Spawning Parvocalanus crassirostris at a high adult density: Explaining low adult population numbers and means for improving their intensive culture

Abstract

In calanoid copepods, intensive culture is preferred, but currently, densities do not exceed a few adults per milliliter. Several explanations exist, but none have allowed increasing the density of adults. This study proposes a new explanation for the problem of adult density in intensive culture, using the copepod Parvocalanus crassirostris as a model. First: eggs (2 h old) were supplied to adults kept at 20 adults mL−1 in 1 L containers with and without microalgae; constant aeration was supplied to determine egg survival to damage caused by the adults. Different samples were taken up to 175 min. Second: A high-density spawning test (5–80 adults mL−1) was performed, using shallow depth (2.5 cm) and supersaturation level of oxygen for rapid egg separation and sufficient oxygen for adults, respectively. The SEP (egg female−1 day−1) and REP (egg mL−1 day−1) were determined. Third: two systems of continuous egg harvesting, filtration and sedimentation, were evaluated under a high density of adults culture (10 adults mL−1). The adults of P. crassirostris quickly damaged the eggs, but the presence of food reduces the damage caused. Adults presented high SEP up to 10 adults mL−1; however, REP increased significantly to more than 170 eggs mL−1 day-1 using densities of 20 and 30 adults mL−1 (p <.05). A continuous harvesting system by filtration generated deformation of the eggs and a lower SEP and REP compared to the passive harvesting system by sedimentation (p <.01). The present study showed that even P. crassirostris, considered herbivore copepod, can damage its eggs. The fragility of newly spawned eggs (without hardened chorion) can generate difficulties when increasing adult density in culture. This new explanation contributes to the generation of new egg harvesting strategies in calanoid copepods of aquaculture importance.