Dietary cholesterol and aggression in Nile tilapia Oreochromis niloticus

Tilapia farmers would benefit tremendously if they could decrease aggression among fish. Conspecific aggression affects the growth, feed conversion, and general well-being of fish. Previous studies established an inverse relationship between blood cholesterol levels and aggression in fish, whereby a decrease in cholesterol led to an increase in aggression. The present study assessed the effect of an increase in dietary cholesterol on blood cholesterol and a possible decrease in the aggression of Nile tilapia oreochromis niloticus. Nile tilapia were stocked in an outdoor recirculation system and then offered one of five diets: 0% cholesterol, 0.5% cholesterol, 1% cholesterol, 1.5% cholesterol, and 2% cholesterol. Five fish of each treatment were moved to a glass tank and monitored for signs of aggression for 10 min, twice a day. This experimental procedure was repeated five times using a new set of fish every time. Results show an increase in cholesterol levels in the blood but that there are no significant differences in aggression among treatments. Accordingly, the present study suggests that an increase in dietary cholesterol increases blood cholesterol in fish but does not have a significant effect on antagonistic patterns in Nile tilapia.