I think the problem is that the word "damages" isn't particularly precise as a term, and means different things to different people. Compare the psychological damage people say their kids get from some racy River Island featuring scatily clad models advertising with the actual damage that kid would get from being hit by a bus.
The scientific evidence that stunting a fish causes physical harm is non-existent. There isn't any evidence at all that the internal organs carry on growing. Many (probably most) species of fish simply don't stunt at all (plecs, giant gouramis, and oscars, for example, all famously get big regardless of the size of the aquarium).
But, if you're saying fish shouldn't be kept in tanks too small, then that's rock-solid good science. Fish need space for exercise, to stimulate behaviours such as exploration and territoriality, and to provide the physical volume to dilute metabolic wastes and buffer chemical changes. Whether denying those things by keeping a plec in a 20 gallon tank is "damaging" is a question of semantics, but it is certainly
dangerous and
cruel to keep said plec in said tank.
So going to your example of a human baby, the question isn't about physically stunting its growth (which wouldn't happen), but rather that a baby trapped in a small box wouldn't be able to exercise (and so develop muscle strength), explore its environment (and so learn motor skills), or interact with other babies (and so learn communication skills).
In my opinion, what aquarists need to focus on is a more holistic approach to the life of the fish than focusing on just one danger, stunting. They need to think about what the fish does and how it responds to its environment. One reason I like community tanks is that fish interact with one another. Even across different species you see things like one species guarding its territory against another, or one fish stealing food from another fish, and so on. This interaction exercises the fish and prevents boredom. Hand-training fish is good, too, as it encourages the fishes to interact with us, and to take an interest in things outside the tank.
Cheers,
Neale
My point is: "You wouldn't raise a baby in a 2 foot by 2 foot box, would you? So why would you consider doing it to your fish?" And beginners (or anyone who doesn't know any better for that matter) need to hear that message clearly. This isn't a matter of experimenting to find out the correct or incorrect way to do something. There is no maybe about it. There is no proper way to learn that stunting causing damage is a fact. Back to my baby example, you wouldn't keep it in a 2x2 box until it's 5 years old, only to realize that you're causing damage, and you should take it out. It's very simple: STUNTING FISH DAMAGES THEM. If you are willing to test this theory, you're the person that wouldn't be listening to my previously requested warning anyway. Myself? I spend enough money on my tank, my fish, my various supplies, etc. without having to kill one to no good end, and for no reason other than not doing my research.
Because how many people had actually heard that before joining the forum and talking to other people? Shops, certainly, are unlikely to tell you that, and unless you're a member of an aquarists society, contact between fishkeepers is uncommon.
