The interactive effect of dietary choline and water temperature on the liver lipid composition, histology, and plasma biochemistry of juvenile yellowtail kingfish (Seriola lalandi)

Abstract

Abstract The study examined the interactive effects of choline content (supplied as choline chloride salt (CC); no added CC, 3.0, or 6.0\u202fg CC kg−1 diet) and water temperature (16\u202f°C vs 24\u202f°C) on liver lipid composition, liver histology and plasma biochemistry. Liver and plasma samples were collected from juvenile yellowtail kingfish (Seriola lalandi; YTK; 156\u202fg body weight), fed fishmeal-based practical diets, at the conclusion of an eight-week feeding experiment. The results showed that higher liver lipid content at 24\u202f°C was due to greater triacylglycerol (TAG) accumulation. Liver phospholipids content remained similar regardless of CC supplementation and temperature (P\u202f>\u202f0.05). As expected, liver phospholipids were mainly composed of phosphatidylcholine (PC); however, in most cases liver phospholipids were almost completely made up of PC. Phospholipid classes were also not significantly affected by CC supplementation and temperature. The results indicate that these lipid classes were tightly regulated in the liver of juvenile YTK. Fatty acids composition among TAG, FFA, and phospholipids fractions were different; however, within the phospholipids fraction, the long chain polyunsaturated fatty acids (LC-PUFA) proportion in the liver of YTK remained unchanged regardless of treatments. In general, histological examination did not show severe lesions in fish livers across all treatments. Fish also had significantly more hepatocytes with large nuclei at 16\u202f°C than at 24\u202f°C which is a response that requires further research. Plasma analytes were profoundly affected by temperature rather than by CC supplementation; however, there is no strong evidence indicating compromised health in fish reared at either temperature. This study demonstrates that fish fed fishmeal-based practical diets generally had normal looking livers; nevertheless, some liver and plasma health indicators can be affected in juvenile YTK reared at sub-optimal temperatures and fed diets without supplemented choline.