Pilot evaluation of freeze-dried microalgae in the mass rearing of gilthead seabream (Sparus aurata) larvae

The replacement of live microalgae by freeze-dried Nannochloropsis gaditana (B3 strain) and Isochrysis galbana (T-ISO strain) in the mass rearing of larval seabream (Sparus aurata) was studied. Total substitution of live N. gaditana by freeze-dried cells in 1 m(3) larval tanks produced similar growth and survival in larvae reared from first feeding until day 43 with three different types of rotifer enrichment. Differences in growth of larvae were only due to the type of enrichment used to feed rotifers prior to their addition to larval tanks. This was regardless of the presence of live or freeze-dried N. gaditana in the larval tanks. Specific growth rate (G) of larvae was significantly enhanced (G = 0.106 +/- 0.001; P < 0.05) with a commercial enricher compared to N. gaditana (G = 0.099 +/- 0.003) as rotifer enricher. Feeding the rotifers with freeze-dried I. galbana produced the same larval growth rate (G = 0.109 +/- 0.002; P > 0.05) as the commercial enricher, indicating the high nutritional value of these algae in a freeze-dried state. Larval survival was similar in all treatments. Water quality, in terms of dissolved oxygen and pH, was also similar in the different treatments. Ammonia concentration was higher (P < 0.05) when freeze-dried N. gaditana was added to the larval tanks, but only during the first 15 days of culture, when no water exchange was used. Nitrite did not vary (P > 0.05) during the first 15 days, but increased more for live N. gaditana from day 16 onwards. Results of this study indicate the potential for a complete replacement of live microalgae by freeze-dried microalgae throughout the whole process of mass rearing seabream larvae. (C) 2001 Elsevier Science B.V. All rights reserved.