Interesting question. Judging by the size, I expect you are referring to the gold form of the three spot gourami
Trichogaster trichopterus. I have worked with many of these over the years from hatch to growing old and dying (as broodstock). I have not noticed any natural predisposition to darken with age once maturity is reached, provided the fish remain healthy, however, there is a wide range of other factors that can cause this. (I assume the change has been slow and consistent, over days or weeks, and doesn't change?) Possibilities include most notably:
1. An unfavorable change in water chemistry, especially low pH, but other things can do it too. (Could even be due to a favorable change if the fish has gone from unhealthy pale to a healthier darker color, and some aspect of its environment has changed for the better? Sorry to be complicated!)
2. Some diseases will cause this, e.g. low levels of external parasites, or some internal parasites such as gut protozoa. (You should see other symptoms.)
3. A change in the environment in terms of its exposure to light or background color e.g. a very light, well lit environment can cause some species to become pale and vice versa.
4. Old age and a subsequent decline in health could bring this on in some cases.
Some questions could help to throw some light on it.
Is the fish remaining healthy, judging by body form and feeding? Are you noticing any other symptoms or changes? Has its environment changed or been changed. Any other observations could help.
Hope that's at least a little bit helpful! Always tricky without seeing the situation. Cheers, Brian.
hello all,
My yellow gourami has started to get darker along his back and top of head. Is this normal? Hes about 4-5 inches long now.. It would make sense to me that they would get darker with age, but i havent been able to find anything on it?
thanks guys