Role of fatty acids in cultured mussels, Mytilus edulis, grown in Notre Dame Bay, Newfoundland

Fluctuations in mussel (Mytilus edulis) growth have been attributed to large-scale fluctuations in temperature, salinity and the abundance of phytoplankton. This study examined the effect of fatty acids on the growth (wet weight) of cultured mussels during 2000 and 2001 in Notre Dame Bay, Newfoundland. Mussels were socked in June 2000 and harvested in October 2001. On a monthly basis, the mussels grew at variable rates (mean 10.73 ± 6.86, range 5.9-18.8 mg d− 1 in 2000 and 10.09 ± 8.91, range 5.1-22.9 mg d− 1 in 2001) with the highest growth rate in September of each year. The growth, however, did not demonstrate localized differences. The proportion of polar lipid (PrL) as a percent of total lipid was much higher in mussel samples (mean 71.1 ± 4.8%) than the phytoplankton (mean 44.3 ± 21.2%), and the opposite was observed for the neutral lipid (NL: mean 30.2 ± 4.4% in mussels and 45.3 ± 11.7% phytoplankton). The fatty acid profiles of phytoplankton and mussels were, in general the same, except that the pentaenoic fatty acid, 18:5ω3, was not detected in mussels, and no C22 non-methylene interrupted dienes (NMIDs) were detected in phytoplankton. However, proportions of 22:2NMIDs (as percent of total identified fatty acids) in mussels were relatively high (range 2.5-3.5%) particularly in 2000. The 22:6ω3, 20:5ω3, 16:0, 14:0, 16:1ω7 and to some extent 16:4ω3 were the most abundant fatty acids in the phytoplankton and mussel samples. Of these fatty acids, 20:5ω3 was the only fatty acid in both phytoplankton and mussels that showed a significant positive correlation with growth, while correlations with other fatty acids varied in magnitude or direction (positive or negative) depending on the source of the acid being either phytoplankton or mussel. An interesting observation within the essential fatty acids was that neither 22:6ω3 nor 20:4ω6 was significantly correlated with growth, but when their levels were combined with 20:5ω3 to give the total essential fatty acid in phytoplankton or mussels, the result was a significant positive correlation with growth for both phytoplankton and mussel essential fatty acids. Moreover, the coefficients of correlation for the other physiologically important acids in bivalves, namely the 20:2NMIDs were by far the most significant ones, but only with the mussel NMID, and their correlation with growth was negative. Approximately 140 variables from mussels and phytoplankton were tested in order to construct a model to predict the growth of mussels. Of these variables, four were found to be significant (r2 = 0.725): 20:2NMID1, 18:2ω4 and 22:5ω6 in mussels and 16:1ω9 in phytoplankton.