Copepods are the most common secondary producers in marine environment and the natural prey for the larvae of most marine finfish species. Unlike traditional live feed such as rotifers and Artemia, copepods are rich in essential fatty acids, other essential micronutrients and their nutritional profiles meet the requirement of fish larvae. Moreover, the small size of the copepod nauplii is vital for the first feeding larvae of fish species with small mouth gape sizes such as groupers and snappers. Copepod also stimulates feeding responses in fish larvae through their distinctive swimming patterns. Despite multiple advantages of copepod as live feed, utilization of copepod in aquaculture hatcheries is still sporadic, which is largely attributed to difficulties in their culture on mass scale. Thus the present work was undertaken to develop intensive culture techniques to overcome the current constraints hindering a reliable mass production of calanoid copepod Parvocalanus crassirostris.
Three consecutive trials were conducted to find out the suitable feed as well as optimal stocking density for the culture of P. crassirostris. In the first experiment, the optimal diets for cultivation of P. crassirostris was investigated using different feeds such as Isochrysis galbana, Chaetoceros calcitrans, Nannochloropsis salina, Yeast and a mixture of all the above in equal ratio at the rate of 1x105 cells mL-1 for 10 days. The second experiment was focused on identifying the optimal culture density for P. crassirostris when the nauplii were not removed from the culture. The third experiment was carried out to find the optimum stocking density for culturing copepod when the nauplii were daily harvested without affecting the adult. The stocking density used in the second and third experiment was 0.125, 0.25, 0.50, 1, 2 and 4 nos mL-1 by using the best diets from the previous experiment. The key parameters investigated were egg and nauplii production and population growth of P. crassirostris. Among the five diets tested, the production of eggs and nauplii and the population growth was significantly (p<0.05) higher in Isochrysis sp. and Chaetoceros sp. fed group. However, for longer duration of culture, Isochrysis sp. was found to be more suitable than Chaetoceros sp. The highest copepod density was achieved at the stocking density of 1.00 nos./ml on day 3, when the nauplii were not removed from the culture. From the relationship between stocking density and egg and nauplii production rates for P. crassirostris, a significant decline in production was observed when densities were increased. However, when nauplii were daily removed from the culture, the highest copepod nauplii density was achieved at the stocking density of 0.25 nos. mL-1. A significantly (p<0.05) higher number of nauplii was produced at the stocking densities of 0.125 and 0.25 nos. mL-1, when compared to the other stocking densities. Based on the results of the present study, Isochrysis sp. may be recommended for the intensive cultivation of P. crassirostris and the stocking density for culture may be 0.25 nos. mL-1 when nauplii were harvested daily and 1.0 nos. mL-1 when nauplii were not harvested.