Reproductive performance, growth and development time of a tropical harpacticoid copepod, Nitocra affinis californica Lang, 1965 fed with different microalgal diets

Abstract

This study examines the growth, reproductive performance and survival of a copepod Nitocra affinis californica Lang, 1965 fed with three microalgal food items singly (a diatom, C. calcitrans ; a green algae, N. oculata ; flagellated green algae, T. tetrathele) and in combinations (50% C.calcitrans +50% N. oculata; 50% C. calcitrans+50% T. tetrathele; 50% N. oculata+50% T.tetrathele; 50% C. calcitrans+25% N. oculata+25% T. tetrathele). The experiments were performed under controlled laboratory condition (30ppt salinity, temperature of 30°C, light intensity of 25μmolm−2s−1 and 12h light:12h dark cycle). Feeding densities were maintained at 106 cells ml−1 throughout the study. The highest (p<0.05) egg production was achieved by copepods fed with C. calcitrans and mixed algal diet (50% C. calcitrans+25% N. oculata+25% T. tetrathele) with mean values of 133.6±3.9 and 128.2±2.0 eggs female−1, respectively. Similarly, the highest (p<0.05) offspring production (132.0±3.8 offsprings female−1), survival from nauplii to adult (98.8±0.2) and maximum specific growth rate (K=0.43±0.0) was achieved with N. affinis californica fed C. calcitrans. The shortest (p<0.05) embryonic development time, time interval between egg sac, development time from nauplii to copepodid and copepodid to adult resulted from feeding with T. tetrathele. The longevity of the female N. affinis was found to be longest (p<0.05) when fed with mixed algal diet (42.2±0.7days) and combination of C. calcitrans+T. tetrathele (41.4±0.7days). The present study revealed that amongst the microalgae offered, C. calcitrans was the best food item as indicated by the highest reproductive capacity (eggs female−1 and offsprings female−1) of the N. affinis californica. Significantly higher nutritional values of C. calcitrans compared to other microalgae were probably responsible for the best reproductive and growth performance of N. affinis.