THE EFFECT OF DIFFERENT HUFA ENRICHMENT EMULSIONS ON THE NUTRITIONAL VALUE OF ROTIFERS (BRACHIONUS PLICATILIS) TO LARVAL HADDOCK (MELANOGRAMMUS AEGLEFINUS)

T.J. Blair, J.D. Castell, S. Neil, K. Howes, S. Mercer, J. Reid, P. Sorgeloos

Abstract:

Rotifers (Brachionus plicatilis) have frequently been shown to be deficient in n-3 highly unsaturated fatty acids (HUFA particularly 20:5n-3 or EPA and 22:6n-3 or DHA) when used as the live food for cool water marine fish larvae. Recent research has begun to demonstrate that the n-6 HUFA, arachidonic acid (20:4n-6 or AA) is also important in larval marine fish nutrition. An experiment was designed to determine the effect of different rotifer enrichments during the critical 15 days of larval haddock (Melanogrammus aeglefinus) feeding. Rotifers were enriched with the standard ICES enrichment emulsions 30/4/C (high in DHA or 22:6n-3) and 30/0.6/C (high in both DHA and EPA or 20:5n-3). In addition a special emulsion that contained high AA as well as EPA and DHA. The growth, survival and lipid composition of five replicate tanks (50-liters each with 1000 larvae) of haddock larvae fed for the first 15 days with rotifers enriched with each of these emulsions were compared with larvae fed unenriched rotifers reared on mixed algae (Isochrysis galbana, Nannochloropsis sp., Pavlova lutheri and Tetraselmis suecica). All larvae were fed rotifers cultured on mixed algae from day 15 day 25 and the greatest mean dry weight (0.227 +/- 0.077 mg), followed by those receiving the DHA/EPA/AA enriched rotifers (0.215 +/- 0.074 mg). The smallest larvae were those receiving the ICES 30/06/C (DHA = EPA enriched) rotifers (0.195 +/- 0.086 mg). The DHA enriched rotifers gave the second lowest mean dry weight per larvae (0.200 +/- 0.080 mg). The mixed algae and DHA/EPA/AA enriched rotifers both had 20:4n-6 levels above  2.5% of the total fatty acids while the ICES 30/4/C and 30/06/C enriched rotifers all had less than 2% 20:4n-6. Early results suggest that in addition to DHA, haddock larvae require about 2.5% of their dietary fatty acids as arachidonic acid (20:4n-6). At the time of writing this abstract the experiment is still running. Survival and mean weight at 45 days from first feeding will be reported.

(Department of Fisheries and Oceans, Biological Station, 531 Brandy Cove Road, St. Andrews, NB E5B 2L9, Canada; e-mail: blairt@mar.dfo-mpo.gc.ca)

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