The effects of temperature and salinity on population growth and egg hatching success of the tropical calanoid copepod, Acartia sinjiensis

Abstract

The tropical calanoid copepod, Acartia sinjiensis, has good potential for mass culture as a live feed for tropical reef fish larvae. This study was carried out to investigate the effects of temperature and salinity on population growth and egg hatching rates of A. sinjiensis. At a salinity of 30±1 psu, temperature effects on population growth of A. sinjiensis was determined after 8 day culture at eight temperatures of 10, 15, 20, 25, 28, 30, 34 and 38 °C. Adopting similar experimental protocols, effects of salinity on population growth of A. sinjiensis were investigated under nine salinities of 10, 15, 20, 25, 30, 35, 40, 45 and 50 psu, with culture temperature set at 30±1 °C. In addition to population growth experiments, egg hatching rates (%) after 48 h of incubation at various temperature and salinity conditions were also examined. For all experiments, five replicates were set up for each treatment. A. sinjiensis were fed an identical binary algal diet of Tetraselmis chuii and the Tahitian strain of Isochrysis sp. (T-ISO), photoperiod was maintained at 12 L:12D.The results showed that temperature had significant effects on both population growth and egg hatching rates. Population growth at 30 °C (with an initial number of 10 adults/replicate, final mean population reached 677.2±136.6) was significantly higher (p<0.001) than the other temperature treatments except that of 25 °C and 28 °C treatments. The egg hatching rate did not differ significantly (p<0.05) when incubated at temperature 25, 30 and 34 °C although the highest hatching rate was recorded at 34 °C (96.3±2.2%). Salinity also had significant effects on both population growth and egg hatching rates. The highest population growth (final mean population: 669.0±111.3) and egg hatching rate (98.0±1.4%) both occurred at salinity of 30 psu. Population growth at 30 psu was significantly higher (p<0.001) than all other treatments except that of 25 and 35 psu, while there was no significant difference (p<0.05) between egg hatch rates at all salinity levels tested.The results of this study suggest that for maximum population growth and egg hatching success, A. sinjiensis should be cultured at 30 °C with a salinity of 30 psu.