Exploring the role of photoperiod in regulating the physiological state of the calanoid copepod Pseudodiaptomus hessei in aquaculture cultures

In adult copepods, the photoperiod can promote egg production while reducing longevity, reflecting a strong influence of photoperiod on metabolism. This study tested whether the metabolism of Pseudodiaptomus hessei, a resilient and indigenous calanoid species, is modulated over a photoperiod gradient of 06:18, 12:12 and 18:06 hours of light: dark using measurements of the activities of the mitochondrial enzymes citrate synthase and cytochrome c oxidase, as well as lipid peroxidation. Significant differences between the high-light treatment and both the moderate- and low-light treatments were observed across all three markers. The shorter photoperiods (06:18 and 12:12) appeared to promote culture conditions below stress thresholds, as displayed by lower metabolic rates and lower oxidative damage in P. hessei under the conditions tested. Future studies should confirm the relationship between photoperiod, metabolism and fecundity in this live food candidate for aquaculture.