Do instream habitat variables and the abundance of brown trout Salmo trutta (L.) affect the distribution and growth of stone loach,Barbatula barbatula (L.)?

Abstract –  Along a stream, we investigated whether the abundance of stone loach ( Barbatula barbatula , L.) was related to the presence of brown trout ( Salmo trutta , L.) and instream habitat variables. First, a field survey was carried out where different habitat variables and the densities of both species were quantified and subjected to principal components analysis. Then the abundance of stone loach was related to the scores of the retained axes (eigenvalues >1). The abundance of stone loach was positively correlated to substrate particle size, amount of shade, temperature, discharge and current velocity, but negatively correlated to brown trout abundance. Secondly, a month-long field enclosure experiment in a stream was performed to test for any negative effects of brown trout on stone loach growth. Four treatments were used: intraspecific competition (stone loach at double density), interspecific competition (stone loach + small trout), predation (stone loach + large trout) and a control (stone loach alone). The results showed that large trout tended to have negative effects on final stone loach biomass. The absence of a negative effect of large trout on resource density suggests that nonlethal effects rather than resource competition caused this trend.     

Seasonal changes in abundance and age structure of burbot Lota lota (L.) and stone loach Barbatula barbatula (L.) in the littoral zone of a large pre-alpine lake

Abstract – Seasonal changes in the abundance and age structure of the stone loach and burbot populations in the littoral of Lake Constance, Germany were examined. The abundance of both species was lowest during the summer months and highest during autumn. The stone loach population in the littoral comprised age classes 1 to 3 plus, in autumn, age class 0. The burbot population showed distinct seasonal changes in both length and age composition. During spring and summer, only age class 1 was present in the littoral whereas, in autumn, only age class 0 was caught. This remarkably strict habitat segregation of two age classes by season is discussed with respect to a possible mechanism for avoiding conspecific predator risk in a cannibalistic species.     

High microsatellite genetic variability of the stone loach, Barbatula barbatula, in anthropogenically disturbed watercourses

Abstract  Genetic variation within and among stone loach, Barbatula barbatula L., populations inhabiting anthropogenically degraded watercourses in Flanders (northern part of Belgium) was assessed using five microsatellite markers. High levels of genetic diversity were observed at all sampling sites, (MNA: 6.2–11.2; H _O: 0.64–0.75; H _E: 0.67–0.85). Estimates of the effective population size varied between 1535 and 3021 individuals and there were no indications of recent severe bottlenecks. Significant genetic differentiation was observed among sites belonging to different river systems and drainage basins. These results suggest human activities, such as pollution and river engineering, have not impacted significantly on genetic variability in the stone loach populations investigated. It is possible that this lack of genetic erosion may be attributed to species-specific characteristics such as pollution tolerance and ecological flexibility.     

The influence of predation risk on habitat selection and food intake by Arctic charr, Salvelinus alpinus (L.)

Abstract— Large piscivorous fish are assumed to affect habitat selection and food intake of prey fish. To study the effects of cannibalistic Arctic charr, Salvelinus alpinus (L.), on smaller stunted charr, we sampled the prey fish in littoral and pelagic habitats using gill nets, before and shortly after the release of large charr in a small lake (0.52 km²). In the habitats where the risk of predation was highest, the catch per unit effort de creased from 13.3 to 4.8 fish per 100 m² of gillnet after release of pred ators. The large decrease in numbers of charr < 18 cm corresponded with the predicted vulnerable prey sizes, according to a model based on the size distribution of predators. The occurrence of planktivorous fish and weight-specific food intake decreased in the high risk habitat and remained unaffected in the low risk habitats. Changes in the food intake of prey fish could not be explained in terms of fish length, indicating that prey fish changed diet when the risk of predation was high.     

Estuarine predation on radiotagged wild and domesticated sea trout (Salmo trutta L.) smolts

Abstract – Avian predation on emigrating wild and domesticated sea trout smolts was investigated in a fjord in the western Baltic Sea. In April 1997, 50 domesticated and 50 wild smolts were intraperitoneally tagged with radio-transmitters and released in a small coastal stream. Predation was recorded by signal interception in an estuarine breeding colony of cormorants and herons near the outlet of the stream. Of the 78 emigrating smolts, 51 (65%) were recorded as eaten. Predation rates were significantly higher among small than large smolts and significantly higher among domesticated smolts. The first 2 days after entering the sea, both wild and domesticated smolts suffered a severe daily predation rate (range 20–34%). The results support the hypothesis of a transient period immediately after exposure to full-strength sea water, where smolts experience an elevated risk of predation. A transient increase in postsmolt mortality may be found also in moderately saline environments (20–23 ppt).     

