Biology and assessment of the painted sweetlips (Diagramma pictum (Thunberg, 1792)) and the spangled emperor (Lethrinus nebulosus (Forsskål, 1775)) in the southern Arabian Gulf

The population biology and status of the painted sweeplips (Diagramma pictum) and spangled emperor (Lethrinus nebulosus) in the southern Arabian Gulf were established by using a combination of size-frequency, biological, and size-at-age data. Transverse sections of sagittal otoliths were characterized by alternating translucent and opaque bands that were validated as annuli. Comparisons of growth characteristics showed that there were no significant differences (P>0.05) between sexes. There were well defined peaks in the reproductive cycle, spawning occurred from April to May for both species, and the mean size at which females attained sexual maturity was 31.8 cm fork length (LF) for D. pictum and 27.6 cm (LF) for L. nebulosus. The mean sizes at first capture (21.1 cm LF for D. pictum and 26.4 cm LF for L. nebulosus) were smaller than the sizes for both at first sexual maturity and those at which yield per recruit would be maximized. The range of fishing-induced mortality rates for D. pictum (0.37−0.62/yr) was substantially greater than the target (Fopt=0.07/yr) and limit (Flimit=0.09/ yr) estimates. The range of fishing-induced mortality rates for L. nebulosus (0.15/yr to 0.57/yr) was also in excess of biological reference points (Fopt=0.10/yr and Flimit=0.13/yr). In addition to growth overfishing, the stocks were considered to be recruitment overfished because the biomass per recruit was less than 20% of the unexploited levels for both species. The results of the study are important to fisheries management authorities in the region because they indicate that both a reduction in fishing effort and mesh-size regulations are required for the demersal trap fishery.

Reproductive biology of female Rikuzen sole (Dexistes rikuzenius)*

The annual ovarian cycle, mode of maturation, age at maturity, and potential fecundity of female Rikuzen sole (Dexistes rikuzenius) from the North Pacific Ocean off the coast of Japan were studied by 1) histological examination of the gonads, 2) measurement and observation of the oocytes, and 3) by otolith aging. The results indicated that ovulation occurs from September to December and peaks between September and October. Vitellogenesis began again soon after the end of the current season. Maturity was divided into eight phases on the basis of oocyte developmental stages. Mature ovaries contained developing oocytes and postovulatory follicles but no recruiting oocytes, indicating that this species has group-synchronous ovaries and is a multiple spawner. Almost all females matured first at an age of 1+ year and spawned every year until at least age 8+ years. Potential fecundity increased exponentially with body length and the most fecund fish had 15 times as many oocytes as the least fecund fish. Potential fecundity and relative fecundity were both positively correlated with age from 1 to 6+ years, but were negatively correlated, probably because of senescence, in fish over 7 years. These results emphasize that the total productivity of a D. rikuzenius population depends not only on the biomass of females older than 1+ but also on the age structure of the population.

Cellular and molecular responses of zebrafish to legacy and emerging pollutants: the specific cases of PAHs and metal oxide nanoparticles

270 p.