International Journal of Aquaculture, 2024, Vol.14, No.1, 9-19 http://www.aquapublisher.com/index.php/ija 13 keep them active, and this results in death (Hansen et al., 2020). Starvation in copepods results in more than 50% loss in body weight and a decrease in Polyunsaturated Fatty Acids, leading to death (Koussoroplis et al., 2014). However, Eudiaptomus gracilis and Calanus sp. are able to regulate the fatty composition of their cell membranes to slow down metabolism and prolong their survival with time (Titocci and Fink, 2022) and this aligns with the current findings where more than 50% survival was observed after the 10th day of the experiment for all temperatures. The significantly higher survival rate of the copepods at 12 °C and 8 °C could be attributed to the relatively higher temperatures that increase the enzymatic activity of the organisms (Koussoroplis et al., 2014; Bai and Wang, 2020). Additionally, moderate temperatures (6 °C~15 °C) increase the survival of Thermocyclop sp. since the energy reserve depletion related to oxygen consumption is decreased (Werbrouck et al., 2017). This survival pattern has also been seen in adult Calanoid sp. (Devreker et al., 2009) with higher survival at 10 °C compared to lower temperatures of 3 °C. This suggests that the survival of copepods rises with temperature until reaching a maximum threshold, beyond which survival decreases with further temperature increases (Van Dinh et al., 2019). Thermocyclop sp. stored at 4 °C in the current study experienced higher mortalities than other temperatures. The decreased survival rate of Thermocyclop sp. at 4 °C may be associated with the impairment of their enzymatic activity, leading to mortality (Payne and Rippingale, 2001; Werbrouck et al., 2017). Temperature can directly affect the activity of enzymes by changing their physical structure and thereby changing catalytic efficiency (Cailleaud et al., 2007; Svetlichny et al., 2022). Moreover, various studies have found that different species of estuarine copepods reduce their metabolism to a minimum to sustain physiological activity in low temperatures and conserve energy in high temperatures (Koussoroplis et al., 2014; Werbrouck et al., 2017). These observations are consistent with the results obtained in the current study. Studies by Frisch and Santer (2004) observed higher mortality of Cyclops strenuus at 5 °C, and this is in line with the current findings where higher mortality was recorded at 4 °C. Therefore, the results of the present study demonstrate that the Thermocyclop sp. can be collected daily from the tank culture units. Copepods can be stored at 8 °C or 12 °C, and more than 50% of the copepods would be available after 10 days post-harvesting for use as a live starter feed for fish larvae. 2.2 Effect of different densities on survival of Thermocyclop sp. The density of the copepod population can significantly impact their growth, survival, development, and fecundity (Frisch and Santer, 2004). The percentage survival of Thermocyclop sp. increased with a decrease in packaging densities. The lowest survival of the Thermocyclop sp. at 5000 individuals/L could be attributed to density-dependent mortality. High copepod packaging densities result in many types of stressors including limited food resources, oxygen depletion, accumulation of metabolic products, and physical interaction with other individuals (Jepsen et al., 2015; Rajkumar and Rahman, 2016; Punnarak et al., 2017). Therefore, the accumulation of such higher metabolic wastes and low oxygen levels could have resulted in higher mortalities at 5000 individuals/L. Densities ranging from 50 to 1000 mature Calanoid Acartia tonsa /L have shown little or no negative effects on the Cyclopoid copepods (Jepsen et al., 2015). Higher density of adult copepods up to 6000 individuals/L has shown negative effects like higher mortalities as well as cannibalism for each other (Drillet et al., 2015; Franco et al., 2017). Different studies show that several omnivorous copepods become carnivores when phytoplankton concentration decreases in the culture medium (Drillet et al., 2015; Punnarak et al., 2017; Franco et al., 2017; Heneghan et al., 2023). In the current study, the copepods were starved throughout the experiment, which may have elicited cannibalism thus reducing the number of Thermocyclop sp. at higher densities. Similar rates of survival (67%) at 1000 individuals/L were reported for Acartia tonsa (Drillet et al., 2015). This confirms that it is possible to store copepods at 1,000 Individuals/L while keeping low mortality for 14 days without feeding and achieving a more than 50% survival rate. 2.3 Impacts of temperature and density on fatty acid profiles of Thermocyclopsp. The general decrease of FA content with time in the present study could be due to the degradation of the cell organelles of the Thermocyclop sp. (Mäkinen et al., 2017; Werbrouck et al., 2017). In degradation processes, these
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