Water exchange rate and stocking density on the larviculture of the scallop Nodipecten nodosus in recirculation aquaculture system

Abstract

Nodipecten nodosus is an important scallop species with high commercial value. Hatchery seed production of this species is crucial for aquaculture. A recirculation aquaculture system (RAS) was tested for larviculture of N. nodosus using three stocking densities (100, 250, and 500 larvae∙mL⁻¹) and three water exchange rates (WER; 1.2, 2, and 3 times per hour of the larviculture tank volume). The experiment was carried out with four replicates of each treatment, totaling 36 experimental units. Samples were collected to assess daily larval growth and larval numbers after 3, 8, and 10 days (T3, T8, and T10) of culture. Total larvae number was used to calculate larvae survival (compared to initial larval number) and the number of competent larvae for settlement (larvae retained in the mesh 145 μm, with eyed spot and the foot start to appear) was used to calculate yield after 8 and 10 days (T8 and T10) of culture (compared to initial larval number, T0) and final yield of competent larvae at T10 (compared to total larvae number at T10). Thiosulphate Citrate Bile and Sucrose Salts (TCBS) medium was used to evaluate the presence/absence of Vibrio ssp. in samples from the larvae, microalgae, and RAS water system (different parts) collected at T0 and T10. Results showed effects of stocking density on larvae number, survival and yield. In all water exchange rates tested, higher total larvae numbers were observed in high densities and higher survival in low stocking density. Analyzing competent larvae for settlement at T8 and T10 concerning T0, besides yield were high for low-densities, high numbers in the same tank volume were registered in high-density treatment in water exchange rates three times. In contrast, high numbers of competent larvae were observed in low-density treatments for all water exchange rates tested. However, stocking densities tested did not affect the final yield of competent larvae for settlement concerning the total larvae number at T10. High stocking density affects larvae growth rate. Consequently, larviculture of scallop N. nodosus in RAS is feasible in both the low, medium, and high stocking densities tested. Additionally, high-water exchange rates promote better larvae yield and high-densities can optimize hatchery space and resources for more sustainable scallop seed production.