Histopathological evaluation of bivalves from the southwest coast of India as an indicator of environmental quality

Joshy, Aswathy and Sharma, S R Krupesha and Mini, K G and Suja, G and Pranav, P (2022) Histopathological evaluation of bivalves from the southwest coast of India as an indicator of environmental quality. Aquatic Toxicology, 243. pp. 1-14.

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Abstract

Bivalve molluscs have been regarded as excellent bioindicators of environmental pollution as they persistently accumulate toxic contaminants present in their ecosystem. Histological alterations in the digestive gland and gills of three bivalve sp., Viz. edible oyster (Magallana bilineata), green mussel (Perna viridis) and black clam (Villorita cyprinoides) from ecologically sensitive regions of international significance on the southwest coast of India were evaluated using a semi-quantitative histopathological index to assess the environmental quality. The prominent tissue alterations included tubular vacuolation, haemocytic infiltration, parasitosis, lamellar disorganization, and the presence of prokaryotic inclusions. The presence of ten trace metals was also evaluated in the digestive gland of bivalves. The histopathological indices were evaluated season-wise and region-wise. Seasonal variation in all the reaction patterns was observed in the digestive gland across sampling zones, with the highest indices observed during post-monsoon. The indices for all the reaction patterns in the digestive gland were significantly higher in bivalves from Vembanad Lake (Z4), followed by Periyar River (Z5). The indices for cellular changes and parasitosis in gills were the highest in the Ashtamudi estuary (Z1) and Z5, respectively. The global histopathological indices of the digestive gland and gills were also the highest in Z4, followed by Z5. Principal component analysis revealed that Z4 was distinct with the highest metal pollution index. A positive relation was observed with heavy metals, digestive gland histological alterations, and season and region of sampling.

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