Biotechnology Tools in Fish Breeding

Hein van der Steen

PIC international Group

2929 Seventh Street, suite 130

Berkeley, CA 94710

Hvandersteen@pic.com

ABSTRACT

Breeding programs in fish are in general in early stages of development. The combination of know-how from plant breeding, animal breeding and genomics however creates an opportunity to further develop such programs. Faster growth rate, improved product quality and disease resistance will increase the economic viability of aquaculture. Before we can start a breeding program however, the reproductive cycle in an aquaculture setting needs to be under control. The commercial success of a fish-breeding program depends on product differentiation and genetic protection. Many livestock breeders protect their investment in developing superior performing animals by only releasing crossbred animals to farmers. In fish, it may be possible to protect stocks by only releasing female triploid fish, which are sterile.

KEYWORDS: fish breeding, implementation, genetic protection, biotechnology

INTRODUCTION

More or less sophisticated breeding programs have been developed for poultry, pigs and cattle. Fish differ substantially due to the higher reproductive rate of the females, the more limited impact of inbreeding, and the low cost of an individual. This creates the opportunity to combine both the theory and methods of animal and plant breeding for the development of fish breeding programs. Concepts such as elite inbred lines, mutagenesis and polyploidy can be introduced into an animal breeding program. Fish breeding can leapfrog existing animal breeding programs by making efficient use of new and emerging technologies, avoiding the pitfalls encountered in terrestrial animal breeding such as a narrow genetic base, product quality issues, and physiological problems associated with fast growth rate.

TECHNOLOGIES

Advanced DNA and reproductive technologies that offer opportunities for faster genetic gain are available to genetic improvement companies. However, inappropriate application of these techniques may in fact reduce gain and promote loss of genetic variation. Advances in mathematical genetic theory for managing genetic variation in a sustainable and optimum way have been developed for animal breeding and can be further developed for the design of fish breeding programs.

DNA identification, gene discovery and mutagenesis can contribute significantly to the development of more suitable genotypes. The identification of genes and markers controlling the genetic variation in economically important traits enables the development of Marker Assisted Selection (MAS) as an important component of the breeding program. This is of particular interest for traits such as survival and meat quality that are difficult to improve through traditional quantitative breeding programs. The generation of new mutations can also lead to genetic variation that can be exploited through MAS. Experience in plant breeding can be used to evaluate mutagenesis as a new useful tool for genetic improvement. It is an interesting opportunity in fish due to the high reproductive rate, the low cost per individual and availability of molecular tools to exploit favourable mutations. Basic work on manipulation of gametes and embryos (polyploidy, sex-reversal) will increase efficiency of genetic development and of production.

GENETIC DIFFERENTIATION

Investment in fish breeding, as in other animal breeding industries, can only be sustained if the genetic margins are adequate. This will be the case if a clearly differentiated product can be developed. Development of specialized sire and dam lines creates an opportunity for crossbreeding and heterosis. In all lines we need to put emphasis on survival, growth and product quality. Given the reproductive capacity, the commercial generation can be crossbred while the parents are most likely purebreds. In this case egg production by females and semen production by males is added as an objective for Dam and Sire lines, respectively.

GENETIC PROTECTION

The high reproductive rate in fish makes it unattractive for breeding companies to sell brood stock. Production of second-generation progeny will lead to low genetic margins per unit of end product. In that case serious investment in genetic development will not take place. Several routes to genetic protection can be explored.

Optimal line development will result in a differentiation between Sire and Dam lines. The degree of differentiation will depend on economic values and genetic parameters. The differentiation will be largest if we only put weight on growth efficiency in the Sire lines and on reproductive efficiency in Dam lines. This strategy can contribute to genetic protection but would not be powerful enough in its own right.

The use of Artificial Reproductive Technology (ART) can lead to a reduced efficiency of natural mating and might provide a tool to overcome species barriers in crossbreeding. This would result in the production of a terminal generation that is not suitable for the production of an F2 generation.

Triploids and tetraploids can be produced using cold shock. Triploids are sterile and might grow faster than diploids. Application of this technology would require permanent induction of triploids for commercial use or the production of fertile tetraploids that, mated with diploids, produce the triploid commercial generation.

Females grow faster than males. Sex reversal has been achieved in fish but the challenge will be to produce 100% success rate. An 80% success rate would be valuable for commercial production but would not give us the genetic protection that we need. Ultimately, the production of a triploid, all female terminal generation would be a powerful tool to develop genetic protection.

The number of parents in fish production is relatively low. We can fingerprint Grand Parents and produce mating schemes that result in the production of progeny (Parents) with known marker genotype. Many different procedures can be envisaged. The important conclusion is that genetic protection through molecular identification is possible and can go hand-in-hand with traceability schemes.

CONCLUSIONS AND RECOMMENDATIONS

Short-term (1-3 years):

1. Develop reproductive technology to facilitate reproduction of additional species in an aquaculture setting.
2. Develop optimum fish breeding programs
3. Develop polyploidy

Mid-term (4-7 years)

4. Develop mono-sex production systems
5. Develop genetic markers for traits that are difficult to improve with quantitative genetic programs

Long-term (8-10 years)

6. Develop a variety of lines in different species to facilitate fish production (aquaculture) in a way that is sustainable with respect to the environment and customer requirements.