Thanks for the link.
I can certainly believe that there are some deficiencies in aquarium conditions- this is what motivated me to ask the question in the first place. I would love to figure out what is missing - size, chemistry, something else? - and fix it. Also, are some fish more susceptible than others? Finally it raises the question as to whether fish in aquariums are doomed to an unhealthy and stressed life compared to their wild relatives. The above answers seem to suggest this is the case. Which of course would be very troubling. Alternatively, may be it is simple interactions of some harmless chemicals and has no bearing on the health and stress of the fish. Unfortunately it seems like there are few scientific studies that can provide answers.
Yeah, as mentioned this is a really complicated topic because there are so many variables that go into it, so studying it in such a way as to have the findings be useful/meaningful for mutliple species would be incredibly time consuming (and there would likely be numerous potentially confounding variables for any mixed-species setups like the typical reef tank).
*For an example of a confounding variable, two different fish species might not show any stunted growth when kept by themselves, but then show stunted growth when kept together. In a situation like that, it could be a chemical put out by the other species inhibits the other’s growth, it could be caused by an interaction between chemicals put out by the two species, it could be a stress response, a response to aggression, a response to food competition, an attempt to appear less threatening, etc. (On the other side of this example, two fish species may show stunted growth when kept separately, but not together - this is, again, a whole can of confounding variable worms.)
With regards to fish in aquariums being “doomed to an unhealthy and stressed life,” I wouldn’t necessarily make that assumption. Just because a fish doesn’t grow to its maximum wild size doesn’t mean it’s unhappy (or even stressed at all). While that assumption is (to my knowledge) entirely possible, there are also a number of different possible explanations for the difference in growth (including, in addition to the possibilities listed above - though arguably unlikely - that the fish grow bigger in bigger tanks because they feel they need to in order to survive or increase their odds of survival; in other words, it’s possible- albeit unlikely- that they grow bigger in response to specific stressors::::similarly, the fish might stay small in smaller tanks because of some advantages it provides - such as requiring less food, as food would [at least theoretically in the fish’s mind] be less abundant because of the small available space for food to grow/hide).
Regardless though, I’d honestly assume the general health and happiness of the fish probably depends less on tank size (though I certainly believe it plays an extremely important role) and more on the care given them by the aquarist. A proper size of tank and proper care would likely provide a good quality, safe, stress-free, happy life for a fish. As was mentioned above, however, many people can’t keep their fish alive for a decent length of time (and fish that die young were probably pretty stressed).
Personally - disease aside - I’d guess a lot of premature fish deaths are largely because of improper diet (speaking candidly here, the more I learn about pet nutrition and pet food - and not just with fish - the more I realize that most pet foods, while possibly good enough to keep a pet alive for a while, are not good enough to keep a pet healthy/in peak physical condition long-term) and improper care (be it through poor water quality, bad tankmates, improper habitat, etc.). When you have proper care and proper diet, the fish live for long times (in some/many cases matching or exceeding their wild lifespans) and are happy enough to reproduce readily and exhibit their natural, wild behaviors. So, personally, I’d guess those fish are quite happy and content with their lives.
