Effects of Digestible Protein and Lipid Levels on the Growth Performance, Substance Metabolism and Antioxidant Capacity of GIFT Fingerling (Oreochromis niloticus)

PurposeTo study effects of digestible protein (DCP) and lipid (DL) levels on growth performance, digestive enzyme activities, substance metabolism and antioxidant capacity of genetic improvement of farmed tilapia (GIFT, Oreochromis niloticus).

MethodNine hundred adult tilapias (average body weight 50 g) were randomly divided into twelve groups with triplication, fed one of the diets with different digestible crude protein to digestible energy (DCP/DE) containing four DCP levels (20%, 22%, 24% and 26%) and three DL levels (3%, 5% and 7%).

Result(1) Weight gain and specific growth rate increased with the increasing of dietary DCP and DL supplementation level. Among them, the 20% DCP diet was significantly lower than other protein treatment diets (P<0.05), and the 3% DL diet was significantly lower than other lipid treatment diets (P<0.05). DCP22DL7 treatment had the highest growth performance. (2) The activity of amylase of liver increased firstly and then declined with the increasing of dietary DCP supplementation level, and the highest was 22%. The activity of intestinal trypsin declined with the increasing of dietary DL supplementation level, and the 7% DL diet was significantly lower than 3% DL diet (P<0.05). DCP22DL7 treatment had the highest digestive enzymes activities. (3) The activity of glutamate dehydrogenase increased firstly and then declined with the increasing of dietary DL supplementation level, and the lowest was 7% DL diet. (4) The ratio of low-density lipoprotein cholesterol/high-density lipoprotein cholesterol declined firstly and then increased with increasing of dietary DCP supplementation level, and the lowest was 22% DCP diet. (5) The activity of glucose-6-phosphatase increased firstly and then declined with the increasing of dietary DCP supplementation level, and the highest was 22% DCP diet. DCP22DL7 treatment had the highest enzyme activity related to glycolysis and gluconeogenesis in liver. (6) The activity of superoxide dismutase (SOD) in serum increased with the increasing of dietary DL supplementation level, and the 7% DL diet was significantly higher than 3% DL diet (P<0.05). The activity of SOD and glutathione peroxidase in liver increased firstly and then declined with the increasing of dietary DCP supplementation level, and the highest was 22% DCP diet. DCP22DL7 treatment had the highest antioxidant capacity in liver.

ConclusionThe increase of DCP and DL level in a certain range was beneficial to the growth and development of fish. The suitable DCP level for adult tilapia was 22%, and the DL level was 7%. The optimal DCP/DE was 13.08 mg/kJ.