Abstract
Copepods are considered the best initial live food item for the feeding of many marine fish. However, the culture of copepods on a large scale has been problematic due to the high variability of productivity of cultures and the relatively low density that can be applied in culture. Understanding the impact that different environmental conditions have on copepod population demographics and production characteristics will facilitate the optimization of copepod culture methods. In this study, the commonly cultured calanoid copepods Acartia tonsa and Parvocalanus crassirostris were reared at four salinities (20, 25, 30, 35 ppt). Experiments were conducted in triplicate to assess the impact of culture salinity on sex ratio, egg production, egg hatching rate, and mortality post hatch. The temperature was maintained at 25C for A. tonsa and 27.5C for P. crassirostris, and live Tisochrysis lutea was fed twice daily to maintain food availability above estimated carbon saturation densities for the two species (1,500 g C L-1 for A. tonsa and 1,000 g C L-1 for P. crassirostris). For A. tonsa, the percentage of females varied significantly and inversely (p=0.025) with salinity. For P. crassirostris the percentage of females did not differ significantly among salinity treatments. Survival from initial stocking of early nauplii to the adult stage was not affected significantly by salinity in either species. For both species, daily egg production by individual females significantly decreased (p=< 0.001) over 7 days. The total fecundity over 7 days was significantly higher (p=0.02) at 30 ppt for A. tonsa; salinity had no effect on fecundity in P. crassirostris. Egg hatching rate was not impacted by salinity or age for either species. This study suggests that production by A. tonsa may be optimized at 30 ppt whereas the production by P. crassirostris is minimally impacted within the salinity range tested.
