A preliminary investigation of the fish food web in the Gironde estuary,France, using dietary and stable isotope analyses

Carbon and Nitrogen stable isotopes and stomach contents analyses were used to investigate an estuarine fish food web and identify the contribution of these two methods to the knowledge and understanding of the food web's structure and its functioning. The nine most abundant fish species during the warm period in the Gironde estuary (southwest France, Europe) are examined. Observation of the stomach contents reflects a variety of feeding modes between fish species that consume a diverse assortment of prey, with limited dietary overlap. Nevertheless, when regarding the whole fish community, few prey species dominate the stomach contents. Nitrogen isotope ratios indicate a high intraspecific variability inducing an interspecific covering of the signatures. However, a tendency to δ¹⁵N enrichment according to the trophic position of the species studied was observed. Fish assemblages show a trend towards enrichment of their carbon isotopic signatures from the upper estuary (−20.8 ± 1.8‰) towards the lower estuary (−18.3 ± 1.6‰). But whatever the capture zone considered, most of the individual δ¹³C values for each fish analysed are comprised between −22 and −16‰. Only few specimens, belonging to migratory amphihaline species, have significantly lighter values.     

基于DNA条形码研究中国枪乌贼和鸢乌贼的食物种类组成*

中国枪乌贼(Uroteuthis chinensis)和鸢乌贼(Sthenoteuthis oualaniensis)作为中国南海头足类的关键种, 对海洋生态系统的物质流动与能量循环具有重要影响, 其摄食生态的研究将对海洋食物网的构建具有重要意义。由于传统胃含物分析法难以准确鉴定糜状饵料生物的组成, 本研究利用DNA条码技术, 针对中国枪乌贼和鸢乌贼不可辨认的食物糜提取组织DNA, 选用线粒体基因细胞色素C氧化酶亚基I(Mitochondrial cytochrome oxidase subunit I, COI)作为分子标记, 获得的序列在Genbank中进行比对分析, 并使用GMYC(Generalized Mixed Yule Coalescent)模型进行物种界定和构建系统进化关系。结果成功鉴定出中国枪乌贼饵料物种有13种, 鸢乌贼饵料物种有8种, 共20种(其中1种为共有饵料)。比较发现, 汕头-台湾浅滩渔场的中国枪乌贼主要摄食鱼类、甲壳类和头足类, 而南海中部海域鸢乌贼则主要摄食鱼类和头足类。两物种均存在同类相食现象, 但鸢乌贼表现更明显。     

长江口鱼类食物网与营养结构的研究

鱼类食物网是海洋生态系统中物质循环与能量流动的重要途径,营养结构则是表明能量流动过程中不同消费者的营养水平以及消费者之间的营养关系,二者对研究海洋生态系统中鱼类捕食与被捕食、种间竞争、种群调节以及数量变动等都具有重要意义。但国内、外关于长江口鱼类食物网及营养结构的研究尚未见详细报道。 为探讨三峡工程对河口生态系统的影响,中国科学院海洋研究所于1985年9月至1986年8月对长江口及邻近海域进行了周年综合性本底调查,并对长江口鱼类食物类型作了简单的描述(刘瑞玉、罗秉征等,1987),本文根据以上资料对长江口60种主要鱼类的食物组成、摄食生态类型、食物网与营养结构进行了分析,以期为研究长江口生态系统的功能、生物生产过程以及合理开发利用长江口渔业资源提供科学依据。     

DNA-based identification methods of prey fish from stomach contents of 12 species of eastern North Pacific groundfish

