bluuebunny/crossref_metadata_2025 huggingface dataset:
Habitat use and activity patterns of roach (Rutilus rutilus (L.)), rudd (Scardinius erythrophthalmus (L.)), perch (Perca fluviatilis L.) and pike (Esox lucius L.) in the laboratory: the role of predation threat and structural complexity
Authors: Bean C. W. , Winfield I. J.
Published: July 2006

Abstract– The role of predation risk and structural complexity in determining the habitat use and activity patterns of roach, rudd and perch was assessed using a series of video‐recorded laboratory trials. The time spent in open and structured habitats, vertical swimming heights and activity levels of each species were observed in the presence and absence of a potential, pike, predator. Habitat complexity varied between treatments with artificial stem densities of 200, 400 and 600 stems‘m−2. Predator free trials showed that roach and rudd spent significantly less time in structured habitats than perch. Increasing stem density had no significant effect on the habitat choice of perch but did affect the distribution of roach and rudd. Stem density influenced the vertical swimming height of rudd or perch but not roach, although the effects of habitat complexity on swimming activity were more complicated. Pike were themselves influenced by increases in stem density, only selecting structured habitats when stem densities were less than 600 stems‘m−2. In the presence of a predator, both roach and rudd increased the amount of time spent in structured areas. These observed differences were independent of stem density. Perch, however, decreased the amount of time spent in structural habitats at all stem densities. Predation risk also prompted significant changes in both vertical swimming height and activity levels of potential prey fish. A pike predation success hierarchy of rudd‐roach‐perch was also observed during the study. The reasons for this pattern are discussed.
Intra‐cohort cannibalism among larval stages of perch (Perca fluviatilis)
Authors: Brabrand A.
Published: July 2006

Cohorts of perch larvae, hatched within 24 h, developed into a bimodal body size distribution as early as 6 days after commencement of external food uptake. At this development stage, intra‐cohort cannibalism occurred among larval perch individuals of larval stage V (body size: 10.5±0.26 mm, 95% c. l.) on smaller siblings. In experimental trials the consumption rate (C: no. of prey/predator·hour) increased exponentially with size of predatory perch (L: mm) and at 21°C was expressed by the relationship log C=3.406·log L‐3.848 (n=10, r2=0.98, P<0.001). For predatory perch in larval stage V, consumption rate was reduced when Daphnia pulex were added, while not in later stages. Perch larvae experimentally forced to live as true piscivores without additional food items developed from stage V to stage IX (15.8±1.34 mm) within the same time as those fed on Daphnia alone, but with increased mortality.
Predation as a determinant of size structure in populations of crucian carp (Carassius carassius) and tench (Tinea tinea)
Authors: Brönmark C. , Paszkowski C. A. , Tonn W. M. , Hargeby A.
Published: July 2006

Predation is an important structuring force in many fish assemblages and may have large, direct lethal effects on prey fish populations but also may affect growth rate and survival indirectly through shifts in behavioral patterns. Some species appear more sensitive to predation and earlier studies in a limited set of Finnish ponds suggests that crucian carp (Carassius carassius) is very sensitive to predation, which results in changes in population size‐structure and density. In this study we tested the effect of piscivore presence or absence on crucian carp populations by using data from a large number (>600) of Swedish lakes across a wide geographical area and ranging in size from small ponds to large lakes (0.02–4400 ha). We also included a second species, tench (Tinea tinea), in our analyses. The population size structures of crucian carp and tench were clearly related to the presence or absence of piscivores. In lakes and ponds without piscivores. populations were dominated by small‐bodied individuals. When piscivores were present, populations consisted almost exclusively of large individuals. Densities of crucian carp and tench were much higher in ponds and lakes without piscivores. There were no differences in size structure or relative abundance when catches from electrofishing were compared with gill net catches, suggesting that our results are not an effect of a behavioral shift in the presence of piscivores.
Longevity of longfinned eels Anguilla dieffenbachii in a New Zealand high country lake
Authors: Jellyman D. J.
Published: July 2006

A sample of 146 longfinned eels (Anguilla dieffenbachii), ranging in length from 231–1203 mm, was collected from Lake Rotoiti, Nelson Lakes National Park, New Zealand. Otoliths (n= 114) of eels were difficult to read, mainly due to the considerable age (maximum age 106 years). Growth rate was slow and linear, averaging 9 mm. year−1. These are the slowest growth rate and maximum age from any study of Anguilla spp. to date. Lakes within National Parks provide the largest commercially unfished waters within New Zealand and hence provide reserve breeding stocks of longfinned eels; however, the average generation time of 93 years for female eels from Lake Rotoiti implies that stock management should be conservative.
Effects of season, maturity, and sex on lipid class dynamics in largemouth bass (Micropterus salmoides Lacepede)
Authors: Brown M. L. , Murphy B. R.
Published: July 2006

