The health status and feed conversion efficiency of farmed fish may vary according to management and production methods. Successful aquaculture requires safeguarding the health of the growing fish and optimizing the feed conversion and therefore achieving better FCE thus reducing the amount of feed required to produce farmed fish, reducing the environmental impact generated by fish feed production and reducing aquaculture wastes generated by feed wasted or poorly digested. The present review presents illustrative examples from freshwater aquaculture that suggests the potential dual benefits of focusing on the link between feed conversion and the environmental impact of fresh water fish farms. Apart from the need to support future research on new diets for farmed fish (which is mainly driven by limits in the supply of fish protein and the results price fluctuation of all ingredients used by the aquaculture, feed industry), major improvements can be expected by optimizing feeding regimes and the application of probiotics. Aside from the economic benefits and increased production of fish farms, improved feeding regimes and probiotics are expected to have a significant impact on the welfare of farmed fish as well as on digestion efficiency and the environmental impact of fresh water fish farms.