Stomach content analysis of eastern North Pacific groundfish has been conducted routinely by researchers interested in understanding trophic interactions between key predator species and their prey. Identification of prey by traditional morphological methods has limitations however, due to the loss of identifiable characters from digestion and morphological similarities between taxa. Furthermore, some forage fish (e.g., osmerids, ammodytids, and juvenile gadids), common prey of Bering Sea and Gulf of Alaska groundfish, are difficult to distinguish because of their slender or fusiform shape, disarticulating easily during digestion. DNA-based identification methods were developed to differentiate among 18 fish species, some that are found at depths greater than 200 m, from four taxonomic families: Ammodytidae and Osmeridae (forage fish), Pleuronectidae (flatfish), and Gadidae (gadid fish). Polymerase chain reaction (PCR) amplification of a 739 basepair section of mitochondrial DNA cytochrome c oxidase I and an 862 basepair section of mitochondrial DNA cytochrome b was followed by restriction digest assays and resulted in species level resolution for 16 of 18 species of interest. PCR restriction digest assays applied to fish prey from stomach contents of groundfish indicated the presence of several target species, eulachon (Thaleichthys pacificus), walleye pollock (Gadus chalcogrammus), searcher (Bathymaster signatus), rock sole (Lepidopsetta bilineata), yellowfin sole (Limanda aspera) and either Bering flounder (Hippoglossoides robustus) or flathead sole (H. elassodon). The PCR restriction digest protocols improved the identification rate of predated fish from stomach contents compared to identification by conventional taxonomic methods alone, and DNA sequence analysis further resolved identification of unknown prey fish samples.     

Seasonal changes in the feeding ecology of guillemots (Uria aalge) off north and east Scotland

Stomach contents were examined from 750 guillemots collected at several sites in the northern North Sea. The dietary composition was compared between months and between localities in order to assess seasonal and geographical trends in feeding strategy.From March to August sandeels dominated the diet, but in September a changeover period occurred when clupeid and gadoid remains became increasingly frequent in the stomach contents. This situation persisted over the winter period, but the importance of the two fish families varied with area, clupeids being more important in more southerly samples and gadoids in the north. Dietary data were considered in relation to available fisheries information and to known guillemot distribution patterns.     

Anchovy Engraulis encrasicolus diet in the North and Baltic Seas

The diet of anchovy (Engraulis encrasicolus) in the North and Baltic Seas was studied using stomach analysis from four sampling events in different areas. Zooplanktivory was confirmed; the most frequent prey items (in over 40% of stomachs) were copepods, malacostracan larvae and fish larvae. In the Baltic Sea, Paracalanus spp. and Pseudocalanus spp. were important in relative terms; in the German Bight, Temora spp. dominated the stomach contents. Relative abundances of prey items varied with area more than absolute abundance or presence absence of items. Moreover, the level of resolution of prey categories influenced which prey categories were considered to be most important in driving variability in stomach content. Anchovy diet is broad across the seasons, years and areas sampled, suggesting that it is not a specialist feeder in the North Sea. The similarity of diet between anchovy and other clupeids, as well as anchovy consumption of larval fish, makes the new increased anchovy population a potential intraguild predator of commercial species like herring.     

Diel feeding of the transparent goby Aphia minuta (Pisces,Gobiidae) in the Northwestern Adriatic Sea in spring time

The present study provides the first estimate of the daily ration for a goby species in the Mediterranean Sea, using a new approach to determine the mass of fish stomach contents through the sum of individual prey dry mass derived indirectly from prey size. Diel feeding activity and daily ration of the pelagic goby Aphia minuta were studied under natural conditions in the coastal waters off Comacchio (Northwestern Adriatic Sea) during the spring season. A total of 318 individuals of A. minuta, collected by 14 trawls carried out on 4 consecutive days, was examined for gut contents. The diel pattern of the vacuity index and the stomach fullness index indicated that A. minuta has nocturnal feeding behaviour. The daily ration, computed over a period of 16 h, was equivalent to 2.23% wet body mass.     

Migration dynamics of clupeoids in the Schelde estuary: A stable isotope approach

Large numbers of young of the year herring (Clupea harengus L.) and sprat (Sprattus sprattus (L.)) typically enter and remain within North Sea estuaries during the winter months. The main purpose of this study was to examine their migration dynamics between the North Sea and the Schelde estuary using C and N stable isotopes. Prior to this, stomach contents were used to verify the isotopic differences between the food sources at the sampling stations. From May 2000 to April 2001 fish were collected monthly in the upper and lower estuary. Muscle tissue and stomach contents were analyzed for δ¹³C and δ¹⁵N using an EA-IRMS. Based on the stomach contents, it was demonstrated that δ¹⁵N could not be used as a tracer for fish migration because the longitudinal estuarine δ¹⁵N gradient had reversed completely during autumn. The δ¹³C gradient, however, was found to be reliable for studying fish movement in the Schelde estuary.Seasonal movements of clupeoids in the Schelde estuary were analyzed by separating the temporal abundance patterns into migration groups based on their muscle isotopic composition. Immigration and emigration seem to occur continuously throughout the year. Most exchange occurred in November. During winter, immigration remained high but gradually decreased. Although the herring and sprat abundance further declined in the estuary during February and March, large seaward emigration was not fully demonstrated. As temporal overlap between immigration and emigration is concluded the results support the hypothesis that migration to estuarine nurseries is individually based.     

