Thanks for the like Byron... I am trying to figure out how to like u back. One last thing, what health effects do keeping cories in schools/shoals give?
Thank you.
Shoaling fish are species that live in groups, frequently very large (hundreds). This need is programmed into the fish species' DNA. The fish "expects" to be in groups of its own, but if this is not provided such as in the aquarium, the fish will be stressed. I'll come back to stress momentarily, but to continue with shoaling...there are beneficial reasons for this. Safety in numbers obviously. Some species develop an hierarchy within the group. Evolution has designed the species to function at its best physiologically in this environment. Stress impacts the fish's physiology and metabolism, and that means health issues.
The numbers in an aquarium obviously cannot duplicate the habitat except in the largest public aquarium tanks. But scientific studies have now shown that when a shoaling species is maintained with less than five, the individual fish develop increased aggression as a direct result of the frustration and stress. Aggressive species (angelfish was one tested) become much more aggressive, and normally peaceful species (black neon tetra was one species tested) become aggressive, which is outside their norm. Less often the fish's reaction is to withdraw and literally waste away. So the numbers within the group clearly impact the fish. We also know that there are species where the group must be much larger than the minimum five or six, and we use the fish's health and longevity to assess much of this.
Now on the stress. Stress is the underlying factor for 95% of all fish disease in the aquarium. The pathogen/parasite obviously has to be present, but it is stress that puts the fish in the position of being unable to deal with the issue. This is because stress severely weakens the immune system. It also affects negatively the metabolic processes so the fish is now having to spend much more energy just to maintain the "normal" internal processes. Not surprisingly, this "extra effort" adds even more stress, so things simply continue to spiral downward for the fish. At some point, it will be unable to "fight back" and dies. Fish do not die for no reason, but aside from predation it is stress that usually causes it. Stress on its own can cause the fish to die, or the stress can make it impossible for the fish to fight off pathogens and disease.
The minimum number for groups of a species are just that. minimum; I can think of no case where having more beyond the minimum is not going to improve the fish's health. The more the merrier is generally true. Which is why tank space is so important; the space must be able to allow the group to be large enough that the fish gain maximum benefit rather than being constantly "on edge."