The aim of this study was to assess the effect of high temperature on cadmium (Cd)-induced skeletal deformities in juvenile Mosquitofish, Gambusia affinis. For this purpose, 188 juveniles (1 day old) were equally divided into the control group, which was maintained in Cd-free water at 24 degrees C, and three treated groups exposed either to Cd (0.4 mg/l as Cd Cl(2)) at 24 degrees C, to high temperature (32 degrees C), or to Cd at 32 degrees C for 30 days. The results showed that Cd exposure at 24 degrees C significantly increased the Cd accumulation (P < 0.0001) in the whole tissues of juveniles as well as the incidence of skeletal deformities (P < 0.01) compared with control animals. Exposure to high temperature also led to a significant increase in the incidence of skeletal deformities (P < 0.01) with respect to the control group. Interestingly, our results showed that the combined exposure to Cd and high temperature led to a more significant increase in Cd accumulation and in the frequency of spinal deformities than exposure to Cd or high temperature alone. These results confirm that temperature increases Cd toxicity and needs to be taken into account for the accurate prediction and assessment of Cd-induced spinal deformities in fish.

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.

This study aims to demonstrate the influence of animals' origin on their sensitivity toward heavy metals. For this purpose, we compared LC(50) of cadmium in two populations of Gambusia affinis captured in two geographically isolated environments in the east of Tunisia; Oued El Gsil in the city of Monastir (S2) and Oued Chenini in the region of Gabes (S1). Although physicochemical parameters of the water (pH, dissolved oxygen and salinity) are similar in the two studied sites, cadmium concentrations in water, sediments and fish tissues from S1 are significantly higher (P < 0.01) than those from S2, 48-h and 96-h LC(50) of the (S1) population are significantly higher than those from S2. In the same way, the offspring of the polluted site (S1) population exhibit 48-h and 96-h LC(50) values much higher than those of the reference site (S2) population. These results show that the population of the Gabes region is more resistant to cadmium than that of the Monastir region and that this resistance could have a genetic basis. These results indicate the influence of the origin of animals that has to be taken into account not only in laboratory toxicity tests, but also in field ecotoxicological studies.

The impact of heavy metal levels (Cd, Cu, and Zn) on the reproductive parameters in natural populations of the Mediterranean killifish Aphanius fasciatus was monitored in four sites of the Tunisian coast. Our study covered a period of the reproductive cycle, from April to November 2009. The significantly higher levels of Cd, Cu, and Zn in the liver and gonads for both sexes (p<0.05) were observed in the most polluted site (Sfax coast). During the reproductive cycle of A. fasciatus, an unbalanced sex ratio in favor to females was observed for all the studied populations. The progression of the hepato- (HSI), gonadosomatic (GSI), and K-factor revealed a spatio-temporal variation between populations during the sampling period. Estradiol-17β amounts in the gonad tissues of females captured from the studied sites showed a significant difference, and the highest concentrations were noticed in the control site (Luza). Taking together, our data provide the first evidence of a physiologically stress and a disturbance of the reproductive status in natural populations of A. fasciatus.