Food habits of small fishes in a common reed <Emphasis Type="Italic">Phragmites australis</Emphasis> belt in Lake Shinji,Shimane, Japan

To clarify the feeding habits of reed fishes, the gut contents of 13 fish species collected in a Phragmites australis belt in Lake Shinji were examined. Six species showed ontogenetic and/or seasonal changes in food use patterns. Smaller individuals generally preyed on small planktonic items (e.g., calanoid and cyclopoid copepods) or small crustaceans (gammaridean amphipods), subsequently changing to other prey items (e.g., mysids and filamentous algae) with growth. The most important dietary items for the reed fish assemblage comprised planktonic copepods, gammaridean amphipods and mysids. However, the relative importance of these changed seasonally, gammaridean amphipods being the most important in autumn and winter, and planktonic copepods and mysids the most important in spring and in summer. Cluster analysis based on dietary overlaps showed that the reed fish assemblage comprised five feeding guilds (planktonic-copepod, mysid, gammaridean-amphipod, filamentous-algae, and detritus feeders). Of these, the three former guilds were the most abundantly represented, whereas detritivores were represented by a single species.     

Some aspects of the biology and ecology ofKnipowitschia caucasica (Teleostei: Gobiidae) in the Evros Delta (North Aegean Sea)

Some aspects of the biology and ecology of the gobyKnipowitschia caucasica were studied over a period of 13 months in a poly-to euhaline area in the Evros Delta (North Aegean Sea). This fish grows rapidly in the summer and autumn after hatching, matures after its first winter, breeds from the end of April to the end of July, and grows rapidly again in July–September. The older males perish after their second February, whereas some females have a second breeding season at the end of April/beginning of May, shortly before their death. The fish grows to about 40 mm in total length. There is a positive correlation between the total length (TL) and the standard length (SL) or the cleaned body weight (CW). SL increases slower than TL, whereas CW increases slower than TL in immature individuals and faster in males and females. There is no difference between immature individuals, males and females, in the growth rate of SL, TL and CW, TL. The mean monthly values of the condition factor varies from 0.289 to 0.576 in females and from 0.313 to 0.548 in males. The overall sex ratio of females to males is 1: 1.46. Fecundity ranges from 60 to 217 eggs with a mean value of 109.8 and depends upon size, whereas relative fecundity varies between 968 and 2170 with a mean of 1558. The fish feeds predominantly on benthic amphipods and polychaetes.     

Feeding habits and trophic morphology of inshore lizardfish (Synodus foetens) on the central continental shelf off Veracruz, Gulf of Mexico

The inshore lizardfish, Synodus foetens, is one of the most common coastal demersal predators on the continental shelf of the Gulf of Mexico (GOM), but the biology and feeding ecology of this species is virtually unknown. Between November 2001 and January 2003 (10 collections), 603 individuals of S. foetens ranging from 112 to 420 mm standard length (SL) and 13 to 630 g (wet weight) were collected from the continental shelf of Alvarado, Veracruz, Mexico. About 60% of the individuals had empty stomachs with the stomach fullness of the remaining individuals being distributed as follows: 5% full (24.8%), 50–75% full (13.5%), and completely full (1.7%). The mean (± SD) wet weight of stomach contents was 12.1 ± 10.8 g during the rainy season, and 19.0 ± 13.0 g during the nortes season. Seventeen prey items were identified, with the majority thereof being fish. The most important prey items were Upeneus parvus, Loligo pealei, Engyophrys senta, Trachurus lathami, and Anchoa hepsetus. Seasonal changes in the diet were observed, with U. parvus and L. pealei being the most important prey during the nortes season, whereas E. senta and L. pealei were the main items during the rainy season. Prey size selection was evident among size classes of S. foetens, although no trophic overlap was observed among size classes (C_ik ≤ 0.004). High trophic level values were determined for all size classes by season (rainy season = 4.67, nortes season = 4.84), and indicated this species belongs to the piscivorous trophic guild that preys upon both demersal and pelagic species.     

