The cyclopoid copepod Oithona colcarva has great aquaculture potential as a feed for marine finfish. Newly hatched nauplii are small (45 μm), have a weak escape response, and are natural prey for many fish larvae in the wild. These characteristics make O. colcarva an ideal candidate for feeding larvae of marine fish species with small mouth gapes. Since established production protocols for O. colcarva are lacking, a series of experiments were conducted to explore the impacts of culture density, photoperiod, and diet on nauplii production.
Similar experimental designs and protocols were used for all experiments and results were used to inform and modify subsequent experimental protocols. For the first study, four rearing densities (8, 12, 16 and 24 nauplii per ml) were evaluated in replicate microcosms. The mean cumulative nauplii production was significantly greater at the highest tested density with a three-fold increase compared to the lowest stocking density. In the next experiment, three photoperiod regimes (12L:12D, 16L:8D, 24L:0D) were tested and no significant differences in reproductive output were observed among treatments. Subsequent diet studies employed a 12L:12D photoperiod. The first tested four live algae diets (Chaetoceros muelleri only, Tisochrysis lueta only, Tetraselmis chuii only, and a 1:1:1 mix of C. muelleri, T. lueta, and T. chuii). The mean cumulative nauplii production was significantly greater in the mixed algae control. The C. muelleri only diet had low nauplii production but the T. lutea only and T. chuii only diets had close to zero nauplii production. The second diet study tested three algae mixes (1:1:1 live mix, 1:1:1 paste mix, and a commercially available "Shellfish Diet"). The experiment was stopped on day 9, when adults would have been stocked into new cups to monitor nauplii production, because growth was stunted and the copepods were only in the copepodite developmental stage. The experiment was instead harvested to take pictures and measurements and to assess survival rate from initial stocking. The live mix had the highest survival rate, with an average of 68% surviving to day 9. The paste mix had a comparable average survival rate of 67.2% but the Shellfish Diet had a significantly lower survival rate of 49.3%.
Further studies are needed to identify the ideal and maximum stocking densities, minimum light thresholds for nauplii production, and if O. colcarva can fully develop and produce nauplii on a diet of algae paste. Defining these culture parameters will increase the success and reliability of Oithona colcarva cultures and possibly even facilitate the domestication of this species and eliminate the reliance on live microalgae for nutrition. Future implications of this research include mass production of Oithona colcarva in aquaculture facilities and larviculture of challenging marine finfish species.