. FAO Fisheries Technical Papers 350/1 and 350/2. Rome, FAO.

Froese, R. and D. Pauly (eds.). 1996. FishBase 1996: concepts, design and data sources. Manila, ICLARM. 179 p.

Garibaldi, L. 1996. List of animal species used in aquaculture. FAO Fisheries Circular No. 914.Rome, FAO.

Gjedrem, T. 1997. Selective breeding to improve aquaculture production. World Aquaculture 28: 33- 45.

Gupta, M. V. and B. O Acosta. 1996. Proceedings of the Third INGA Steering Committee Meeting, Cairo, Egypt, 8-11 July 1996. International Network of Genetics in Aquaculture. Manila, ICLARM.

Lie, O., R. Danzmann, R. Guyomard, L.E. Holm, B. Hoyheim, R. Powell, A. Slettan and J. Taggart. 1997. Constructing a genetic map of salmonid fishes: SALMAP. Poster presentation to the Sixth International Symposium on Genetics and Aquaculture, June 24 - 28, 1997,, Stirling, Scotland.

Mair, G.C., J.S. Abucay, J.A. Beardmore and D.O.F.Skibinski. 1995. Growth performance of genetically male tilapia (GMT) derived from YY males in Oreochromis niloticus L.: on station comparisons with mixed sex and sex reversed male populations. Aquaculture 137: 313-322.

Pullin, R.S.V. and D.M. Bartley. 1996. Biosafety and fish genetic resources, p. 33-35. In R.S.V. Pullin and C.M.V. Casal (eds.). Consultation on Fish Genetic Resources. International Center for Living Aquatic Resources Management and CGIAR System-wide Genetic Resources Programme, 11 - 13 December 1995, Rome, Italy.

TECAM. (In press). Report of the Seminar on Genetics and Breeding of Mediterranean Aquaculture Species. Network on Technology of Aquaculture in the Mediterranean (TECAM). Zaragosa, International Center for Advanced Mediterranean Agronomic Studies, and Rome, FAO.

Wongteerasupaya, C., S. Wongwisansri, V. Boonsaeng, S. Panyim, P. Pratanpipat, G. Nash, B. Withyachumnarnkul and T. Flegel. 1996. DNA fragment of Penaeus monodon baculovirus PmNOBII gives positive in situ hybridisation with white-spot viral infections in six penaeid shrimp species. Aquaculture 143: 23- 32.