On the food of the European eel, Anguilla anguilla (L.), in the upper zone of the Tagus estuary, Portugal

The estuarine food habits of the European eel, Anguilla anguilla (L.), in the upper zone of the Tagus estuary have been studied through the analysis of 210 specimens collected during 1988. Eels, measuring from 136 to 627 mm in total length, fed on prey organisms ranging from 2.0 to 76.0 mm in length. Amphipods and the shore crab, Carcinus maenas (L.), were the most important food items found. In more saline muddy bottom areas polychaetes, bivalves and shrimp increased their importance as prey, replacing the amphipods as preferential food. Fish were always a secondary, although significant, prey item. The occurrence of seasonal variations in eels' diet could be attributed to fluctuations in prey densities. There was evidence of a close relationship between the quantity of prey organisms in the benthos and the composition of eels' stomach contents, but a certain degree of food selection based on size, concealment capacity and motility of prey, was found.     

Feeding habits of juvenile slime flounder <Emphasis Type="Italic">Microstomus achne</Emphasis> in the coastal area of southern Hokkaido

A total of 45 juvenile [30.0–57.4 mm total length (TL)] slime flounder Microstomus achne were collected in the coastal area of southern Hokkaido from April to July in 2001 and April to June in 2002. Their diets were analyzed. Slime flounder juveniles of 30.0–39.9 mm TL fed predominantly on small crustaceans (gammarid amphipods, harpacticoids and cumaceans) and those of 40.0–57.4 mm TL on gammarid amphipods, cumaceans and polychaetes. The major prey items changed with growth from small crustaceans (e.g., harpacticoids) to polychaetes, although gammarid amphipods were the major prey items throughout the juvenile period (30.0–57.4 mm TL).     

Feeding habits of ocellate spot skate,Okamejei kenojei (Müller & Henle, 1841), in coastal waters of Taean,Korea

The feeding habits of Okamejei kenojei were studied using 592 specimens collected in the coastal waters of Taean, Korea from April 2008 to March 2009. O. kenojei is a bottom‐feeding carnivore that consumes mainly shrimp, fishes, and crabs. Its diet also includes small quantities of amphipods, mysids, cephalopods, euphausiids, copepods, isopods, and polychaetes. The total length (TL) of individuals in this study ranged from 8.2 to 49.0 cm. Cluster analysis based on %IRI (index of relative importance) identified three size classes. Group A (< 20 cm TL) ate primarily caridean shrimp and amphipods; group B (20–30 cm TL) ate exclusively shrimp; and group C (> 30 cm TL) ate penaeoidean shrimp, fishes, and crabs. O. kenojei showed ontogenetic changes in feeding habits. Although shrimps were the primary food consumed by all size groups, the proportion of shrimp in the total diet decreased and the consumption of fishes and crabs gradually increased with the body size of O. kenojei. Size of the prey organisms also increased. Smaller individuals fed mainly on small prey, such as amphipods, mysids, and small shrimp, whereas larger individuals preferred larger prey, such as larger shrimp, fishes, and crabs. The size‐related diet breadth and the percentage of empty stomachs were significant; the diet breadth gradually increased with body size, whereas the percentage of empty stomachs decreased. Seasonal changes in the O. kenojei diet were not significant, but shrimp constituted 97.3% of the summer diet by %IRI. Seasonal changes in diet breadth and the percentage of empty stomachs were not significant.     

The early life history of kurosoi,Sebastes schlegeli (Scorpaenidae), in the Sea of Japan

