Life‐history traits of the long‐nosed skate Dipturus oxyrinchus

This work investigates life‐history traits of the long‐nosed skate Dipturus oxyrinchus, which is a common by‐catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4–117·5 cm total length, L_T) attained larger sizes than males (14·5–99·5 cm L_T). To evaluate age and growth, a sub‐sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length‐at‐age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L_∞ mean ± s.e. : 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm L_T) and 15 years (96·0 cm L_T), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado‐somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.     

Diet and feeding strategy of blackmouth catshark Galeus melastomus

Diet and feeding strategy of the blackmouth catshark Galeus melastomus in the deep waters of the eastern Ionian Sea were investigated. Sampling was carried out using experimental bottom longline fishing at depths ranging from 300 to 855 m in summer and autumn 2010. Diet variability with fish size, season, area, sex and depth zone was tested and only season was found to significantly affect the diet of the species. Of the 870 stomachs examined, only 1·4% were empty. Cumulative prey curves showed that the sample sizes were adequate to describe the main prey items of the diet for both seasons. Prey identified belonged primarily to three major groups: fishes, cephalopods and dendrobranchiatan and caridean shrimps. In autumn, the above three major groups were found as principal prey, whereas in summer cephalopods followed by fishes were the principal prey and shrimps were found as secondary prey. SIMPER analysis indicated high dissimilarity between seasons and highlighted that Sepiolidae, Myctophidae, fishes, cephalopods, shrimps and other crustaceans contributed to seasonal differences in the diet of G. melastomus. The prey diversity index was higher in autumn than in summer. A high dietary overlap was observed between the two seasons. Galeus melastomus behaved as an opportunistic predator with a variety of unimportant prey in its diet. Feeding strategy indicated that G. melastomus holds a generalist niche with a considerable specialization at the individual level. This strategy seems to be an adaptation to a food‐scarce environment, as typified in deep‐water habitats.     

Effects of intrinsic and extrinsic factors on the diet of Bathyraja macloviana,a benthophagous skate

The effects of intrinsic (sex, maturity stage and body size) and extrinsic (depth and region) factors on the diet of Bathyraja macloviana, in the south‐west Atlantic Ocean, were evaluated using a multiple‐hypothesis modelling approach. Bathyraja macloviana fed mainly on polychaetes followed by amphipods, isopods and decapods. Effects of intrinsic and extrinsic factors on diet composition of this species were found. The consumption of polychaetes had a humped relationship with total length (L_T), and isopods and decapods increased with increasing L_T. Immature individuals preyed on amphipods more heavily than mature individuals. Furthermore, region and depth had an important effect on the consumption of isopods, decapods and amphipods. Such ontogenetic changes and spatial patterns may provide insights into understanding the regulatory mechanisms of marine communities.     

Oviducal gland microstructure of Raja miraletus and Dipturus oxyrinchus (Elasmobranchii,Rajidae)

We studied the morphology and histology of the oviducal gland (OG) in the brown ray (Raja miraletus) and the long‐nosed skate (Dipturus oxyrinchus) to understand its functional role in the reproductive strategy of these species. The external morphology of the gland was similar in both species, with lateral extensions like those found in other members of the Rajidae. Microscopic analysis showed a similar internal organization in both species. Immature and developing glands did not react to histochemical techniques. On reaching maturity, the OG had the largest width due to an increase in the production of secretory materials. In both species, the club zone of the gland showed a strong reaction to Periodic acid‐Schiff (PAS) and alcian blue (AB) stains, indicating production of neutral and sulfated acid mucins. The secretory material produced by the papillary zone varied greatly between the two species. Both displayed tubular glands similar to those observed in the club zone, but in D. oxyrinchus the region near the lumen was intensely PAS+, whereas the last row of tubules of the brown ray stained intensely for a mixture of neutral and sulfated mucins. The baffle zone was the most conspicuous and extensive segment of all OGs, and it did not react to PAS/AB. The terminal zone, which is responsible for production of hair filaments, differed between the two species in terms of composition and organization of serous and mucous glands. This difference probably is related to the different substrates in which they release the egg capsules. Individual sperm detected in the brown ray baffle lamellae could be the result of a recent mating, whereas their presence in the deep recesses of the baffle and in the terminal zone of the long‐nosed skate might indicate sperm storage. J. Morphol. 276:1392–1403, 2015. © 2015 Wiley Periodicals, Inc.     

