I dont think there really is a general growth rate for them, alot will say about an inch per year and then after a decent size is met then it could be as little as 1 cm per year lol.
All that you really need to know is there very slow growers
I've been measuring my group of Royals for a bit over a year now. Across my group, 13 currently, amongst the 10-20cm fish I've measured a minimum of 3cm and maximum of 7cm. My largest, 40cm, grew 2cm in the past year.
Common Plecos grow so quickly, lol when I first started fishkeeping, I had a common pleco in a tiny tank
Within a year it has tripled in size from around 1.4 inches to 4.5 inches
Common Plecos grow so quickly, lol when I first started fishkeeping, I had a common pleco in a tiny tank
Within a year it has tripled in size from around 1.4 inches to 4.5 inches