Abstract Factors that can influence changes in lipid class concentrations in specific tissues have not been reported for largemouth bass Micropterus salmoides. We investigated patterns of lipid composition by measuring seasonal levels of total lipid and major lipid classes in the muscle and liver tissues of juvenile and adult largemouth bass and gonad tissue of adults. Fish were collected in December, February, April and July to correspond with key stages of the sexual cycle. Total lipid concentrations were substantially greater in hepatic (32.8 [female] to 56.6 [male] mg. g−1) and gonadal tissues (34.4 [F] to 204.0 [M] mg. g−1) than in muscle (7. 5 [F] to 11.4 [M] mg. g−1). Muscle lipid concentrations in juveniles were significantly higher (10.9 [F] and 11.4 [M] mg. g−1) in summer than in winter in adult muscle tissue (8.6 [F] and 9.4 [MI mg. g−1). A 44% increase in ovary lipid was observed from preparatory to prespawn stages, followed by a 78% decline after the spawn. Additionally, seasonal hepatic lipid concentrations were substantially higher in juveniles. Concentrations of lipid classes (free cholesterol [C], triacylglycerol [TAG], free‐fatty acids [FFA], esterified cholesterol [CE] and phospholipid [PL]) of all tissue types varied significantly among season, sex, and maturity categories. Changes with all lipid classes in the ovary coincided with those occurring in total ovarian lipid. Mobilization and transport of TAG and PL from the liver to the ovary appeared to occur during gametogenesis. All class concentrations in juveniles were invariably higher in liver than in muscle, but seasonally variable among hepatic and gonad tissues of adults. Juvenile males showed slightly greater hepatic C concentrations than other groups. Muscle and hepatic C were generally higher in juveniles.
Density of juvenile brown trout and Atlantic salmon in natural and man‐made riverine habitats
Authors: L'Abée‐Lund J. H. , Heggberget T. G.
Published: July 2006

The density of juvenile brown trout (Sulmo trutta L.) and Atlantic salmon (Salmo salar L.) was significantly higher along river bank areas protected against erosion than along natural river banks in the River Gaula, Central Norway. A habitat shift appeared in Atlantic salmon, and a behavioural shift was demonstrated by brown trout from August October. The effect of habitat on densities of juvenile salmonids should be taken into account as mitigation measures on eroded river banks and when assessing fish production in rivers.
Food consumption of northern pike (Esox lucius L.), estimated with a bioenergetics model
Authors: Heikinheimo O. , Korhonen A. P.
Published: July 2006

Abstract– A bioenergetics model was used to estimate the food consumption of northern pike (Esox lucius L.) in two lakes in northeastern Finland, and the results compared with those obtained by a method based on stomach contents and gastric evacuation rates. The annual specific food consumption was 7–5 g per one gram pike for one‐ and two‐year‐old pike, and 4–3 g g−1 in age groups 3–6 years old, according to the bioenergetics model. The proportion of ingested food used for growth was 10–30%, and was highest in the youngest age groups. The food consumption rates estimated by the stomach contents method were considerably lower, only about half those produced by the bioenergetics model. The method based on stomach contents tends to underestimate the food consumption. The bioenergetics model was considered more valid for estimating food consumption, but some of the parameter values for northern pike may differ in populations from different latitudes. According to a sensitivity analysis, the food consumption estimate of the bioenergetics model was most sensitive to parameters in the allometric function for respiration.
Habitat use, size and age structure in sympatric brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) stocks: resistance of populations to change following harvest
Authors: Langeland A. , L'Abée‐Lund J. H.
Published: July 2006

Abstract– Habitat use and population dynamics in brown trout Salmo trutta and Arctic charr Salvelinus alpinus were studied in an oligotrophic lake over a period of 10 years. Previous studies showed that the species segregated by habitat during summer. While brown trout occupied the surface water down to a depth of 10 m, Arctic charr were found deeper with a maximum occurrence at depth 10–15 m. Following the removal of a large number of intermediate sized fish in 1988–89, habitat segregation between the species broke down and Arctic charr were found in upper waters, while brown trout descended to deeper waters. The following year, both species were most frequently found in surface waters at depths of 0–5 m. During the last four years, the species reestablished their original habitat segregation despite another removal experiment of intermediate‐sized fish in 1992–1994. The removal of fish resulted in an increased proportion of large (≥ 25 cm) fish in both species. Furthermore, the charr stock responded by reduced abundance and increased size‐at‐age. The results revealed plasticity and strong resistance to harvest populations of brown trout and Arctic charr. This is probably due to internal mechanisms of intraspecific competition within each population, which result in differential mortality among size classes.
Size‐related factors causing individual variation in seasonal reproductive success of fluvial male Dolly Varden (Salvelinus malma)
Authors: Kitano S.
Published: July 2006

Abstract– Reproductive activities of individually identified fluvial Dolly Varden (Salvelinus malma) were observed during a breeding season in a small stream. Males and females both established dominance hierarchies based on body size. Females spawned from late October to late November, with no apparent peak, and larger females spawned earlier than small ones. Males competed for access to females by adopting two types of mating tactics: pairing and sneaking. The tactic used depended on the male's position in the dominance hierarchy of the breeding group. Seasonal reproductive activity and mating success of males were positively correlated with body size, with only the largest male monopolizing most of the mating opportunities, and the small males were rarely successful in mating. Smaller males, however, lost as much weight as large males during the breeding season. Females preferred the largest male in the breeding group as a mate, while males courted females of any size. It is suggested that the polygynous mating pattern is a consequence of size‐related differences in competitive ability among males, and the degree of monopolization is affected by both the temporal distribution and the spawning tactics of the females.
Sampling fish assemblages in forested floodplain wetlands
Authors: Knight J. G. , Bain M. B.
Published: July 2006

