Catchability of Individual Tilapia Tilapia mossambica in Tank.

Abstract

To determine the individual catchability of fish, angling experiments were conducted using five groups of tilapia in an outdoor concrete tank 10 X 5 X 0.65 m in dimensions. The effects of previous experience of hooks, the hunger level, and the presence of eggs on catchability were determined using chi-square analysis. Five different baits were used at random to eliminate the effect of bait preference. At the start of experiments, about half of each group were hooked, marked by fin clips, and released back in to the tank with the unmarked fish. A recapture trial was repeated twice by angling and tallying marked and unmarked fish. Fish were thus hooked a total of three successive times, twice, only once, or not at all. After the angling experiments, fish were given pellets and allowed to feed for 10-20 minutes, then examined for the amount of intake and the presence of eggs. Results indicated that fish that had been hooked earlier tended significantly to be hooked again. Fish did not learn to avoid hooks. Fish that had been hooked tended to eat more. Fish with eggs tended to be less catchable, but individual differences in catchability were also found among those without eggs.