Age,growth, reproduction and feed of longnosed skate,Dipturus oxyrinchus (Linnaeus, 1758) in Saros Bay,the north Aegean Sea

The age, growth, reproduction, and feeding of longnosed skate (Dipturus oxyrinchus) were studied using 179 specimens from the Saros Bay (North Aegean Sea) between March 2005 and December 2007. Composition was 49.7% females and 50.3% males. Total length of females ranged from 14.9 to 100 cm (disc width, 9.8–65 cm), and of males from 15.2 to 86.5 cm (disc width, 10–57.5 cm). Total length‐weight and disc width‐weight relationships are described by the equations W = 0.0008*TL^3.35 and W = 0.0043*DW^3.29, respectively. The age data, derived from vertebrae readings, were used to estimate the growth parameters of the von Bertalanffy equation: L_∞ = 256.46 cm, K = 0.04 year^?1, t₀ = ?1.17year. The maximum age was 9 years. Males matured at 64–65 cm (disc width, 43.5 cm) and females at 82–83 cm TL (disc width, 53 cm). The stomach contained mainly Parapenaus longirostris, IRI: 93.47%.     

Ontogenetic shift and feeding habits of the European hake (Merluccius merluccius L., 1758) in Central and Southern Tyrrhenian Sea (Western Mediterranean Sea): A comparison between past and present data

The present paper aims to investigate the ecological role of Merluccius merluccius, Linnaeus, 1758, in southern and central Tyrrhenian Sea (GSA 10, Resolution GFCM/33/2009/2 General Fisheries Commission for the Mediterranean), analyzing ontogenetic diet shifts, geographical variations on prey composition, and feeding habits. A total of 734 hake specimens ranging in size between 6 cm and 73 cm (Total Length, TL) were collected in 2018. In order to evaluate ontogenetic shifts in prey composition, samples were divided into five size classes and for each class the quantitative feeding indices have been calculated. The statistical analysis, based on index of relative importance percentage (%IRI), resulted in three trophic groups. The most abundant prey found in the immature hake specimens (size class I) were the Euphausiids, Stylocheiron longicorne and Mysidacea, while for samples with a total length over 10.5 cm were crustaceans and fish. Engraulis encrasicolus was the most abundant fish prey identified, followed by Boops boops and Myctophids. The high presence of Euphausiids, Mysids, Myctophidae, and Sternoptychidae in classes I, II, II, and IV (6–23 cm) showed the relevant role of mesopelagic fauna in hake diets, with an essential organic matter and energy flow from the mesopelagic to the epipelagic environment. Additionally, decapod crustaceans were found in the stomach contents of hakes belonging to class V (with size over 36 cm TL), which is notable considering that our study area includes an important decapod crustacean fishing area.     

Diet composition and diel feeding behaviour of the banded guitarfish Zapteryx xyster along the Pacific coast of Costa Rica,Central America

The diet and diel feeding behaviour of the banded guitarfish Zapteryx xyster were examined along the Pacific coast of Costa Rica. A sample of 235 stomachs was collected between March 2010 and December 2011 as part of an ongoing shrimp‐trawl by‐catch monitoring programme. Samples from multiple day and night periods allowed testing the hypothesis that Z. xyster is more active at night, thus increasing the amount of food intake during night‐time. Overall, shrimps (52·3% prey‐specific index of relative importance, P_SIRIi) and teleosts (27·2% P_SIRIi) were the most important prey categories. Juveniles fed primarily on smaller shrimps (Solenocera spp.), while adults shifted to larger prey. The amount of food consumed (as % of bodymass) by juvenile and adult Z. xyster increased significantly between 0400 and 1200 hours, while the proportion of empty stomachs decreased during the same time interval. These findings contradict the hypothesis that Z. xyster is more active and feeds at night. The study also revealed that Z. xyster, particularly juveniles, forage on several shrimp species and overlap spatially with the Costa Rican bottom‐trawl fisheries. This has important management and conservation implications as Z. xyster may be experiencing high by‐catch rates, and because of their life history is presumed to be vulnerable to intense levels of exploitation.     

