Seasonal availability of calanoid copepods (genus Acartia) in eastern Thailand using a light trap, as food organisms for marine fish larval rearing

Zooplankton collected by the torch lighting method were investigated in a tropical coastal seawater pond in eastern Thailand. Copepods of the genus Acartia, such as A. sinjiensis, A. erythaea and A. pacifica, were predominant among the zooplankton collected. A. sinjiensis occurred almost throughout the year with a prolonged peak season from August to April. The highest abundance of adult A. sinjiensis aggregated under the light reached 35,700 individuals•l-1. The occurrence of A. erythaea and A. pacifica was intermittent with a short-term peak from March to April, during which their abundance was higher than A. sinjeinsis. The combination of water temperature and salinity was suggested to affect or regulate the biomass of these Acartia species. Among the Acartia species, A. sinjiensis seems to be the most important as a food organism available for marine fish larval rearing in eastern Thailand.W e are grateful to Dr. Hiroshi Ueda, University of Ehime, for his guidance on species identification of the genus Acartia

Salinity tolerance of larvae of the mangrove red snapper (Lutjanus argentimaculatus) during ontogeny

Salinity tolerance and the effects of salinity on growth, condition factor and chloride cell (CC) densities were evaluated for Lutjanus argentimaculatus larvae during ontogeny. Tolerance of L. argentimaculatus larvae to abrupt changes of salinity from 32 ppt varied with age. Periods to 50% mortality (LT50) were significantly (P<0.05) longer for 0-day-old larvae than for 7-, 14- and 21-day-old larvae. Tolerance of abrupt salinity change increased remarkably, starting on day 28. Although abrupt transfer to test salinities caused substantial mortalities, L. argentimaculatus larvae, regardless of age (0-, 7-, 14-day-old), showed significantly longer LT50 when abruptly transferred to 8 and 16 ppt than for transfers to 24 and 40 ppt (P<0.05). Growth of L. argentimaculatus larvae at 16, 24, 32 (control) and 40 ppt was not significantly different either at the end of the first rearing phase (days 0–21) or second phase of rearing (days 22–50). Survival was significantly lowest at 40 ppt (4.3%) at the end of first phase of rearing (P<0.05). There were no significant differences in survival rates at the end of the second phase of rearing; however, the condition factor (K) of larvae reared at lower salinities was significantly higher than that of fish at 40 ppt (P<0.05). Gill epithelia of 42- and 50-day-old larvae showed increasing density of CC with increasing salinity