COPEPODS AS FOOD FOR MARINE ORNAMENTALS LARVAE.

Copepods are the preferred natural prey of most marine fishes during the larval phase. They show a wide range of body size between nauplii and adults, typical movement that stimulate the predatory activity of the larvae, and they also have a high content of highly unsaturated fatty acids (HUFAs). These fatty acids are extremely important for larval fish survival and growth and several studies have demonstrated that they are essential in larval diets. At date, most of the commercial fish species are still reared using rotifers (B.plicatilis, B. rotundifornis) and Artemia nauplii since they can be cultured in large quantities at high densities. Unfortunately, using rotifers and Artemia during this early period in life history, does not always result in optimal larval growth since these live prey may contain an inadequate fatty acid profile and, in some cases, be of an inappropriate size. 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 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 still in the research stage. In the present study culture techniques for both calanoid and harpacticoid copepods are discussed as well as a new technology able to produce different sized preserved copepods that maintain, through the time, their fatty acid composition.  In particular, different  feeding studies on ornamental species such as Centropyge flavissimus, Amphiprion clarkia, polymnus and ocellaris, Meiacanthus grammistes and Hippocampus reidi are discussed. Survival and growth rates are related to prey and larval fatty acid composition.  In addition, the gene expression of genes involved in larval fish growth, lipid metabolism and metamorphosis is analyzed. In particular, the relative gene expression of genes involved in fish growth (Insuline like growth factor I and II and myostatin), lipid metabolism  (peroxisome proliferator activated receptors α and β) and  fish metamorphosis (Thyroid receptor α and β) were analyzed by Real Time PCR. While both hapracticoids and preserved copepods improved larval survival and growth when used as supplement to the traditional diet based on rotifers and Artemia,  the calanoid copepods (Acartia tonsa, Centropages typicus and Parvocalanus crassirostris), which are entirely pelagic and thus more available for the feeding larvae, were able to improve larval fish survival and growth when used solely. These studies evidenced that all the copepods species analyzed can be considered a valuable source of HUFAs in ornamental fish larviculture and may improve larval fish survival and growth.