Impacts of light regime on egg harvests and 48-h egg hatching success of Acartia tonsa (Copepoda: Calanoida) within intensive culture

We examined the effect of light regime on daily egg harvest (EH, eggs tank− 1 d− 1), and 48-h egg hatching success (HS, %) by Acartia tonsa (Copepoda: Calanoida) in intensive 130-l cultures. Since this copepod produces more eggs during darkness than in the light, we tested whether EH could be increased by utilizing unnatural light regimes. Egg harvests were between 0.85 to 1.20 million eggs culture− 1 wk− 1 and mean EH was not significantly different among tanks maintained at 3 h:3 h, 4 h:4 h, 6 h:6 h and 12 h:12 h light:dark. HS was not significantly different for eggs produced in the different light regimes and incubated at 12 h:12 h. In a second experiment, cohorts were reared (from nauplii) in constant darkness (D) and constant light (L) and eggs produced in each cohort were incubated in darkness (D–D, L–D) or light (D–L, L–L). Mean(± SE) HS was significantly different among the treatments, increased with increasing light exposure, and equal to 3.7(1.1), 32.2(15.1), 38.3(0.8) and 52.2(16.5)% for D–D, L–D, D–L and L–L treatments, respectively. These and published data were combined to generate an equation predicting 48-h HS for eggs produced and incubated at photoperiods between 0.5 and 24 h. Our experiments indicated that light can be an important factor affecting the success of intensive cultures of A. tonsa and that copepod culture protocols should include information on light regimes used during rearing and incubation of eggs.