Seasonal determination of fatty acid composition of phospholipid (pl) subclasses in different tissues (muscle, liver, gonat) of Silurus triostegus living in the Tigres River

In this study, sex- and season-related changes in fatty acid composition in the phospholipid subclass fractions, such as phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), and phosphatidylethanolamine (PE), of muscle, liver, and gonats of Silurus triostegus distributed in the Tigris River were investigated. Fish samples were collected from the Tigris River in four-month periods between October 2024 and July 2025. According to gas chromatography results, six saturated fatty acids, three monounsaturated fatty acids, and ten superunsaturated fatty acids were identified in tissues such as muscle, gonat, and liver of the fish. When muscle, liver, and gonat tissues were examined, saturated fatty acids 16:0 (palmitic acid) and 18:0 (stearic acid); monounsaturated fatty acids 18:1n-9 (oleic acid); and polyunsaturated fatty acids 20:4n-6 (arachidonic acid), 22:6n-3 (DHA), and 20:5n-3 (EPA) were identified as the major fatty acids. When examined seasonally, PUFA levels increased in all tissues in April due to 20:5n-3 and 22:6n-3. In January and October, SFA percentages were generally high, while PUFA percentages were low. While MUFA levels decreased in July, increases were observed in some PUFAs (especially omega-6). When examined by sex, SFA and MUFA levels generally showed more pronounced seasonal fluctuations in male individuals. In females, PUFA levels, particularly DHA and EPA, remained more stable but decreased in some months (e.g., July). In April, a simultaneous increase in omega-3 fatty acids was observed in both sexes. Analysis of ∑SFA revealed high levels in all tissues in January and October, with a decreasing trend in April and July. ∑MUFA was found to be high in males in January and females in October, and low in most tissues in April. ∑PUFA was high in all tissues in April, but decreased in October and January. The omega-3/omega-6 ratio increased in all tissues in April and decreased in October and July. When tissue distribution was examined, PUFA levels in liver tissue, particularly in the PE and PI fractions, showed a significant increase. Omega-3 fatty acids were highest in April. In gonatal tissue, fatty acids such as 16:1n-7 and 18:2n-6 in the PC and PE fractions showed seasonal variation. The omega-3/omega-6 ratio was generally found to be low. In muscle tissue, PUFA (especially DHA and EPA) in the PC and PE fractions was highest in April and decreased in July and October. MUFA was found to be lowest in muscle.