Abstract
The aim of this study was to evaluate the use of gonadal alterations in the thinlip grey mullet (Liza ramada) as a biological indicator in assessing aquatic ecosystems health, with particular emphasis to river ecosystems exposed to sewage discharges. For this purpose, the reproductive status and the presence of gonadal alterations were studied in 206 mullets collected from two sites on the low course of the Tiber River, downstream of a large urban sewage treatment plant and in the estuarine area, and from an uncontaminated pond considered as reference site. Intersex and irregularly shaped gonads were observed in 20.8% of the mullets from the most polluted site, and intersex gonads in 10.3% of those from the estuarine area. No alterations were detected in the fish from the reference site, which also showed distinct stages of gonadal development. Conversely, unclear stages of testicular and ovary development were observed in the fish from the two polluted river sites. The results of this study suggest that L. ramada may represent a sentinel species in environmental risk assessment and support the use of gonadal alterations of this species as a bioindicator for extensive monitoring of pollution in lower stretches of rivers and estuarine areas.
Highlights
Fish are commonly used as bioindicators in aquatic ecosystems, because they may respond to environmental stresses at the different levels of biological organization, from sub-cellular to community levels [1,2,3]
We observed the presence of intersex and irregularly shaped gonads only in thinlip grey mullets living in two sites of the same riverine ecosystem, both located downstream the effluent of a large urban sewage treatment plant and characterized by high levels of contamination
Gonadal anomalies were not observed in fish belonging to the same population but moved and stocked in the unpolluted reference site C, where fish had undergone growth, sexual differentiation, and maturation
Summary
Fish are commonly used as bioindicators in aquatic ecosystems, because they may respond to environmental stresses at the different levels of biological organization, from sub-cellular to community levels [1,2,3]. The anatomical, histological, and biochemical evaluation of the status of the gonads of wild fish populations has been increasingly used to assess the impact of pollution on aquatic ecosystems [9,10,11,12], with respect to the possible reflections on human health. Among the contaminants of human origin, the endocrine disrupting chemicals/compounds (EDCs) have an effect analogous to sex steroids and can cause a wide variety of impairments in fish [13], including reduction in gonad weight and volume, disorders in gonadal maturation, gonadal atresia, and especially an increased occurrence of intersex [9,10,11,12]. Intersex, which is the condition whereby there is the simultaneous occurrence of male and female cells in the same gonad [7,14], have been detected in wild populations of several aquatic animals and interpreted as a signature effect of exposure to EDCs [8,15,16]
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