Annual cycle of plasma lipids in captive reared striped bass: effects of environmental conditions and reproductive cycle

Protein, lipid and fatty acid concentrations in plasma of eight male and ei ght female six year old captive striped bass (Morone saxatilis) were monito red monthly over the course of two reproductive cycles as part of an effort to investigate the time course of lipid class mobilization and subsequent deposition in gonads. Total protein levels (44.2 +/- 0.67 mg ml(-1), range 20.6-86.4) showed seasonal fluctuation, but did not vary with sex. Total li pid concentrations in the plasma of both males (17.7 +/- 0.61 mg ml(-1)) an d females (14.1 +/- 0.64 mg ml(-1)) showed seasonal fluctuations with the l owest levels in late Spring during spawning. Plasma lipids in females were significantly (p < 0.0001) lower than those of the males except during earl y ovarian secondary growth. Analysis of the lipid class composition reveale d that the decrease in plasma lipid concentrations in females prior to spaw ning is primarily due to a decrease of up to 50% in the phospholipid conten t of the plasma relative to males. Striped bass vitellogenin was found to c ontain approximately 20% lipid by weight with nearly 80% of the lipid being phosphatidyl choline (PC). Vitellogenin levels previously measured in thes e individuals were highest during the winter months and decreased in the 2 months prior to spawning. Although mature striped bass oocytes are rich in wax esters, no wax esters or fatty alcohols were found in the plasma. Analy sis of the fatty acyl composition of separated lipid classes suggests that PC is the primary carrier of the essential (n=3) fatty acids 22:6 (DHA) and 20:5 (EPA) to the gonads. Fatty acid analysis of the lipids associated wit h vitellogenin revealed that levels of essential fatty acids were low relat ive to vitellogenin-borne lipids from other teleosts. The lack of detectabl e wax esters in plasma lipids of female striped bass suggests that these ab undant lipids in mature eggs are synthesized within the oocytes.