Comparative study of longevity, growth, and biomarkers of metal detoxication and oxidative stress between normal and deformed Aphanius fasciatus (Pisces, Cyprinodontidae).

This study compared fish longevity, growth, and oxidative stress between normal and deformed Aphanius fasciatus collected from the Gulf of Gabes. For this purpose, fish were collected from control (S1) and polluted (S2) sites in Tunisian coast and percentages of spinal deformities were determined. Oxidative stress biomarkers were also compared between normal and deformed fish, including levels of protein sulfhydryl (SH), malondialdehyde (MDA), and metallothioneins (MT), as well as activities of superoxide dismutase (SOD) and alkaline phosphatase (AP). Levels of heavy metals (Cd, Cu, and Zn) and polycyclic aromatic hydrocarbons (PAH) were also measured. Data showed that the highest occurrence of deformities was observed in younger fish and decreased significantly thereafter with age. Chemical analysis demonstrated high levels of heavy metals and PAH at polluted sites compared to a reference location. In deformed fish, a growth perturbation marked by a decrease of growth rate and condition index (CI), a high accumulation of Cd was noted. In addition, oxidative stress marked by changes in the studied biomarkers was observed. Taken together, oxidative stress, diminished longevity, and a disturbance of growth may be considered to be responsible factors contributing to spinal deformities.

Structural and molecular analysis of pollution-linked deformities in a natural Aphanius fasciatus (Valenciennes, 1821) population from the Tunisian coast.

The Eastern coast of Tunisia hosts a mosaic of populations of the Mediterranean killifish A. fasciatus, an excellent monitoring species for the analysis of environmental impact in coastal Mediterranean areas. Among these populations, fish from the Sfax area, in the Gulf of Gabès, are known for presenting a high prevalence of different physiological alterations, including spinal deformation. Compared to a reference clean area, Luza, Sfax water and sediments are polluted with heavy metals (20 to 40 times more Cd, for example) and other compounds like PAHs (10 times higher levels). Histological analyses of deformed fish from this area showed an abnormal abundance of collagen fibers infiltrated in the spinal area, either as a physiological mechanism to alleviate the consequences of the deformation of the bones or as a secondary effect of the same pathological/toxicity mechanism inducing bone deformation. Deformed fish from Sfax showed elevated (4-5 fold) levels of transcripts from the collagen COL1A2 gene in bone tissue, compared to either non-deformed animals from the same location or normal animals from the reference Luza site. These results are consistent with an overexpression of collagen in the bone tissue, in agreement with the histological results. We propose that the deformation observed in the Sfax Aphanius population is a degenerative process occurring in adult animals and probably terminal, as it results in severe limitations on the fish capacity to swim, to catch food, and ultimately to survive.