Tolerance of un-ionized ammonia in live feed cultures of the calanoid copepod Acartia tonsa Dana

Optimal water quality is considered as being a restriction for marine copepod cultures for live feed. There is a lack of knowledge on the water-quality conditions in copepod cultures and the effect on copepods. Few studies have investigated the effect of ammonia on copepods, and fewer reports No Observed Effect Concentrations (NOEC) and Lowest Observed Effect Concentrations (LOEC), which provides safety levels before cultures are affected. This study investigates the tolerance of Acartia tonsa nauplii and adults to ammonia, using mortality as the endpoint after 24, 48 and 72h of exposure. Nauplii were exposed to levels from 0 to 5127g NH3L-1 and adults to levels from 0 to 8481g NH3L-1. Nauplii NOEC was 30g NH3L-1 and LOEC was 81g NH3L-1. Adult NOEC was 477g NH3L-1 and LOEC was 1789g NH3L-1. 50% Lethal Concentrations (LC50) for nauplii of 48 and 72h was 1257 and 220g NH3L-1. LC50 for adults was 2370 (24h), 972 (48h) and 770 (72h). Combining NOEC with excretion rates of NH4/NH3 a model was developed to calculate densities in batch cultures. We recommend that for batch cultures of A.tonsa, NH3 is kept below NOEC for nauplii and that levels of NH3 together with pH are monitored weekly.