L.A. McEvoy, A. Estevez, J.G. Bell, R. Shiels, B. Gara, J.R. Sargent
Abstract:
Turbot and halibut larvae were fed until metamorphosis on live-prey enriched with high, medium or low levels of either eicosapentaenoic acid (EPA, 20:5n-3) or arachidonic acid (ARA, 20:4n-6) in order to investigate the role of these fatty acids in determining pigmentation in flatfish. The enrichment diets comprised of blends of specialty triglyceride oils emulsified in seawater with soya phosphatidylcholine (PC) added at 12% (w:w). A previously employed enrichment comprising of 12% soya PC:88% tuna orbital oil was included as a control diet. Ascorbyl palmitate and a-tocopherol acetate were added to all diets at concentrations of 100 mg/kg oil. Turbot larvae in triplicate 60-L containers (750 larvae/tank) were fed from day 3 to 14 post-hatch on rotifers enriched for 6 h with these diets, followed from day 11 to 45 by a diet of Artemia nauplii enriched on the experimental diets for 12 h. Similarly, 18 day post first feeding halibut larvae in triplicate 100-L tanks (40 larvae/tank) were fed Artemia nauplii enriched for 12 h on one of the 7 diets for 43 days. Following metamorphosis, all surviving fry were counted, measured and weighted, and the incidence of normal pigmentation in each tank assessed. Pooled brain samples were taken from each tank for fatty acid analysis. Brain fatty acid profiles reflected the dietary treatments. There was a significant positive correlation between high levels of ARA in turbot brain and an increased incidence of malpigmentation (r=0.945, P=0.000), with a converse relationship between high levels of EPA and decreased numbers of malpigmented fry (r=0.610, P=0.010). Levels of EPA and ARA in halibut brains showed similar trends with respect to malpigmentation, but the correlations were less statistically significant (r=0.560, P=0.010 and r=0.389, P=0.093 in ARA and EPA, respectively). Both species showed a significant, positive correlation between the incidence of normal pigmentation and brain EPA:ARA rations (r=0.871, P=0.001 in turbot, and r=0.547, P=0.034 in halibut), with increased numbers of malpigmented fry occurring when their brain EPA:ARA ratio fell below 1:1.
(Unit of Aquatic Biochemistry, University of Stirling, FK9 4LA, Scotland, UK)