Production and predation rates in a cannibalistic Arctic char (Salvelinus alpinus L.) population

Abstract – Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11–14.30) kg · ha⁻¹. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50–1.06) kg · ha⁻¹. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74–8.03) kg · ha⁻¹ · year⁻¹, and production (±95% CL) of cannibalistic char to 0.19 (0.15–0.33) kg · ha⁻¹ · year⁻¹. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%.     

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

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.     

The pathology caused by Pomphorhynchus laevis Müller in the alimentary tract of the stone loach, Noemacheilus barbatulus (L.)

Abstract. Changes induced in intestinal and rectal structure of the stone loach, Noemacheilus barbatulus (L.) by Pomphorhynchus laevis Müller infection are described. Within the gut, the main effect of the infection is the abrasion and flattening of the mucosa by the parasite. Where the praesoma penetrates the gut wall, there is a marked inflammatory response. This inflammatory response tissue is well vascularized and displays esterase activity. Granulocytes and phagocytic cells, which are found both within the inflammation tissue and within capillaries, are probably host leucocytes. The integument of P. laevis appears undamaged by granulocytes in its proximity and it is unlikely that the host's inflammatory response is capable of rejecting the parasite.     

Growth and mortality of juvenile sunfishes (Lepomis sp.) under heavy predation

The relationship among growth, energy storage and mortality of juvenile bluegills (Lepomis macrochirus, Rafinesque) experiencing heavy predation was experimentally investigated in a large reservoir where piscivorous largemouth bass (Micropterus salmoides, Lacépède) were abundant. I conducted experiments evaluating interspecific competition, density-dependent growth and lipid content and habitat-specific growth and mortality rates of juvenile bluegills in this reservoir. Enclosure experiments showed that the growth rates of bluegills were unaffected by presence of other Lepomis species but decreased with increasing bluegill density. However, at densities corresponding to those found in the reservoir, the growth rates of bluegills were high, and competition appeared to be relatively unimportant. The percentage lipid content of bluegills was unaffected by the presence of other species, density of bluegills or habitat. The growth rates of bluegills in vegetated refuge areas were significantly higher and mortality rates were significantly lower compared with open water habitats. The low densities and high growth rates of juvenile bluegills in refuge environments suggests that there is a strong lethal effect of predators on this population of bluegills.     

Effects of cell-cycle arrest agents on cleavage and development of loach (Misgurnus anguillicaudatus) embryos

The aim of this study was to determine the lowest concentration of nocodazole and colchicine to arrest blastomere division during the cleavage stage of loach embryos and to assess the reversibility and toxicity of the treatments in the treated embryos. Eight-cell loach embryos were incubated for 4, 8, 12, or 16 h in 1/10× Holtfreter supplemented with either nocodazole, an inhibitor of tubulin polymerization, or colchicine, an inhibitor of tubulin assembly. Complete arrest of cell cycle was observed, at a colchicine concentration of 0.996 mM and at a nocodazole concentration of 0.275 μM, respectively (the lowest effective concentration). No major morphological alteration in chromatin was observed. Reversibility and toxicity of both agents were dose and exposure period dependent. For both agents, prolonging cleavage arrest for more than 4 h (at the effective concentrations) is detrimental to development of embryos. Nocodazole treatment was less cytotoxic, whereas the concentrations of colchicine which induce cleavage arrest were detrimental to development beyond the blastula stage. Toxic effects beyond the blastula stage could be minimized for both agents by reducing the period of treatment and concentration. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of predation on stunted and nonstunted white perch

Gosch NJC, Pierce LL, Pope KL. The effect of predation on stunted and nonstunted white perch.
Ecology of Freshwater Fish 2010: 19: 401–407. © 2010 John Wiley & Sons A/S Abstract – Predation is widely regarded as a means to prevent or minimise the establishment of a stunted (high density of slow growing individuals) population. We investigated the effect of predation on two different white perch Morone americana populations (stunted and nonstunted) by examining the stomach contents of piscivorous fishes. White perch and gizzard shad dominated piscivore diets in Branched Oak Lake, whereas white perch dominated piscivore diets in Pawnee Lake. White perch consumed in the stunted population (Branched Oak Lake) were larger and older than white perch consumed in the nonstunted population (Pawnee Lake). Many of the consumed white perch in the stunted population were sexually mature and had the opportunity to spawn at least once. In contrast, all of the consumed white perch in the nonstunted population were sexually immature. Predation may have reinforced the stunting of white perch in Branched Oak Lake through removal of the largest, oldest individuals.     

