Piscivorous fishes diet dominated by the Asian cyprinid invader,topmouth gudgeon (<Emphasis Type="Italic">Pseudorasbora parva</Emphasis>)

Predation on the non-native cyprinid, Pseudorasbora parva, was reported during an annual study in a small connecting canal about 40 km south of Brno, Czech Republic. Two cyprinid fish species (Pseudorasbora parva, Rutilus rutilus) were identified in the diet of 23 piscivores belonging to three native fishes (Perca fluviatilis, Sander lucioperca, Esox lucius). The relative abundance of prey fishes changed seasonally and was dominated by the topmouth gudgeon in spring. Thereafter roach incidence continuously increased. In contrast, topmouth gudgeon was found to be a more sized-available prey and was the most dominant prey species in the diet of all piscivorous fishes during the whole season. Strong piscivory towards this alien might be beneficial for its eradication or control to support ecological integrity in natural and modified seminatural habitats.     

Clinostomum complanatum (Trematoda: Clinostomatidae) in five new fish hosts in Japan.

Metacercariae of Clinostomum complanatum were found in six species of natural freshwater fishes collected at Koyama Pond in Tottori City of Tottori Prefecture, Japan. Five of these fish species are reported here as new records for second intermediate hosts of C. complanatum in Japan: the silver crucian carp (Carassius gibelio langsdorfi), the deepbodied crucian carp (Carassius cuvieri), the carp (Cyprinus carpio), the topmouth gudgeon (Pseudorasbora parva) and the rose bitterling (Rhodeus ocelatus).     

An experimental study of body size and food size relations in crucian carp,Carassius carassius

Synopsis In dense, single-species assemblages of crucian carp, competition is intense and results in populations of stunted fish. To explore mechanisms underlying this competition, we measured handling times, return rates, and prey choice for five sizes of crucian carp feeding on six sizes of a standardized food. Handling times increased with prey size and decreased with fish size. Return rates (dry mass ingested per unit handling time) increased dramatically with fish size, and generally decreased with increasing prey size, especially for small fish. Patterns of return rates among size-classes suggested that one or more size-related shifts in feeding efficiency exist for crucian carp; combined with physiological stresses related to winter anoxia, the inability of fish to make these shifts may contribute to size structures observed in high-density populations. Comparisons of relations among fish size, prey size, and return rates for crucian carp and bluegill, Lepomis macrochirus, suggest that similar intraspecific competitive relations exist between generalist species with size-structured populations. Despite differences in return rates among prey sizes, the extent of food selectivity based on prey size exhibited by crucian carp in two types of choice trials was less than predicted. Crucian carp commonly take in several items before mechanically processing food with their pharyngeal apparatus; this multiple prey processing may contribute to disparities between observed choice patterns and those predicted based on return rates for single prey.     

Predation risk and feeding patterns of crucian carp

As part of an experimental study of the direct and indirect effects of piscivory on prey fish, the diets of crucian carp Carassius carassius were compared across sections of a divided pond; two sections were stocked with crucian carp alone and two with crucian carp plus perch Perca fluviatilis . Analysis of crucian gut contents indicated that the composition of invertebrate prey did not differ in the presence v . absence of perch. However, crucians, particularly small individuals (<10cm) that were most vulnerable to predation, displayed a lower intake of invertebrate prey in sections with perch. Although diet composition differed between crucians caught in inshore v. offshore habitats (with habitat use being related to crucian size and the presence or absence of perch), no clear pattern existed between habitat and total food intake. Overall, the major effects of predators on the diet of crucian carp appeared to be caused by increased ecological density (resulting from confinement of small crucians inshore) and reduced activity levels, rather than simple shifts to safer habitats.     

