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.