| The estuarine tapertail anchovy Coilia nasus is an important commercial fish in China. It once belonged to one of the main fishery species in the Yangtze River. However, due to overfishing, habitat(e.g., spawning site, mirgartion channel) degradation, water pollution, etc., the resource of C. nasus is constantly declining. Body miniaturization and younger-age trend of this fish has become increasingly prominent. The protection of fishery species is of great significance. As an anadomous species, C. nasus migrates from sea water to spawn in fresh water. Its recruitment must be very important to the C. nasus resource in the Yangtze River, its connected lakes, estuary, and adjacent seas. Consequently, the investigation and conservation of spawning sites, distribution areas will play significant roles to play significant roles to protect and sustainable utilization of C. nasus. The Poyang Lake is the largest freshwater lake in China. In history, the Poyang Lake was believed as one of the spawning grounds of anadomous C.nasus. Beside, another ecotype of freshwater resident C. nasus(once named C. brachygnathus) was also reported distributing in the lake. Discrimination of ecotypes of anadromous and freshwater resident C. nasus is still very difficult, although long(> head length, namely C. nasus) or short(< head length, namely C. brachygnathus) supramaxilla traditionally was considered as a morphological feature to seperate the anadromous or freshwater resident ones. The taxonomy of the two ecotypes remains controversial until today. Recently, it was reported that in the Yangtze River, anadomous C. nasus might only distribute in lower reaches below Anhui section and can not move further upstream or enter the connected lakes(e.g., the Poyang Lake). The anchovy may merely be C. brachygnathus in the Poyang Lake. Unfortunly, this hypothesis is very difficult confirmed by traditional capture survy methods.It is noteworth that the advanced approaches on fish otolith research have been used more broadly to identify resource stocks, reconstruct life histories, reverse habitat “figerprints”, and derive migration patterns in recent years. Otolith morphometric features can be effectively applied to identify differenet populations, while otolith microchemical features(i.e., accumulative characterastics of metal in otolith) can be effectively utilized to reconstruct habitat usage at different stages duing fish life history. Especially, the deposition variation of element strontium(Sr) and calcium(Ca) is often used for the inversion of habitat “figerprints” of different salinity water bodies(e.g., sea and freshwater), because their contents are closely correlated with ambient salinity conditions.Using the corresponding approaches for reference, the morphometry and microchemistry were systematically studied, in the present study, by sagittal otolith of C.nasus collected from near shore waters and mouth areas of main tributaries around the Poyang Lake. It is hoped to find out the characteristics of ecotype group, population composition, life history and the distribution of the spawing grounds of C. nasus around the Poyang Lake, and providing a theoretical basis and technical support for the reasonable assessment of Coilia nasus resources and the protection of the spawing grouds of the anchovy. The main results are as follows:1. Using a truss morphological framework based on 12 distance measurements, otoliths were comparatively investigated by of C. nasus and C. brachygnathus sampled around the Poyang Lake. The morphological differences were more apparent between the two different ecotypes than the same ecotype anchovies collected from different sampling waters. The mutual discriminant accuracy was as high as 100% between otoliths of C. nasus and C. brachygnathus while that was only 42~71% for a single ecotype of C. nasus between different sampling waters. The morphological features were relatively close between the otoliths of C. nasus collected at the Hukou and Xingzi sites in comparison with those of fish from the Duchang and Yugan sites. A certain difference on otolith morphology was also found between C. brachygnathus from the different waters, but the discriminant accuracy was only 30-75%. The otolith morphological features of the fish from the Xingzi, Yongxiu, Nanchang and Yugan waters were relatively close in comparison with those from the Hukou and Duchang waters.2. Coexistence of anadromous(C. nasus) and freshwater resident(C. brachygnathus) was confirmed by Sr and Ca microchemical ?ngerprints of the anchovies collected from the Hukou waters of the Poyang Lake. The transect analyses and X-ray intensity map analyses showed the complex change process from the core to the edge of otolith. The Sr/Ca ratios presented a variation process of low(1.69±1.1), high(4.55±1.02) and low(2.13±0.97) values in anadromous C. nasus. In contrast, the otolith Sr/Ca ratios from the core to the edge in C. brachygnathus showed consistently low values(1.13±0.74), reflecting a stable freshwater life history. Noteworthyly, otolith of individual HKCB05 of C. brachygnathus has a usual high(3.16±0.5) value of Sr/Ca ratio, implying that this C. brachygnathus fish might also experience an anadromous migration process.3. Coilia nasus and C. brachygnathus coexisted in the Xingzi waters of the Poyang Lake, being confirmed by Sr and Ca microchemical ?ngerprints. The Sr/Ca ratios also presented a variation process of low(1.74±0.9), high(5.41±1.53) and low(2.45±1.1) values in anadromous C. nasus. Contrastly, in C. brachygnathus the otolith Sr/Ca ratios from the core to the edge presented consistently low level of 1.13±0.74, coinciding with a habitat “figerprints” of freshwater. A usual high(3.64±0.5) value of Sr/Ca ratio was documented with otolith of C. brachygnathus individual XZCB29, suggesting that this C. brachygnathus fish might have the ability for anadromous migration.4. Both C.nasus and C. brachygnathus were found in the Duchang waters of the Poyang Lake, based on Sr and Ca microchemical ?ngerprints. The variation process of low(1.48±1.27), high(3.65±1.18) and low(1.34±0.84) Sr/Ca ratio levels was noted in anadromous C. nasus. At the same time, consistently low Sr/Ca ratio was found in C. brachygnathus, reflecting their freshwater habitat history.5. Only C. brachygnathus were found in the Nanchang waters of the Poyang Lake. The transect and X-ray intensity map analyses showed otolith Sr/Ca ratios of the fish from the core to the edge always kept at a low(1.76±0.79) level, indicating that the C. brachygnathus consistently lived in freshwater environment. The phenomenon of no C.nasus in the Nanchang waters might relate to that there might be special distribution pattern and migration route for anadromous C. nasus in the Poyang Lake.6. Coilia brachygnathus were merely found in the Yongxiu waters of the Poyang Lake. Low(1.47±0.61) Sr/Ca ratio fingerprints were observed in otolith from the core to the edge of almost all of the fish samples. However, individual YXCB08 showed a usual high(3.28±0.59) area of Sr/Ca ratio in otolith, suggesting that this C. brachygnathus fish probably migrated anadromously.7. Coexistence of C. nasus and C. brachygnathus was confirmed for the anchovies in the Yugan waters(including the section of Xinjiang River near the Poyang Lake) of the Poyang Lake by both transect and X-ray intensity map analyses of Sr and Ca microchemical ?ngerprints. The Sr/Ca ratios showed a variation process of low(1.54±0.76), high(4.35±0.94) and low(1.73±0.69) levels in C. nasus. But, the otolith Sr/Ca ratios from the core to the edge in C. brachygnathus showed consistently low level of freshwater habitat. The Sr/Ca ratio microchemical ?ngerprints intuitively verified, for the first time, the existence of anadromous C. nasus in the Yugan waters of the Poyang Lake, and the Xinjiang River. These locations are about 1000 km far from the Yangtze River estuary, strongly reflecting an extremely strong migration ability of anadromous C. nasus. Moreover, this phenomenon implied that there might be spawning sites for anadromous C. nasus in the Xinjiang River. |
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