Changes in Tissue-Specific Fatty Acid Composition of the Freshwater Alewife (Alosa pseudoharengus) in Response to Temperature

Ectotherms are known to alter the composition of the cell membrane in response to changes in environmental temperature. Tissue-specific fatty acid composition in the alewife (Alosa pseudoharengus) was examined in response to both warm and cold temperature challenges administered over an approximate one month period. Gill, muscle, and liver tissues were analyzed prior to the start of the temperature challenge (initial), following the temperature challenges (survivors), and on those fish that did not survive the temperature challenges (mortalities). Significant differences were found between fatty acid composition of initial fish and survivors for membrane-incorporated fatty acids (polar) and for stored fatty acids (neutral). In the cold challenge, gill tissues exhibited significant remodeling in membrane fatty acids (polar), including decreases in palmitic acid and saturated fatty acids and increases in highly unsaturated fatty acids. In the warm challenge, significant increases in saturated fatty acids were observed in polar lipids of muscle and liver tissue. Notably, a large increase in palmitic acid (C16:0) was observed in response to increased temperatures. Fatty acid profiles of fish that died during the cold challenge exhibited significantly higher levels of C16:0 in muscle tissues when compared to survivors. The observed changes in membrane (polar) fatty acids would be expected to promote appropriate membrane fluidity in response to temperature. Results of this study suggest that freshwater alewives respond to temperature challenges in accordance with what would be predicted by homeoviscous adaptation, although the pattern and extent of changes in response to temperature differed greatly among the tested tissues