Abstract
This study was designed to investigate the effect of dietary lipid levels on the mRNA transcripts of lipid metabolic regulatory genes. Nine combinations of experimental diets containing graded lipid (80, 100 and 120 g/Kg) and protein (450, 500 and 550 g/Kg) levels were fed to the Clarias magur (Indian walking catfish) larvae from 14-35 dph (day post hatching). All the lipolytic genes such as lipoprotein lipase (LPL), pancreatic triacylglycerol lipase (PL) and bile salt-activated lipase (BAL) and genes for long chain poly unsaturated fatty acid (LC-PUFA) biosynthetic enzymes like fatty acyl desaturase-2 (FADS2), fatty acyl desaturase-5 (FADS5) and elongase (ELOV) were expressed in a wide range of tissues. High abundance of mRNA transcript levels of lipolytic genes was detected in intestine and liver, and similarly, desaturases and elongase were predominantly found to express in liver, brain and intestine. Among the diets a significantly high expression of both lipolytic and LC-PUFA biosynthetic genes were observed at 8% dietarylipid level. The expression of all the studied genes was down-regulated at 12% dietary lipid contents. Hence, the present study concludes that the efficient nutrient utilization and the lipid metabolic pathway occur at the optimum dietary lipid level of 8% in C. magur larvae.
Highlights
Dietary lipids are considered to be the important source of energy and the essential fatty acids for the fish among all the nutrients besides acting as the carriers of fat soluble vitamins (Liu et al, 2018)
The feeding trial was carried to evaluate the effect of the experimental diets on the relative mRNA expression of lipid metabolism-related genes viz. lipoprotein lipase (LPL), pancreatic lipase (PL), bile salt-activated lipase (BAL), fatty acyl desaturase-2 (FADS2), fatty acyl desaturase-5 (FADS5), and fatty acyl elongase (ELOV)
Nucleotide sequences of 612 and 507 bp were acquired from C. magur for FADS2 and FADS5 genes, respectively (Figure 1)
Summary
Dietary lipids are considered to be the important source of energy and the essential fatty acids for the fish among all the nutrients besides acting as the carriers of fat soluble vitamins (Liu et al, 2018). The high dietary lipid level might lead to lipid accumulation in the body which should not mislead to a pathological condition but could be a strategy in the natural environment of fish in order to survive during the periods of starvation (Kjaer et al, 2009; Han et al, 2011). A plethora of reports revealed the impact of dietary lipid levels on the lipid metabolic enzymes of fish (Alvarez et al, 2000; Wang et al, 2005; Zheng et al, 2010). The high dietary lipid beyond the optimal level leads to negative impact on the metabolic enzymes like lipoprotein lipase (LPL), pancreatic lipase (PL), and hepatic lipase (HL) during the early larval development of Darkbarbel catfish (Zheng et al, 2010). Li et al (2016) concluded that dietary lipid level had a great impact on the lipid metabolism related genes in orange-spotted grouper
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