Food habits of fishes in a freshwater reed belt in Lake Kitaura,eastern Japan,in summer

The diets and feeding guild structure of a freshwater reed belt fish assemblage (30 species) were examined in Lake Kitaura, part of the Lake Kasumigaura system, eastern Japan, from June to September in 2009 and 2010. Ontogenetic dietary shifts were recognized in 14 species, including several species (e.g., Cyprinus carpio, Tridentiger brevispinis and Hyporhamphus intermedius) targeted by local fisheries. Juveniles of these species generally fed on zooplankton, later switching to other prey items (e.g., benthic chironomid larvae, gammaridean amphipods, shrimps, juvenile fishes, diatoms and decomposing reeds) with growth. A cluster analysis based on dietary overlaps showed that the reed belt fish assemblage comprised five feeding guilds (plant, zooplankton, benthic invertebrate, terrestrial insect and fish feeders). Of these, zooplankton feeders were the most abundantly represented in terms of species numbers, suggesting that the main food items for the fish assemblage were zooplankton (e.g., cladocerans, and calanoid and cyclopoid copepods). Fish feeders included five species, of which one was an alien species introduced from another region in Japan (Opsariichthys uncirostris) and three were from foreign countries (Micropterus salmoides, Lepomis macrochirus macrochirus and Ictalurus punctatus).     

Temperature,discharge and development shape the larval diets of threatened green sturgeon in a highly managed section of the Sacramento River

Feeding at early fish life stages is a key determinant of survival to recruitment. To understand the environmental and developmental determinants of early life stage feeding in ESA‐threatened green sturgeon (Acipenser medirostris), we performed a diet study in a highly managed section of California's Sacramento River, where temperature and discharge are controlled by dam releases. Utilising field collections from 2012 to 2016, we assessed the impacts of temperature, discharge and morphological development on the composition and number of prey items in larval green sturgeon diets. Results show that there are more empty stomachs at colder temperatures. Higher discharge conditions decreased prey taxon richness and counts, especially the abundance of cyclopoid copepods in diets. Fish smaller than 30 mm had teeth on the oral jaws and showed a strong reliance on zooplankton prey. The developmental loss of teeth in fish greater than 30 mm was associated with decreased zooplankton consumption and increased richness of benthic macroinvertebrates in diets. Our results show that river management through dam releases has the potential to impact the earliest life stage of green sturgeon by reducing the prevalence of favoured zooplankton prey in diets.     

Diet overlap of non‐native alewife with native yellow perch and spottail shiner in nearshore waters of southwestern Lake Michigan, 2000–2007

Abstract – Lake Michigan has experienced many ecological changes as a result of introductions of non‐native species. Arguably the most significant was that of alewife (Alosa pseudoharengus), yet studies on diet overlap with native species are lacking. We analysed diet trends of alewife, spottail shiner (Notropis hudsonius) and yellow perch (Perca flavescens) collected in summer and fall 2000–2007 near Waukegan, IL, in 3–10 m depths. Mean percentage composition by dry weight for 23 prey taxa was used in multivariate analysis to test whether diet differed across species and size classes. We also tested whether zooplankton and benthic invertebrate community composition changed over time. Fish diets were similar over all years but differed seasonally. In summer, diets of large alewife were similar to both small alewife and small yellow perch, with Bosminidae, chironomid larvae and copepods as primary common prey. During fall, alewife and yellow perch size classes exhibited strong intraspecific diet overlap, while there was low diet overlap between species. Primary distinctions between species’ diets in fall were higher consumption of amphipods by yellow perch and dreissenids by spottail shiners compared to alewife, which consumed higher proportions of zooplankton. Overall, high yellow perch diet overlap with alewife during summer and with their larger conspecifics during fall could lead to negative implications for yellow perch growth before the critical overwintering period. Detailed insights into diet overlap and prey availability are critical first steps in understanding competitive interactions between native and non‐native fish that dominate the nearshore community in southwestern Lake Michigan.     

