Abstract:
To investigate the effects of dietary lipid level on growth performance, digestive enzyme activity and lipid metabolism of gibel carp
Carassius auratus gibelio, 5 diets were formulated with lipids level of 4% (L4), 8% (L8), 12% (L12), 16% (L16) and 20% (L20), respectively, for a 340-day trial. The initial weight of fish was (11.33±0.03) g, and fish were sampled five times at day 63 (D63, the juveniles stage), day 110 (D110, the prophase of cultivation), day 223 (D223, overwintering stage), day 275 (D275, after overwintering stage) and day 340 (D340, the middle and late cultivation period), respectively. The results showed that the appropriate dietary lipid level of gibel carp at the juvenile stage was 8%, and the optimal dietary lipid level of gibel carp at the prophase of cultivation was 12%, while there was no significant difference in the dietary lipid demand at other growth stages. Dietary lipid levels significantly affected the intestinal digestive enzymes activity at the juvenile stage of gibel carp. The activity of lipase first decreased with the increase of dietary lipid level and then increased. The activity of intestinal trypsin and amylase in gibel carp at the juvenile stage (D63) was higher than those in the overwintering stage and the middle and later cultivation period, indicating that the lipid demand of gibel carp at the juvenile stage was lower than other stages. The gene expression levels of
pparγ and
fas in gibel carp at the juvenile stage (D63) showed a tendency to increase first and then decrease with the increase of dietary lipid, and the highest gene expression level was in the L8 group. The transcription level of
lpl and
cpt1a in the L4 group was significantly lower than those in other groups. After overwintering stage (D275), the gene expression level of
fas in the L4 group was significantly higher than that of the other group, indicating that fish at different growth stages have different response strategies to lipid intake, and both high lipid or low lipid intake had a negative impact on lipid metabolism of gibel carp. The results suggested that appropriate dietary lipid level (8%—12%) can promote the growth of gibel carp during the juvenile stage and the prophase of cultivation and improve the ability of lipid metabolism, while larger size gibel carp were not sensitive to the change of dietary lipid.