Monitoring and assessment of environmental disturbance on natural Gambusia affinis populations--histopathological analysis.

Physiological investigations are often used to assess the toxic effects of aquatic pollutants in fish and to establish criteria for water quality. In the present study, we tend to investigate the growth performance, skeletal abnormalities, and histological alterations noticed in three natural populations of the mosquitofish Gambusia affinis captured from three estuary sites. The analysis of growth performance demonstrated that the studied populations showed different growth patterns. Additionally, various types of skeletal deformities were observed, and the most commonly affected were the hemal and pre-hemal regions of fishes. For the histological study, gills, liver, and kidney tissues were selected for field monitoring. The major alterations observed in gill tissues were partial fusion of adjacent secondary lamellae, hypertrophy of epithelial cells, and disorganization of pillar cells in many areas of the secondary lamellae. In the liver, significant desquamation of tissues, congestion of the central hepatic vein, and hypertrophy of hepatocytes were noticed. For the kidney tissue, the frequencies of histological alterations showed a significant difference between the studied sites. Moreover, the histological aberrations consisted mainly in glomerule alteration and vacuolation of tubular epithelial cells. Taken together, these data support the hypothesis that the physiological alterations noticed in the present investigation are indicators of sensitivity towards environmental disturbance.