...when you cross a donkey with a zebra?



You get a zedonk with striped knee socks!

A female donkey (Equus africanus asinus) crossed with a male zebra (E. quagga) results in a zedonk, as shown above. A female horse (E. caballus) crossed with a male donkey (E. africanus asinus) results in a mule. If you cross a female donkey with a male horse, the offspring is called a hinny. These hybrids are all infertile, which I believe is true for all mammal hybrids, but it is not true for most, if not all, fish hybrids.

Fish don't go around looking to mate with a fish of a different species, it only happens in areas of overlapping ranges where the population of one species greatly exceeds the population of the other species. At least that's how it happens with Centropyge hybrids.