Increased profits in aquaculture through optimised dissemination schemes

Abstract

We studied a typical breeding nucleus with dissemination of genetic material directly from the nucleus to the grow-out level by stochastic simulation. Profits could be increased through production and dissemination of specialised stocks suited for specific production environments or markets. Truncation selection of 50 sires and 200 dams (trunc ♂2.5% ♀10%) and of 5 sires and 25 dams (trunc ♂0.25% ♀1.25%) were compared to random selection of 50 sires and 200 dams (rand ♂2.5% ♀10%). Higher profit was obtained for all truncation selection schemes as compared to random selection, and increasing with decreasing proportion selected. By optimising the selection of parents, which are used for dissemination from the nucleus to the grow-out, instead of using randomly selected nucleus parents, an additional response corresponding of approximately 1.5 generations of selection in the nucleus was achieved. The effect of the correlation between the nucleus breeding goal and the breeding objective of the grow-out was that profit was highest when the correlation was high. With a negative genetic correlation between the traits, profit was still high if the trait with the highest heritability (i.e. the trait measured on candidate itself) had the highest economic value. The range of ΔF in the 7th generation in the nucleus was [− 0.0075–0.0269] with SD equal to 0.0056. The average over all the replicates was 0.0095. This study showed that selection of specialised stocks for specific breeding objectives from the nucleus to the grow-out level will give the grow-out producers a direct and extra genetic improvement and that selecting breeders in the nucleus for dissemination gives also more flexibility for a final product, by adapting economic weights for each grow-out producer.

Introduction

Some marine aquaculture species, e.g. Atlantic cod (Gadus Morhua), sea bass (Dicentrarchus labrax), and sea bream (Sparus aurata) have very high fecundity. For example, female Atlantic cod can spawn millions of buoyant eggs in multiple batches over a period of about two months (Kjesbu, 1989), depending on the size of the female. In European sea bass fecundity range between 300,000 and 650,000 eggs kg^− 1 (Carrillo et al., 1989, Mylonas et al., 2003), and sharpsnout sea bream (Diplodus puntazzo) can produce between 2.36 and 4.95 million eggs kg^− 1 body weight (Papadaki et al., 2008). Therefore, large amounts of surplus eggs can be produced in a breeding nucleus and facilitate dissemination of high volumes of improved material (typically fertilised eggs) to the grow-out producer without time lag caused by use of dedicated multiplier units as required for species of lower fecundity like salmonids. Assuming intermediate to high survival of eggs and fingerlings, only a relatively low number of breeders is needed to meet the demand for animals at the grow-out level. For example, an Atlantic cod of 90 cm will be able to produce 8 million eggs (Otterå et al., 2005) and with a survival rate of 25%, this results in 2 million slaughter fish per female, which implies that the entire Norwegian production of farmed Atlantic cod harvested in 2008 could be obtained with only 10 females (Lassen, 2009).

Much attention has been paid to optimise the nucleus selection schemes in aquaculture (Bentsen and Olesen, 2002, Gjerde et al., 1996, Martinez et al., 2005, Martinez et al., 2006). However, we are not aware of any published study directed towards optimisation of dissemination schemes and exploitation of the potential for additional selection response stemming from non-random selection of parents from the nucleus to the grow-out level for aquatic species. It is more common in other species, like in crop production, where non-random selection is generally practiced, to tailor crops suitable for specific conditions, e.g. highland and lowland productions (Kizito et al., 2007). In cattle breeding it is also common to provide farmers with EBVs for individual traits for each of its bulls allowing customers to select sperm for their cow herd according to their specific needs and farming environment (A.G. Larsgård, pers. comm. 2009). Following current practices in the aquaculture industry, it is likely that material provided to the grow-out level reflects the average genetic level of the nucleus material, because the simplest way to distribute the breeding material to the producers is that all grow-out farms are offered fry from parents that are randomly selected from the nucleus. Here, we hypothesise a potential for increased profits at the grow-out level by producing specialised genetic material that is suited for a specific production environment or a market segment, achieved through intensive selection among potential parents of the dissemination animals resulting in increased selection differentials. For example, grow-out producers in areas with a high risk for outbreak of a specific disease can receive progeny only from nucleus parents with the highest possible EBV for resistance against the specific pathogen involved. Alternatively, grow-out producers in a specific market that has an extraordinary demand for meat quality (for example), can have progeny from parents with the highest breeding values for this trait.

The aim of this study was to compare and quantify the expected profit for marine fish species at the grow-out level under two main scenarios: a) a standard aquaculture breeding scheme where parents for dissemination material are selected randomly from the nucleus, and b) selection of parents by truncation selection with two different proportions of selection. We assumed a breeding program for species with very high fecundity, marketing fertilised eggs from broodstock of high genetic value. It is further assumed that the breeding program that we consider has overcapacity in terms of egg production, i.e. that production capacity exceeds market demand, which is the case for most commercial aquaculture breeding programs. The overcapacity is needed to be competitive. In addition, overcapacity exists, because it is not possible to reduce the number of candidates to only use the very few sires and dams that are actually needed to serve e.g. all Norwegian producers of Atlantic cod, because this will result in unacceptably low effective population sizes of the population. The variables investigated were i) the selection proportion from the nucleus, ii) the correlation between the breeding goals of the nucleus and for the grow-out level, iii) the correlation between the traits in the nucleus, and iv) economic weights assigned to the traits in the nucleus and for the grow-out level. The profit of the different selection methods and proportions were compared in generation 7.