Effects of dietary arachidonic acid on larval performance, fatty acid profiles, stress resistance, and expression of Na+/K+ ATPase mRNA in black sea bass Centropristis striata

Dietary arachidonic acid (ARA, 20:4n-6) supplementation on larval performance, tissue fatty acid profiles, resistance to hypersaline stress and expression of Na+/K+ ATPase mRNA was studied in black sea bass Centropristis striata from the first feeding through metamorphosis at 24 days post-hatching (d24ph). Thirty 15-L aquaria were stocked with d1ph yolksac stage larvae at 100 ind/L. Salinity (34 g/L), temperature (22 °C), photoperiod (18L:6D), light intensity (1000 lx), diffused aeration (100 mL/min) and D.O. (> 5 mg/L) were held constant. Non-viable microalgae Nannochloropsis oculata was maintained at 300,000 cells/mL as background. To evaluate the effects of dietary arachidonic acid (ARA) supplementation, live prey, rotifers Brachionus rotundiformis and Artemia sp., was enriched with emulsions containing 10% docosahexaenoic acid (DHA, 22:6n-3) and five different levels of ARA (0, 6, 8, 10 and 12% total fatty acids, TFA). In a sixth treatment, live prey was enriched with a premium commercial fatty acid booster (26% DHA, 0% ARA). Rotifers were fed from d2 to d20ph at 10–23 ind/mL, while Artemia were fed from d18 to d22ph at 0.5–3 ind/mL. On d24ph, larval fatty acid profiles reflected dietary levels, and no significant (P > 0.05) differences in larval growth (notochord length, wet and dry wt.), survival (range = 24.3–32.7%), or hypersaline stress resistance (ST-50 = 27.1–31.8 min) among treatments were evident. However, larvae fed diets supplemented with ARA (6–12% TFA) demonstrated a significant (P < 0.05) increase in Na+/K+ ATPase mRNA 24 h after a sublethal salinity (43 g/L) challenge, whereas larvae fed 0% ARA and the commercial diet (devoid of ARA) showed no significant increase. The results suggested that dietary supplementation with ARA at 6–12% promoted the adaptive physiological responses to hypersalinity stress and hypo-osmoregulatory ability in black sea bass larvae.