Any scientific definition of ‘fish’ which includes all the things we commonly consider to be fish also includes basically all animal life on earth (including humans and, presumably, pterodactyls).
Edit: Though generally this is avoided by declaring that ‘fish’ is not an evolutionary category.








Sorry, I wasn’t trying to claim that your gut biome doesn’t effect your mood, just that the serotonin in your gut isn’t making it’s easy to the serotonin receptors in your brain that make you feel happy