Impacts of Global Warming on Quality of Male Fishes: Evidence From A Meta-Analysis of Temperature Effects on Sperm Motility Kinematics

Studies have demonstrated adverse effects of global warming on aquatic ecosystems. However, the effects of increased water temperature (IWT) on fish reproduction are still doubtful in species spawning at low or high temperatures. In this meta-analysis, we elucidated the effects of global warming on spermatozoa functions, key determinants of male fertility. We recruited 245 data records from 20 studies spanning 20 cold- and warm-water fishes to identify the effects of IWT on sperm quality. Data were re-processed and re-analyzed to determine the overall effects of IWT on sperm kinetics such as percentage of motile spermatozoa (MOT), duration of spermatozoa motility (DSM), curvilinear velocity (VCL), straight line velocity (VSL), average path velocity (VAP), as well as on enzymatic activities for energy supply (EAES) and antioxidant enzyme activity (ANEA). The standardized mean difference was calculated for each study, with positive values indicating higher performance under IWT. Results showed that (a) the overall effect size for MOT was larger negative in cold-water fishes (−1.22) than in warm-water fishes (−0.95). (b) Each 1°C increase in the activation medium reduced MOT by 1.30% (cold-water fishes) and 3.47% (warm-water fishes). (c) IWT negatively affected DSM, decreasing it by 10 s (cold-water species) and 5.64 s (warm-water species) per degree of IWT. (d) Spermatozoa velocity (VCL and VSL) increased by IWT in warm-water species. (e) In cold-water species, IWT-induced detrimental effects on EAES were associated with adverse impacts on sperm motility kinetics. In conclusion, IWT negatively affects sperm motility kinetics, suggesting an impact of global warming on fish reproduction.