Analyses of stomach contents and stable isotopes reveal food sources of estuarine detritivorous fish in tropical/subtropical Taiwan

Detritivorous fish generally refers to fish that primarily ingest unidentified organic detritus. We analyzed stomach contents in combination with stable isotopes to trace and compare the food sources of the large-scale mullet Liza macrolepis and other detritivorous fish species in subtropical mangrove creeks and a tropical lagoon in Taiwan. The volume of organic detritus always contributed >50% of the stomach content of L. macrolepis in the two habitats. However, consumed items were distinct between the two habitats and corresponded to the types in which they reside. The consumed items in the lagoon were more diverse than those observed in the mangroves. In the mangroves, the diet composition of L. macrolepis was primarily determined by season, not by body size. In the lagoon, there were no clear seasonal or size-dependent grouping patterns for the diet composition. There were significant seasonal and spatial variations in δ¹³C and δ¹⁵N values of potential food sources and L. macrolepis. However, neither δ¹³C nor δ¹⁵N values of L. macrolepis were correlated with fish body size. Joint analyses of stomach contents and stable isotopes indicated that benthic microalgae on sediments were the most important assimilated food in both seasons for the dominant detritivorous fish in the mangroves, whereas a greater reliance on microalgal and macroalgal periphyton on oyster-culture pens was observed in the lagoon. Mangrove and marsh plants and phytoplankton, which are mostly locally produced within each habitat, were of minor importance in the assimilated food.     

舟山海区几种藤壶的食性分析

舟山海区五种藤壶的食性成分分析表明：其胃含物可分为浮游动物、浮游植物、有机碎屑及无机颗粒四类。浮游动物以挠足类为主，浮游植物以硅藻为主。不同大小个体的藤壶摄食偏向有所差别：大个体藤壶较多地摄食大型的烧足类等浮游动物，而小个体藤壶较多地摄食小型的硅藻等浮游植物和有机碎屑。藤壶食物成分种类与其生活海区中的浮游生物种类相一致，并随海区中浮游生物种类和数量变化而变化。通过测定发现，分布于外海的三角藤壶的食物颗粒度明显大于近海虾塘中的纹藤壶的食物颗粒度。     

Diet of Phycis blennoides (Gadidae) in Relation to Fish Size and Season in the Western Mediterranean (Spain)

Abstract. Despite its commercial value, little is known about the feeding ecology of the greater forkbeard, Phycis blennoides (Brünnich 1768). The stomach contents of 2631 greater forkbeard were taken at monthly intervals off the coast of the Gulf of Valencia (western Mediterranean). They were examined in order to assess the diet and to determine the fish size- and season-related dietary variation of the species. Prey items were identified to the lowest taxonomic level possible. The basic food consisted of epibenthic species, mostly Decapoda, Mysidacea and Teleostei. A change in food composition based on fish size was observed and seasonal variation in diet was also recorded. The food overlap analysis indicated a high convergence in diet among similar size groups.     

Feeding Habits of Trisopterus minutus capelanus (Gadidae) Off the Eastern Coast of Spain (Western Mediterranean)

Abstract. The stomach contents of poor cod, Trisopterus minutus capelanus (Lacepède), were taken at monthly intervals off the eastern coast of the Gulf of Valencia (Spain). A total of 1276 were analyzed to determine diet according to fish size and season. The basic food consists of crustaceans (Mysidacea and Decapoda) and teleosts. Feeding habits varied with size: decapods and fishes were more abundant in the stomachs of larger specimens. Little seasonal variation in food habits was recorded.     