黄海南部不同体长鳀对食物粒级的选择

基于2000年6月和2014年11月黄海南部采集的浮游动物和不同生长阶段鳀(Engraulis japonicus)的胃含物(饵料)组成分析资料,研究鳀的饵料粒级分布与摄食粒级选择性及其与环境生物组成的关系,旨在推进粒级在传统摄食生态分析中的应用。结果显示:黄海南部鳀的饵料种类组成与环境中生物种类组成有关;各体长组中,鳀的饵料粒级多样性与种类多样性分布趋势相似;体长为110 mm左右的鳀的饵料种类多样性和粒级多样性水平最高;鳀的饵料粒级均值随鱼体体长增加而增加;体长约为30 mm和≥70 mm的鳀有明显的饵料粒级转换。根据上述结果,认为在鳀胃含物分析过程中,整合环境中饵料生物的相对组成和粒级大小,可有效评价鱼类对饵料的粒级选择性。     

Prey selectivity in planktivorous juvenile fishes associated with floating objects in the western Mediterranean

Aspects of the feeding ecology of planktivorous juvenile fishes were assessed by comparing stomach content samples from purse seine catches with food environment samples from vertical hauls of a WP-2 mesozooplankton net. Sampling was performed fortnightly over 2 years, around moored experimental floating objects and at open water control stations in oceanic Mediterranean waters. Species composition, abundance and seasonal occurrence of both potential prey (zooplankton) and predators (fish) were studied. Dietary composition was examined for six fish species, and prey selectivity was assessed by means of several selectivity indices: Ivlev's selectivity index, linear food selection index and forage ratio. A comparison of the results showed significant variations among indices, related to both the degree of selection and the relative abundance of the food type in the environment. Most fish caught were pelagic juveniles, and had fed on plankton; however, there was variability in diet composition and prey selectivity among species allowing their separation into generalists and specialists. The pilot fish Naucrates ductor (Linnaeus) was a specialist, preying upon neustonic hyperiid amphipods, whereas the three congeneric species of Trachurus: T. picturatus (Bowdich), T. trachurus (Linnaeus) and T. mediterraneus (Steinachner) fed on copepods and other planktonic crustaceans. The species studied appeared to partition food resources to minimize the overlap in use of a very specific habitat.     

Feeding ecology and habitat of the threespine stickleback, Gasterosteus aculeatus microcephalus, in a remnant population of northwestern Baja California, México

Abstract – The feeding ecology and habitat of the threespine stickleback ( Gasterosteus aculeatus microcephalus Girard, 1854) was studied from November 1996 to May 1997 in a remnant population of northwestern Baja California, México. The analysis of the stomach content of 179 individuals (25 to 56 mm standard length [SL]) showed a diet dominated by cyclopoid copepods (43.8%) and chironomid larvae (39.1%). Diet in relation to size and sex of the fish was dominated by copepods in autumn and winter and by chironomid larvae during spring. Diet overlap (Schoener's index) was significant (≥60%) between fish size-classes in January, March and April and between sexes for most sampling months. The average size of prey consumed was independent of fish mouth size. The feeding strategy of the threespine stickleback shifted from opportunist in winter to specialist in spring.     

Water outflow as a cause of changes in trophic conditions for zooplanktivorous fish in reservoirs

The seasonal changes and vertical distribution of zooplankton, the export of zooplankters by outflow through water management installations, and the feeding of zooplanktivorous fish were studied in two Bulgarian reservoirs. In a bottom-draining reservoir, planktonic crustacea > 1.0 mm were found to be selectively exported as a result of their diurnal vertical migrations. Increases in water outflow for irrigation resulted in a decrease in total zooplankton abundance, as well as changes in zooplankton size and species composition at the beginning of the summer. At the same time, major changes occurred in the feeding patterns of bleak, Alburnus alburnus (L.), and juvenile pikeperch, Stizostedion lucioperca (L.), the principal zooplanktivores in this reservoir. It is easy for bleak to switch to feeding on an alternative food, but a lack of available large prey organisms is suggested as the main cause of the downstream movement of pikeperch juveniles. In a surface-draining reservoir, the pattern of zooplankton export corresponded to those in natural lakes. Discharged water carried with it mainly small-sized epilimnetic zooplankton from the most numerous groups (i.e. rotifers, juvenile copepods and cladocerans) in the reservoir. Furthermore, outflow exports represent a relatively small part of total zooplankton number, and thus, do not disturb the natural zooplankton succession, and changes in abundance and composition Coincidental changes in the trophic responses for zooplanktivores (mainly juvenile cyprinids and percids) were not found.     

