An 8-week feeding trial was conducted to evaluate the effect of replacing soybean meal (SBM) with cottonseed meal (CSM) on growth and health of grass carp. Four isonitrogenous diets containing 0, 16.64, 32.73 and 48.94% of CSM, respectively, as replacements of 0, 35, 68 and 100% of SBM were fed to fish (initial body weight 7.14 ± 0.75 g/fish) in triplicate aquaria twice daily. The results indicated that fish fed diet containing 16.64% CSM as a replacement of 35% of SBM was not affected in weight gain (WG), feed efficiency ratio (FER) and feed conversion ratio (FCR) (P > 0.05), while fish fed diets containing higher level of dietary CSM (32.73 and 48.94%) significantly decreased WG and PER and significantly increased FCR (P < 0.05). Fish fed diets containing 16.64% of CSM had significantly increased hematocrit (Ht) and hemoglobin (Hb) values compared with fish fed with other diets (P < 0.05). The activity of catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), gene expression levels of GSH-Px and CAT, and content of malondialdehyde (MDA) were significantly lower for fish fed diets containing 16.64% CSM compared with fish fed other diets (P < 0.05). These results showed 16.64% CSM could be used to replace 35% SBM in the diets of juvenile grass carp and without health impact.

A 4-week study was conducted to determine the effect of starvation on activities and mRNA expression of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) in hybrid tilapia (Oreochromis niloticus x O. areus). The tissue samples were sampled once a week. Results showed that body weight (BW) and hepatosomatic index (HSI) were decreased significantly (P < 0.05) during starvation. The percentages of crude fat and crude protein in the whole body and the fat content in muscle decreased significantly (P < 0.05), while the rate of moisture and crude ash increased significantly (P < 0.05). The response of LPL, HSL activities and mRNA expression in tissues was tissue dependent. The activities of LPL and HSL in muscle at day 7 were elevated by 2.5 times (P < 0.05) and 11.8 times (P < 0.05) of the value at day 0, respectively, and both then decreased to pre-starvation levels at day 14 and finally stabilized at a certain level afterward. LPL and HSL mRNA abundance in muscle remained relatively stable between 0 and 14 day; then, a significant increase was seen after 14 days. In the liver, LPL activity maintained a significantly increasing trend during starvation, while HSL activity rose dramatically at day 7 of starvation by 2.35 times (P < 0.05) and finally stabilized at a certain level. The mRNA abundance of liver LPL increased significantly during the whole process of starvation (P < 0.05), whereas the mRNA abundance of liver HSL decreased significantly at day 7 of starvation, elevating significantly afterward (P < 0.05).

This study was designed to investigate the effects of dietary lipid levels on growth performance, lipid deposition and activities of lipid metabolic enzymes in hybrid tilapia (Oreochromis niloticus × O. aureus). Four isonitrogenous (300 g/kg crude protein) experimental diets containing graded levels of lipid (25, 55, 85 and 115 g/kg) were randomly assigned to triplicate groups of 180 juvenile fish. Fish were fed twice daily for 8 weeks. At the end of the experiment, the growth performance and proximate composition of fish were determined. The activities and gene expression of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) were assessed as well. Fish fed the diets with 55 and 85 g/kg lipid had a significantly (p < 0.05) higher body weight gain than those fed the diets with 25 and 115 g/kg lipid. The whole-body and liver lipid contents were significantly (p < 0.05) elevated with increasing dietary lipid levels. Moreover, the activities and mRNA abundances of LPL and HSL in the liver, dorsal muscle and fat tissues were markedly altered by dietary lipid levels. Our data demonstrate a profound influence of dietary lipid levels on the growth and lipid deposition in hybrid tilapia, which is likely associated with the regulation of lipid metabolic enzymes including LPL and HSL.