The aim of this paper is to evaluate to what extent, the study of feeding regimes of fish could be valuable to indicate the possibilities and the constraints of their domestication. Though the natural feeding regime of fish seems to be disadvantageous for their domestication, as protein requirement is high, different species could be considered as domesticated. These species are herbivorous, detritivorous, omnivorous as well as carnivorous. In the same way, there are large differences in gut anatomy, but domestication concerns species with or without stomach, and species with short or very long intestine. Nutritional requirements do not allow predicting species that could be domesticated. Some species seem to be able to use vegetable protein in substitution to fish meal, and it appears that even the most carnivorous species can be fed in large part with a mixture of vegetable protein. Some species can tolerate high dietary lipid levels, others can utilize carbohydrates. These physiological trends must be taken into consideration in their domestication process. But domestication would certainly affect nutritional metabolism and consequently fish biochemical composition as well.