Ontogenetic shift in dietary preference and low dietary overlap in rohu (<Emphasis Type="Italic">Labeo rohita</Emphasis>) and common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) in semi-intensive polyculture ponds

In order to investigate ontogenetic changes in diet and diet overlap between rohu (Labeo rohita) and common carp (Cyprinus carpio) in polyculture ponds, food preferences of different size classes of these fishes were quantified. Rohu diet consisted of both phytoplankton and zooplankton, and there was a distinct ontogenetic shift in the relative importance of these food items. Zooplankton was the dominant food for rohu up to 20.6 cm total length (TL) and then gradually decreased in importance as fish grew. Phytoplankton was initially a minor component of rohu diet but gradually increased in importance and became the dominant food for rohu at 24.2 cm TL. Phytoplankton biovolume in rohu guts was positively correlated with fish size (TL). Chesson’s α indicated that rohu of all sizes preferentially selected Cladocera and avoided Cyanophyceae and Euglenophyceae. Young rohu initially preferred Rotifera and Copepoda but gradually switched to Bacillariophyceae and Chlorophyceae. Common carp diet consisted of phytoplankton, zooplankton, and benthic macroinvertebrates, but was dominated by benthic macroinvertebrates (63–92% of total diet). As common carp grew, the proportion of zooplankton ingested decreased and the proportion of benthic macroinvertebrates increased. Benthic macroinvertebrate biovolume in common carp guts was positively correlated with fish size. Common carp of up to 15.4 cm TL preferentially selected zooplankton, but common carp larger than 18.9 cm TL avoided this food item. Common carp of all sizes avoided phytoplankton. A low dietary overlap was found between rohu and common carp (Schoener overlap index: 0.08–0.35), probably due to ingestion of smaller quantities of zooplankton by the latter. Dietary overlap also decreased with increasing rohu and common carp size because of divergent ontogenetic shifts in dietary preferences of the two species.     

Diet spectrum of great cormorants (<Emphasis Type="Italic">Phalacrocorax carbo sinensis</Emphasis> L.) at the Donji Miholjac carp fishponds in eastern Croatia

This paper reports the results of a diet analysis from the digestive tracts of 203 great cormorants shot at the Donji Miholjac fishponds in eastern Croatia, in the period 2000–2002. Eight fish species were determined. The dominant species was common carp (Cyprinus carpio) with a relative frequency of 73.4%, followed by grass carp (Ctenopharingodon idella) (11.6%), bighead carp (Aristichthys nobilis) (7.2%), pikeperch (Sander lucioperca) (2.0%), wels catfish (Silurus glanis) (1.7%), pike (Esox lucius) (1.5%), topmouth gudgeon (Pseudorasbora parva) (1.5%) and Prussian carp (Carassius auratus gibelio) (1.1%). The diet spectrum of the great cormorants from the Donji Miholjac fishponds was in accordance with the structure of the fish population in the fishponds. The average stomach weight per bird was 244 g. When birds shot with an empty stomach were excluded, the average stomach weight increased to 286 g. The length of consumed fish ranged from 40–335 mm, with 47% of the fish belonging to the length category 100–149 mm. The study revealed no significant relationship between the weight of the consumed fish and the body weight of male and female cormorants.     

不同捕食者暴露对鲫幼鱼行为、运动和形态特征的影响

自然界中鱼类的捕食者种类繁多,为验证猎物鱼针对不同捕食者是否会做出相异的反捕食策略选择,选取鲫（Carassius auratus）幼鱼为猎物鱼,乌鳢（Channa argus）和胡子鲶（Clarias fuscus）为捕食者,将鲫幼鱼分别暴露于空白（对照）、乌鳢、胡子鲶和双捕食者（同时存在乌鳢和胡子鲶）环境中持续2个月,随后考查不同组鲫幼鱼的生长、行为特征、形态和运动能力等指标之间的差异。结果表明：经过2个月的捕食胁迫处理,鲫幼鱼的自发运动、隐蔽场所利用率和勇敢性等行为指标在4个组之间均未表现出显著性差异。相比对照组,乌鳢、胡子鲶和双捕食者暴露组鲫幼鱼的快速启动反应时滞显著缩短（P<0.05）;但所有处理组中仅乌鳢暴露组鲫幼鱼的快速启动120ms移动距离（S_120ms）和体高（BD）显著高于对照组（P<0.05）。另外鲫幼鱼的临界游泳速度（U_crit）和活跃代谢率（M_O2active）在各组之间也未表现出显著差异。乌鳢暴露组鲫幼鱼快速启动能力的提升可能与形态上体高的提高有关;另外相比临界游泳能力,快速启动能力可能在鱼类逃避捕食者过程中更为关键;鲫幼鱼表现出对乌鳢的反应最为明显,可能与乌鳢口裂较大,给鲫幼鱼带来的威胁更大有关。整体而言,应对捕食胁迫时,鲫幼鱼仅表现出形态和快速启动能力的反捕食响应,其行为特征的保守性可能是对生长作出的妥协,这对于鱼类适应生境中长期存在的捕食胁迫十分关键。     

