IME, most captive specimens only reach about 75%-80% of their max "wild" size. This is most likely due to nutrition (no matter how we try, we simply can't duplicate a fish's diet "properly"), but "tank stunting", caused by "under-tanking" a given species can also cause this.
We can't do a lot about the first issue (nutrition) other than try our best, but we CAN try not to undertank the fish in question. What I've seen in undertanked fish are big changes in behavior, which usually manifest themselves as elevated aggression (due to territory or "cabin fever"), increased "pacing", or in the case of others, almost a complete lack of swimming (I've seen this a lot in lionfish that are cramped). Additionally, in predatory or "messy" eaters, water quality often takes a hit in smaller setups.
We spend a lot of time playing musical tanx because we typically buy very young fish, and they need "upgrades" as they grow towards their final "target tank".
JM .02...