Effects of formalin on total haemocytes count and histopathological changes in the shrimp Litopenaeus schmitti ( Pérez-Farfante & Kensley 1997 )

Formalin is used in shrimp industry to eliminate ectoparasites and as a disinfectant. However, the effect of formalin on shrimp's defense mechanism is unknown. Several biomarkers were used to assess the immune response of juveniles of the shrimp Litopenaeus schmitti exposed to different concentrations of formalin (10, 25 and 50 mg L⁻¹) during 24 and 48 h. Formalin concentrations of 25 and 50 mg L⁻¹ produced a significant reduction in the total haemocyte count at both 24 and 48 h. Peroxidase and phenoloxidase activity did not show variations. The total protein concentration in haemolymph of shrimps was not significantly different between experimental groups. Histological analysis showed hyperplasia in the gills of animals exposed at 10 mg L⁻¹ for 24 h; however, the exposure at 25 and 50 mg L⁻¹ caused necrosis in gills, hepathopancreas and the antennal gland.