Diet of the western carp gudgeon (Hypseleotris klunzingeri Ogilby) in an Australian floodplain lake: the role of water level stability

To examine temporal variation in diet, two size classes of western carp gudgeon Hypseleotris klunzingeri were collected from macrophyte habitats in Dugays 2 billabong, a floodplain lake on the River Murray, Victoria, Australia, for 1 year. Fish were collected bimonthly during the day and at night between October 1995 and September 1996. Western carp gudgeon consumed a range of prey, including caddisflies, odonates, shrimps and detritus. The bulk of their diet volume, however, consisted of chironomids and zooplankton. The diets of small and large western carp gudgeon were similar and did not change from day to night. There was, however, high variability across sampling trips in fish diets, both at the community level and among selected prey groups, particularly chironomids, zooplankton and detritus. Community analysis revealed that diets of fish collected from the billabong following stable antecedent water levels were similar and showed little variation, while those collected following fluctuating antecedent water levels showed much more variation. These patterns were mirrored in the volumes of individual diet components.     

昆承湖优势种鱼类时空-营养生态位

为了解昆承湖优势种鱼类资源利用情况,首先利用生态位方法计算了时间、空间及营养三个资源维度的生态位宽度及重叠值,然后根据时空-营养生态位宽度值将优势种鱼类划分为广位种、中位种和窄位种,最后讨论了生态位宽度及重叠的可能原因。结果显示：刀鲚Coilia nasus、蒙古鲌Chanodichthys mongolicus、似鱎Toxabramis swinhonis、似鳊Pseudobrama simoni、鳙Hypophthalmichthys nobilis、鲢Hypophthalmichthys molitrix、花鱼骨Hemibarbus maculatus、似刺鳊鮈Paracanthobrama guichenoti、大鳍鱊Acheilognathus macropterus和鲫Carassius auratus为优势种。在时间维度：鲢的生态位宽度最大,似鳊的最小;生态位重叠具有显著意义的有24对,占总的53.33%。在空间维度,似刺鳊鮈最大,鲢最小;生态位重叠具有显著意义的有36对,占总的80%。在营养维度,最大的为鲫,最小的为花鱼骨;生态位重叠具有显著意义的有8对,占17.78%...     

Molecular characterization of trypsinogens and development of trypsinogen gene expression and tryptic activities in grass carp (Ctenopharyngodon idellus) and topmouth culter (Culter alburnus)

This study examined the gene structures and expression of trypsinogens, as well as the trypsin activities of the grass carp Ctenopharyngodon idellus (herbivorous) and the topmouth culter Culter alburnus (carnivorous), which are commercially important freshwater species of the family Cyprinidae in China. Isolated full-length trypsinogen cDNA clones were 869 bp and 857 bp. The deduced amino acid sequences were 242 aa and 247 aa long, both containing the highly conserved residues essential for serine protease catalytic and conformational maintenance. The results from isoelectric and phylogenetic analyses suggest that grass carp trypsinogen is grouped with teleost trypsinogen group I, while topmouth culter trypsinogen is grouped with group II. The expression pattern of trypsinogen mRNA was similar between these two species, appearing 2 days post-hatching (dph) and reaching peaks at 11 and 23 dph. The trypsin-specific activities in both species were detected 2 dph and reached the major peaks at 8 dph, however the minor peaks were observed at 20 dph in the grass carp and 17 dph in the topmouth culter. The trypsin-specific activity was significantly higher in the grass carp than in the topmouth culter, which may be attributed to the nature of their different nutritional habits.     