Prey selectivity and diel feeding chronology of juvenile chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon in the Columbia River plume

We studied salmon feeding selectivity and diel feeding chronology in the Columbia River plume. Juvenile chinook and coho salmon were caught by trawling at 2–3 h intervals throughout a diel period on three consecutive days (21–23 June 2000) at stations located 14.8 and 37 km offshore from the mouth of the Columbia River. A total of 170 chinook salmon were caught at the inshore and 79 chinook and 98 coho salmon were caught at the offshore station. After each trawl, potential prey were sampled at different depths with 2–3 different types of nets (1‐m diameter ring net, bongo net, neuston net). Despite the variability in zooplankton abundance, feeding selectivity was surprisingly constant. Both salmon species fed selectively on larger and pigmented prey such as hyperiid amphipods, larval and juvenile fish, various crab megalopae, and euphausiids. Hyperiid amphipods were abundant in the salmon diets and we hypothesize that aggregations of gelatinous zooplankton may facilitate the capture of commensal hyperiid amphipods. Small copepods and calyptopis and furcilia stages of euphausiids dominated the prey field by numbers, but were virtually absent from salmon diet. Juvenile chinook salmon, with increasing body size, consumed a larger proportion of fish. Stomach fullness peaked during morning hours and reached a minimum at night, suggesting a predominantly diurnal feeding pattern. In general, both chinook and coho salmon appear to be selective, diurnal predators, preying mostly on large and heavily pigmented prey items, in a manner consistent with visually oriented, size‐selective predation.     

Feeding ecology of the walleye (Percidae,Sander vitreus), a resurgent piscivore in Lake Huron (Laurentian Great Lakes) after shifts in the prey community

Recovering populations of piscivores can challenge understanding of ecosystem function due to impacts on prey and to potentially altered food webs supporting their production. Stocks of walleye (Percidae, Sander vitreus), an apex predator in the Laurentian Great Lakes, crashed in the mid‐1900s. Management efforts led to recovery by 2009, but recovery coincided with environmental and fish community changes that also had implications for the feeding ecology of walleye. To evaluate potential changes in feeding ecology for this apex predator, we assessed diets in the main basin of Lake Huron and in Saginaw Bay, a large embayment of Lake Huron, during 2009–2011. Walleye switched their diets differently in the main basin and Saginaw Bay, with non‐native round goby (Gobiidae, Neogobius melanostomus) and rainbow smelt (Osmeridae, Osmerus mordax) more prevalent in diets in the main basin, and invertebrates, yellow perch (Percidae, Perca flavescens) and gizzard shad (Clupeidae, Dorosoma cepedianum) more prevalent in diets in the bay. Feeding strategy plots indicated that there was a high degree of individual specialisation by walleye in the bay and the main basin. Bioenergetic simulations indicated that walleye in Saginaw Bay need to consume 10%–18% more food than a walleye that spends part or all of the year in the main basin, respectively, in order to achieve the same growth rate. The differences in diets between the bay and main basin highlight the flexibility of this apex predator in the face of environmental changes, but changes in diet can alter energy pathways supporting piscivore production.     

Temperature,plankton and conspecific density influence dynamics of age‐0 gizzard shad: implications for a gape‐limited piscivore

Age‐0 gizzard shad Dorosoma cepedianum are the main prey fish for white crappies Pomoxis annularis in many US reservoirs. However, these prey fish commonly outgrow their vulnerability to white crappie predation in some, but not all, northern Missouri reservoirs. Potential variables that could influence abundance, growth and mortality of age‐0 gizzard shad were examined in three reservoirs that differed with respect to age‐0 gizzard shad growth rates. Because of thermal effluent from a power plant, gizzard shad spawned earlier in Thomas Hill Lake and initial densities of larvae were greater than in the other reservoirs. Larval and juvenile gizzard shad grew slowest in Thomas Hill Lake, followed by Mark Twain Lake and Long Branch Lake. Growth rate of larvae increased with increasing water temperature and food abundance, but decreased with increasing conspecific density. Similar relationships were found for juvenile growth, except that growth declined with increasing temperature. The slower growth of larvae and juveniles in Thomas Hill Lake was probably a consequence of their greater densities relative to their food abundance and higher water temperatures during the juvenile stage. Conversely, both larvae and juvenile gizzard shad grew more rapidly and juveniles attained large sizes in Long Branch Lake owing to their lower densities relative to their available food. Mortality of larvae and juveniles was mostly similar among the reservoirs. Because of their greater abundance and slower growth, gizzard shad were available as prey for white crappies for a longer period in Thomas Hill Lake than in the other reservoirs.     

