Well. That’s why they call them fighting fish. They are highly territorial. It’s their instinct.

That being said, many are probably inbred, in pet stores. All kinds of problems could sprout from that…

I was fishing one night and caught the same darn bluegill three times in about ten minutes.
Yes, fish must be mentally ill sometimes.
I got so angry with that stupid little thing I finally kept it, and fed it to a friend’s piranha the next day.

yes

I think there’s a difference between stupid, or maybe desperate, and mentally ill.

When I “beat the banks,” in the spring for bream, it’s common to catch the same little guys over and over again. When they’re in beds, they’ll hit anything. Even if it has negative consequences.

Sorry to hear about your fish. Siamese fighting fish are highly aggressive/territorial, so this kind of story actually isn’t unusual. For that reason, people will often recommend not keeping them in tanks with other fish or mirrors.

As for fish in general, not much is really known about their cognition. They react to things in some ways that suggest emotions, e.g. they exhibit signs of “stress” if kept in a tank that doesn’t have hiding places to help them feel safe, and some of the more intelligent species show signs of “boredom” if their tank is too small or empty. Their lifespans can be shortened by these negative “emotions.” But it’s unclear whether they actually experience these feelings as emotions in a way thats meaningfully comparable to human emotion, or if it’s all just instinct and impulse.

^Probably depends on the species. I wager that solitary predators, have higher brain function, than schooling fish.

Even if the fish’s behavior is abnormal for its species, how do you distinguish instinctive behavior from intentional acts?

Trying to judge the mental state of other animals is a tricky proposition. My gut feeling is that definitely other primates and maybe all other mammals and at least some bird species have some form of sentience, but I don’t know how you can create a definitive test for it.

For a Siamese fighting fish, it would be considered menatlly ill if it didn’t try to attack itself in a mirror.

Don’t anthropomorphize your perception of fish behavior.

You don’t see much mental illness in fish because the ones that suffer from it get eaten.