Effects of Water Temperature on Gonad Development in the Cold-Water Fish, Kumgang Fat Minnow Rhynchocypris kumgangensis

Effects of preventing a temperature decrease during winter on reproduction of male small-egged Kajika, Cottus pollux SE

To investigate the effects of preventing temperature decrease on the reproductive activity of the male cold-water teleost, Cottus pollux SE, testicular development, serum 11-ketotestosterone (11-KT) levels, and physiological responses associated with nesting behavior (i.e., elevation of serum 11-KT levels and accumulation of urine in the urinary bladder) were observed from November to January. Specifically, males were exposed to three different cooling regimes (control, 16 to 6 °C; H1, 16 to 11 °C; H2, 16 to 14 °C), and the results were compared. In addition, the effects of temperature on male reproductive behavior were also clarified. At higher water temperature regimes, the rate of testicular development and serum 11-KT levels were both higher from November to mid-December than from mid-December to January. However, the results showed that high water temperature regimes in the coldest period of winter did not suppress spermatogenesis completely. Conversely, the physiological responses to nesting were affected by high water temperatures, with serum 11-KT levels increasing and urine accumulation in the urinary bladder being suppressed. Furthermore, frequencies of two behaviors associated with nesting, i.e., body undulation and face displays, were also suppressed under high water temperatures (~ 14 °C) compared with normal temperatures (~ 7 °C) during the breeding season. Based on the physiological and behavioral responses to nesting, findings showed that preventing a water temperature decrease during winter suppresses reproductive activity in Cottus pollux SE.

Histopathological Evaluation of Combined Impacts of the Synthetic Progestin Levonorgestrel and Temperature on the Female Zebrafish Maturation Using a Semi-quantitative Grading Analysis-Is it Enough?

Pharmaceuticals contamination (e.g., synthetic progestins), and global climate change, represent two of the most stressful factors affecting aquatic species. To our knowledge, there is huge gap of data regarding the combined effects of both stressors on vertebrates' reproduction. Thus, it is crucial to implement rapid screenings of measurable histopathological alterations in fish gonads. For that, we propose: (1) an evaluation of the combined effects of progestin (levonorgestrel) and temperature on maturation of zebrafish female gonads, using a semi-quantitative method (i.e., grading) and (2) testing the robustness of the grading analysis comparatively to a quantitative method (i.e., stereology). Grading analysis showed a decrease on maturation stage of ovaries exposed to both stressors. Although grading is less robust than stereological analysis, it is recommended for a preliminary approach, since it gives a correct idea on trends and it is fast and cost-effective. For a detailed histological assessment, we recommend a stereological study.