Acclimation to increasing temperatures modulates lipid contents and fatty acid profile in catfish Horabagrus brachysoma (Günther)

Understanding fish physiological responses to thermal acclimation is crucial for addressing global climate change threats to aquaculture sustainability. We investigated lipid and fatty acids in the muscle and liver of the catfish Horabagrus brachysoma acclimated to 26 (control), 31, 33 and 36 degrees C for 30 days. The total lipid, phospholipid, triglyceride, and free fatty acid significantly decreased, while cholesterol significantly increased (P < 0.05) in both tissues at 33 and 36 degrees C. At 26 degrees C, total saturated fatty acids (SFA), particularly palmitic (C16) and stearic (C18) acids, accumulated in fish muscle and liver at levels 1.6 to 2.25 times higher than those in the feed (Tubifex worms). With increase in the acclimation temperatures, the SFA rose in muscle but reduced (P < 0.05) in liver, though both tissues still maintained nearly double the SFA content than in Tubifex. The muscle and liver unsaturated fatty acids (UFA) were 25% and 48% lower than in Tubifex at 26 degrees C, however, the muscle UFA decreased (P < 0.05) further with rising acclimation temperatures while liver UFA increased (P < 0.05) at 33 and 36 degrees C. Compared to the feed, oleic acid levels in the muscle and liver increased two- and threefold, respectively, with muscle content significantly peaking at 36 degrees C (P < 0.05). The ability of the catfish to deposit n-3 PUFA or to reduce n-6 PUFA to over twice the amount found in the feed (Tubifex) was disrupted at 33 degrees C, with muscle n-3 PUFA decreasing by 35% and n-6 PUFA by nearly 50% at 36 degrees C. A temperature-dependent decrease in DHA in muscle was also noted. Such reduction indicates decreased transfer of PUFA in the higher trophic levels and may also affect growth, development and disease resistance of the fish. Additionally, the content of oleic acid in catfish muscle nearly doubled compared to its feed at 26 degrees C, with levels increasing significantly with the rise in rearing temperatures (P < 0.05). It can be concluded that modulation of lipid and fatty acids is one of the ways by which H. brachysoma will attempt to acclimate to temperature rise due to global warming.