Abstract

The concept of continuous egg and adult separation was studied to evaluate the possibility of cultivating the copepod Acartia tonsa at high density (> 2.5 adults mL−1). First experiment: Densities of 5, 10, 15, 30, and 45 adults mL−1 were evaluated. For this, eggs spawned were allowed to settle quickly, harvested, and counted to determine the specific and relative egg production (SEP and REP, eggs female−1 day−1 and eggs mL−1 day−1, respectively). Second experiment: Mature females were spawned on slides to observe the shape of the freshly spawned eggs. Third experiment: respiratory rate under four corporal velocities in the filter system were evaluated (57, 115, 173 and 231 PL min−1; PL, prosome length), corresponding to four water exchange rates (50, 100, 150 and 200 volumes day−1). Fourth experiment: A high-density (7 adults mL−1) prototype based on continuous egg separation was designed and compared with daily egg harvest for siphon (control system). The specific egg production (SEP, egg female−1 day−1) and relative egg production were determined (REP, eggs mL−1 day−1). The SEP decreased with culture density (p <.05), but quickly egg separation allowed a high REP when a density of 10 adults mL−1 was used. Freshly spawned eggs were elongated for the first 7 min, which suggests fragility when freshly spawned. Water velocity increased adult respiratory rate (p <.05), and egg production reached a maximum at 100 volumes per day (p <.05). The above suggested a great potential to increase egg production at a high adult density (>2.5 mL−1), which was confirmed by higher REP in the prototype (100 eggs mL−1 day−1) than in the control system. This study contributes to intensive A. tonsa culture; a superior density of 5 mL−1 is possible with a high water exchange rate and careful egg harvesting.