| Coilia fish belong to Clupeiformes, Engraulidae. Amongst these fish, C. nasus, C. mystus and C. grayii are widely distributed in China. Besides the anadromous population, two freshwater resident populations, i.e., C. nasus taihuensis and C. brachygnathus, have been also documented. All of Coilia fish in China are always important fishery species. Unfortunately, the resources of Coilia have been sharply decreased up to date, because of anthropogenic impacts, e.g., overfishing, water pollutions, habitat degradation. Especially, C. nasus has been the most seriously impacted by the influences, and its traditional fishing seasons in the Yangtze River Estuary are more and more difficult formed in recent years. Miniaturization and trend of younger age become two great problems faced by the resources of C. nasus. Likewise, C. mystus is suffering anthropogenic impacts too; and furthermore, the resources in the Yangtze River Estuary have almost lost harvest value. Sharp decline of the Coilia resources is attracting increasing attention now. More and more corresponding studies have been undertaken at different levels. However, due to the limitations of approaches, it is very difficult to clearly understand the population dynamics, habitat features, and the characteristics of their spawning, over-winter, feeding grounds, and migratory routes. In turn, stopping the decline crisis resources is a big challenge for Coilia fish in China.It is noteworthy that all Coilia species in China are almost diadromous fish. The complex life history and wide range of activities make some traditional research methods difficult to get the objective knowledge on the migratory ecology, e.g., environmental history, connectivity among different resource stocks and diadromous migratory patterns. Fortunately, the recent advances in otolith morphometry and microchemistry of fish provide a powerful means to possibly settle down these challenge s and problems in Coilia fish.Otolith is one kind of hard tissue located in fish’s inner ear. Commonly, there are three pairs of otoliths which are termed the lapilli, astersci and sagittae. Because within the growth of fish body, some special annuli (yearly rings) can be formed in otolith, it is usually believed as an important tool to determine the age of fish. Meanwhile, because of the stabilization, the morphological characterizes were always used in population discrimination. In addition, with the otolith formation, no resorption will happen for all elements in otolith accumulated from fish living habitats. Therefore, the elements can be used to reconstruct habitat history of fish. Based on the aforementioned advantages, corresponding otolith studies become one of the most important and active fields on fish ecology.The sagittae are the largest pair among the three pairs of otoliths. moropholometric and microchemical characters of sagittae were investigated in the present study in order to get the knowledge on population composition and connectivity, migratory patterns and life history of each Coilia species in Chinese waters. Furthermore, the suitable methods of otolith microchemistry are hoped to be established for further research on migratory ecology of Coilia fish.The morphological results of sagittal otoliths obtained by the truss network analysis showed some different characters among different Coilia species/populations. Among the 12 distance measurements, D12/D3 was significantly different among the Coilia species studied (P<0.05), implying that the length of antirostrum reflected by D12/D3 might be an important character to separate the Coilia species each other. Moreover, the otolith of C. nasus was narrower and the size of antirostrum, rostrum was quite similar. The otolith of C. brachygnathus population could be wider than that of C. nasus, but was still narrower than those of C. mystus and C. grayii, and its antirostrum was not obvious. The otolith of C. mystus expended to the back and abdomen, while that of C. grayii showed extrusion to the direction of back end, and the peak of back was more rearward. Discrimination analysis showed that the truss network developed could be effectively used to identify C. nasus and C. brachygnathus, and the accuracy rates were as high as 98.8% and 96.8%, respectively. At the mean time, C. grayii was also distinguished well with an accuracy rate of 90%. Among different populations of C. nasus, individuals from Panjing sea region near the Daliaohe Estuary can be distinguished from those collected in other regions, e.g., the Zhoushan Island, Yellow Sea and Dongying near the Yellow River Estuary. This phenomenon suggested that there might be some similarity among the latter populations and the population of C. nasus from Panjing sea region might be much more independence of the other populations (even population from the near water region of the Dongying).Based on the results of otolith morophology, the relative complete investigations on otolith microchemistry were further carried out so as to get knowledge about the migratory habits, discuss the connectivity between different Coilia populations and make sure about the intra-/interspecies relationship among these Coilia fish.At first, in order to get the prefect otolith planes for microchemical analysis, several grinding pre-treatment methods (e.g., transverse plane and sagittal plane) were compared in this study to affirm the effectiveness of the annuli rings obtained in otolith of Coilia nasus and Coilia mystus. Meanwhile, two etching techniques (1%HCl and 5%EDTA) were used to assure which could yield better otolith planes. Results showed that sagittal plane grinding was easier and could supply the biggest plane. In this case, different parts of otolith could be easily separated, but the annuli on this plane were not so clear. Even after being etched, only the first annuli could be determined. In contrast, although transverse plane grinding required to grind both sides of the otolith, it was easier to find out the annuli on the plane even different annuli might be relatively closer each other than sagittal plane. Therefore, our results suggested that grinding with sagittal plane should be better for microchemical studies, while that with transverse plane would be better for annuli research. Noteworthyly, otolith growth characters of C. nasus and C. mystus were special in different transects. On the transverse plane, it showed that with the growth