Ecological operation of hydraulic engineering is essential for the conservation of fishery resources. Water velocity is known to affect the spawning of fishes delivering drifting eggs. This study aims to explore the effects of water velocity stimulation on the ovarian maturation and antioxidant capacity of adult grass carp (Ctenopharyngodon idellus) through laboratory experiments in order to understand the physiological mechanism underlying the response of natural reproduction to ecological flows. We examined the histology, sex hormones and vitellogenin (VTG) concentrations of ovary, and the transcripts of key genes in the hypothalamus-pituitary-gonad (HPG) axis, as well as the antioxidant activities of ovary and liver in grass carp. The results showed that although there was no discernible difference on the ovarian development characteristics of grass carp under water velocity stimulation, estradiol, testosterone, progesterone, 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DHP), and VTG concentrations were elevated, which was related to the transcriptional regulation of the HPG axis genes. The gene expression levels (gnrh2, fshβ, lhβ, cgα, hsd20b, hsd17b3, and vtg) in the HPG axis were significantly elevated under water velocity stimulation, while those of hsd3b1, cyp17a1, cyp19a1a, hsd17b1, star, and igf3 were suppressed. In addition, appropriate water velocity stimulation could enhance body health status by increasing the activities of antioxidant enzymes in the ovary and liver. The results of this study provide the fundamental knowledge and data support for ecological operation of hydropower projects and river ecological restoration.
Introduction
The Three Gorges Dam (TGD), located in the middle stretch of the Yangtze River, is the world’s largest hydropower project and plays a crucial role in harnessing and exploiting the river’s power (Tang et al., 2016). However, the operation of the TGD not only significantly alters the hydrological processes of rivers but also threatens aquatic habitats both upstream and downstream of the dam site, thereby contributing to the degradation of riverine ecosystems (Zhang et al., 2021). In detail, the regulation of reservoirs homogenizes the flow processes of rivers and weakens or eliminates the natural flood peaks, thus leading to a decrease in fish eggs (She et al., 2023).
Fish spawning activity is likely influenced by a variety of environmental factors, including water velocity, water temperature, and dissolved oxygen. By influencing hormone synthesis and secretion, these environmental factors affect the gonadal development of fish (Liu et al., 2021). In particular, water velocity has been recognized to affect the spawning of fishes delivering drifting eggs in rivers (Chen et al., 2021a). In order to mitigate the adverse effects of dam operations on fish spawning, it is necessary to establish specific eco-hydrological processes to stimulate fish spawning (Wang et al., 2020).
The four major Chinese carps (FMCC), including black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix), and bighead carp (Hypophthalmichthys nobilis), which are highly sensitive to hydrological processes, represent the most economically important fishes in China. The FMCC population would migrate to the spawning sites and start spawning in response to high-flow pulses from March to June, while the construction and operation of TGD alter the natural hydrological rhythm and hinder fish migration (Zhang et al., 2023). Therefore, incorporating ecological flow into the operation scheme of TGD would be a mitigation measure to protect the spawning of FMCC. It has been demonstrated that implementing controlled man-made floods as part of the TGD operation enhances the reproductive success of FMCC in downstream regions (Xiao et al., 2022). Since 2011, several attempts have been organized to promote the spawning behavior of FMCC in order to mitigate the decline in FMCC from the Yangtze River. It was found that the water velocity that induces FMCC spawning ranged from 1.11 to 1.49 m/s (Cao et al., 2022), with an optimal flow velocity of 1.31 m/s was identified for the spawning of FMCC in rivers (Chen et al., 2021a). Although water velocity plays a crucial role in the reproduction of FMCC, there is a notable scarcity of research on the physiological mechanism underlying the response of natural reproduction to ecological flows.
Post time: Aug-05-2024