Food and feeding of Loligo vulgaris reynaudii from St Francis Bay,South Africa

Change of colour, consistency and pH in contents of the caecum and the stomach of laboratory-maintained long-finned squid Loligo vulgaris reynaudii were determined. There was relatively little variability in any of these parameters of the specimens investigated. Colour and consistency of food or emulsion were used as a basis of analysis of stomach-caecum contents of wild squid. Most squid fed late during the night and/or during the early morning, and the frequency of caecum colour categories did not change much between trawls. Wild squid preyed upon different organisms according to their size. Squid of 69–125 mm dorsal mantle length fed mainly on euphausiids (95% by frequency of occurrence, 87,5% by mass) and those of 126–240 mm mainly on fish (78 and 74,3% respectively) with Bregmaceros ?macclellandii and hake as important components. Unidentified fish in the stomachs (i.e. those from which no otoliths were available) probably also belonged to these two species.     

A note on the stomach contents of fur seals Arctocephalus pusillus pusillus beached on the south-east coast of South Africa

The stomach contents of 36 South African fur seals beached over a 20 year period along the south-east coast of South Africa were examined. In all, 15 fish and nine cephalopod prey types were identified. Five species of fish (Merluccius capensis, Trachurus trachurus capensis, Cynoglossus zanzibarensis, Pterogymnus laniarius, Austroglossus pectoralis) and two cephalopods (Loligo vulgaris reynaudii, Octopus sp.) were of major importance in the diet. The proportion of demersal species in the diet is higher than previously reported, suggesting that the seals forage extensively on the sea floor. The most important fish species in the diet was M. capensis, and the most important cephalopod was L. v. reynaudii. Male and female seals showed distinct prey selection, suggesting possible intraspecific resource partitioning. There is no evidence of competition between seals and other top predators.     

Gastric lavage as a non-lethal method for stingray (Myliobatiformes) diet sampling

Understanding the trophic interactions of ecologically important mesopredators such as Myliobatiformes (stingrays) is vital, but, given their susceptibility to overexploitation, the collection of stomach contents for dietary analysis necessitates the use of non-lethal methods. We provide a detailed method of using gastric lavage to collect stomach contents from the ‘Vulnerable’ porcupine ray Urogymnus asperrimus at the St Joseph Atoll of the Amirantes Group, Seychelles. Rays were captured by hand, inverted and restrained while a plastic hose, connected to a bilge pump, was inserted into the stomach to flush out the contents. A high percentage (94.5%) of gastric lavage attempts resulted in the collection of stomach contents. There was no visual evidence of stress or short-term, post-release mortality and, given the success and relative ease of this technique, we conclude that the described method of gastric lavage is an effective, non-lethal means of obtaining stomach contents from stingrays.     

The diet of Patagonian hake Merluccius australis polylepis and its daily ration of Patagonian grenadier Macrouronus magellanicus

The diet of the Patagonian hake Merluccius australis polylepis in 1986 was determined by analysis of stomach samples collected from commercial trawl catches. The major prey items were Patagonian grenadier Macrouronus magellanicus and, to a lesser extent, southern blue whiting Micromesistius australis. Large (81–100 cm) hake are mainly piscivorous and consume more grenadier than smaller (51–80 cm) hake. The smaller hake feed both on fish and invertebrates. There was no difference by sex in terms of stomach contents. The daily feeding cycle was also investigated from samples collected during 1991. Hake feed principally on 1-, 2-, and 3-year-old grenadier, which they seem to catch mainly at night. The daily ration of grenadier was between 0,043 and 0,26 per cent of body mass (1,692–9,849 g). The results are similar to those for other hake species in terms of composition of the diet, daily feeding cycle and daily ration.     

