Copepods are a critical resource to culturing many species of marine ornamental fish. Unfortunately, culturing marine copepods can be time consuming, difficult, and expensive, and copepods have pronounced escape responses used to avoid predation by larval fish. Methods have been identified to suppress the escape responses of two species of copepod, the calanoid Parvocalanus crassirostris and the cyclopoid Oithona colcarva, to improve feeding success of two fish species, the Pacific Blue Tang (Paracanthurus hepatus) and Golden Domino Damselfish (Dascyllus auripinnis).
Copepods’ escape responses were suppressed using acute exposures to an extreme temperature and salinity. Previous experiments tested three temperature and salinity treatments on the escape behaviors of these copepods, and the most effective temperature and salinity were used as treatments, in addition to a control, in larval experiments. Four experiments evaluated the effects of the two copepod species on the growth, feeding incidence, and survival of the two fish species. P. crassirostris treatments were 1°C for 40 minutes, 60 g L-1 for 1 hour, and untreated copepods serving as a reference diet. O. colcarva treatments were 40°C for 15 minutes, 80 g L-1 for 1 hour, and untreated copepods as a control.
Larval tanks (15L) were maintained at 26°C with 35 g L-1 saltwater, a 16h light : 8h dark photoperiod, and the microalgae Tisochrysis lutea (150,000 cells mL-1 for D. auripinnis or 300,000 cells mL-1 for P. hepatus). The D. auripinnis experiment was stocked with 300 larvae tank-1 and the P. hepatus experiment was stocked with 750 eggs tank-1. Starting 3 days post hatch (DPH), copepods were treated and fed to larval tanks (n=6 treatment-1) twice daily until the 5 DPH. Fish were sampled at 3 DPH to assess growth and feeding incidence and tanks were fully harvested 5 DPH to quantify growth, feeding incidence, and survival.
A diet of cold-treated (1°C) P. crassirostris led to the highest survival of D. auripinnis at 5DPH and untreated P. crassirostris resulted in the highest survival of P. hepatus. However, P. hepatus survival in the O. colcarva experiment was highest in the high temperature (40°C) treatment. D. auripinnis fed O. colcarva showed the best survival in the high salinity treatment (80 g L-1). These results showed that suppressing the escape responses of copepods can lead to improved survival at 5DPH but efficacy is species specific.