Is there anything on the package that says for freshwater or saltwater fish, or both? I would only be wary of feeding it to freshwater fish because of the salt. Brine shrimp are hatched in very very salty water, and if it is sold as a marine fish food there is probably a lot of that salt left. If you want to feed it to the freshwater fish, maybe you could try putting some of the gel into a very fine net (brine shrimp net) and rinse it with some dechlorinated water.