We examined the relative importance of growth-related processes operating during the larval and early juvenile stage in explaining variability in year-class success of Japanese flounder off the Pacific coast of northern Japan. Early growth trajectory of larvae and juveniles sampled in 2005 (strong year class) and in 2006 (weak year class) was estimated from the analysis of the lapillar otolith. The larval pelagic stage was characterized by lower growth and developmental rates, as well as high selection for fast growth in the metamorphosis/settlement period, during the strong recruitment event of 2005 relative to 2006. Growth appeared higher in 2005 only after settlement despite high density in the nursery, which likely reflected superior productivity during that year combined with an increased probability of cannibalism from early settlers on late settlers. This implies that larval growth dynamics did not play an important role in determining recruitment strength in the two years considered. The decreasing distance from the nursery areas of pelagic larvae through ontogeny in 2005, combined with low age at settlement, suggest that larvae benefited from positive transport conditions during the dominant year class. To the contrary, unfavorable hydrographic conditions likely prevailed in 2006 as distance from the nurseries increased with ontogeny and settlement occurred later than in 2005 despite faster growth potential and developmental rate. We conclude that transport conditions to the nursery grounds, rather than larval growth potential, represented the most important determinant of year-class success in the two years considered.

Three-day rearing experiments were conducted to study the effect of turbulence on the feeding intensity and survival of pelagic larvae of Japanese flounder Paralichthys olivaceus. Four levels of turbulence as control (10(-7.2) m2 s(-3)), low (10(-6.2) m2 s(-3)), mid (10(-5.6) m2 s(-3)) and high (10(-5.0) m2 s(-3)) were set by changing the flow rate of water pumped through pipes set on the bottom of the tanks. In B-stage larvae, defined as having buds of elongated dorsal fin rays, the feeding intensity and growth were higher in the low and mid turbulence levels, while survival was highest in the control level. Most of the larvae surviving in the control level, however, were judged to be in a seriously starved condition leading to subsequent high mortality. Because the three-day span of the rearing experiments was thought to be a little shorter than the periods before starvation-induced, high mortality occurs. In contrast, for D-stage larvae, their feeding and growth were optimal in the control and low levels. Feeding was more adversely affected in the high level for D-stage larvae compared with B-stage larvae. This is probably due to the compressed body shape and elongated dorsal fin rays of D-stage larvae, which may be more strongly affected by turbulence and, as a consequence, the larval feeding behaviour such as pursuit and capture of prey organisms becomes less efficient than in lower turbulence. Considering the vertical distribution of B and D-stage larvae in the oceanic water column, the optimum turbulence level range found in the present study corresponded to a wind speed of 7-10 m s(-1). Therefore, moderate weather conditions of this wind speed range are considered to potentially enhance survival of early larval stages of P. olivaceus.