Influence of a multistress (cadmium and temperature) on the reproduction of the three-spined stickleback (Gasterosteus aculeatus)

Human activities introduce significant amounts of organic and inorganic pollutants (trace metals) into aquatic environments. However, this contamination occurs within a large context that concerns the scientific community since the last decades: global warming. The complex nature of the interactions between toxic substances and temperature presents new challenges to improve the risk assessment for aquatic environments. Thus, the study of these interactions proves an essential priority for toxicologists. This study aims to evaluate the effect of chronic exposure to both chemical (cadmium) and physical stress (temperature) on the reproduction of a river fish widely used in ecotoxicology: three-spined stickleback (Gasterosteus aculeatus). For this, juvenile sticklebacks were exposed to 1µg.L-1 of cadmium for 4 months in semi-static conditions at two different temperatures, i.e. 16°C and 21°C. Water quality and cadmium concentration in the water were monitored throughout the experiment. Parameters such as somatic indices (height, weight, GSI) were measured at 15, 60, 90 and 120 days interval after cadmium exposure. Reproductive capacity was evaluated by performing several rounds of in vitro fertilization and monitoring of the offspring. The fertilization rate, mortality and birth defects were evaluated until the end of the larval stage (21 days post fertilization “dpf”). In total, 20 in vitro fertilizations were performed during this experiment with different results for each group. A decrease in fertilization rate was observed under the effect of temperature 21°C (84.79 ± 12%), which seems to be accentuated by the presence of cadmium (77.26 ± 31%). Similarly, the rate of embryonic and larval mortality seems to follow the same trend, with a rather large effect of temperature, especially in the presence of cadmium. Temperature 21°C in presence of cadmium delays the moment of hatching about two days compared to controls (10.5 ± 0.71 dpf Vs 8.67 ± 1.15 dpf). Several malformations were observed in all groups including the control group with predominance in groups from parents exposed to cadmium at 16°C (11.79 ± 10.8%). Our results showed fairly significant and worrying effects of a very low dose of cadmium (1µg.L-1) on the parents and their offsprings. Most studies reported in the literature on the effects of cadmium were demonstrated with much higher doses than used in our study. Further experiments are needed to complete and validate these results