Get a couple of peas and stick them in boiling or hot water for a minute to soften them up. Squeeze the pea and the skin should come off, throw that bit away. Mush up the remaining pea and offer to the fish.
I buy frozen peas then thaw them in warm water. Then I de-shell them and smash them with my fingers until they are a kind of mush. Then they fish have an easier time eating them.