Mainak Kundu and Rajarshi Ghosh
Abstract
Heavy metal contamination poses a persistent threat to aquatic ecosystems, impacting both environmental balance and fish health. Fish are widely recognized as sentinel species, yet traditional biomarkers often overlook subtle microbial responses to toxic stress. The gut microbiota has emerged as a promising indicator of heavy metal exposure, as metals like lead, cadmium, copper, and arsenic trigger distinct patterns of dysbiosis. Lead exposure, for instance, reduces microbial diversity while enriching lipopolysaccharide-producing and pathogenic taxa such as Bacteroides and Plesiomonas, alongside a loss of beneficial microbes like Akkermansia. Similarly, cadmium and copper exposure decrease Lactobacillus, Bacillus, and short-chain fatty acid-producing bacteria, while promoting opportunistic pathogens, including Pseudomonas and Acinetobacter. These microbial shifts reflect both physiological stress and environmental contamination levels. Thus, gut microbiota composition and function provide a sensitive, non-invasive biomarker for heavy metal pollution, offering valuable insights into ecological risk assessment and fish health monitoring in contaminated freshwater environments.