F. Powell, P. Brooking, J. Castell, T. Blair
Abstract:
In an attempt to improve the enrichment protocol for producing nutritious Artemia nauplii to feed to larval halibut (Hippoglossus hippoglossus) three different enrichment media (a high protein microdiet mixed 50:50 with cod liver oil, DHA Selco or Algamac-2000) were fed at two different concentrations (1 or 2 g/million nauplii, 0.1 million nauplii/L) for 6, 12 or 24 h exposure period. There was a significant effect of enrichment media, exposure time and exposure concentration on total lipid content and fatty acid composition of nauplii lipids. Both DHA Selco and Algamac were successful in increasing nauplii 22:6n-3 (DHA) to over 7% of the total fatty acids. The Algamac-2000, which had a DHA/EPA ratio of over 26, resulted in the highest DHA/EPA ratios in the nauplii (2.9 after 12 h/2 g). The microdiet-cod liver oil emulsion enrichment had the least effect on Artemia nauplii lipids and appeared to be poorly assimilated and, therefore, could not be recommended for further enrichment trials. A second trial with 2, 3 and 4 mg of DHA-Selco and Algamac-2000 per 1 million nauplii for 12 or 24 h was conducted. The highest level of DHA (16+/-3%) and the highest DHA/EPA ratio (3.3) in Artemia nauplii was achieved with 2 g of Algamac-2000 and 24 h exposure. The highest DHA level achieved with DHA-Selco was 13+/-1% using 3 g/million for 24 h. The DHA-Selco resulted in significantly higher total lipid content, which was well correlated with both concentration and exposure time with the DHA-Selco (ranging from 17+/-1 for 12h/2 g to 24+/-2 after 24 h/4 g). Unfed Artemia nauplii dropped from an initial lipid content of 14+/-0.5 to 9.9+/-0.5% lipid after 12 h. Algamac-2000 fed Artemia contained 15 to 17 % lipid (the highest level 17.7+/-0.9% was for 2 g/24 h). The Algamac-2000 resulted in cleaner, less oily nauplii and, being a complete algal meal, supplied a more complete nutrient package, including proteins, amino acids, vitamins and minerals, in addition to essential fatty acids.
(Martitime Mariculture Inc., St. Andrews, NB E0G 2X0, Canada)