The effect of tissue docosahexaenoic and arachidonic acids levels on hypersaline tolerance and leucocyte composition in striped bass (Morone saxatilis) larvae

Larval striped bass (M. saxatilis), tissue docosahexaenoic (DHA) and arachi donic (AA) acids levels were modulated through dietary enrichments and the effect on growth and survivorship examined. Mean growth was significantly g reater in larvae enriched with AA than in larvae enriched with DHA (F-value for AA treatment was 20.5 versus only 5.1 for the DHA treatment). Dietary treatment did not have a significant effect on larval survivorship (56.0 +/ -2.4%, p > 0.05). When challenged with hypersaline (25 psu) immersion, DHA enriched larvae survived better than AA enriched larvae, but larvae with bo dy tissue levels of 15.4 mg AA g(-1) and 7.2-15.4 mg DHA g(-1) dry weight p rovided maximal survivorship to the challenge. Elevated levels of body tiss ue AA was generally associated with elevated levels of whole body cortisol. On the other hand, increasing levels of DHA mainly affected the kinetics o f cortisol increase to hypersaline exposure. Larvae injected intraperitonea lly with formalin fixed Staphylococcus aureus responded by altering the pro portion of lymphocytes, monocytes and neutrophils in perpherial blood. Lymp hocytes, which accounted for the largest percentage of white blood cells (o ver 70%), decreased in all challenged larvae during the first 6 hours post injection then returned to pre-challenge levels after 44 hours. Conversely, the relative proportion of monocytes and neutrophils rose from 14% and 2% up to 28% and 6% of the total circulating leucocytes, respectively. The lar gest increase occurred in larvae fed a moderate level of both DHA and AA.