Effects of larval ontogeny, turbulence, and prey density on survival in red sea bream Pagrus major larvae

The effect of turbulence on red sea bream larvae survival was tested at two prey densities and four turbulence levels in the laboratory for red sea bream. The effect of ontogenic stage on feeding behavior parameters was examined. The range of turbulence at which red sea bream larvae could survive and ingest prey increased with larval growth. Therefore, turbulence is an important condition impacting survival of small larvae during the initial period of feeding. At low prey density, larvae fed at the highest feeding rate and had a high RNA : DNA ratio at a medium turbulence level on the order of 10(-6.5)m2s(-3). Thus, an optimum turbulence level induces faster growth, and it can be concluded that turbulence plays an important role in larval growth and survival. For interspecific comparison, a feeding success index calculated by numerical modeling in sea bream was compared to that of Pacific bluefin tuna using data reported by Kato et al. (2008). There were large differences in the index. The equivalent curve for red sea bream showed a linear relationship, while that for Pacific bluefin tuna showed a dome-shaped relationship. These results suggest that open-ocean-dwelling Pacific bluefin tuna likely prefer prey that is moving and under conditions of moderate turbulence. Further, tuna requires a greater degree of turbulence during initial feeding periods than does red sea bream.