Abstract– Four quantitative (area‐standardized electrofishing, trap nets, small‐mesh [1.3 and 2‐cm bar mesh] gill nets, large‐mesh [2.5 and 5‐cm bar mesh] gill nets) and two qualitative (non‐standardized electrofishing, dip netting) sampling techniques were concurrently used to capture larval to adult fish in forested wetland habitats on seasonally inundated floodplains of two Alabama (USA) streams. Standardized area electrofishing appeared to be the best sampling technique for collecting and quantifying species because of high catch rate, broad species and size coverage, and rapid sampling. Electrofishing accounted for most fish (47 and 57% of pooled catch), almost all taxa, and a broad range of fish sizes. Large‐mesh gill nets captured few fish (2% and 8%), a distinct subset of the species present, and the largest fish. Light traps were the most efficient and taxa‐comprehensive sampling technique for larval fish. Light traps captured the vast majority of the pooled larval fish catch, including 6 of 7 families recorded at the sites. Larval fish dip netting captured larval fish of most families known to be present but in low numbers. For surveys of species composition and rapid bioassessments, nonstandardized electrofishing and larval fish dip netting appear adequate. For intensive research studies, the combination of area electrofishing, large‐mesh (and in some cases small‐mesh) gill nets, and light traps provide thorough and comprehensive data on wetland fish assemblages.
The effects of lakes on growth in yearling brown trout (Salmo truttaL.)
Authors: Degerman E. , Johlander A. , Sers B. , Sjöstrand P.
Published: July 2006

Abstract–Data from the Swedish Electrofishing Register were used to study the effects of lakes on the growth of yearling (0+) brown trout in outlet streams. It was found that growth increased close to lakes. On average, the length of the longest yearlings was 10% greater 0‐100 m downstream from lakes as compared with more than 1 km downstream. Growth enhancement was most pronounced downstream from large lakes. This was exemplified with maximum yearling lengths in September in inlet streams (maximum yearlings 50‐100 mm) and outlet streams (65‐130 mm) of Lake Stora Le (area 200 km2), and inlet streams (50‐75 mm) and outlet streams (65‐95 mm) of Lake Anten (area 18 km2). It is suggested that this is a combined effect of both increased water temperature and outflow of lake seston. The growth pattern found was not correlated to population abundance or to the abundance of competitors or predators.
Changes in the population density of pelagic salmonids in relation to changes in lake enrichment in Windermere (northwest England)
Authors: Elliott J. M. , Fletcher J. M. , Elliott J. A. , Cubby P. R. , Baroudy E.
Published: July 2006

From July 1989 to December 1994, an echo sounder provided monthly estimates, usually for both day and night, of pelagic salmonid densities in the North and South Basins of Windermere, the largest natural lake in England. Sampling was along contiguous transects, three in the North Basin and five in the South Basin. Records for Arctic charr (Salvelinus alpinus) could not be separated from those for brown trout (Salmo trutta), but previous sampling by gill‐nets and anglers showed that charr formed over 90% of this mixed population in the North Basin and about 60–75% in the South Basin. Associated with the increasing eutrophication of the lake, there has been a decline in anglers' catches of charr and, since 1984, an increase in brown trout taken in the pelagic zone of the South Basin. The echo‐sounder data showed that pelagic salmonid density in the North Basin was about two to five times that in the more eutrophic South Basin in 1989, 1990 and 1991. Since the start, in April 1992, of the reduction of phosphorus discharged from sewage works, this ratio has decreased, especially at night when the highest densities were recorded. This improvement was chiefly due to a significant (P<0.001) increase in the density of small fish (length <20 cm), in both the upper (depth <20 m) and deeper (depth >20 m) water layers. Although a similar improvement has still to be shown in the upper water layer by larger fish above the size limit for removal by angling (20 cm), there has been a significant increase (P<0.01) in the density of these fish in the deeper water layer of the South Basin. The increased density of small fish suggests that the stock available to charr anglers (fish >20 cm at water depths <20 m) should increase in the next few years, especially in the South Basin. It is therefore important to continue the monitoring program and thus ensure that there is advance warning of any marked changes in charr stocks.
Observations on the natural history of the Gulf of Mexico sturgeon (Acipenser oxyrinchus de sotoi Vladykov 1955) in the Suwannee River, southeastern United States
Authors: Carr S. H. , Tatman F. , Chapman F. A.
Published: July 2006