Larval and juvenile stages of kurosoi,Sebastes schlegeli, are described and illustrated from wild specimens. Some ecological aspects of larvae and juveniles are also described. Notochord flexion occurred between 5.6–7.5 mm SL. Transformation occurred between 13–20 mm SL. Preflexion and flexion larvae ofS. schlegeli can be distinguished from similar larvae by the pigmentation of the dorsal and ventral midlines of the tail and absence of pigmentation on the ventral portion of the rectum. After notochord flexion, the dorsal and lateral regions in both larvae and pelagic juveniles were heavily pigmented, suggesting adaptation for neustonic life style. Larvae and juveniles were caught at many coastal stations, but did not occur in cooler offshore waters. Larvae smaller than 20 mm SL inhabited surface waters. Until ca. 40 mm SL, juveniles inhabited mainly surface waters (without drifting seaweed), but also used other habitats, such as the drifting seaweed, and near the sea bed. Small larvae (<7 mm SL) fed mainly on copepod nauplii. Larger larvae fed on calanoid copepodites andEvadne nordmanni. Pelagic juveniles fed mainly on fish eggs, with fish larvae also being important food items for some individuals. Most food items taken by juveniles that were associated with drifting seaweed were eggs with attaching filaments (Cololabis saira andHyporhamphus sajori), suggesting that the high density of such food items both attracts and keeps juveniles around drifting seaweed.     

The land/inland-water ecotones and fish population of Lake Valley (West Mongolia)

New data on fish populations of a closed desert watershed of Mongolia were obtained in 1990 and 1991. For this region periodic droughts, with the accompanying disappearance of lakes and some parts of rivers, are typical. Two forms of a Cyprinid species Oreoleuciscus humilis (dwarf Altai osman) occur in this region during wet periods which usually last for 10-30 years. The dwarf form, is characterized by a maximum SL of 200 mm and early maturation (SL = 70 mm, four years of age). It inhabits small desert rivers in dry periods which last for 3–5 years and both rivers and the riparian zone of lakes during wet periods. The larger lake form occurs only in lakes during the wet periods. It can attain a maximum size of 450 mm and matures in six years, SL = 200 mm. These two forms of O. humilis differ in feeding habits, rates of growth, and morphology. The dwarf form feeds mainly on insect larvae and on plants. The lake form consumes the same food items until it reaches 180 mm SL and then becomes piscivorous. Populations of O. humilis in lakes are restored after a dry period, originating anew from river populations of the dwarf form.Currently there is a transition from a dry period to a wet one. Orog-Nur (one of the lakes of Lake Valley) has been filling with water since 1990. In July 1991 the depth of this lake reached 0.5–1.0 m and fish were found in the lake. The large individuals of dwarf form which came to the lake from the Tuyn-Gol River became cannibals, and their growth rate increased rapidly. The homogeneous environment and low food supply in the restored lakes are suggested to be the main causes of these phenomena.     

Food habits of fishes in azostera marina bed at aburatsubo, central japan

To clarify the feeding habits of seagrass fishes, the gut contents of 31 fish species collected in aZostera marina bed at Aburatsubo central Japan, were examined. Ontogenetic changes in food preference were recognized in 12 species. In general, juveniles of the latter preyed mainly on small crustaceans (e.g., gammaridean amphipods) or planktonic animals (e.g., calanoid and cyclopoid copepods), subsequently changing to other prey items (e.g., hard-shelled animals) with growth. Cluster analysis based on dietary overlaps showed that the seagrass fish assemblage comprised seven feeding guilds (small-crustacean, planktonic-animal, large-crustacean, polychaete, fish, hard-shelled mollusc and detritus feeders). Of these, small-crustacean feeders and planktonic-animal feeders were the most abundantly represented, including juveniles of several species, which, when adult, transferred to other feeding guilds. On the other hand detritivores were represented by a single species.     

Habitat-specific feeding by cownose rays (Rhinoptera bonasus) of the northern Gulf of Mexico

Past studies have suggested that increases in cownose ray (Rhinoptera bonasus) abundance may pose problems for fisheries management due to their specialized diet of exploitable mollusks. However, more recent work has identified cownose rays as opportunistic generalists, consuming mainly non-commercial prey (e.g. soft-bodied invertebrates) most abundant in their locale. To better assess the generalist vs. specialist foraging behaviors of cownose rays, including their impact to commercial shellfish of the north-central Gulf of Mexico, we conducted gut content analysis on 201 individuals from coastal Alabama. Prey items were analyzed for frequency of occurrence and percent composition by weight, which were used to develop an index of importance. Our diet analysis indicated a minimal impact of cownose rays to exploitable shellfish species of coastal Alabama. Further, we observed important spatial and ontogenetic diet variability: adult diets were dominated by crustaceans along barrier islands and open waters of the Gulf of Mexico, whereas juvenile and young-of-the-year individuals almost exclusively consumed bivalves in riverine and estuarine areas. Individual cownose ray diets were primarily monotypic (54.3%) and appeared selective for amphipods (i.e. Haustorius sp.) when hyperabundant along gulf barrier islands and bivalves at estuarine sites regardless of ambient densities. While this study highlights the importance of locality in determining dietary composition of cownose rays, we do not suggest this species is opportunistic or completely mollusk-specialized. Alternatively, we propose cownose rays exhibit a continuum of foraging behaviors between specialization and generalization, depending on locale and prey availability.     

