EFFECTS OF CHOLINE ON LIVER LIPID COMPOSITION, LIVER HISTOLOGY AND PLASMA BIOCHEMISTRY OF JUVENILE YELLOWTAIL KINGFISH Seriola lalandi
Choline is an essential nutrient typically supplemented in aquafeed. Effects of choline-deficiency in animals include reduced growth, liver lipid accumulation and dysfunction. Yellowtail kingfish (Seriola lalandi; YTK) has a relatively high dietary choline requirement. A greater understanding of liver lipid composition and health condition can provide greater insight into the effect of choline on YTK health. Thus, this study aimed to identify the effects of dietary choline on liver lipid composition, liver histology and plasma biochemistry of juvenile YTK.
An eight-week feeding experiment was conducted in a recirculated aquaculture system where fish (initial weight 156.27 ± 15.27 g) were reared at 16°C and fed five isonitrogenous and isocalorific semi-purified diets containing 0.59, 1.25, 1.56, 3.11, 6.22 g choline kg−1 diet (Diet 1 to Diet 5) by adding graded levels of feed-grade choline chloride (CC). Diet 1 to Diet 5 contained three grams of 2-amino-2-methyl-1-propanol (AMP) kg−1 diet to prevent de novo choline synthesis. A control diet devoid of AMP (Diet 6; measured choline 3.29 g kg−1) was formulated the same as for Diet 4. After the feeding experiment, apparent digestibility of choline and lipid was determined.
After eight weeks, increasing dietary choline significantly improved choline and lipid digestibility. For liver, free fatty acids were the main component of lipid in fish fed diets containing AMP instead of triacylglycerol. Increasing dietary choline did not affect liver phospholipid and sterol content; however, plasma cholesterol increased significantly. Bile duct necrosis was affected by dietary choline (P<0.05; Fig. 1a) whereas hepatocyte necrosis was affected by AMP (P<0.05; Fig. 1b) indicating that this compound may be toxic. This study indicates that improved choline and lipid digestibility might be the driver for increased neutral lipid deposition in juvenile YTK liver. It appears that dietary choline, at least in the form of CC, does not significantly alter the liver lipid composition; instead, it aids lipid digestion and protects liver health.
