Fish meal based diets are important in fish farming. As with other living organisms, the growth, health and reproduction of fish are dependent on adequate nutrient supply, and feed quality has a significant impact on the quality of fish meat. The aquaculture consumes 70 per cent of the global production of fish oil and 34 per cent of the total fishmeal. It is estimated that the demand for fish meal (FM) for feed will increase even more. This increased demand will surpass the natural fish supply and so it is crucial to find alternative protein sources to reduce pressure on the natural fish ecosystem. It is essential that the alternative sources compare well with the fish by-products and do not harm the fish health and growth. Therefore, this study examined the suitability of UK produced rapeseed meal (RM) as an alternative to FM to prepare nutritious diets to maintain mature fish and their impact on the water quality. Common carp (fish) was selected for their ability to cope with variable situations and for their low rearing cost.