Population genetic analysis of white shrimp,Litopenaeus setiferus,using microsatellite genetic markers

The white shrimp (Litopenaeus setiferus) is a commercially and recreationally valuable species, yet little is known of its population structure or genetic diversity. White shrimp are distributed along the Atlantic coast of the United States and from the west coast of Florida to the Bay of Campeche, Mexico. In this study, shrimp were collected from North Carolina, South Carolina (four separate collections were taken from 1995 to 1999), Georgia, the Atlantic and Gulf coasts of Florida, Louisiana, Texas and Mexico. DNA was isolated from these individuals, and genetic variation was assessed at six microsatellite loci. These loci were, for the most part, highly polymorphic with an average expected heterozygosity of 0.68. Deviations from Hardy-Weinberg proportions were observed over all samples, but experimental results suggested the presence of null alleles, which confounded a biological interpretation of this result. Pairwise tests of the similarity of allele frequency distributions and distance measure analyses showed broad-scale genetic homogeneity superimposed over occasional indications of random geographical and temporal differentiation. FST and RST estimates over all loci and samples were 0.002 or less and indicated little population structure. Weak but significant genetic differentiation was evident only between pooled western Atlantic and pooled Gulf of Mexico samples. Within the Gulf of Mexico or within the western Atlantic, the large-scale genetic homogeneity observed may be a consequence of genetic mixing resulting from pelagic larvae and adult migrations, while the random local genetic differentiation may be a result of genetic sampling or experimental sampling error. The weak differentiation between shrimp from the Gulf of Mexico and the western Atlantic can be explained by a relatively recent separation of these two populations and/or small amounts of ongoing gene flow.     

Spatial and seasonal changes in the diet of Oligosarcus hepsetus (Characiformes, Characidae) in a Brazilian reservoir.

We assessed spatial and seasonal changes in the diet of Oligosarcus hepsetus in order to describe the strategy developed by this species that allows their very high abundance in Lajes reservoir, Rio de Janeiro, Brazil. Fish samplings were carried out using gill nets, deployed during ca. 12 and 24 hours, between April 2001 and May 2002. A total of 289 individuals were examined, of which 97 showed gut contents. We used the index of relative importance (IRI) to compare probable dietary shifts, and the frequency of occurrence (% OC) to analyze possible ontogenetic influences on feeding. O. hepsetus showed carnivorous habits, feeding preferably on fish and insects, the latter of which occurred in 71.0% of the guts presenting contents. O. hepsetus consumed different items along the three reservoir zones: insects (61.0% IRI) and Cichla monoculus (38.9% IRI) in the lower zone; Lepidoptera (57.0% IRI) in the middle zone; and C. monoculus (77.0% IRI) in the upper zone. Food items changed seasonally with C. nonloculus predominating in autumn 2001, and Hymenoptera and Lepidoptera in the winter. In spring almost all food was Lepidoptera (99.8% IRI), while in the summer Hemiptera dominated in the diet. In autumn 2002 Hemiptera (97.0% IRI) was dominant, in significant contrast with the previous autumn. Individuals smaller than 190 mm SL fed heavily on insects, while fishes predominated in the diet of individuals larger than 190 mm SL. Shifts in prey-capture ability among length classes suggest decreasing intraspecific competition. A higher food plasticity seems to be the strategy employed by this opportunist species, which used food resources available in the reservoir.     

