No abstract

Growth and mortality rates of larval Japanese Spanish mackerel (Scomberomorus niphonius) were estimated by using otolith daily increments in 1997 and 1998 in the Sea of Hiuchi, central Seto Inland Sea. There was no day^night di¡erence in the abundance and size-distribution of S. niphonius larvae in the 3^10 mm sizeclasses, indicating the larvae were e⁄ciently collected by the larva-net used for sampling (1.3 m mouth diameter, 0.5 mm mesh). Mean absolute growth rate (0.748 mm d 71 in 1997, 0.821mm d 71 in 1998), weight speci¢c growth coe⁄cient (G: 0.402 in 1997, 0.444 in 1998) and mortality coe⁄cient (M: 0.784 in 1997 and 0.625 in 1998) were among the highest reported for marine ¢sh larvae. Scomberomorus niphonius seems to have evolved survival strategies characterized by fast growth with strong piscivory that can reduce duration of the larval period with the high mortality. In 1997, spatial distribution of the larvae was not well corresponded to that of their prey, clupeid larvae, and the larval feeding incidence was lower than in 1998. Recruitment potential assessed by examining the ratio of G:M was lower in 1997 (0.513 in 1997, 0.711 in 1998) due to the lower G and higher M values. Prey ¢sh availability may be one of the important determinants for the recruitment potential by controlling the larval mortality due to starvation and/or starvation-related predation.

SUMMARY: Diel successive samplings of Japanese Spanish mackerel Scomberomorus niphonius larvae were conducted throughout 24 h both in the sea and in captivity in order to estimate their daily ration. Using the Elliott and Persson model, the instantaneous gastric evacuation rate was estimated from the depletion of stomach contents (% dry bodyweight) with time during the night for wild fish (3.0–11.5 mm standard length) and from starvation experiments for reared fish (8, 10, and 15 days after hatching (DAH)). Japanese Spanish mackerel is a daylight feeder and exhibited piscivorous habits from first feeding both in the sea and in captivity. Feeding activity peaked at dusk. The estimated daily ration for wild larvae were 111.1 and 127.2% in 1996 and 1997, respectively; and those for reared larvae ranged from 90.6 to 111.7% of dry bodyweight. Based on the estimated value of daily rations for reared fish, the total number of newly hatched red sea bream Pagrus major larvae preyed by a Japanese Spanish mackerel from first feeding (5 DAH) to beginning of juvenile stage (20 DAH) in captivity was calculated to be 1139–1404.