Copepods, a member of zooplankton group, hold a critical role in aquaculture due to their varied sizes and valuable nutritional attributes. A calanoid copepod, Pseudodiaptomus sp. is widely used as live food for the rearing of various economically significant fish larvae. Nevertheless, the density and overall biomass of Pseudodiaptomus sp. in aquaculture ponds often remain low.
The objective of this study is to investigate the optimal culture conditions for the growth Pseudodiaptomus sp. at different salinity and temperature. The species was exposed to different ranges of salinity (15ppt, 20ppt, 25ppt, 30ppt, 35 ppt and 40ppt) and temperature (14, 18, 22, 26, and 30 ℃) using the Heat Exchanger Fouling Test Unit System that was facilitated from Japan by SASTREPS-OTEC Project in I-AQUAS as the culture water. All copepods were reared in 1-litre beakers over 21 days, under a 12-hour light and 12-hour dark photoperiod, stocked at a rate of 20 gravids per litre. Throughout the experiment, the copepods received twice-daily feedings of Pavlova sp. for 21 days. The population density of Pseudodiaptomus sp. was monitored and assessed based on the number of nauplii, copepodites, and adults every two days.
At a salinity level of 25ppt (Table 1), Pseudodiaptomus sp. exhibited a significantly higher total population and specific growth rate. Changes in salinity levels had a profound impact on the speed of population growth among calanoid copepods. At 40 ppt, it was observed that copepod population reduced to only 10 individuals per liter. On the other hand, the temperature experiment showed the greatest population density observed at 26°C (Table 2). High copepod mortality was observed in the treatment of 30°C on the 12th day, while at 14°C, survival was limited to only 8 days. These findings suggested a combination of 26°C water temperature and 25ppt salinity as the optimum parameter for the development of a sustainable mass culture of this calanoid species as live food in hatcheries.