The effect of season and sex on trophic levels of marine fishes

The diet of 76 species from Greek waters (north Aegean Sea) was examined for the determination of trophic level by species, season and sex. Trophic level estimates were derived from TrophLab software based on collected stomach content data. Such estimates are important for the implementation of marine management indicators, such as the marine trophic index. The mean ± s . e . difference between minimum and maximum trophic levels among seasons within species was 0·45 ± 0·04 and for 28·8% of the species this difference was larger than the corresponding s . e . of the trophic level of the pairs of seasons examined. Depending on which seasonal trophic level ( i.e. autumn, winter, spring or summer) was used for assigning a species into a functional trophic group 33·9 and 8·5% of the species changed one and more than one group, respectively. Finally, the mean ± s . e . absolute difference of male and female trophic level was 0·18 ± 0·02, and only for 6·6% of the species this difference was larger than the s . e . of trophic level for each sex separately. Depending on the trophic level used for assigning the species into a functional group ( i.e. male v. female), only 6·6 and 3·2% of the species changed one and more than one groups, respectively. It is therefore clear that all measures used in this study indicated that the effect of season on trophic level estimates was higher, compared to that of sex, the latter being of minor importance to feeding studies. Hence, future effort on stomach content analysis should focus on the examination of seasonal, small to moderate sample sizes.     

Diet and feeding strategy of thornback ray Raja clavata

The diet and feeding strategy of thornback ray Raja clavata, from the eastern-central Adriatic Sea, were investigated. Stomach contents of 428 specimens, total length (L(T) ) of 14·0-75·1 cm, were collected from commercial bottom trawls. The prey items identified in the stomachs belong to eight major groups: Cephalopoda, Polychaeta, Stomatopoda, Decapoda (Natantia and Reptantia), Mysidacea, Isopoda, Amphipoda and Teleostei. Decapods were the most important prey (index of relative important, %I(RI) ,= 72·8) followed by teleosts (%I(RI) = 20·4), whereas other prey groups were only occasionally ingested. Small-sized individuals (<25 cm L(T) ) fed primarily on small crustaceans (mysids and amphipods), whereas large-sized specimens consumed larger prey, such as decapods, cephalopods and teleosts. Diet composition showed little seasonal variation; decapods were the most important prey in all seasons. There was high dietary similarity between sampling locations. The percentage of empty stomachs did not differ significantly among size classes and seasons. In terms of composition by species, the diet of R. clavata was characterized by a variety of rare or unimportant prey. As a result, R. clavata could be considered a generalist predator.     