Determination of genetic diversity of wild and cultured topmouth culter (Culter alburnus) inhabiting China using mitochondrial DNA and microsatellites

The topmouth culter (Culter alburnus) is one of the most commercially important freshwater fish species inhabiting China. However, very limited information is available regarding its genetic diversity and population structure, thus hindering the effective management of this fish stock. Understanding the genetic diversity of wild and cultured topmouth culter populations is highly relevant for successful hatchery management. This study evaluated the genetic diversity and structure of five wild and two cultured populations of topmouth culter in China by using microsatellites and mitochondrial DNA. The genetic diversity of wild populations was found to be lower than that of cultured populations. This finding indicates that wild topmouth culter resources should be protected to prevent further degeneration and extinction. Moreover, it demonstrated that cultured populations have greater breeding potential than wild ones. Subdivisions among wild populations were observed, which should be considered as different units for conservation and hatchery management.     

Diet composition of starry smooth-hound Mustelus asterias and methodological considerations for assessing the trophic level of predatory fish

The stomach contents of 640 starry smooth-hound Mustelus asterias from the north-east Atlantic were examined. The diet was dominated by crustaceans (98.8% percentage of index of relative importance, %IRI), with the two main prey species being hermit crab Pagurus bernhardus (34% IRI) and flying crab Liocarcinus holsatus (15% IRI). Ontogenetic dietary preferences showed that smaller individuals [20–69 cm total length (L_T) n = 283] had a significantly lower diversity of prey than larger individuals (70–124 cm L_T, n = 348); however, 18 prey species were found exclusively in smaller individuals and eight prey taxa were found exclusively in larger individuals. Larger commercially important brachyurans such as edible crab Cancer pagurus and velvet swimming crab Necora puber were more prevalent in the diet of larger individuals. Specimens from the North Sea ecoregion had a lower diversity of prey types for a given sample size than fish from the Celtic Seas ecoregion. Whilst cumulative prey curves did not reach an asymptote, this was primarily due to the high taxonomic resolution utilized and 95% of the diet was described by just seven crustacean taxa. The trophic level (TL) was calculated as 4.34 when species-level prey categories were used. This fine-scale taxonomic resolution resulted in a TL estimate close to a whole level above that estimated using wider taxonomic groupings. This large bias has important methodological implications for TL studies based on categorized prey data, particularly those of predatory fish.     

Consequences of the size structure of fish populations for their effects on a generalist avian predator

Size-structured interspecific interactions can shift between predation and competition, depending on ontogenetic changes in size relationships. I examined the effects of common carp (Cyprinus carpio), an omnivorous fish, on the reproductive success of the red-necked grebe (Podiceps grisegena), an avian gape-limited predator, along a fish size gradient created by stocking distinct age-cohorts in seminatural ponds. Young-of-the-year (0+) carp were an essential food source for young grebes. Only adult birds were able to consume 1-year-old (1+) fish, while 2-year-old (2+) fish attained a size refuge from grebes. Amphibian larvae were the principal alternative prey to fish, followed by macroinvertebrates, but the abundance of both dramatically decreased along the carp size gradient. Fledging success was 2.8 times greater in ponds with 0+ versus 1+ carp; in ponds with 1+ carp, chicks received on average 2.6–3 times less prey biomass from their parents, and over 1/3 of broods suffered total failure. Breeding birds avoided settling on 2+ ponds. These results show that changes in prey fish size structure can account for shifts from positive trophic effects on the avian predator to a negative impact on the predator’s alternative resources. However, competition did not fully explain the decrease in grebe food resources in the presence of large fish, as carp and grebes overlapped little in diet. In experimental cages, 1+ carp totally eliminated young larvae of amphibians palatable to fish. In field conditions, breeding adults of palatable taxa avoided ponds with 1+ and older carp. Non-trophic interactions such as habitat selection by amphibians or macroinvertebrates to avoid large fish may provide an indirect mechanism strengthening the adverse bottom-up effects of fish on birds.     