From 1986 to 1994, we collected 3,098 Gulf of Mexico sturgeon (Acipenser oxyrinchus de sotoi) during their spring migration from the Gulf of Mexico to the Suwannee River, Florida. We estimated population size and described migratory and seasonal growth patterns of sturgeon in the Suwannee River, using data from tag returns, movement of ultrasonic‐lagged fish and weight records. Population size estimates for 3.0‐ to 81.0‐kg Gulf of Mexico sturgeon in the Suwannee River ranged from 1,504 to 3,066 fish. Sturgeon migrated from the Gulf of Mexico into the Suwannee River from mid‐February to early May. Fish moved upstream and remained within a 2‐km upstreamdownstream “home” area. These sites were closely associated with undenvater springs that discharge into the river. Sturgeon migrated downstream and into the Gulf of Mexico in October and November. In the Gulf of Mexico, ultrasonic‐tagged fish were located in the Suwannee Sound area just north of Cedar Key, Florida. On an annual basis, fish gained an average of 20% of their body weight while in the Gulf of Mexico and lost about 12% of their weight during their stay in the Suwannee River. We observed movement of tagged sturgeon between the Suwannee and Apalachicola Rivers.
Distribution of and reproductive isolation among color morphs of a rock‐dwelling Lake Victoria cichlid (Haplochromis nyererei)
Authors: Seehausen O.
Published: July 2006

Geographical, macro‐ and microhabitat distribution of and mate recognition among color morphs of a complex of Lake Victoria cichlids was studied. The distribution of most morphs was mutually exclusive but two morphs overlapped extensively and differed only in microhabitat requirements. Coloration differences between them were inherited, and wild fishes were homozygous in this respect. Positive morph assortative female mate choice was demonstrated. Over the largest part of their common geographical range intermediate phenotypes are absent and the two morphs are to be considered two biological species. However, in populations at one end of the range intermediate phenotypes with continuously varying male coloration make up the majority of the individuals. It is suggested that the status of color morphs as phenotypes of one species or as separate biological species is a function of environmental conditions that vary considerably between the localities. The data support the hypothesis that polymorphisms can be a step preceding speciation in cichlid fish.
Effect of water temperature and growth variation on the sex ratio of experimentally reared eels
Authors: Holmgren K.
Published: July 2006

In a controlled experiment, elvers (Anguilla anguillaL.) were reared for 137 weeks at 17, 20 and 26°C. Most eels with macroscopically sexable gonads were males. The proportions of females were 14% of sexable individuals at 26°C and 7–8% at 17 and 20°C. During the first 15 weeks, 20–50% of initial numbers were lost, but this early mortality was not significantly size selective. In spite of a long term experiment, a significant number of the survivors never attained a sexable size. Nongrowers (7–9 cm) were still alive nearly three years after being caught as glass eels. Among the earliest fast growers, 5% females, or less, were found. The proportion of females increased in later grading groups, but the pattern of increase did not indicate that males and females have separated mean ranks in a fixed growth hierarchy. Water temperature influenced observed sex ratios, but probably not through direct influence on the sex differentiation. Some alternative hypotheses, dealing with population density and individual growth status, are discussed.
Possible increase in catch of Atlantic elver Anguilla anguilla in 1993 and 1994
Authors: Moriarty C. , Tesch F.‐W.
Published: July 2006

Data on catches of O+ elvers from nine countries in Europe and of juvenile eels ascending the St. Lawrence River in Canada are presented and compared with previous records. Consideration of a parallel decline in recruitment in Canada supports the theory that oceanic conditions are responsible for the observed fall in catches. A substantial increase in the Loire, to 95 tons in 1994, may indicate an overall improvement in stocks.
Habitat utilization and diel behavior of juvenile bull trout (Salvelinus confluentus) at the onset of winter
Authors: Thurow R. F.
Published: July 2006

Abstract— Underwater observations were used to describe habitat use and diel behavior of juvenile bull trout (Salvelinus confluentus) at the onset of winter (0.8°C) in a second‐order central Idaho stream. All fish observed during daytime counts were concealed beneath “home stones” (mean dimensions 32.3 by 21.9 cm) in primarily pool and run habitats. Focal point depths and velocities averaged 57.2 cm and 4.7 cm/s (home stone removed). Fish maintained stations over substrate with low percentages of fine (< 2 mm, mean= 5.2%) sediment. Concealed bull trout were not evenly distributed across the stream channel. Significantly more home stones were distributed near the midline of the channel, compared to the channel margins. Fish size was positively correlated with home stone size. At night, bull trout exhibited a diel behavioral shift, some fish moved out of daytime concealment cover into the water column. At night, bull trout were observed feeding and resting, primarily in pool and run habitats. During both day and night, bull trout used riffles significantly less frequently than those habitats were available.
Patterns of foraging and distribution of bluegill sunfish in a Mississippi River backwater: influence of macrophytes and predation
Authors: Dewey M. R. , Richardson W. B. , Zigler S. J.
Published: July 2006

Abstract— We studied the trophic interactions and spatial distributions of bluegills Lepomis macrochirus and largemouth bass Micropterus salmoides in a macrophyte bed in Lake Onalaska, a backwater lake in the upper Mississippi River. The diets of adult and age‐0 bluegills were similar and changed seasonally probably in response to changes in life stages of macroinvertebrates (i. e. emergence of winged adults). Diets and diel patterns of abundance of bluegill suggest that age‐O and adults were feeding in the vegetated, littoral zone. Predation by age‐O largemouth bass appears to influence use of vegetated habitat by age‐0 bluegills. In summer, when most age‐O bluegills were vulnerable to predation by age‐O largemouth bass, bluegill abundance was strongly correlated with vegetation biomass. In October and November, piscivory by age‐O largemouth bass was limited by gape. Consequently, the relationship between the abundance of age‐O bluegills and vegetation biomass was weakened because predation risk by age‐O largemouth bass was reduced.
Effects of predation and intraspecific interactions on habitat use and foraging by brown trout in artificial streams
Authors: Greenberg L. A. , Bergman E. , Eklöv A. G.
Published: July 2006