Feeding habits of several mass shrimp species in the Sea of Okhotsk

Information on the qualitative and quantitative characteristics of the feeding habits of two pandal shrimp—the humpy shrimp (Pandalus goniurus) and the northern shrimp (Pandalus borealis) and one species of crangonids (Crangon communis) is submitted. The materials were collected in April–May 2006 and 2007 during complex surveys at West Kamchatka. The size and sex composition of the shrimp, as well as the composition of their food were analyzed. The food of all the considered species basically consisted of polychaetes, amphipods and, to a lesser extent, other shrimp. The daily ration (DR) of a shrimp with a body length of 40–60 mm was calculated for the first time—it was 7.9% of the body weight. The DR of a northern shrimp 61–80 mm in length was 5.8% of its body weight. Individuals of the third species, Crangon communis, generally did not feed.     

Trophic relationships among concentrated populations of small fishes in seagrass meadows

Changes in available food and utilized foods for a densely populated guild of animals can uncover periods of niche displacement among particular consumer species or their separate size classes. Dense populations of small fishes and their foods were çensussed for 13 months and studied experimentally in shoalgrass and turtlegrass meadows of Redfish Bay, Texas. Feeding habits were determined with respect to prey availability, and illustrated the extent to which seasonal partitioning of food corresponded to food depletion among these abundant consumers in seagrass meadow food webs. The darter goby, code goby, pinfish, and Gulf pipefish were the most common species throughout the year. Although the darter goby did not show distinct ontogenetic changes in food habits, the code goby, Gulf pipefish, and pinfish demonstrated major ontogenetic progressions of foods selected.Food availability in the seagrass meadows changed seasonally. When major prey such as amphipods were abundant, during spring, many fish species showed high overlap in food use. Regardless of food availability, the code goby and Gulf pipefish fed mainly on amphipods or copepods. The more common darter goby and pinfish seasonally changed their diets with changes in food availability; the darter goby and pinfish were more carnivorous during spring, but they largely consumed epiphytic algae during summer. Cage experiments were used to monitor foods confined with elevated densities of pinfish and darter gobies, relative to control cages at natural overall densities. Prey items in the former cages decreased sharply, with corresponding dietary shifts by these common fishes. During resource depletion, these changes in resource use by these naturally concentrated consumers appeared as temporary partitioning of available resources. This shift occurred during both natural (seasonal) and experimental depletions of food, and appears to result from increased interspecific and intraspecific competition during periods of depleted preferred foods.     

Patterns of gammaridean amphipod abundance and species composition associated with dominant subtidal macroalgae from the western Antarctic Peninsula

The communities of gammaridean amphipods associated with eight dominant macroalgal species were examined near Palmer Station, Western Antarctic Peninsula. A total of 78,415 individuals belonging to 32 amphipod taxa were identified with mean densities ranging up to 20 individuals/g algal wet wt. The most abundant amphipod taxon, Metaleptamphopus pectinatus, was found to associate predominately with the brown alga Desmarestia menziesii, while the second most common taxon, Jassa spp. occurred primarily on the red alga Gigartina skottsbergii. Non-metric multidimensional scaling analysis demonstrated that the population densities of each amphipod species and amphipod species composition were similar on the same algal species but dissimilar on different species of algae. Comparisons of amphipod communities associated with a given algal species but from different sampling sites indicated that although the structure of species-specific macroalgal-associated amphipod communities can vary across spatial scales of 3 km, 50% of the macroalgal species examined showed no significant inter-site differences in associated amphipod community structure. Spearman rank correlation analyses showed that higher abundances of amphipods occurred on the macroalgae with the highest number of branches. As many Antarctic amphipods are known consumers of macroalgae, their remarkable abundances are likely to play a significant role in mediating energy and nutrient transfer in nearshore Antarctic Peninsular macroalgal communities.     

