The Amazing World of Gumball - Season 4

When Mum sees Darwin gazing longingly at a fish-tank she thinks their mammalian lifestyle isn't fulfilling her adopted son and that deep down he longs to connect with his fishy roots. So the family tries to re-connect him with his aquatic culture; they try fish-food, fish-language, even fish clothes. But when none of it works, they realise they may have to let him go.