Food habits of fishes in the mangrove estuary of Urauchi River,Iriomote Island,southern Japan

The food habits of 67 fish species collected from the mangrove estuary of the Urauchi River, Iriomote Island, southern Japan were investigated using gut content analysis. Ontogenetic changes in food preference were recognized in nine species, including mugilids, gerreids, mullids, gobiids and tetraodontids. In most cases, juveniles of these species fed mostly on small crustaceans (e.g. calanoid and cyclopoid copepods and gammaridean amphipods) or detritus. With their subsequent growth, larger prey items (e.g. crabs and polychaetes) became dominant. A cluster analysis based on dietary overlaps showed that the mangrove fish assemblage comprised eight trophic groups (zooplankton, small benthic crustacean, large benthic crustacean, polychaete, fish, detritus, plant and insect feeders). Of these, large and small benthic crustacean feeders, which consumed mainly crabs and gammaridean amphipods, respectively, were the most abundantly represented in terms of species, whereas polychaete and insect feeders were each represented by only two species.     

Declines in the energy content of yearling non‐native alewife associated with lower food web changes in Lake Michigan

Juveniles of non‐native alewife, Alosa pseudoharengus (Wilson), were collected in Lake Michigan in 1998, 1999, 2010, 2011 and 2013 to evaluate changes in energy content during a period of major ecosystem changes. Consistent with historical data, energy content of yearling alewife declined from late winter into late spring and was at its lowest point in June. Energy density and length‐adjusted, entire‐body energy were lower in 2010, 2011 and 2013 than in 1998 and 1999. Energy losses over the first winter in the lake were more severe for the 2010 year class (56% decrease) than for the 1998 year class (28% decrease). Alewife diets in late spring of 2010–2013 reflected the loss of major prey such as Diporeia spp. and a shift towards lower energy prey. The recent decline in energy content of yearling alewife can be linked to recent changes in productivity and abundance of key components of the lower food web of Lake Michigan following the dreissenid invasion.     

Relationships among condition indices, feeding and growth of walleye in Lake Erie

Abstract  Condition indices are often used as surrogates of fish health, growth, and feeding and to compare ecological well-being among fish populations. In an effort to identify easily measured indices, growth and food consumption were compared with gonadal-somatic index, liver-somatic index (LSI), fat-somatic index and relative weight ( W _r) for ages 1–3 walleye, Sander vitreus (Mitchill), in Lake Erie from 1986 to 1988. The LSI and W _r were significantly correlated with growth rate or food consumption, but correlations were too small to be considered biologically meaningful. Furthermore, no consistent relationships between condition indices and growth or consumption were found among combinations of fish age and season. None of the indices are considered reliable surrogates for more laborious estimates of growth and food consumption for Lake Erie walleye. Significant relationships between W _r and relative abundance of key prey species warrant further investigation.     

Prey partitioning and use of insects by juvenile sockeye salmon and a potential competitor,threespine stickleback,in Afognak Lake,Alaska

Freshwater growth of juvenile sockeye salmon (Oncorhynchus nerka) depends upon the quality and quantity of prey and interactions with potential competitors in the foraging environment. To a large extent, knowledge about the ecology of lake‐rearing juvenile sockeye salmon has emerged from studies of commercially important runs returning to deep nursery lakes, yet information from shallow nursery lakes (mean depth ≤ 10 m) is limited. We examined seasonal and ontogenetic variation in diets of juvenile sockeye salmon (N = 219, 30–85 mm) and an abundant potential competitor, threespine stickleback (Gasterosteus aculeatus; N = 198, 42–67 mm), to understand their foraging ecology and potential trophic interactions in a shallow Alaska lake. This study revealed that adult insects made up 74% of all sockeye salmon diets by weight and were present in 98% of all stomachs in Afognak Lake during the summer of 2013. Diets varied temporally for all fishes, but small sockeye salmon (<60 mm) showed a distinct shift in consumption from zooplankton in early summer to adult insects in late summer. We found significant differences in diet composition between sockeye salmon and threespine stickleback and the origin of their prey indicated that they also separated their use of habitat on a fine scale; however, the two species showed overlap in size selectivity of zooplankton prey. Considering that aquatic insects can be a primary resource for juvenile sockeye salmon in Afognak Lake, we encourage the development of nursery lake carrying capacity models that include aquatic insects as a prey source for sockeye salmon.     

