Light microscopic studies to evaluate fish scales as non-invasive indicators of heavy metal-contaminated waters

Heavy metal pollution in aquatic bodies is a matter of serious concern for aquatic fauna and human health. This study evaluated the effect of heavy metals on structural aberrations in fish scales of freshwater Indian major carp Labeo rohita. Scales from two size groups-lesser than and equal to 40 cm and greater than 40 cm-collected from three markets of Ludhiana district for a period of 6 months were assessed. The values of Pb, Zn and Cr in fish scales exceeded the permissible limits. Structural alterations such as distorted focus, damaged and eroded circuli, distorted pattern of circuli, damaged margins of scales, dispersed chromatophores, disorganised radii and damaged tubercles were observed on the dorsal surface of scales using light microscopy. It is postulated that heavy metals would be responsible for structural anomalies on scales as their accumulation was higher in larger fishes which have been exposed to metals for longer duration. These observations clearly suggest that fish scales are effective non-invasive indicator of water quality where fish have been reared and cultured.