What is known from keeping these fish in aquariums smaller than several hundred gallons is that the end result is a fish with stunted growth. The extent of the growth stunt is directly proportionate to the aquarium size. Following Choat and Axe (1996) and the understanding that Acanthurids obtain 80% of their growth in their first 15% of life, you can get an idea of how fast they should be growing in your aquarium. Combine this with an expected 35 years of age per Acanthurid (Chaot and Axe, 1996), we come up with 80% growth obtained in 5.25 years. Let's take this a step further and plug in the expected maximum size for Paracanthurus hepatus, roughly 12". After doing the math you should get the answer of Paracanthurus hepatus obtaining 9.6 inches at 5.25 years of age. Following the same reference, which states the first 80% growth is fairly consistent, you can take it yet one step farther to learn that your Paracanthurus hepatus should be 1.8 inches after the first year, and continue to grow nearly two inches every year from then until five years of age, where their growth will slow and nearly stop, at which time it should be nearly ten inches. You could also use this same formula when trying to obtain an age of a newly imported specimen.