Abstract— We studied habitat use, foraging rates and behavior of 10 cm and 12 cm long brown trout, Salmo trutta, at two densities, 1.5 and 3.0 fish. m−2, in artificial streams that contained either the amphipod, Gammarus pulex, alone or G. pulex together with the piscivore, northern pike, Esox lucius. Gammarus were stocked in and largely restricted to the pools at a density of 128 Gammurus. m−2. pool−1 Large trout (12 cm) used pools more and riffles less when small trout (10 cm) were present than when small trout were absent. Small trout consumed fewer Gammarus when together with large trout than when alone, but showed no difference in habitat use in the presence and abscnce of large trout. Habitat use and number of Gammarus consumed per trout were not affected by trout density for either size‐class when alone. For both size‐classes of trout, use of pools and foraging rates were higher in the absence than in the presence of pike, and pike primarily resided in the pools. The number of aggressive interactions by both size‐classes of trout decreased when pike was present. Our results indicate that for habitats that differ in food resources and predation risk, size structure may affect habitat use and foraging by brown trout.
Habitat selection by three littoral zone fishes: effects of predation pressure, plant density and macrophyte type
Authors: Chick J. H. , Mlvor C. C.
Published: July 2006

Abstract— We conducted laboratory experiments which demonstrated that three littoral zone fishes differentially selected among three macrophytes when seeking refuge from predation. In the presence of a predator (a juvenile Micropterus salmoides), mosquitofish (Gambusia holbrooki), sailfin mollies (Poecilia latipinna). and dollar sunfish (Lepomis marginatus) displayed ferential use of four tank areas containing patches of either Hydrilla verticillata, Potamogeton illinoensis, Panicum hemitomon, or no plants. Patterns habitat selection, and the consistency of these patterns among replicates, differed among the three fishes and among three plant‐density treatments ‐ natural (each macrophyte presented at its mean field density), equal (all three macrophytes at the same density), and control (no plants). Selection for H. verticillata by mosquitofish was significant for both the equal and natural treatments, and thus was not caused by differences in plant density alone. Sailfin mollies displayed significant selection for H. verticillata only in the natural plant‐density treatments. Dollar sunfish showed less consistent habitat selection than either mosquitofish or sailfin mollies. Significant habitat selection was not found in the absence of a predator, and there was no evidence for lection among the tank areas in control treatments. Patterns of habitat selection by the three fishes in our laboratory study corresponded to observed habitat use in Lake Okeechobee.
Genetic variability of the Japanese eel Anguilla japonica (Temminck & Schlegel) related to latitude
Authors: Chan I. K. K. , Chan D. K. O. , Lee S. C. , Tsukamoto K.
Published: July 2006

Abstract— Isozyme genotypes of 400 glass eels recruiting to 4 localities along the east Asian coast, stretching from Taiwan to the Yalu River of northeastern China, were studied using starch gel electrophoresis. Geographic cline was found to exist in two loci: NADP‐isocitrate dehygenase‐1 and 6‐phosphogluconate dehydrogenase. Frequencies of the most common allele of these two loci increased from south to north. In the latitudinal range of 25°N to 40°N, the magnitude of difference of IDH100 and PGD100 was 13% and 9% respectively. However, deviations from Hardy‐Weinberg equilibrium were found to be insignificant in both loci at three of the four localities. The cline was, therefore, unlikely to have resulted from selection. Migration time‐lag from different parts of the continent to the spawning ground in the western Pacific was suggested to be a possible reason for the formation of the cline.
Stable carbon and nitrogen isotopic evidence for ecotonal coupling between boreal forests and fishes
Authors: France R. L.
Published: July 2006

Abstract— As a result of water turbulence effects on boundary layer diffusion resistance and carbon isotopic discrimination, the δ13C values (ratios of 13C: 12C) of attached algae may often overlap those of terrestrial plants, thereby making it impossible to distinguish between the relative importance of these two potential food sources for aquatic animals. The present study used a dual isotope approach (δ13C and δ15N) to refine measurements of the incorporation of allochthonous organic matter into freshwater fishes. The dependence of five species of littoral fishes on terrestrial detritus for part of their energy sustenance was demonstrated. The littoral zones of boreal Canadian Shield lakes are, therefore, not isolated from their surrounding riparian forests in terms of carbon flow as present day timber management guidelines erroneously assume, but instead exhibit a measurable degree of ecotonal land‐water coupling. As a result, clearcut logging of riparian forests to the lakeshore edge, permissible by law in most Canadian provinces containing boreal forests, may have to be reassessed as a forest harvesting strategy.
Variation in thermal tolerance and routine metabolism among spring‐ and stream dwelling freshwater sculpins (Teleostei: Cottidae) of the southeastern United States
Authors: Walsh S. J. , Haney D. C. , Timmerman C. M.
Published: July 2006

