Effects of saline-alkaline water on growth performance, nutritional processing, and immunity in Nile tilapia (Oreochromis niloticus)

Abstract

Given the recent decrease in fresh water resources, available space for fresh water aquaculture is in decline. Thus, saline-alkaline water aquaculture has become one of the ways to accommodate this growing need. In this study, the influence of saline-alkaline water on growth performance, nutrient digestion and absorption, and non-specific immunity in Nile tilapia (Oreochromis niloticus) was investigated. A total of 360 fish (180.37 ± 7.54 g) were randomly allocated to groups in triplicate. Aquarium conditions contained mixed sea salt (fixed salinity at 10 parts per thousand) with varying concentrations of sodium bicarbonate (14 mmol/L (SAW14), 28 mmol/L (SAW28), and 42 mmol/L (SAW42)) to simulate the saltine-alkaline water environment. A freshwater group was the control (FW). All of the experimental fish were cultured for 60 days. The results showed that there was no significant difference in growth performance (measured by average daily gain (ADG), weight gain rate (WGR), specific growth rate (SGR), and feed conversion rate (FCR)) between fish in the SAW14 group and the FW group, but there was a significantly higher difference between the SAW28 and SAW42 groups. In assessing nutritional processing in the fish, the activity of pancreatic amylase (PA) in the SAW14, SAW28, and SAW42 groups was significantly lower than the FW group. The mRNA expression of glucose transporter 2 (GLUT-2) and the liver glycogen content in the SAW14 group were significantly higher than the other groups. In addition, trypsin activity in the SAW28 group was significantly higher than the other groups. The mRNA expression of peptide transporter 1 (PEPT-1) in the SAW14, SAW28, and SAW42 groups significantly increased compared with the FW group. However, the content of liver protein in the SAW28 group was significantly lower than the other groups. The activity of pancreatic lipase (PL) in the SAW42 group was significantly higher than the other groups, and the content of liver lipids was significantly lower. In assessing health parameters in the fish, the activity of lysozyme in the serum of the SAW28 and SAW42 groups was significantly higher than the other groups. In addition, the number of white blood cells (WBC), red blood cells (RBC), and the activity of alanine aminotransferase (ALT) in the serum of the SAW14, SAW28, and SAW42 groups were significantly lower than the FW group. The activity of superoxide dismutase (SOD) in the serum of the SAW28 and SAW42 groups was significantly higher than the FW group. Taken together, this study revealed the growth performance, nutrition process, and health status of Nile tilapia in saline-alkaline water. The data indicated that the SAW14 group showed better than other treatments, and were not seriously inhibited in higher treatment groups. These results provide important insights for the possibility of commercial cultivation of Nile tilapia in saline-alkaline water.