Differences in food composition between territorial and aggregative juvenile crimson sea bream Evynnis japonica

Food composition, fork length and condition factor of juvenile crimson sea bream Evynnis japonica were examined for two behaviorally distinct types of fish inhabiting a nursery ground. Studies were carried out from March to September 1996 at Morode Cove, Ehime Prefecture, Japan. One type of fish is solitary and territorial and the other type is aggregative. The food compositions of the two types of fish were different. Solitary fish foraged mainly on Gammaridea and Caprellidea (benthic organisms), and Copepoda (planktonic organisms); while aggregative fish foraged mainly on Copepoda, Appendiculata and Cladocera (planktonic organisms). These findings suggest that when we study food composition of E. japonica, it is imperative to consider whether the samples used for the analyses are from solitary (territorial) fish. Solitary fish showed significantly greater fork length and condition factor than aggregative fish, suggesting that the former will have a greater fitness value than the latter.