Abstract— Evolutionary theory predicts that some aquatic organisms may adapt by directional selection to limiting physical environmental conditions, yet empirical data are conflicting. We sought to test the assumption that sculpins (family Cottidae) inhabiting thermally stable springs of the southeastern United States differ in temperature tolerance and metabolism from populations inhabiting more thermally labile stream habitats. Spring populations of pygmy sculpins (Cottus pygmaeus) and Ozark sculpins (C. hypselurus) differed interspecifically in thermal tolerance from populations of stream‐dwelling mottled (C. bairdi) and Tallapoosa sculpins (C. tallapoosae), and both stream and spring populations of banded sculpins (C. carolinae). No intra‐ or interspecific differences in thermal tolerance were found among populations of C. bairdi, C. talla poosae, or C. carolinae. Cottus pygmaeus acclimated to 15°C differed intraspecifically in routine metabolism from fish acclimated to 20° and 25°C. Cottus pygmaeus and stream‐dwelling C. bairdi and C. carolinae acclimated to temperatures of 20° and 25°C showed no interspecific differences in routine metabolism. Our results suggest that some spring‐adapted populations or species may be more stenothermal than stream‐dwelling congeners, but a greater understanding of the interactions of other physical and biological factors is required to better explain micro‐ and macro habitat distributions of eastern North American sculpins.
A critical consideration of the metamorphosis zone when identifying daily rings in otoliths of European eel, Anguilla anguilla (L.)
Authors: Antunes C. , Tesch F.‐W.
Published: July 2006

Otoliths of glass eels and larvae collected from the Rio Minho (Portugal/Spain) as well as from the Iberian continental slope from the Bay of Biscay were analyzed by scanning electron microscopy. Preliminary data are presented on the total radius of the otolith and the width of the zone exhibiting a diffuse structure which, in the literature, is suggested to be the zone of metamorphosis. It was found that the radius increased from the development stage I through stage II to the glass eel stage (Vb). The width of the diffuse zone also exhibited an increase. Calculations of the dimensions of the diffuse zone of specimens older than stage I revealed that the area of metamorphosis amounts to about 28–60% of the total diffuse zone. From these results it is evident that part of the diffuse zone must have formed during a larval phase of retarded growth, during which no formation of daily growth rings takes place. Only the outer portion of the diffuse zone can be accounted for by the metamorphosis. For these reasons, an exact age determination by counting daily rings seems impossible. A determination of the oceanic life of the eel recruits is difficult for other reasons too: all earlier and recent studies have indicated that Anguilla leptocephali and their metamorphosis stages do not occur on the continental shelf, which could add an additionally high amount of time needed until arrival at the coasts.
Variability in growth rates of freshwater eels (Anguilla spp.) in New Zealand
Authors: Jellyman D. J.
Published: July 2006

Abstract— Both species of New Zealand freshwater eels (the shortfinned eel Anguilla australis and the longfinned eel A. dieffenbachii) are widespread and abundant, supporting important commercial and recreational fisheries. This article reviews growth studies from 35 widely distributed sites throughout New Zealand and discusses factors that influence growth rates. Length at given age is characterized by high intra‐ and inter‐population variability; growth rates for eels >30 cm are typically slow (2–3 cm per year) and linear, with females generally growing faster than males. Water temperature affects the length of the growing season, although growth rates are not correlated with latitude. Other factors suggested as affecting growth rates are eel density, quantity and quality of food, and interactions between both eel species. Al though growth of some New Zealand eel populations is the slowest recorded for any species of Anguilla, growth in culture can be rapid, similar to that of other temperate eel species.
Winter mortality of young‐of‐the‐year pikeperch (Stizostedion lucioperca)
Authors: Kirjasniemi M. , Valtonen T.
Published: July 2006

Abstract— The wintering success of young‐of‐the‐year pikeperches (Stizostedion lucioperca) was examined in the laboratory during the winter of 1993‐1994. From September to November half the fishes were offered artificial fishfood; the others received plankton with river water. Pikeperch did not eat the fishfood properly, and poorer condition of the smallest fish fed artificially was reflected in a lower amount of lipid in the whole fish at the beginning of the experiment in November. The autumnal diet played an important role in determining the wintering success even when the effect of size was removed. In contrast, feeding during the experiment did not affect survival. However, feeding fishes had more lipid at the end of the experiment in April than starved ones and their protein content also increased during the winter.
Perch (Perca fluviatilis) as an indicator species for structural degradation in regulated rivers and canals in the lowlands of Germany
Authors: Wolter C. , Vilcinskas A.
Published: July 2006

Abstract— Simple morphological characteristics and fish assemblage data were collected in representative numbers from 12 inland waterways in the northeastern lowlands of Germany between 1992 and 1995. Fish abundance data were pooled and classified into three main groups: perch Perca fluviatilis (L.), roach Rutilus rutilus (L.) and other species. Spearman rank correlations between fish abundance and type of embankment revealed that perch showed a statistically significant numerical dominance in waterways consisting predominately of an artificial shoreline, suggesting that perch may be used as an indicator of the structural degradation of watercourses.
Environmental characteristics of black crappie (Pomoxis nigromaculatus) nesting sites in two South Dakota waters
Authors: Pope K. L. , Willis D. W.
Published: July 2006