Diet composition and feeding behaviour of juvenile Greenland halibut (Reinhardtius hippoglossoides) in the Svalbard area

The diet of trawl-captured juvenile Greenland halibut (Reinhardtius hippoglossoides Walbaum) from three locations on the western and northern coasts of Svalbard, Norway, in December 1995 and January 1996 is described. Stomach fullness was recorded for 1216 fish of 7 to 65 cm length, and stomach contents were analysed for 353 non-empty stomachs. The diet differed only slightly between the sampling areas and no differences were found between males and females. The overall percentage of empty stomachs (PES) was comparable to other nursery areas and lower than recordings from feeding and spawning areas. PES decreased and prey size increased as predator length increased. Fish and crustaceans dominated the diet, the most important prey species being Atlantic cod (Gadus morhua), polar cod (Boreogadus saida) and northern shrimp (Pandalus borealis). The relative importance of fish and crustaceans, respectively, was independent of predator length. However, a size-dependent variation in preferred prey was found, as smaller fish preyed upon small crustaceans and polar cod while larger individuals displayed a preference for northern shrimp, juvenile Atlantic cod, and other larger fish. Finally, there was a close resemblance between the length distribution of prey species from the trawl and from the stomachs.     

东太平洋赤道海域鸢乌贼(Sthenoteuthis oualaniensis)和茎柔鱼(Dosidicus gigas)的食性比较研究

柔鱼亚科(Ommastrephinae)近缘种鸢乌贼(Sthenoteuthisoualaniensis)和茎柔鱼(Dosidicus gigas)为重要的大洋性经济头足类,二者在东太平洋赤道海域均有分布。研究以同一航次捕获的两种头足类为研究对象,结合传统胃含物分析和DNA条形码技术对二者食物组成及其差异开展研究,以分析同域近缘头足类间的摄食习性及差异。结果表明,鸢乌贼和茎柔鱼均以鱼类、头足类和甲壳类为主要食物来源,ANOVA显示,两者在Shannon多样性指数和饵料生物头足类和鱼类N%上均存在显著差异, SIMPER分析进一步表明,种间胃含物组成差异最主要体现在鱼类的种类组成和个数百分比上。研究结论直观反映了同域近缘头足类物种食物特化的现象,为后续探究头足类近缘种共存机制提供了数据支持。     

Feeding ecology of Japanese Spanish mackerel(Scomberomorus niphonius) along the eastern coastal waters of China

Feeding activities provide necessary nutrition and energy to support the reproduction and development of fish populations. The feeding ecology and dietary plasticity of fish are important factors determining their recruitment and population dynamics. As a top predator, Japanese Spanish mackerel(Scomberomorus niphonius) supports one of the most valuable fisheries in China. In this study, the feeding ecology and diet composition of Japanese Spanish mackerel spawning groups were analysed based on samples collected from six spawning grounds along the eastern coastal waters of China during spring(March to May) in 2016 and 2017. Both stomach contents and stable isotope analysis were conducted. Stomach content analysis showed that spawning groups of Japanese Spanish mackerel mainly fed on fish, consuming more than 40 different prey species. Diets were significantly different among sampling locations. The most important prey species were Stolephorus in Fuzhou, Japanese anchovy Engraulis japonicus in Xiangshan, Euphausia pacifica in Lüsi, sand lance Ammodytes personatus in Qingdao and Weihai, and Leptochela gracilis in Laizhou Bay. Stable isotope analysis showed that the trophic level of Japanese Spanish mackerel was relatively high and generally increased with latitude from south to north. In the 1980 s, the diet of Japanese Spanish mackerel was dominated solely by Japanese anchovies in the eastern coastal waters of China. The results in the present study showed that the importance of Japanese anchovies declined considerably, and this fish was not the most dominant diet in most of the investigated waters. Both the spatial variations in diet composition and changes in the dominant diet over the long term indicated the high adaptability of Japanese Spanish mackerel to the environment. Combining the results of stomach analysis and stable isotope analysis from different tissues provided more comprehensive and accurate dietary information on Japanese Spanish mackerel. The study provides essential information about the feeding ecology of Japanese Spanish mackerel and will benefit the management of its populations in the future.     

福州沿海龟足的食性研究

龟足（Capitulum mitella Linnaeus）的食物组成可分为4类,动物性食物、植物性食物、有机碎屑和无机颗粒。动物性食物主要以桡足类为主,植物性食物主要以硅藻类为主,有机碎屑在龟足的食物组成中占据重要地位。龟足食物的食物多样性指数在夏季最高,冬季最低。小规格龟足主要摄食植物性食物和有机碎屑,未见摄食动物...