That's a great question and one that could use a lot of research since there are a lot of saltwater fish that will not live in fresh water but would be great to raise. Cobia would be my choice. What research I have seen has focused on plants that thrive on ammonia rather than converting it to nitrates. One such plant is ulva, or sea lettuce. This does not have to be dried and is useful in a variety of ways including salads, soups, and even in ice cream. No, I don't think it is ulva flavored ice cream. It seems to be a thickening agent. Further research could be done in experimenting with gradually increasing the saltwater tolerance level of fresh water vegetables. Research has already been done in lowering the salenity level for some species of saltwater fish successfully. So a happy medium might be realized with some fish and some more common food plants. The other comment previously made about dried seaweed is certainly true. Here's a link to the use of seaweed in saltwater aquaponics. http://www.aquaponicsjournal.com/docs/a ... inator.pdf