Selectivity and accessibility of prey in captive juvenile red drum, Sciaenops ocellatus Linnaeus

Abstract

Selective feeding on live prey was studied in juvenile red drum (25~37 cm in total length). Live prey selected included young fish (the hybrid tilapia Oreochromis aureus×O.niloticus), shrimp (Palaemon macrodactylus), polychaete ragworm (Neries virens), and crab (Chiromantes dehaani). They were presented simultaneously in equal number to the red drum. After feeding for one hour, prey that was not consumed was collected, counted and weighed. The red drum were individually retrieved and dissected for examination of stomach contents. Iv lev's electivity index (E) was used to determine the degree of preference to or avoidance of different prey by predators. Relationships were established between red drum size and electivity index for different prey. Results suggest that the selective ability of juvenile red drum might vary with its size. Larger red drum became more piscivorous. Smaller red drum preferred polychaete and shrimp over fish. Crab was the least favorable prey among all four items. A size profile, derived from the size of predators and the size of prey in the stomach, showed that the size range of prey consumed by the red drum increased with the size of the predator. Accessibility of the prey was deduced from a comparison of prey selection using ”dead” and ”live” preys. The result indicates that shrimp is favored by smaller red drum because it is most accessible of the four prey offered. Polychaete ragworm was less accessible than the shrimp, but it was most preferred by the red drum among four prey. Fish is more accessible to larger than smaller red drum. Crab is most avoided by red drum juveniles because it is most difficult to access. This study demonstrated that juvenile red drum selected prey according to its inherent preference, and prey size and accessibility.