Stress Quantification in Penaeus vannamei Exposed to Varying Levels of Turbidity

Abstract

Increased water turbidity in the intensive farming of Penaeus vannamei is one of the environmental stressors. Investigations were carried out on the effect of inorganic clay particle induced turbidity (NTU) levels (T1-30, T2-60 and T3-120) on survival, immunological response: total hemocyte count (THC), activity of phenoloxidase (PO) and superoxide dismutase (SOD), and stress metabolites: Osmolality (O), glucose (G) and lactate (L) in P. vannamei exposed to 21 days. T3 and T2 registered 20 and 10% mortality respectively compared to 5% in T1 and control. Shrimp in T1, T2, and T3 showed 1.1, 1.9 and 4 times more risk of dying compared to control. THC, PO, and SOD decreased significantly (p ≤0.05) from day-1 to 21 in all the treatments compared to control. T3 showed significantly low immunological activity (THC: 119±2.8 x 105 cells ml-1 ; PO: 0.369±0.001 U ml-1 ; SOD: 0.230±0.001 U ml-1) compared to control (THC: 167±13.4 x 105 cells ml-1 ; PO: 0.546±0.002 U ml-1 ; SOD: 0.284±0.001 U ml-1 ). Physiological stress metabolites increased significantly with exposure time in T3 (G: 85.2±0.071 mg ml-1; L:8.2±0.007 mg dl-1 ) compared to control (G: 77.2.2±0.163 mg ml-1 ; L: 7.1±0.16 mg dl-1). Osmolality was high in T3 (961.7±148.6 mOsm kg-1) compared to control (858.3±3.4 mOsm kg-1). High turbidity of >60 NTU in the rearing medium caused the gills blockage apparently as a compensating reaction to the disruption of osmotic and ionic balance. Shrimps exposed to T3 treatment showed intracellular deposits of the clay particles within the filament and lamellar epithelium of gills in Scanning Electron Microscopy (SEM) images. The present study concluded that <30 NTU water turbidity as safe level for P. vannamei