Effect of body colour of Oreochromis mossambicus (Peters) on predation by dragonfly nymphs

Abstract

Abstract. Gold and black Oreochromis mossambicus (Peters) fry were stocked in 0.043-m3 hapas along with early instar dragonfly nymphs to determine the effect of body colour of the tilapia on vuinerability to predation by the insect. Hapas were stocked with either: 10 gold fry, 10 black fry and no dragonfly nymphs (10-10-0); 5 gold fry, 5 black fry and 2 dragonfly nymphs (5-5-2); 10 gold fry, 10 black fry and 2 dragonfly nymphs (10-10-2); or 10 gold fry, 10 black fry and 3 dragonfly nymphs (10-10-3). Four levels of predation were assessed: no predation, 1 dragonfly nymph per 5 fish, 1 per 6.7 fish, and 1 per 10 fish. Hapas were censused daily for 14 days. Fish that had been eaten were replaced with similar-sized fish to restore stocking densities. Average daily predation rate ranged from 0.24 to 3.0 and averaged 1.94 fry/dragonfly nymph/day. Average daily predation rates for all treatments were significantly (P = 0.05) different and were a function of both dragonfly and fish stocking rates. Dragonfly nymphs ate significantly more black fish than gold fish in the 10-10-2 and 10-10-3 treatments: overall (10-10-2, 10-10-3 and 5-5-2 treatments combined), dragonfly nymphs ate significantly more black (324) than gold (245) tilapia. Results from this study indicate that the bright body colour of the gold tilapia does not increase rate of predation by dragonfly nymphs.