Productivity of the calanoid copepod Acartia tropica in response to different salinities and multigenerational acclimatization.

Abstract

Copepods form the natural prey item for the vast majority of marine fish larvae in the wild. The tropical es- tuarine calanoid copepod Acartia tropica is a potential live feed for finfish larviculture because of their higher fecundity and wide salinity tolerance. The present study was aimed at identifying the optimal salinity for ob- taining maximum production of A. tropica nauplii. Population growth, intrinsic rate of population increase, egg production (eggs female−1 day −1), egg hatching success (EHS) and nauplii survival (%) of A. tropica were assessed at different salinity levels. Similarly, the effect of long term acclimatization on population growth of A. tropica was also studied. The experimental salinity range was set to be 5-30 ppt based on the abrupt salinity change experiment. Highest mean population count (1265 ± 209) and intrinsic rate of population increase (0.493 ± 0.01) were recorded at 15 ppt which was significantly higher (p˂0.05) than other salinity treatments except for 20 ppt (1005 ± 129, 0.481 ± 0.01). The lowest mean population count and intrinsic rate of population increase were recorded at 30 ppt (80.75 ± 17.86, 0.32 ± 0.003). The highest mean daily egg production was recorded at 15 ppt (33.42 ± 5.88) which was significantly different (p˂0.05) from all other treatments. Nauplii survival at 15 ppt (79.73 ± 4.86) was significantly higher (p˂0.05) except for 20 ppt (73.81 ± 5.62). However different salinity conditions did not affect EHS and sex ratio of adults in the present study. Multigenerational acclimatization significantly improved the population growth and mean daily egg production of A. tropica at 30 ppt (558.30 ± 35, 25.80 ± 4.00). Hence the present study suggests that the salinity range of 15-20 ppt supports the maximum productivity of A. tropica and it can be well adapted to higher salinity conditions through multigenerational acclimatization.