Abstract— A biotelemetry study was undertaken during spring 1995 to identify black crappie (Pomoxis nigromaculatus) nesting sites in two South Dakota water bodies. Individually coded ultrasonic transmitters were implanted into the body cavity of 15 adult male black crappie in each water body prior to spawning. Available habitat characteristics were recorded at 75 randomly selected sites within each water body, and habitat characteristics at nesting sites were recorded for each male black crappie believed to be nesting. Of the habitat characteristics analyzed, only substrate firmness did not differ (P=0.79) between water bodies. In Richmond Lake, black crappie selected nesting sites with live cattails (Typha spp.) that were protected from prevailing south winds. In Brant Lake, black crappie selected nest sites with vegetation (usually woody debris) and silty substrate that had warmer water and were protected from wind and waves. It appeared that black crappie nested in the most protected areas available.
Temporal variation in Lake Balaton and its fish populations
Authors: Bíró P.
Published: July 2006

Abstract— Dramatic changes have occurred in Lake Balaton in the last 40–45 years. Variations in water quality have resulted in a decrease in fish and invertebrate diversity. Fish assemblages have changed in response to human‐induced eutrophication, environmental perturbations, introduction of exotic fish species, over‐fishing and species‐habitat interactions. Fish biomass and productivity first increased during the early 1970s with enhanced primary production, then decreased with the reduction of exploitation since the late 1970s and induced intra‐ and interspecific competition. Previous stable populations began to oscillate, and the majority of stocks became fragile by the mid‐1980s. Extinction of native fish and invasion of new alien species alternate. Alien species have transformed the food webs, causing long‐lasting ecological changes. Reduced and non‐selective exploitation has resulted in higher fish density and lower production rates. Recent studies have revealed differences in the carrying capacity of fish between the littoral zone and the open water areas.
Efficacy of a vacuum benthos sampler for collecting demersal fish eggs from gravel substratum
Authors: Ruetz C. R. , Jennings C. A.
Published: July 2006

Abstract— We used two densities of eggs (low=900 eggs/m2; high=5100 eggs/m2) in laboratory experiments to estimate the recovery efficiency of the Brown benthos sampler for collecting fish eggs from gravel substrate and to determine if differences (e. g., 5‐fold) in egg density in the substratum could be detected with the sampler. The mean egg recovery efficiency of the sampler in the low and high density treatments was 30% (SE=8.7) and 35% (SE=3.8), respectively. The difference between the treatment means was not significant. Therefore, data from the two treatments were pooled and used to estimate the recovery efficiency of the sampler (32.7%, SE=4.4). However, we were able to detect a 5× difference in the number of eggs collected with the sampler between the two treatments. Our estimate of the recovery efficiency of the sampler for collecting fish eggs was less than those reported for the sampler's efficiency for collecting benthic macroinvertebrates. The low recovery efficiency of the sampler for collecting fish eggs does not lessen the utility of the device. Rather, ecologists planning to use the sampler must estimate the recovery efficiency of target fauna, especially if density estimates are to be calculated, because recovery efficiency probably is less than 100%.
Diel feeding periodicity in larvae of the vendace (Coregonus albula L.) and influence of food availability and environmental factors on food intake
Authors: Huusko A. , Sutela T.
Published: July 2006

Abstract— Samples were taken every 2 h for 10 days to determine diel foraging periodicity of vendace larvae in the littoral zone of Lake Lentua, northern Finland and to assess environmental factors affecting food intake. Feeding was associated with daylight conditions, so feeding ceased in the dark. Soft‐bodied, rapidly digested rotatorians indicated the periodicity more clearly than hard‐shelled prey such as cladocerans and copepodites. Wind events and waves in the littoral zone were the major factors affecting food abundance and feeding by the larvae. Waves induced by strong inshore winds reduced zooplankton density, increasing the occurence of larvae with empty guts to 80%. Reduced food availability was reflected in the guts of larvae within 6 h. The density of suitably‐sized zooplankton, together with wind effects and photoperiodism, explained most of the variation in gut content in the larvae.
Predation risk from piscivorous fish influencing the diel use of macrophytes by planktivorous fish in experimental ponds
Authors: Jacobsen L. , Perrow M. R.
Published: July 2006

Abstract— This study investigated interactions between zooplanktivores (roach and perch) and piscivorcs (pike and large perch) in experimental ponds (16 m2) with open water habitat and three densities of natural macrophytes. Fish habitat selection was determined both day and night and was supported by daytime observations to study anti‐predator behavioural patterns. Diel migration out from among macrophytes was seen in the absence of predators, particularly for roach, which changed from 13% of individuals being in open water during the day to 90% at night. The risk of predation from piscivores influenced the habitat selection of the zooplanktivores. Roach seemed to be the most vulnerable to predation from pike and selected the open water (90‐92%) during daylight hours, but kept a 1‐m distance from the macrophytes edge. The presence of pike thus reduced the use of macrophytes by roach, which in turn may improve macrophytes and the edge area as a refuge for zooplankton. Pike appeared to have less impact on the gross habitat selection of O+ perch, which were associated with the macrophytes (58–89%), though they were still vulnerable to predation. Adult perch, which was a generally less effective predator than pike, showed subdued behavior, concealing them selves in the macrophytes most of the time. No effect of the simultaneous presence of two predator species was found.
The influence of instream cover and predation risk on microhabitat selection of stone loach Barbatula barbatula (L.)
Authors: MacKenzie A. R. , Greenberg L.
Published: July 2006

