Effects of salinity on survival, reproductive performance, population growth, and life stage composition in the calanoid copepod Acartia bilobata

Abstract

Copepods are a critical live prey item for most marine finfish larvae in the natural environment. The calanoid copepod belonging to species Acartia is a potential live food for the larval rearing of marine finfishes because of their higher productivity and tolerance to wide range of salinities. The present study was conducted to determine the effect of salinity on production parameters to standardize the optimal salinity for Acartia bilobata culture. For selecting the optimal salinity range, the adult copepods were exposed to abrupt salinity change from 30 g L−1 to ten salinity levels, including 0, 5, 10, 15, 20, 25, 30, 35, 40 and 45 g L−1 and their survival estimated after 24 h. Further, the effect of salinity (15, 20,25,30, and 35 g L−1) on egg production, hatching success and population growth were studied. Following sudden salinity change, A. bilobata could tolerate a wide range of salinities from 15 to 35 g L−1, and no copepod survived below 10 g L−1 and above 35 g L−1. Average daily egg production was significantly higher at 25 and 30 g L−1 (32 ± 1 and 34 ± 2 eggs female−1 day−1). A remarkably low egg hatching success was recorded at 15 g L−1 salinity; however, all other tested salinities showed similar egg hatching success. Different salinity levels did not affect the sex ratio of A. bilobata. A significantly higher total population number (1539 ± 75) and intrinsic population growth rate (0.50 ± 0.00) was observed at 30 g L−1, followed by 25 g L−1 salinity. The lowest mean population (518 ± 19) and population growth rate (0.39 ± 0.00) were recorded at 15 g L−1 salinity. The study results suggested that 25–30 g L−1 is the optimal salinity range to achieve maximal production of A. bilobata.