Advancing the selective breeding of seabass and sea bream

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It is now unthinkable to farm Atlantic salmon without an advanced selective breeding program. The sea bass and sea bream sectors have been slower to adopt them, but genetic research in the MedAID project funded by H2020 has helped to improve the farming of these two main aquaculture species in the Mediterranean.

Selective breeding is a long-term process, where the goal is to improve desirable characteristics, such as production efficiency, disease resistance and product quality.

The potential of selective breeding is great. Average genetic gains for growth-related traits are 12 percent per generation in all species, and genetic gains for growth are estimated at € 0.2 per kilo of fish for gilthead seabream and Atlantic salmon. MedAID has contributed with tools, methods and knowledge in biology and genetics to improve European seabass and seabream production.

Selective breeding status of sea bream and European sea bass

The first commercial sea bream breeding programs were initiated in the early 2000s. Since then, the sector has been consolidated and breeding programs have developed accordingly. In 2016, it was estimated that around 50 percent of farmed European bass came from selective breeding programs..

Compared to the Atlantic salmon industry, which catches much larger volumes of fish than sea bream and European sea bass, there are a relatively high number of breeding programs for these Mediterranean species. However, such programs are often integrated into juvenile production facilities, rather than taking place in specialized selective breeding units. The complexity of breeding goals differs, but some rely on disease resistance traits in addition to more commonly used productivity traits, such as growth rate.

Below are some of the technical discoveries made by genetic researchers involved in MedAID. Together they provide the opportunity to conduct further selective breeding of European seabass and sea bream.

1. A new genomic resource has been developed

High throughput genotyping chips are essential tools for genetic studies. Genetic markers representative of the entire genome are placed on a chip and can provide information at the individual level very efficiently.

MedAID, in cooperation with the Performfish project, developed a combined genotyping set called MedFish for seabass and bream. It contains around 30,000 genetic markers per species.

This information can, for example, be used to estimate genomic selection values, map genes, estimate (genomic) parameters – including effective population size (a parameter inversely related to loss of genetic variability) – and understand the genetic structure of populations.

2. Lipids for fish and human health and production efficiency

We have worked with lipid-related production traits in MedAID. Excess fat is linked to lower production efficiency in all animal productions. In smolts, we showed that the feed conversion rate (kg feed / kg fillet) was improved by about 4 percent when reducing body fat content by 1 percent, which reduced feed costs accordingly at the farmer level. It is also known that the excessive deposition of lipids in the body and internal organs increases the risk of metabolic disorders, oxidative stress and inflammation. Thus, studies on the compartmentalisation of lipids in different organs can provide information on the state of health of fish.

The main parameter for a trait’s potential to be improved by selective breeding is its heritability. In MedAID, we showed that the heritability of muscle fat content is moderately high in European seabass (0.59) and sea bream (0.34), which means that 59 and 34 percent of the variation muscle fat can be explained by genetics and not by the influence of the environment. Weak genetic correlations between muscle fat and body weight in both species indicated that genetic variation in muscle fat content is largely independent of growth. In European sea bass, we have also shown that the total fat content of the liver, which is the main organ of lipid metabolism and transport, and of the tenderloin are to a large extent independent traits. This suggests that these two lipid deposits are regulated independently. In gilthead sea bream, we have found indications that there is a strong genetic component for the rate of lipid synthesis in muscle. This is not seen in Atlantic salmon.

However, not only the total fat content but also the individual fatty acid content is studied in fish, especially the marine long-chain omega-3 fatty acids EPA and DHA, due to their beneficial effects on the health of the fish. fish and humans. Our results showed that both species had high levels of these fatty acids and that selective breeding is a promising tool to increase their content in fillets of sea bream and sea bass, with heritability for the percentage of DHA of 0.33 and 0.51, respectively. In sea bass, using genomic markers, we have identified candidate genes for omega-3 traits.

3. The major traits depend on the interaction between genes and the environment

Genotype-by-environment interaction (GxE) is the phenomenon that occurs when different genotypes behave differently in different environments. If it exists for a species, breeding strategies need to be adapted or environment-specific breeding programs need to be developed. MedAID results on sea bream show that harvest weight, growth rate and net weight all showed strong GxE interactions between the eastern (Greece) and western Mediterranean (Spain). Genetic improvement programs for crop weight, net weight and growth rate must take into account the target production environment. The most important environmental effect in this study was differences in sea temperature (identical feeds were used), indicating the need to breed fish with better ability to cope with changing environmental conditions. rapid, for example caused by climate change.

4. Genetic stratification of wild and farmed populations

The results of a population genetics study showed a greater stratification of seabass populations than of sea bream populations. The MedFish Matrix can distinguish wild populations from farmed populations and determine the genetic diversity that exists within the populations. There is a clear differentiation between wild and farmed populations in the two species, indicating that care should be taken to avoid breakouts that could have unwanted genetic effects in native populations. Several breeding populations had small effective population sizes, demonstrating the need to apply selection and mating approaches designed to control inbreeding and loss of genetic variability to ensure the sustainability of breeding programs. .

The history of the project

The roots of the MedAID project can be traced back to the meeting of the European Aquaculture Society (EAS) in San Sebastian, in 2014, where EAS and EATIP organized a session to identify areas of cultivation of these species that were underutilized and could be improved. They included fish health, fish nutrition but also genetics. Comparisons with the Atlantic salmon industry have been made.

The report of this session was an important background document for the European Commission for the establishment of a call for the H2020 framework program on Mediterranean aquaculture with a holistic and integrated approach, with both science activities social and technical.

The two sister projects MedAID (www.medaid-h2020.eu) and PerformFISH (www.performfish.eu) were born. MedAID was led by CIHEAM (Spain). MedAID genetics work was led by Nofima (Norway). The University of Edinburgh – Roslin Institute (UK), INIA (Spain), Wageningen University (Netherlands) and Ege University (Turkey) were research partners. The main R&D activities were carried out in collaboration with industrial partners ABSA-Culmarex (Spain) and Galaxidi Marine Farm (Greece). In addition, anonymous farmers from all over the Mediterranean sent fish samples for analysis.

This is a very good example of collaboration between research and industry partners, with the aim of improving the European aquaculture sector through genetics and selective breeding.

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