Fish, like reptiles are paraphyletic. The cladistic revolutionaries want to abolish the category altogether, or reduce it to just the ray-finned fishes—excluding coelacanths, lungfish, the cartilaginous fish (sharks, rays, skates and chimaeras), and the cyclostomes (hagfish and lampreys).
The result is that some sources will use fish as equivalent to the monophyletic group actinopterygii and others use the traditional polyphyletic pisces. Anytime you see a generalisation about fish that isn’t true of sharks, there’s a good chance that the original source was using fish to mean actinopterygii.
In many ways, it’s a more useful classification − 96% of fish species are in actinopterygii, and there is an awful lot of anatomy that is shared by the actinopterygii but not by the rest of the fish. If you’re going to exclude cetaceans because they have more in common with land animals than with actinopterygii then why not exclude lungfish and coelacanths for the same reason?
The problem is that it begs the question—using “unborn baby” defines it into the same ethical category as a born baby, different only in location. When you dig down enough, usually that’s the point at dispute—is the thing growing in a womb entitled to rights in the manner of a (born) baby, or is it not so entitled.
There are some property-rights thinkers who do hold that it is the location that matters, i.e. the baby is trespassing on the mother’s womb, and she’s entitled to use deadly force to remove it, but that’s not the usual argument.