Size and feed dependent cannibalism with juvenile snakehead Channa striatus

Abstract

A linear regression model was developed to predict cannibalism in juvenile snakehead Channa striatus. Based on morphological measurements of mouth width, head width and body length, the model relates maximum prey length (TL; mm) to predator TL (TL prey = 26.168 + 0.278 TL predator). This model was verified with a set of independent data, indicating an underestimate of maximum prey size for a certain predator size. The revised model should be: TL prey = 25.809 + 0.405 TL predator (mm). Size differences substantially increased the rate of cannibalism, but prey: predator TL ratios decreased with increased predator TL. Cannibalism rate was 100% during a 5 day trial when the TL ratio of smaller fish to larger fish was 0.35; but the cannibalism rate decreased to 43% when the TL ratio of smaller fish to larger ones increased to 0.64. Increased availability of formulated feed also reduced cannibalism. With no feed offered, cannibalism was 83%; but decreased to 43% when daily feeding rate was 15% of the larger fish's body weight. Our results indicate that cannibalism is unavoidable with this species, but can be greatly reduced among juvenile fish by size grading and ad libitum feeding.