I know this seems like a novice question, but it has always been said that schooling fish must be kept with their own kind, but in the back of my mind, I've always wondered whether this long-held belief is actually valid, or if it is just one of those old conventions that we never strayed from. Especially when there are schooling species like pacu, dats, and flagtail prochilodus which are quite often kept singly in the hobby and seem to do just fine. For sure, many species just aren't as appealing when kept by themselves, and obviously they don't exhibit some of their natural behavior if they're kept alone, but I wonder if there is actually any real concern to the fish's health.
I can see how it is beneficial for reducing stress, especially when acclimating fish to a new aquarium, but whenever I've kept tetras or danios, I've noticed that once they're fully acclimated, they really don't display much schooling behavior, except when they feel threatened, and at night after the lights go off. Also, under various circumstances in the past, I've ended up in situations where I had just a single zebra danio, a single black neon, a single kuhli loach, etc., and it seems that they always adjust pretty well, regardless. So ultimately, what's the real harm?
I can see how it is beneficial for reducing stress, especially when acclimating fish to a new aquarium, but whenever I've kept tetras or danios, I've noticed that once they're fully acclimated, they really don't display much schooling behavior, except when they feel threatened, and at night after the lights go off. Also, under various circumstances in the past, I've ended up in situations where I had just a single zebra danio, a single black neon, a single kuhli loach, etc., and it seems that they always adjust pretty well, regardless. So ultimately, what's the real harm?
