This depends on the fish you're growing, carnivores like trout and bass would prefer a higher protien diet, somewhere in the range of 40-50% protein. Omnivorous fish like tilapia, koi, or catfish require less protein, around 32%. Ensuring that your fish are getting the right nutrients means that they'll be able to provide your plants everything they'll need to grow.
You'll typically want to feed your fish as much as they can eat in around 5 minutes, scooping out any extras to keep the water clean. Fish can go a long time without food, lean on the side of under rather than overfeeding. If you're cycling your system with your fish, you'll want to feed them as little as possible during this time in order to minimize the amount of ammonia being released. Too much food means a lot of waste, and a lot of ammonia for your bacteria to handle, this can hurt your fish if the levels get too high.
