Cold stored Acartia tonsa eggs as a new food in the ornamental aquaculture industry: a feeding study.

The use of cultured copepods in intensive fish larviculture has involved both calanoids and harpacticoid but the best results have been obtained using calanoid copepods which have a higher content of HUFAs, are entirely pelagic and usually have very small naupliar stages which are more readily captured by fish larvae with small gapes at first feeding. Unfortunately, there are several difficulties in culturing calanoid copepods on a continuous basis, since they are usually cultured at very low densities, in large tanks, and need to be fed different algal combinations. As a consequence, the technology for mass scale production of copepods is in the research stage. In order to meet the demand of hatcheries for large quantities of copepods, suitable storage techniques (i.e. cold storage) of copepod eggs are considered of great interest. Since it has been demonstrated that the copepod embryon still develops and retains a physiological activity during the cold storage period, their fatty acid composition may change over the time of storage thus possibly affecting eggs viability and larval survival and growth. Currently, there is no reported research investigating the effects of fatty acids modification in copepods obtained from cold stored eggs on larval fish survival and development. For this reason the aim of the present study was to compare the effects of a standard rotifers/Artemia diet to one based on A. tonsa produced through a continuous small scale system and a diet based on A. tonsa obtained from 6 months cold stored eggs on survival and growth of Amphiprion polymnus larvae. This study showed that subitaneous A. tonsa eggs can be easily produced, they do not need to remain in a refractory phase before hatching and that they can remain viable for periods of time which could prove useful for feeding larvae. However, the final survival and growth of A. polymnus larvae fed these copepods was lower compared to larvae fed rotifer and Artemia or A. tonsa obtained from continuous culture. This can be related to the fact that the cold stored copepod embryos still develop and retain a physiological activity during the cold storage period, and their fatty acid composition may change over the time of storage with a consequent impact on larval fish development. The best storage time to maintain an optimal fatty acid profile in the newly hatched copepod nauplii is actually under investigation.