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

SIMPLE SUMMARY: The reproductive processes of fish are known to be sensitive to water temperatures. However, the mechanism by which altered water temperature by river damming affects fish reproduction remains unclear. This study investigated the effects of altered water temperature on the development of fish gonads by differential expression of temperature-sensitive transcripts. Particularly, the regulatory mechanism of oocyte meiotic division and the accumulation of nutrient materials were explored. We found that elevated temperatures, from a low value to a physiological optimum temperature, was conducive to cell division and vitellogenin accumulation; while elevated temperatures, from physiological optimum temperature to a high temperature within a certain range, was favorable for cell division but not vitellogenin accumulation. Although a warm winter temperature favors early gonadal development, it can impair final spawning quantity and quality in spring or summer. These results provide robust evidence that under the impacts of reservoir operation, the altered water temperature regime affects the gonadal development in temperate fish. ABSTRACT: 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.