基于耳石核心氧同位素SHRIMP分析研究青海湖裸鲤繁殖特征

青海湖裸鲤是中国重要的内陆珍稀鱼种，在青海湖湖泊生态系统中起着核心作用。繁殖环境是鱼类种群延续的关键因素，能获取青海湖裸鲤的繁殖环境参数和明确最佳产卵场，对于保护和扩大其渔业资源量也非常重要。本文尝试利用耳石的微区原位氧同位素组成分析青海湖裸鲤的繁殖特征，利用SHRIMP Ⅱ离子探针测定5尾青海湖裸鲤耳石微区原位δ18O组成，沿着最长生长轴到边缘打点，束斑直径大约25μm，束斑深度约2~3μm。分析结果表明，裸鲤耳石的δ18O值变动范围分别是−4.88‰~3.46‰、−0.28‰~3.91‰、−1.43‰~2.94‰、−1.81‰~3.35‰，并且耳石间歇带的δ18O值高于成长带。耳石间歇带是裸鲤在湖水中形成，而成长带是在河水中形成，上述结果与青海湖湖水的δ18O值显著高于河水的δ18O值一致，因此记录了裸鲤的洄游行为。核心区域差异性的δ18O值则反映了裸鲤的产卵地和水温状况，表明有的裸鲤在水温较低的河口产卵孵化，有的在水温较高的河流上游产卵孵化。与其他样品不同的是，其中1尾裸鲤耳石的δ18O变动范围是−9.36‰~−5.21‰，表明该裸鲤固定在河流里生长繁殖，不发生洄游行为。这一发现为进一步优化青海湖裸鲤的人工繁殖和利用耳石化石探究青海湖水环境演变提供了研究基础。

Analyzing the Reproductive Characteristics of the Naked Carp Gymnocypris Przewalskii (Kessler) Based on the Oxygen Isotopes of Otolith Core Using SHRIMP

BACKGROUNDIt is of great significance to study the breeding environment of the naked carp in Qinghai Lake for the conservation and restoration of natural habitat. The naked carp is the only economic species in Qinghai Lake, colloquially called “Huang Yu”, and plays a core role in the lake ecosystem. As an anadromous species, the naked cap migrates between Qinghai Lake and major rivers to spawn such as the Buha, Shaliu, Quanji, Heima, and Hargai rivers from April to August every year. Due to intensive fishing, arid climate, and the lack of spawning rivers, the amount of the naked carp’s resources has dropped sharply, from 28000 tons in the 1960s to 2263 tons in the 1990s. In view of its important ecological status, it is urgent to restore and protect the resources of naked carp in Qinghai Lake. Since 1982, Qinghai Province has forbidden fishing to restore and protect the fish resources. At the same time, it has established fish conservation bases and artificial breeding and releasing stations around Qinghai Lake. By 2022, the fish resources of the naked carp had increased to 108500 tons, 42 times as many as in the early stages of protection. The breeding environment is the key factor for the continuation of the fish population, and different fish require different parameters of the spawning ground, such as river, light, sediment and water temperature. It is also very important to obtain the reproductive environmental parameters and determine the optimal spawning ground for the protection and expansion of the fish resources. At present, only Zhou et al.[3] have discussed the environmental requirements of natural reproduction of the naked carp by indoor artificial simulation. Therefore, it is of great significance to study the breeding environment of the naked carp for the conservation and restoration of natural habitat.　　 Otolith δ18O provides a method for fish population identification, migration and environment exploration of spawning ground. Otolith, a calcium carbonate mineral in bony fish, has both auditory and balancing functions and is known as the “recorder” of time and water environment. Microchemical analysis of otolith can reveal the life history and water environment changes of fish. Especially, the core area of otolith is formed at the early stage of incubation, and its microchemical composition can reflect the hydrochemical characteristics of the habitat and solve the problem of fish identification. The otolith δ18O is closely related to water temperature. Under normal salinity conditions, the δ18O change of 1‰ corresponds to the seawater temperature change of about 5℃. For example, the higher otolith δ18O values of Pacific bluefin tuna, which migrated across the Pacific from the Western Pacific (WPO) to the Eastern Pacific (EPO), reflected the cold-water temperatures encountered during migration. Similarly, the lower δ18O value in otolith core of Oncorhynchus keta, which migrated between freshwater and marine environments, indicated that Chinese salmon were also anadrotic spawning fish, returned to the ocean after hatching. Yuan et al.[12] analyzed the δ13C and δ18O values in the otolith of small yellow croaker in the Yellow Sea and the Bohai Sea, the population of southern Yellow Sea was subdivided into offshore and coastal populations for the first time, and no station crossing between the two populations was recorded. The overall successful rate of discrimination was recorded to be 82.6% by cluster analysis. Tatsuya et al.[13] conducted otolith δ18O and microstructure analyses to investigate nursery habitat temperatures and early life growth rates. In conclusion, the otolith δ18O provides a method for fish population identification, migration, and environment exploration of spawning ground. In this study, the SHRIMP Ⅱ ion probe was used to determine the otolith δ18O of the naked carp in Qinghai Lake. Combined with the hydrochemical composition of lake water and river water in Qinghai Lake, the optimal migration and spawning sites and environmental conditions of the naked carp were investigated to provide effective information for further revealing its life history.