Bristlenose plecos will grow to their maximum length of three to five inches in about two years. Determining the precise growth rate of bristlenose plecos can be difficult, as their development will depend on their age, condition, and diet.
Generally, bristlenose pleco fry tend to grow very slowly, staying under an inch in length during their first three months of life.
After three months, they usually hit a growth spurt, growing an extra two or three inches until they reach six months of age. By this point, you can start to sex and breed them. Finally, their growth rate will slow down again until they reach their maximum size at two years old.