Bathymetric distribution and feeding habits of two sympatric cheilodactylid fishes at Miyake-jima,Japan

Habitats including depth, diurnal activity patterns, and diets of the two cheilodactylid fishesCheilodactylus zonatus andC. zebra were studied at Igaya Bay, Miyake-jima, Japan. Both species occurred at nearly equal densities in identical habitats and depths. They preyed on benthonic organisms from early morning to shortly before sunset, when feeding activities decreased remarkably and intraspecific social behavior greatly increased. Gut analyses showed a high degree of dietary overlap, but proportions of food items in their diets differed slightly.C. zonatus was more of a food generalist thanC. zebra, showing a higher niche breadth value.C. zebra tends to feed on epifauna, especially gammaridean amphipods and decapods, whileC. zonatus takes both epifauna and infauna including polychaetes.     

Diet and Food Web Support of the White Perch, <Emphasis Type="Italic">Morone americana</Emphasis>, in the Hackensack Meadowlands of New Jersey

Synopsis I analyzed stomach contents of white perch, Morone americana, caught throughout the year in the Hackensack River in northern New Jersey. The dominant prey items were amphipods, with shrimp and fish being less important. Stable isotope analysis indicated that the primary producers of importance in the food web leading to white perch were benthic or planktonic microalgae and secondarily Phragmites australis, the dominant macrophyte in the Hackensack Meadowlands. Despite their large size, white perch do not generally appear to feed any higher in the food web than killifish, Fundulus heteroclitus.     

Variation of diet and food consumption of the scaldfish Arnoglossus laterna(Walbaum, 1792)

Although Arnoglossus laterna (Walbaum, 1792) is a common benthic fish in Portugal, several aspects of its feeding ecology remain incomplete. In this study, diet was examined and the food consumption estimated on inshore waters in the central coast of Portugal. The diet of the scaldfish included mainly mysids, amphipods and polychaetes, while the decapod Philocheras bispinosus Hailstone was the most frequent prey. Variation in the diet according to fish size (two size‐classes), sex and spawning/non‐spawning seasons was examined. Significant differences in diet composition were found between seasons, whereby the most frequently consumed prey in the non‐spawning season were crustaceans, while polychaetes and nemerteneans comprised most of its diet in the spawning season. The average value of the vacuity index was very similar between seasons (24.7% non‐spawning season and 25.0% spawning season). Diet overlap between size‐classes and sexes was high, but low between the two seasons. Food consumption of A. laterna was estimated based on diet characterization and evacuation rate. The estimate of the daily food consumption was 1.15 mg dry weight for the non‐spawning season and 1.67 mg dry weight for the spawning season. Significant differences in consumption rates were found between size‐classes and sexes. Larger individuals showed a higher consumption rate than smaller individuals. Females consumed more food than males in the non‐spawning season, while in the spawning season males consumed more than females.     

Epizootiology of the parasitic dinoflagellate Hematodinium sp. in the American blue crab Callinectes sapidus

Hematodinium sp. is a parasitic dinoflagellate that infects and kills blue crabs Callinectes sapidus. Periodic outbreaks of dinoflagellate infections with subsequent high host mortalities prompted a study of the epizootiology and distribution of the crab pathogen. Hemolymph samples from over 13000 crabs were assessed for infections over 8 yr. Moderate to high prevalences were found at several locations along the Atlantic and Gulf coasts of the United States. In the coastal bays of Maryland and Virginia, prevalence followed a seasonal pattern, with a sharp peak in late autumn. Infections were significantly more prevalent in crabs measuring less than 30 mm carapace width; host sex did not influence prevalence. Prevalences were highest in crabs collected from salinities of 26 to 30%o; no infected crabs were found in salinities below 11%o. Intensity of infection did not vary among crab sizes, molt stages, or sexes. Naturally and experimentally infected crabs died over 35 and 55 d in captivity, with a mean time to death of approximately 13 and 42 d, respectively. Several other crustaceans, including gammaridean amphipods, xanthid (mud) crabs, and the green crab Carcinus maenus, were found with Hematodinium-like infections. Considering its widespread distribution and high pathogenicity, we suggest that Hematodinium sp. represents a significant threat to blue crab populations in high salinity estuaries along the Atlantic and Gulf coasts of the USA.