Environmental impacts of genetic improvement of growth rate and feed conversion ratio in fish farming under rearing density and nitrogen output limitations

Today, fish farming faces an increasing demand in fish products, but also various environmental challenges.Genetic improvement in growth rate and feed conversion ratio is known to be an efficient way toincrease production and increase efficiency in fish farming. The environmental consequences of geneticimprovement in growth rate and feed conversion ratio, however, are unknown. In this study, weinvestigated the environmental consequences of genetic improvement in growth rate and feed conversionratio in an African catfish farm, using Recirculating Aquaculture System (RAS). In RAS, total fishproduction of the farm is limited by rearing density or by the capacity to treat dissolved nitrogen. Toevaluate the environmental consequences of genetic improvement in growth rate and feed conversionratio, we combined life cycle assessment and bioeconomic modelling of genetic response to selection.Weexplored different impact categories, such as climate change, eutrophication, acidification and energyuse, and we expressed impacts per ton of fish produced. Results show that the environmental impact ofgenetic improvement in growth rate and feed conversion ratio varies among impact categories anddepends on the factor limiting production at farm level (i.e. rearing density or nitrogen treatment capacity).Genetic improvement of feed conversion ratio reduces environmental impacts in each scenariotested, while improving growth rate reduces environmental impacts only when rearing density limitsfarm production. Environmental responses to genetic selection were generally positive and show similartrends as previously determined economic responses to genetic improvement in growth rate and feedconversion ratio in RAS. These results suggest that genetic improvement of growth rate and feed conversionratio for species kept in RAS will benefit both the environmental impacts and the economics ofthe production system