Effects of salinity on growth and metabolism in blue tilapia (<i>Oreochromis aureus</i>)

Abstract

Tilapia were acclimated to the water source which had 8 precipitation (ppt) of salinity in the experimental unit before the experiment started and then, they were transfered to five different saltwater (SW) treatments: SW (8 ppt), 50% SW (12 ppt), 100% SW (16 ppt), 150% SW (20 ppt), and 200% SW (24 ppt). The objectives of this study were; to investigate the effects of five different salinities on specific growth rate (SGR), weight gain (WG), food intake (FI) and survival of tilapia in the long term trial (30 days) and find out how salinity affects muscle water content, hematosomatic index (HSI), and blood chemistry (sodium, chloride, potassium, glucose, total protein and triglycerides) in the short term trial (6 to 12 h). In the long-term trial, six fish were stocked in each aquarium. They were fed with commercial feed (Bagcı trout) to satiation twice a day and individually weighed at ten-days interval. Growth rate was highest in the 50% SW (SGR 0.95 ± 0.18% per day); there was no significant difference among the first three treatments. Growth rate was lowest in 200% SW (SGR 0.23 ± 0.08% per day). Weight gain and food intake showed identical results as SGR. Survival was high in the first three groups (72.2 ±1 9.2 to 100.0 ± 0.0) but it was lowest in the 200% SW treatment (22.2±19.2%). In the short-term trial, six tilapia were placed per aquarium. They were exposed to SW, 50, 100, 150 and 200% SW treatments and the fish were gradually acclimated to salt water. Blood samples were taken to analyse plasma sodium, chloride, potassium, total protein and triglycerides. Liver and muscle samples were collected for HSI and moisture values. Plasma sodium chloride increased in parallel with salinity rise. Total protein and triglycerides significantly reduced as salinity increased. Glucose and potassium were not altered significantly. HSI and muscle water content decreased when salinity concentration was elevated. Blood chemistry demonstrated that isosmotic water concentration was between 8 and 12 ppt. Salinity did not affect HSI and moisture until it reached as much as 16 ppt (100% SW). The results show that the optimum condition for farming blue tilapia, Oreochromis aureus, both with respect to growth rate and metabolic parameters is at salinities lower than 12 ppt. This is an important finding for the tilapia industry.

Keywords: Tilapia, salinity, growth, survival, metabolism

African Journal of Biotechnology Vol. 12(19), pp. 2715-2721