EGG HARDENING OF COPEPODS Acartia tonsa AND Parvocalanus crassirostris: A NEW EXPLANATION FOR INTENSIVE CULTURE PROBLEM

The  copepods Acartia tonsa and Parvocalanus crassirostris have been widely studied as a high-quality live feed for aquaculture. The intensive culture is preferred as volume and/or, rearing area decreases; however, the increase in adult density creates difficulties in its cultivation. Several explanations have been proposed for such issue, and other answers are still necessary to continue with the increasing of the culture density. The present research was realized in a mariculture laboratory from AUNAP (Colombia) and made a new explanation using the fragility of freshly spawned eggs (FSE). Adults of  A. tonsa were allocated on slides under an optical microscope to record the morphologic changes in FSE. Adults of  P. crassirostris were spawned in darkness for 3 h into 5 L tank with lid, without aeration and a density of 30 adults mL^-1 . Pure oxygen was used to maintain high oxygen levels in the water. Exp. 1: FSE were exposed to adult and survival was deter mined from 0-25 min. Exp.  2: Eggs harvested were filtrated in a 40 µm sieve from 0 to 90 min post-harvest, and the recovery of the eggs was determined at different times . The FSE in  A. tonsa presents irregular characteristics before obtaining the circular shape. In  P. crassirostris , FSE survival declined very quickly when exposed to adults, and  recovery of viable eggs  post-filtration increase with time post-spawns. In conclusion: The FSE (without chorion ) presents high  sensibility to the adult presence and mechanical filtration . This information allows a new explanation for the actual problems present in the high culture system.