Are there mixed-breed fishes or birds?

Do fish and bird species have the same kind of ‘breeds’ that dogs and cats do? You know that dogs, for example, can interbreed among different breeds to make all kinds of mixed-breed ‘mutts’. I suppose that is because the ‘species’ are the same, and the breeds are simply manipulations of various genes already extant within the species.

Are there fish and/or bird species that are similar enough, one to another, that a ‘mixed-breed’ fish or bird could be created? I don’t think this would be likely among birds without human intervention, since birds mate ‘personally’, but since most fish have females laying eggs on the sea floor and males swim over and fertilize ‘the area’, couldn’t sperm from another fish species also fertilize some eggs?

I don’t suppose we’re likely to see any guppy-sharks, but still… there could be some interesting combinations.