Biology and Culture of a Tropical Harpacticoid Copepod, Nitocra Affinis Californica Lang

The complete post-embryonic development of Nitocra affinis was studied on specimens cultured under normal laboratory conditions (30ºC and 12:12hours L:D cycle). Egg sac is produced 1-2 days (0.95±0.08 days) following a successful insemination. Female produced an average of 7.0±0.0 broods, minimum of 6.0±0.0 and a maximum of 8.0±0.0. The average number of eggs per sac was 18.3±0.25 (ranges from 12-25 eggs per sac). The egg sacs were carried for 18-29 hours or 22.8±2.0 hours on average. Development of nauplii (stages NI through NVI) is completed within 4-5 days (4.66±0.06 days) while copepodid development (stages CI through CVI) occurred within 5-7 days (6.21±0.15 days). The total generation time (egg to adult) was 9-12 days (10.91±0.18 days). Body length of nauplii ranged from 65.4±0.6 µm (NI) to 214.1±2.8 µm (NVI) while copepodid ranged from 235.2±2.9 µm (CI) to 389.6±7.2 µm (CVI or adult). 0Usin0g different food items (three different algal species; Chaetoceros calcitrans, Nannochloropsis oculata and Tetraselmis tetrathele and their combinations; and three artificial food; baker’s yeast, shrimp feed and rice bran) and feeding densities (104, 105, 106 and 107 cells/ml for algal food and 0.02, 0.04 and 0.06 mg/ml for artificial food), the growth and development of N. affinis were studied. In both single and combined algal food, the highest (p<0.05) egg and copepod production/female was achieved using the density 106 cells/ml whereas 0.06 mg/ml was the best (p<0.05) feeding for artificial diet. The highest (p<0.05) fecundity was achieved with copepod fed with mixed algal diet with an average of 18.3±0.3 eggs/sac. The highest (p<0.05) offspring production was achieved with N. affinis fed C. calcitrans (with mean total production reaching a maximum of 132.0±3.8 offspring/female), followed by those fed with mixed (124.8±1.7 offspring/female) and combination of C. calcitrans:T. tetrathele (113.0±1.3 offspring/female). Likewise the highest (p<0.05) survival from nauplii to adult (97-98%) and highest (p<0.05) maximum specific growth rate (K=0.43±0.0) was achieved by copepod fed algal food C. calcitrans, and all its combinations. The shortest (p<0.05) time for egg maturation and time interval between egg sac was found in the T. tetrathele fed copepod. Likewise the shortest (p<0.05) development time from nauplii to copepodid and copepodid to adult resulted from feeding with T. tetrathele. The effects of some environmental parameters (salinity, temperature, and light conditions) on the reproduction and development of harpacticoid copepod, N. affinis under controlled laboratory conditions were determined. Seven different salinity levels (5-35 ppt) four different temperatures (20-35˚C) three light intensities (25-130 µmol/m2/s) and three different photoperiods were employed in this study. The highest (p<0.05) reproduction and fastest development time were achieved by copepods reared under 30-35 ppt salinity and lowest light intensity (25 µmol/m2/s). The optimum temperature for the maximum reproduction was 30ºC while development time was shortest (p<0.05) and maximum length achieved by adult copepods was longest (p<0.05) under 30ºC and 35ºC compared to other temperature levels. Continuous light (24h:0h LD) inhibited the egg production while continuous darkness (1h:23h LD) and 12h:12h LD significantly favoured the overall reproductive activity of the female. Photoperiods 1h:23h and 12h:12h LD yielded highest total (p<0.05) offspring/female coupled with highest (p<0.05) survival percentage and longest (p<0.05) total body length of copepods. A study to describe a relatively simple and reliable small scale mass production and the nutritional composition of N. affinis was undertaken. The result confirmed the feasibility of maintaining N. affinis on a small scale for a long period. Within six weeks (42 days) operations a minimum harvest of 87.2 x 103 copepods/2L and maximum of 89.0 x 103 copepods/2L was obtained. Using several numbers of basins for mass production it was feasible to harvest 30 x 103 copepods/2L daily after two weeks of inoculation. Nitocra affinis has a great potential as live food because they contain high protein (39-52%), lipid (13-23%) and carbohydrates (8-11%). It also contains high level of n-3 HUFA (up to 44%) and n-6 HUFA (up to 14%). In addition it contains high amount of DHA (up to 19%) and EPA (up to 25%). Moreover, levels and ratios of fatty acids closely match both the requirements of marine finish larvae and of marine shrimp. Survival and specific growth rate of Penaeus monodon larvae (postlarvae stage 1-15) fed with different live feeds (Artemia nauplii and N. affinis) and artificial diet were evaluated. The highest (p<0.05) survival was achieved by shrimp larvae fed with N. affinis (60.6%), followed by those fed with artificial diet (43.0%) and a combination of Artemia nauplii and N. affinis (4.1%). The larvae fed with Artemia nauplii suffered high mortality probably due to the abrupt change from algal diet to a diet of relatively large Artemia nauplii. Likewise, highest (p<0.05) specific growth rate was achieved by shrimp fed with N. affinis followed by shrimp fed artificial diet.

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