Discus fish are hugely popular in the fishkeeping world, not just because of their Frisbee shape and their beauty, but also because of their unusual spawning behaviors. Both parents care for the eggs, and both continue to care for the fry after hatching. That part isn’t unique, but this is: both parents also produce a nutritious mucus on their skin, which the fry nibble on. This mucus is the sole food source for the fry until they reach a size at which they begin looking for live prey.