Abstract— The microhabitat selection of stone loach (Barbatula barbatula) in relation to instream cover and predation risk was investigated in artificial streams. In one experiment, stone loach were presented different combinations of shelter structures, two at a time, that provided visual isolation, flow refuge, both, or none. In all cases, visual isolation shelters were selected by the fish, with little use of clear shelters and no apparent selection of flow refuges. In a second experiment, diel activity patterns and habitat selection of stone loach were measured when visual isolation structures were placed in the riffle only, pool only, both riffle and pool or in no habitat. Stone loach were marked with passive integrated transponder tags and a sensor plate was placed between the riffle and pool habitats to measure diel activity patterns. Habitat use was measured by releasing drop gates between the two habitats at the end of each trial. More stone loach used the pool than the riffle in all treatments, but use of the riffle increased when cover was present only there. Furthermore, stone loach were most active between 2100 and 0300. To determine the effect of predation threat on habitat use by stone loach, one adult brown trout (Salmo trutta) was added to each pool. The presence of trout caused stone loach to move into the riffle, especially the smaller loach. Overall, the study showed that stone loach used cover in a visual isolation context, preferring deeper water when there was no predation risk, but made more use of shallower water in the presence of brown trout.
Spawning of the broad‐finned Galaxias, Galaxias brevipinnis Günther (Pisces: Galaxiidae) in coastal streams of southeastern Australia
Authors: O'Connor W. G. , Koehn J. D.
Published: July 2006

Abstract— The broad‐finned galaxias, Galaxias brevipinnis, spawned during high flows in mid autumn. Spawning took place over inundated riparian areas where eggs were laid amongst substrate, mainly in the interstices of cobbles and pebbles. Between subsequent high flows, eggs were out of water for days or weeks, lying up to 7 m from the water's edge. When exposed, eggs and streamside substrate remained damp, shaded by surrounding forest. Hatching would only occur when eggs were inundated by a subsequent flood. In the field, most eggs had hatched within 30 days of the spawning period, but some remained unhatched for up to 60 days. In the laboratory, eggs remained unhatched for up to 57 days under moist conditions but out of water, and up to 120 days when kept in water. However those kept under drier conditions died. It would appear that riparian cover may be important in providing shaded and moist conditions for the survival of eggs in the wild. Evidence of some adult mortality following spawning was noted. Newly hatched larvae were carried to sea during high flows. Predation on eggs by both adult G. brevipinnis and introduced brown trout Salmo trutta Linnaeus was found to occur.
The breeding biology of Clarias albopunctatus Nichols & LaMonte, 1953 in semi‐intensively managed ponds in the floodplain of the River Anambra, Nigeria
Authors: Ezenwaji H. M. G.
Published: July 2006

Abstract— In ponds in the floodplain of the River Anambra, Nigeria, Clarias albopunctatus matured after the first year when they were 101–150 mm in total length. Gonad development was more rapid in males than in females. The breeding season lasted from March to September, and recruitment of the clariids into the artisanal fishery began from the latter month. The number of oocytes in both ovaries ranged from 1974 to 9310. Fecundity‐weight relationship was linear and positively correlated: Y= 1451.64+ 77.19x, r2= 0.82. Spawnable oocytes, which constituted over 91% of gonad weight, ranged from 1.05 to 1.75 mm in diameter. A minor and major communal spawning involving Clarias macromystax, C. agboyiensis and C. albopunctatus took place in the inundated grassy areas of the floodplain. Migration of 4‐month‐old juveniles towards the main river or floodplain ponds, which appeared to be triggered by current speed in the spawning ground, occurred during the night and in groups.
Larval development of Nannatherina balstoni Regan (Nannopercidae), with a description of ontogenetic changes in diet
Authors: Gill H. S. , Morgan D. L.
Published: July 2006

Abstract— This article describes the larval development and ontogenetic changes in diet of Nannatherina balstoni and constitutes the first description of flexion and postflexion larvae for the family Nannopercidae. Larvae were collected from pools in southwestern Australia. Larvae are elongate to moderately deep, lack head spines, have a moderate to large head and are moderately to heavily pigmented. Notochord flexion is complete by approximately 11 mm, i. e., longer than in members of the closely related Percichthyidae (≤ 9 mm). The sequence of fin completion, C, D2, A, D 1→P1→P2, also differs to that reported for percichthyids, but is the generalized condition within the percoids. The retention of a prominent notochord tip in postflexion larvae of N. balstoni is a characteristic that occurs in few teleosts. Nannatherina balstoni exhibits marked ontogenetic changes in diet. Larvae feed predominantly on cladocerans, copepods and dipteran larvae, whereas juveniles and adults ingest a large proportion of terrestrial fauna.