of otolith, the extension of otolith tended opposite the fish body axis. And on the sagittal plane, the extension of otolith of C. nasus would present significant difference before and after the first annuli, and especially the antirostrum was observed started to better extend.Then, according to the above understanding of otolith grinding methods, sagittal plane was chosen to take otolith microchemical analysis of C. nasus (including the individuals believed as C. brachygnathus) in the Xingzi water area in the Poyang Lake for making sure whether all individuals were anadromous ones or not. By comparison with the otolith microchemical characters of C. nasus and C. brachygnathus, Sr/Ca ratios in otolith of C. brachygnathus were consistently low (1.66±0.54), indicating a freshwater resisdent pattern as all life histories of the fish were spent throughout in freshwater habitat. Contrastly, the individual of C. nasus showed a diadromous pattern for which otolith had a complex Sr/Ca ratio pattern with three phases of 1.82±0.50,5.79±0.91,and 4.14±0.88, suggesting the fish experienced not only the freshwater, but also the seawater and brackish water during different stages of life history. Furthermore, the C. nasus was very likely to enter the Poyang Lake and use the Xingzi water area for spawning.For further estimating whether the vicinity of the Xingzi water area in the Poyang Lake was a spawning site of diadroumous C. nasus from the Yangtze River,15 individuals were collected from Huoyanshan region of the Xingzi water area and used for microchemistric and gonad maturity stage analyses on June and July,2014. Results of the otolith microchemistry showed that all fish were anadromous ones. Furthermore, the gonad of two individuals had developed to mature stage (Ⅳ) on June and one had even developed to spawning stage (Ⅴ) on July. All these facts strongly proved, for the first time, that the vicinity of Huoyanshan region of Xingzi water area in the Poyang Lake should be one of the spawning sites of diadromous C. nasus from the Yangtze River.The results of otolith morophology showed that there should be several different populations of C. nasus along Chinese coast. To make sure the connectivity among these possible different populations, the habitat use and the migratory patterns of different C. nasus fish from the Yellow River Estuary, Yangtze River Estuary, Qiantang River Estuary and Oujiang River Estuary were studied by examing the environmental signature of Sr and Ca in their otoliths and comparing the Freshwater Coefficient (Fc=Lf/LT) in otolith. The results showed that the life patterns were quite similar between the individuals from the Yellow River Estuary and Yangtze River Estuary, but considerably different from those of the Qiantang River Estuary and Oujiang River Estuary. Most of the C. nasus were typical anadromous fish, but several individuals were brackish-water residents. The aformentioned difference suggested that C. nasus from different estuaries may probably be a natal homing fish.By means of LA-ICPMS analysis, the trace element character in otolith core of C. nasus was determinated to further invesitigate the connectivity between different populations. The results showed that C. nasus fish from Lianyungang region were significantly different from those collected at other water areas. The elemental pattern in otolith core reflected that relatively close relationships were found between the C. nasus juveniles from the Yangtze River and C. nasus fish from several other waters (e.g., the Poyang Lake), suggesting that C. nasus from the Poyang Lake might supply the fish resource in the Yangtze River, and, moreover, the resource from the Yangtze River could possibly supply the C. nasus resource in other sea areas.In addition, the element patterns of otolith suggested that there might be two breeding population in the Poyang Lake, implying that there might be more than one spawning sites for C. nasus in the Poyang Lake.Using an isotope ratio mass spectrometry, preliminary research was conducted on the stable isotope ratios of δ13C and δ18O in otoliths of juvenile C. nasus from the Yangtze River Estuary. The correlation of δ13C versus δ18O showed that the juveniles in the present study might originate from two different hatchery sites in the Yangtze River. Food organism and the distance between spawning ground and sampling site in the estuary might result in the difference of δ13C and. δ18O.The Sr and Ca fingerprint were analyzed with the otolith of C. mystus fish from the Yangtze River Estuary, Oujiang River Estuary and Zhujiang River Estuary. The results showed that all individuals of C. mystus might be born in estuarine brackish water, except for the individuals from the Zhujiang River Estuary. By comparison of the migratory patterns among the C. mystus fish from three different estuaries, it was believed that the individuals from the Yangtze River Estuary might belong to estuarine brackish populations. They could possibly use freshwater environment during certain period, but might seldom use the sea water habitats with high salinity. There might be two populations of C. mystus in the Oujiang River Estuary, one was nearshore type and the other was offshore type. In contrast, the C. mystus fish from the Zhujiang River Estuary were quite different with those from estuaries of the Yangtze River and Oujiang River. The otolith Sr/Ca ratios were generally lower (especially in the core area), reflecting their habitat history in low estuarine salinity water like freshwater.The otolith Sr and Ca microchemistries were analyzed with the Gray’s grenadier anchovies C. grayii collected from Shiwuyong water area in the Zhujiang River Estuary. Both the line transect and mapping analyses clearly showed that the Sr concentration and Sr/Ca concentration ratios in the otoliths changed with the salinity of the habitat during their life-history, implying their fluctuation migration patterns. A period of freshwater life history seemed to be necessary for the hatching and early ontogenetic development for this species, while much more flexible migration patterns among fresh, brackish, and marine waters could be found at their continued developmental stages and the difference seemed to be very obvious among the individuals, which suggested the complicated life history strategies in C. grayii of the Zhujiang River Estuary. |
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