Feeding habits and trophic levels of Mediterranean fish

The estimation of fractional trophic levels(TROPHs) is essential for the management offisheries resources as well as for quantifyingthe ecosystem effects of fishing. We gatheredall available information concerning thefeeding habits of 332 fish stocks, belonging to146 species, 59 families and 21 orders,throughout the Mediterranean Sea, and estimatedtheir TROPH values. The latter ranged from 2.0to 4.5 and the following functional trophicgroups were identified: (a) pure herbivores (TROPH = 2.0–2.1, mean = 2.02, SD = 0.03),which were very rare and represented by Siganus luridus, Siganus rivulatus andSarpa salpa, all of which feed on red,brown, green and blue-green algae; (b)omnivores with a preference for vegetablematerial (2.1 < TROPH < 2.9, mean = 2.5,SD = 0.12), but feeding on other prey, such assponges, hydrozoans, anthozoans, polychaetes,ostracods, isopods, amphipods and copepods. This type of omnivore was very rare among thecases reviewed; (c) omnivores with a preferencefor animal material (2.9 < TROPH < 3.7,mean = 3.4, SD = 0.19) feeding on a wide variety ofprey (e.g., algae, foraminifera, brachyurans,balanoids, ascidians, amphipods,appendicularians, annelids, isopods,gastropods, cnidarians, ophiurids, polychaetes,cladocerans, mysids, euphausids, fish larvae,cephalopods). They were the most numerous andwere mainly represented by species of thefamilies Blenniidae, Bothidae, Centracanthidae,Gobiidae, Labridae, Lotidae, Macrouridae,Mullidae, Ophidiidae, Soleidae, Triglidaeand Engraulidae; and (d) carnivores witha preference for large decapods, cephalopodsand fish (3.7 < TROPH < 4.5). They werethe next most abundant group among the casesreviewed. They were mainly represented byspecies of the families Dalatiidae, Lophiidae,Scombridae, Scyliorhinidae, Synodontidae,Torpedinidae, Merlucciidae, Xiphiidae andZeidae. This group was divided into twosubgroups: one exhibiting a preference fordecapods and fish (3.7 < TROPH < 4.0,mean = 3.85, SD = 0.09) and another one exhibitinga preference for fish and cephalopods (4.0 相似文献   

黄海中部高眼鲽的摄食及随体长的变化

对2004年1月-2005年10月在黄海中部采集的622尾高眼鲽样品的胃含物进行分析.结果表明：高眼鲽摄食的食物种类包括11类38种,其中甲壳类和瓣鳃类为优势饵料类群,共占食物相对重要性指数百分比的99%;食物中的优势饵料种类为太平洋磷虾、脊腹褐虾和樱蛤.与20世纪80年代相比,黄海高眼鲽的摄食强度下降,食物组成发生了较大的变化;鱼类不再是优势饵料类群,鳀鱼在食物中所占的比例明显下降.通过聚类分析和列联表检验等方法对高眼鲽摄食随体长的变化进行研究,结果表明：体长在51～370 mm范围内的高眼鲽的摄食强度没有显著的体长变化,但不同体长组摄食的食物种类有一定差异.＜119 mm的主要以磷虾类和底层虾类为食;体长在120～199 mm的除以磷虾类和底层虾类为主要食物外,还摄食相当比例的瓣鳃类和鱼类;＞200 mm的则主要摄食底层虾类和鱼类,磷虾类所占比例减小.     

Temporal variations in the diet of pearly razorfish Xyrichtys novacula (Osteichthyes: Labridae)

The diet of pearly razorfish Xyrichtys novacula, caught monthly along the shores of the Island of Lampedusa, appeared to be mainly composed of crustaceans, followed by colonial ascidians, molluscs and polychaetes. Among prey, sand dwellers and phanerogam‐associated species were recorded. In winter months, the diet was characterized by a small number of prey items, dominated by colonial ascidians, while in spring and summer a wider prey array was recorded. Dietary indices show that X. novacula do not strictly exploit benthic prey but also pelagic organisms, such as copepods. This feeding behaviour reached its peak in March and October, when the abundance of primary consumers was at its highest after phytoplankton blooms. Furthermore, X. novacula caught prey organisms according to their availability and seasonal patterns during their life cycles, irrespective of fish size.     

Trophic interactions among native and introduced fishes in a northern Patagonian oligotrophic lake

In summer the littoral zone of Lake Rivadavia contained almost all the juveniles of the native fish species present in the lake together with juveniles of the introduced salmonid Oncorhynchus mykiss . In particular, a high degree of foraging interaction was found among juveniles of the native species Aplochiton zebra and Percichthys trucha and juveniles O. mykiss. Differences in the juvenile assemblage composition, both in the presence and in the relative proportion of the species were associated with areas with different densities of vegetation. The adults of nearly all species were generalized benthic invertebrate predators. Only adults of A. zebra were absent in the littoral. Juvenile and adult O. mykiss were the only fish that preyed on planktonic organisms. Oncorhynchus mykiss was the only species that performed an ontogenetic diet shift between juveniles and adults, changing main prey categories from benthic to planktonic species.     

