Effect of natural confinement on the gill cell types and bony elements of Lebias fasciata (Teleostei, Cyprinodontidae): A morphological and immunohistochemical analysis

Abstract

Histochemical and immunohistochemical techniques were used to investigate the effect of stress from heavy metals on the respiratory epithelia of the cyprinodont Lebias fasciata living in confined natural environments with different degrees of pollution (brackish swamps of Faro‐Ganzirri and Lesina). This effect was evaluated on cytokeratins and calcium‐binding proteins, with particular reference to the presence of neuronal nitric oxide synthase in the cells of the diffuse neuroendocrine system (DNS). A morphometric examination was also performed to identify possible cranio‐facial and vertebral anomalies; however, the results were negative for all specimens from the two environments. Regarding the presence of heavy metals, only slight differences were found between the two environments, except for the higher concentration of aluminum in the Lesina swamp. In the gills of individuals from the latter environment, the epithelium presented a morphologically and immunohistochemically modified structure, with a concomitant over‐production of mucus; this acts as a barrier to oxygen diffusion, causing strong hypoxia. Therefore, it is hypothesized that the high number of DNS cells and nerve fibers im‐munopositive to nNOS in the respiratory epithelium of Lebias fasciata specimens from lesina is a local reaction to hypoxia.