Transcriptomic Analysis on the Effects of Altered Water Temperature Regime on the Fish Ovarian Development of Coreius guichenoti under the Impact of River Damming.

Field investigation indicated that the reduction in fish spawning was associated with the alteration in water temperatures, even a 2-3 °C monthly difference due to reservoir operations. However, the physiological mechanism that influences the development of fish ovary (DFO) remains unclear. Thus, experiments of Coreius guichenoti were conducted at three different temperatures, optimal temperature (~20 °C, N) for fish spawning, lower (~17 °C, L), and higher (~23 °C, H), to reveal the effects of altered water temperature on the DFO. Comparisons were made between the L and N (LvsN) conditions and H and N (HvsN) conditions. Transcriptomic analysis differentially expressed transcripts (DETs) related to heat stress were observed only in LvsN conditions, indicating that the DFO showed a stronger response to changes in LvsN than in HvsN conditions. Upregulation of DETs of vitellogenin receptors in N temperature showed that normal temperature was conducive to vitellogenin entry into the oocytes. Other temperature-sensitive DETs, including microtubule, kinesin, dynein, and actin, were closely associated with cell division and material transport. LvsN significantly impacted cell division and nutrient accumulation in the yolk, whereas HvsN only influenced cell division. Our results highlight the impact of altered water temperature on the DFO, thereby providing insights for future reservoir operations regarding river damming and climate change and establishing fish conservation measures.

Mismatch between critical and accumulated temperature following river damming impacts fish spawning.

Dam operations considerably influence water temperature regimes in rivers, which affects fish spawning activities. Previous studies have focused on the effects of critical temperature (CT) alterations during the spawning period, and largely ignored the effects of accumulated temperature (AT) alterations on gonadal development. Successful spawning relies on the simultaneous achievement of the two thermal requirements at appropriate times. River damming may cause a mismatch between the times of achieving CT and AT thresholds, and in turn influence fish reproduction. In the present study, spawning events of Coreius heterodon (C. heterodon) from 2009 to 2015 in the upper reaches of the Yangtze River, which are under the influence of cascade dams, were analysed based on the times of achievement of CT and AT thresholds. The CT and AT thresholds for C. heterodon spawning were 18.4 °C and 1324.9 °C·d, respectively. Under pre-impoundment conditions, the time of achievement of the AT threshold was 23 d on average later than that under post-impoundment conditions; however, the time of achievement of the CT threshold was similar under both conditions. The time of achievement of the AT threshold was 10 d earlier than that of achievement of the CT threshold in post-impoundment conditions. Earlier achievement of AT thresholds was followed by reduced spawning. The alteration of temperature rhythm caused by reservoir operations could be the major factor decreasing spawning abundance after river damming. The results of the present study could facilitate sustainable reservoir operations with regards to water temperature management, and thereby improve the conservation of fish resources.