Diet composition and feeding ecology of the naked goby Gobiosoma bosc (Gobiidae) from four western Atlantic estuaries

The feeding ecology of the small‐bodied benthic naked goby Gobiosoma bosc, a western Atlantic species that occurs in estuaries and other inshore habitats from Connecticut to Texas U.S.A., was investigated in a total of four estuaries spanning South Carolina, North Carolina, Maryland and New Jersey. Gut content analysis of 391 individuals revealed that G. bosc is a benthic microcarnivore that feeds primarily on polychaetes, gammarid amphipods and harpacticoid copepods. Diet composition varied with body size, tidal creek within an estuary and geographic region. Analyses of gut fullness suggest that G. bosc is a daytime visual predator and that nest and egg guarding during the reproductive season reduce foraging activity in mature males. Additionally, G. bosc infected with adult digenean parasites of the gut foraged more intensely than uninfected individuals, a relationship that was strongest for reproductively mature males. Regionally, significant variation in dietary breadth was documented and may reflect a foraging response to a decrease in prey diversity moving from estuaries of higher salinity and lower latitude to estuaries of lower salinity and higher latitude. These results contribute to an understanding of the life history of G. bosc and the role played by this common species in estuarine food webs.     

基于高通量测序的象山港海域黑鲷(Acanthopagrus schlegelii)食性分析

选取象山港黑鲷个体为研究对象,以18S rDNA为靶标,利用Illumina Miseq高通量测序方法研究黑鲷饵料生物组成特征,分析不同龄组黑鲷的食性异同。通过序列比对,共在黑鲷胃含物中鉴定出41个属中的62种饵料生物,分属9个门,其中节肢动物门（Arthropoda）、绿藻门（Chlorophyta）和软体动物门（Mollusca）是黑鲷饵料生物的优势组成门类。从饵料生物相对丰度和出现频率上分析,石莼（Ulva lactuca）、熊本牡蛎（Crassostrea sikamea）、胸刺水蚤（Centropages hamatus）、日本蟳（Charybdis japonica）、毛蚶（Scapharca subcrenata）和褐菖鲉（Sebastiscus marmoratus）是黑鲷的优势饵料物种,所占饵料生物总相对丰度的比重达60.90%。相似性分析检验（ANOSIM）结果显示：1至4龄黑鲷个体的饵料生物组成不存在显著性差异。与传统食性分析方法相比,高通量测序法在黑鲷饵料生物检测灵敏性上显现了较为明显的优势,保障黑鲷等重要物种的种群稳定对于该海域具有重要的生态和经济意义。     

Seasonal patterns in feeding ecology of three small fishes in the Biandantang Lake, China

Feeding ecology of three small fish species, Hypseleotris swinhonis, Ctenogobius giurinus and Pseudorasbora parva was studied seasonally in the Biandantang Lake, a small, shallow lake in central China. Gut length, adjusted for total body length, was significantly higher in spring than in other seasons for all the three species. Seasonal changes in gut length were not associated with changes in food quality. Weight of fore-gut contents, adjusted for body weight, was significantly higher in winter and spring than in summer and autumn in H. swinhonis and C. giurinus , and significantly higher in autumn than in spring and summer for P. parva. Percentage of empty fore-guts was highest in summer and lowest in spring for H. swinhonis and C. giurinus , and highest in winter and lowest in autumn for P. parva. Diet of the three small fishes showed apparent seasonal changes, and these changes reflected partly the seasonal fluctuations of food resources in environment. Diet breadth was high in winter and low in autumn for H. swinhonis , high in winter and low in spring and summer for C. giurinus , and high in autumn and low in spring for P. parva. Diet overlaps between pairs of species were biologically significant in most cases, except between H. swinhonis and P. parva in summer and autumn and between C. giurinus and P. parva in autumn.