This has recently been discussed on LinkedIn. Walubita from Zambia was looking for a moist diet that floated for tilapia and catfish in Zambia.
My suggestion was using wheat gluten at around 8-12% inclusion depending on the formulation - I have used this successfully to make floating pellets for the tuna and crocodile farming industry. Stops wastage and the crocs struggle to eat pellets on land, unless you hand feed them and nobody seems to like that job!
There is a moist diet formulation for catfish at http://www.fao.org/docrep/X5738E/x5738e0n.htm - a good place to start but use 10% wheat gluten and 10% flour. You won't need the carboxymethylcellulose but use it if you have some. I would use all fish oil if possible.
Mix all the dry ingredients thoroughly first and the mincer works well with one or more openings or nozzles and a knife cutter to cut the sausage into pellets. I used a mixer mincer which is essentially a large hopper that feeds the mincer so it becomes a little more automated. This pellet really holds together well. Make sure you mix thoroughly beforehand. A dough mixer really does the job well because you need to get the wheat gluten to go "strandy" and bind it all together. It becomes very elastic when well mixed and there is very little wastage.
For crocs, substitute wet fish for red meat if that is more plentiful. We used fresh road kill kangaroo here and it worked a treat.