The distribution of an invasive fish species is highly affected by the presence of native fish species: evidence based on species distribution modelling

Topmouth gudgeon (Pseudorasbora parva) is one of the most invasive aquatic fish species in Europe and causes adverse effects to ecosystem structure and functioning. Knowledge and understanding of the species’ interactions with the environment and with native fish are important to stop and prevent the further spread of the species. Creating species distribution models is a useful technique to determine which factors influence the occurrence and abundance of a species. We applied three different modelling techniques: general additive models, random forests and fuzzy habitat suitability modelling (FHSM) to assess the habitat suitability of topmouth gudgeon. The former two techniques indicated that the abundance of native fish (i.e. biotic variables) was more important than environmental variables when determining the abundance of topmouth gudgeon in Flanders (Belgium). Bitterling (Rhodeus amarus), stone loach (Barbatula barbatula), three-spined stickleback (Gasterosteus aculeatus) and predator abundance were selected as the most important biotic variables and implemented in the FHSM to investigate species interactions. Depending on the preferred food source and spawning behaviour, either coexistence or interspecific competition can occur with bitterling, stone loach and three-spined stickleback. In contrast, the presence of predators clearly had a top down effect on topmouth gudgeon abundance. These findings could be applied as a biological control measure and implemented in conservation strategies in order to reduce the abundance of earlier established populations of topmouth gudgeon.     

Chromosome-level genome assembly and whole-genome resequencing of topmouth culter (Culter alburnus) provide insights into the intraspecific variation of its semi-buoyant and adhesive eggs

Topmouth culter (Culter alburnus) is an ecologically and economically important species belonging to the subfamily Culterinae that is native to and widespread in East Asia. Intraspecific variation of semi-buoyant and adhesive eggs in topmouth culter provides an ideal opportunity to investigate the genetic mechanisms of spawning habits underlying the adaptive radiation of cyprinids in East Asia. In this study, we present a chromosome-level genome assembly of topmouth culter and re-sequenced 158 individuals from six locations in China covering three geographical groups and two egg type variations. The topmouth culter genome size was 1.05 Gb, with a contig N50 length of 17.8 Mb and anchored onto 24 chromosomes. Phylogenetic analysis showed that the divergence time of the Culterinae was coinciding with the time of initiation of the Asian monsoon intensification. Gene family evolutionary analysis indicated that the expanded gene families in topmouth culter were associated with dietary adaptation. Population-level genetic analysis indicated clear differentiation among the six populations, which were clustered into three distinct clusters, consistent with their geographical divergence. The historical effective population size of topmouth culter correlated with the Tibetan Plateau uplifting according to the demographic history reconstruction. A selective sweep analysis between adhesive and semi-buoyant egg populations revealed the genes associated with the hydration and adhesiveness of eggs, indicating divergent selection towards different hydrological environments. This study offers a high-resolution genetic resource for further studies on evolutionary adaptation, genetic breeding and conservation of topmouth culter, providing insights into the molecular mechanisms for egg type variation of East Asian cyprinids.     

鲜活饵料和人工配合饲料对鳜肌肉营养成分和质构特性的影响

研究以饲喂鲜活饵料为对照组,比较分析人工饲料对鳜(Siniperca chuatsi)常规营养成分、氨基酸组成及营养价值评价、脂肪酸组成和肌肉质构特性的影响。实验结果显示,摄食人工饲料组鳜肌肉蛋白质水平与鲜活饵料组无显著性差异(P>0.05),粗脂肪含量显著较高(P<0.05)。在两种饲喂模式下鳜肌肉中氨基酸评分(AAS)、必需氨基酸指数(EAAI)、化学评分(CS)和F值均无显著差异(P>0.05),但第一限制性氨基酸均为蛋氨酸+半胱氨酸(Met+Cys),该结果可为鳜人工饲料配方优化提供指导。人工饲料组鳜肌肉中饱和脂肪酸(SFA)、单不饱和脂肪酸(MUFA)和多不饱和脂肪酸(PUFA)含量均极显著高(P<0.01),其中C20﹕5(EPA)和C22﹕6(DHA)含量极显著高于鲜活饵料组,表明人工饲料可通过营养素的均衡配比以提供更优质的脂肪酸营养。人工饲料组鳜肌肉硬度、咀嚼性、胶黏性及回复性均极显著高于鲜活饵料组(P<0.01),而黏性极显著低于鲜活饵料组(P<0.01),表明人工饲料饲喂提升了鳜的肌肉质构特性。综上所述,相比于鲜活饵料组,人工饲料...     