Diet dynamics of the juvenile piscivorous fish community in Spirit Lake, Iowa, USA, 1997–1998

Abstract – We assessed temporal dynamics and variation among species and age-classes in the diets of age 0 and age 1 piscivorous fish species in Spirit Lake, Iowa, USA during 1997 and 1998. Species included walleye Stizostedion vitreum , yellow perch Perca flavescens , smallmouth bass Micropterus dolomieui , largemouth bass Micropterus salmoides , black crappie Pomoxis nigromaculatus and white bass Morone chrysops. Thirty taxa were identified in diets, including 12 species of fish. We found dramatic differences in diets among species, among age-classes within species and over time. Walleye, largemouth bass, smallmouth bass and white bass were piscivorous at age 0. Black crappie began piscivory at age 1. Yellow perch also began piscivory at age 1, but fish were a very small fraction of age-1 diets. The primary temporal pattern, seen in several species and age-classes, was an increase in piscivory from spring to fall. This pattern was due to the lack of small, age-0 prey fish in spring. Although some patterns were evident, the taxonomic composition of the diets of all species was highly variable over time, making generalizations difficult. A surprising result was the absence of yellow perch in the diet of age-0 walleye, despite their abundance in Spirit Lake and prominence in diets of age-1 walleye and other age 1-piscivores. Age-0 yellow perch were consistently too large to be eaten by age-0 piscivores, which preyed primarily on invertebrates and smaller fish such as johnny darters Etheostoma nigrum and age 0 bluegill Lepomis macrochirus. This finding suggests that predator-prey interactions and resulting population dynamics may be quite different in Spirit Lake than in other systems dominated by walleye and yellow perch.     

Hydroacoustic assessment of young-of-year perch, Perca fluviatilis, population dynamics in an oligotrophic lake (Lake Annecy, France)

Abstract  A cohort of perch, Perca fluviatilis (L.) was monitored from hatching to first winter in the oligotrophic Lake Annecy, France, by combining hydroacoustic and direct capture methods (fish plankton net and pelagic trawl). The total stock of pelagic fish increased by a factor of 10 during the season, reaching a maximum in August and decreasing in autumn. Juvenile perch were mainly pelagic, being aggregated into schools in the daytime and dispersed at night. Migration of young-of-year (Y-O-Y) perch to the pelagic zone of Lake Annecy in late spring did not significantly affect zooplankton population abundance. It did, however, result in changes in zooplankton vertical distribution, with Daphnia remaining deeper in the water column. The increase in Y-O-Y biomass during summer was possibly associated with collapse of the Daphnia population by late July, and copepods one month later.     

Food habits of fishes on unvegetated tidal mudflats in Tokyo Bay, central Japan

ABSTRACT:   To clarify the feeding habits of tidal mudflat fishes, the gut contents of 29 fish species, collected from unvegetated tidal mudflats in Tokyo Bay, central Honshu, Japan, were examined. Ontogenetic changes in food preference were recognized in 21 species, including several of commercial importance (e.g. Acanthogobius flavimanus , Konosirus punctatus , Mugil cephalus cephalus , Plecoglossus altivelis altivelis , and Sardinella zunasi ). In general, larvae and/or juveniles of these species fed mainly on small zooplankton or benthic harpacticoid copepods, later switching to other prey items with growth (e.g. gammaridean amphipods, mysids, polychaetes, detritus, bivalves, and juvenile fishes). A cluster analysis based on dietary overlaps showed that the tidal mudflat fish assemblage comprised six feeding guilds (small benthic and epiphytic crustacean, zooplankton, detritus, mollusc, polychaete, and fish feeders). Of these, small benthic and epiphytic crustacean feeders were the most abundantly represented in the number of species.     

