You mean to collect electricity from them commercially I suppose, we wouldn’t be generating the electricity, the fish do that. The answer is I shouldn’t think so, they need to live and move around. Also to generate a sustained flow of any use you would need tens of thousands of fish connected to your system. I doubt it would be cost effective once you started paying for housing and food. More importantly I think it would be highly immoral, to get the fish to regularly release electricity would require constantly stressing them, which would be the equivalent of torture. Most of the environmental problems on our planet stem from humanity’s attitude of casual abuse towards nature. Fixing this attitude is actually a problem of huge importance for the future of our species and for all life on this planet. There are many better ways of generating electricity.