Food and Feeding Habits of Flounder <Emphasis Type="Italic">Paralichthys Orbignyanus</Emphasis> (Jenyns, 1842) in Bahía Blanca Estuary,Argentina

Specimens of flounder Paralichthys orbignyanus (Jenyns, 1842) were collected in Bahía Blanca estuary between February 1997 and January 1998, and their feeding habits were examined in relation to season and size class. The stomach contents of 823 specimens, ranging from 70 to 875 mm total length, were analysed. Their diet included organisms from 17 taxa. The highest vacuity index values were found during autumn and winter. The stomach fullness index indicated that flounders increased their feeding activity between October and March, reaching a highest point in February and decreasing after February. Fish were the primary prey item in frequency, number and weight, followed by crustaceans, such as shrimps and crabs. A seasonal and size class variation was detected in the diet. During summer all-size flounders consumed mainly fish. In autumn, for all-size classes the main food were fish and crustaceans even though fish were dominant in terms of biomass. In spring, crustaceans (mysids Arthromysis magellanica (Cunningham), shrimps Artemesia longinaris Bate, and prawns Pleoticus muelleri (Bate)) were the dominant prey in terms of number and biomass for flounders ≤ 450 mm TL. Size classes larger than 451 mm TL fed on crustaceans and fish though the most important prey item in terms of biomass was fish. In Bahía Blanca estuary,P. orbignyanus evidenced mainly an ichthyophagou – carcinophagous diet. The results collected from the present study lead to conclude that P. orbignyanus shows, in this region, a clear preference for fish.     

Head morphology and piscivory of European eels,Anguilla anguilla,predict their probability of infection by the invasive parasitic nematode Anguillicoloides crassus

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DNA metabarcoding for dietary analysis of Holland's carp (Spinibarbus hollandi) to evaluate the threat to native fishes in Taiwan

DNA metabarcoding analysis for gut contents has been shown to compensate the disadvantage of traditionally morphological identification and offer higher resolution of prey items in an efficient way. Holland's carp (Spinibarbus hollandi) is a freshwater fish native to southern and eastern Taiwan. In the past two decades, this species has been introduced as a sport fish into the river basins of northern and western Taiwan. The large body size and active predation make it a potential threat for native fishes, but which native species are preyed by Holland's carp remains unknown. In this study, the diet from the gut contents of Holland's carp from the Zhonggang River, an invaded basin, was examined using DNA metabarcoding from 51 individuals and by morphological examinations on 140 samples. Detritus of plants were found in 83.6% samples (117 individuals). Twenty fish species of seven families were identified by DNA metabarcoding, including species of all water layers. Taiwan torrent carp (Acrossocheilus paradoxus) and Rhinogobius spp. are the most common prey items. Based on the results of this study, Holland's carp is considered an opportunistic omnivore because of its diverse diet items, which is an important trait for successful invasive fish species. The population decline of Opsariichthys pachycephalus may not result from the invasion of Holland's carps. Nonetheless, the time lag between successful invasion and the samplings of this study may be a concern because the population size of O. pachycephalus may have declined and become difficult to prey. The Holland's carps consumed the least species in winter; nonetheless, the occurrence frequencies of preys among seasons were not significantly different probably because of limited temperature fluctuation. The smallest Holland's carps consumed the least prey species compared to other size categories, similar to the relationship of prey species number to size of invasive largemouth bass (Micropterus salmoides).