Diet overlap between young-of-the-year perch, Perca fluviatilis L., and burbot, Lota lota (L.), during early life-history stages

Abstract –  The diet overlap between young-of-the-year (YOY) perch and burbot in the pelagic zone of Lake Constance during spring and summer was investigated in relation to gape size limitation. Because perch were larger and grew faster than burbot during their early life history, perch overcame gape size limitation for various zooplankton taxa earlier than burbot. The interspecific diet overlap between perch and burbot decreased continuously until June, but increased slightly, when burbot became able to feed on large daphnids by the beginning of July. All zooplankton taxa could be found within perch stomachs by the middle of June, when perch overcame gape size limitation for large cladocerans. However, there was an increasing tendency for individual diet specialisation of perch, as the similarity between individual perch stomach contents decreased. In contrast, the similarity between individual burbot stomach contents remained at almost 50% until the end of August, indicating that all burbot rely on cyclopoid copepods during their entire pelagic life-history stage. Because by July YOY perch are more abundant by one order of magnitude in the pelagic zone than burbot, YOY perch may be more affected by intraspecific competition than by interspecific competition with burbot. Burbot, on the other hand, may evade strong competition with YOY perch by performing diel vertical migrations, thus being restricted to feed on migrating zooplankton prey.     

海州湾星康吉鳗的摄食生态特征

根据2011年3—12月在海州湾及其邻近海域进行的5个航次的底拖网调查,通过分析516尾星康吉鳗(Conger myriaster)的胃含物样品,对其食物组成、食性类型、摄食强度、营养生态位以及营养级等摄食生态特征进行了初步研究。结果表明,星康吉鳗摄食的饵料种类有40余种,鱼类、虾类和头足类是其最主要的3种饵料类群,优势饵料生物有尖海龙(Syngnathus acus)、矛尾虾虎鱼(Chaeturichthys stigmatias)、鲜明鼓虾(Alpheus distinguendus)、枪乌贼(Loligo sp.)等。星康吉鳗的食性类型以底栖动物和游泳动物食性为主,其食物组成存在明显的季节变化和肛长变化,除在4个季节均摄食大量的鱼类和虾类外,秋季还摄食大量头足类。不同肛长组星康吉鳗摄食的主要饵料种类存在明显差异:肛长小于70 mm的星康吉鳗主要摄食枪乌贼,70~99 mm的星康吉鳗主要摄食绯(Callionymus beniteguri)和鲜明鼓虾,大于100 mm的星康吉鳗则主要以枪乌贼、尖海龙(Syngnathus acus)和鲜明鼓虾为食。星康吉鳗的空胃率和平均胃饱满指数存在明显的季节变化,空胃率夏季最低,春季最高;平均胃饱满指数春季最低,秋季最高。星康吉鳗的营养级为4.17,表明其在海州湾食物网中处于较高的营养位置。本研究发现,海州湾星康吉鳗的摄食随季节和肛长的变化,主要与其栖息海域中优势饵料生物的种类组成和丰度有关,因此,通过定期监测星康吉鳗的摄食可间接了解基础饵料生物种类和数量的变动情况,同时也为食物网的构建和生态系统营养动力学的研究提供基础资料。     

黄海中部小黄鱼的食物组成和摄食习性的季节变化

根据2001年3月至2002年1月在黄海中部海域进行的4个季节的定点底拖网调查,应用聚类分析、单因素方差分析和列联表检验等方法,对小黄鱼(Pseudosciaena polyactis Bleeker)的食物组成和摄食的季节变化进行研究.结果表明,小黄鱼摄食的饵料种类有30余种,甲壳类(磷虾类和虾类)和鱼类是其主要的饵料类群,二者在食物中所占的重量百分比之和为97.45%.优势饵料种类有太平洋磷虾(Euphausia pacifica)、脊腹褐虾(Crangon affinis)、细螯虾(Leptochela gracilis)和赤鼻棱鳀(Thryssa kammalensis).小黄鱼的摄食强度有显著的季节变化,秋季最高,春季和冬季较低.食物组成也随季节的不同而有所变化,夏季主要以虾类为食,其它季节则主要以磷虾类为食.聚类分析的结果表明,小黄鱼春、夏季的食物组成与秋、冬季相比,存在较大差异.通过与历史资料进行比较发现,黄海小黄鱼的食物组成发生了较大的变化,其中鳀鱼(Engraulis japonicus)在食物中所占的比例有明显的下降.