The first year
About two inches a month is typical, with fast months of three or four and slow months of one or less. Nobody has published a measured growth curve for redtails in aquaria yet. Keeper journals are how we build one.
From a three inch start, one to two inches a month puts a fish somewhere between 15 and 27 inches on its first birthday. Two feet is the top of that range, a strong year, not the norm.
Real growth figures
Measured fish, in home and rescue tanks.
| Fish | Change | Over |
|---|---|---|
| Tiny donated juvenile | 2 in to 4 in | 3 weeks |
| Underfed rescue, phantom | 20 times its weight | 3 months |
| Donated fish at 2 ft | +6 in | 3 to 4 months |
| Rescue at 2 ft | +6 in, 2 to 3 times the mass | 5 months |
| Two females, one male | About 4 ft, 4 ft, 3 ft | at 7 years |
| Same fish | 46 in, 40 in, 37 in | at 9 years |
The pattern: very fast while small, still a steady inch or so a month at two feet, then slowing as the fish nears adult size.
Length and weight
The curve uses the standard length-weight formula for this species. Real fish vary: females are heavier than males of the same length, and well-fed captive fish tend to sit above the line.