OPTIMIZING PROTOCOLS FOR USING COPEPODS AS LIVE FEEDS  

The use of copepods has been instrumental in the development of culture techniques for species such as the red snapper, the giant grouper, and several marine ornamentals where first feeding using traditional live feeds had been unsuccessful.  However, data and guidelines for the use of copepods as larval feeds are still largely lacking. Most studies to date report only overall feeding rates and do not account for factors such as the copepod species, the life stages offered to fish larvae, or the environmental conditions under which the copepods were produced.  In recent years, large scale culture techniques for Acartia tonsa and Parvocalanus crassirostris have been developed at the Thad Cochran Marine Aquaculture Center of the University of Southern Mississippi's Gulf Coast Research Laboratory for the purpose of feeding cultured larvae of the red snapper (Lutjanus campechanus). Knowledge of the developmental kinetics of the two copepod species in candidate culture conditions is essential to ensure delivery of the appropriate copepod stage and size to fish larvae.

In this study, the growth and development rate of A. tonsa and P. crassirostris from egg to reproductive adult were assessed at five temperatures (20, 22.5, 25, 27.5, 29.5°C). Experiments were conducted in triplicated small-scale (3L) containers where newly hatched N1 copepods were stocked at a density of 1.0 ml^-1 and fed a diet of Tisochrysis lutea. Copepods were sampled (N ≈ 30) every 4 hours during the first day and twice daily onward until 100% of the population had reached the C6 stage. Copepods in all samples were staged and measured (nauplii - total body length and width, copepodites - prosome length and width). Using the proportion of each copepod stage at sampled times, we calculated the average age (in hours post stocking) of copepods in each stage group. Next, the effect of varying initial age structure on the proportion of each stage group through time will be assessed in an on-going modelling study.

The results of the temperature trial show that increasing copepod culture temperature reduces the duration of each developmental stage and overall developmental time.  For both species, copepod size is inversely proportional to culture temperature. At a given developmental stage, P. crassirostis is smaller than A. tonsa (e.g. at the N1 stage - 81um length x 50.5 um width for P. crassirostris versus 100um length x 59um width for A. tonsa). Based on these results, we suggest that the temperature in the copepod culture systems and that in the larval fish culture tanks along with the stage distribution of copepods being feed need to be accounted for in order to optimize the number of consumable stages for the fish species being reared. These results are discussed in the context of early feeding of the red snapper.