The influence of water depths and inter-specific interactions on cover responses of juvenile Atlantic salmon

Abstract  – The responses of salmon parr, Salmo salar, to instream cover, related to several water depths, were tested in an ellipsoidal stream tank. Opaque plastic covers, most of which were 20 cm in length and 16 cm high, were randomly distributed through the tank, occupying about 3% of the bottom area. Six salmon parr were used for each experiment. In experiments with channel depths of 40 cm, the proportion of salmon under covers was 36.4%, at 30 cm 60.7%, and at 20 cm, 79.4%. Presence of similar-sized brown trout, Salmo trutta, increased the use of covers in channels and greater use of the pool area by salmon. The salmon were completely dominated by the trout, making about four times more more aggressive than salmon. Our findings show that water depth itself provides cover for young salmon.     

The influence of land cover composition and groundwater on thermal habitat availability for brook charr (Salvelinus fontinalis) populations in the United States of America

Abstract – Brook charr (Salvelinus fontinalis) is a sentinel fish species that requires clean, cold water habitats generally resulting from landscapes that allow for surface water flows devoid of sediment and contaminants and high groundwater discharge of cold water. As such, brook charr are impacted by land cover changes that alter stream temperature regimes. We evaluated brook charr populations across their eastern and midwestern range in the United States with reference to thermal habitat availability in relationship to land cover and per cent baseflow. We found that while forest cover does protect brook charr thermal habitat, high levels of groundwater discharge can allow for increased levels of agriculture within a watershed by keeping the water cold in spite of warm ambient summer temperatures. Our study concludes that with enhanced communication among land, water and fisheries managers, society can provide for sustainable stream salmonid populations despite increased threats on cold water resources.     

Foraging behaviour of juvenile pink salmon (Oncorhynchus gorbuscha) and size‐dependent predation risk

Two hypotheses related to effects of juvenile pink salmon (Oncorhynchus gorbuscha) foraging behaviour and size on their predation risk were evaluated using field data collected in Prince William Sound, Alaska 1 995–97. My results supported the hypothesis that low macrozooplankton density leads to dispersion of juvenile salmon from shallow nearshore habitats and greater predation risk, but zooplankton type was an important factor. When the biomass of large copepods (primarily Neocalanus spp.) declined, salmon dispersed from shallow nearshore habitats, and mean daily individual predator consumption of salmon increased by a factor of 5. A concomitant five‐fold increase in the probability of occurrence of salmon in predator stomachs supported the notion that increased predation on salmon was caused by a greater overlap between predator and prey when salmon dispersed offshore, not an increase in the number of salmon consumed per feeding bout. The results also generally supported the hypothesis that the timing of predation events modifies the nature of size‐dependent predation losses of salmon to different predator groups (small and large planktivores and piscivores). Size‐dependent vulnerabilities of salmon to predators were a function of both predator and prey sizes. When simulated predation was shifted from May to June, the vulnerability of salmon became more dependent on their growth than initial size. But, the size‐ and growth‐dependent vulnerabilities of salmon differed more among predator groups than between May and June, suggesting that changes in the composition of predator fields could more strongly affect the nature of size‐dependent predation than changes in the timing of predation losses.     

Brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.)) as predators on three sympatric whitefish (Coregonus lavaretus (L.)) forms in the subarctic Lake Muddusjärvi

Abstract  – Brown trout ( Salmo trutta L.) and Arctic charr ( Salvelinus alpinus (L.)) use whitefish ( Coregonus lavaretus (L.)) as their main prey in the subarctic Lake Muddusjärvi. Brown trout dwelled in littoral and pelagic habitat, whereas Arctic charr lived only in epibenthic habitat. Both species shifted to whitefish predation at a length of 20–30 cm. At this size, brown trout fed on larger whitefish than Arctic charr. Whitefish occur in three sympatric forms, differing in their habitat, ecology and morphology. Both the predators preyed primarily upon the small-sized, densely rakered whitefish form (DR), which was the most numerous whitefish form in the lake. DR used both epibenthic and pelagic habitat, whereas two sparsely rakered whitefish forms dwelled (LSR and SSR) only in epibenthic habitat: LSR in littoral and SSR in profundal areas. Sparsely rakered whitefish forms had minor importance in predator diet.     

Effect of dietary Wolffia arrhiza and Spirulina platensis on growth performance and pigmentation of Queen loach Botia dario (Hamilton, 1822)

The present Present experiment was conducted for 75 days in triplicates groups in 18 aquaria of 50 L each to study the effect of Wolffia arrhiza and Spirulina platensis on growth and pigmentation of Botia dario. Six isonitrogenous diets were prepared with 350 g/kg crude protein (CP) level. Diet 1 (T1) was prepared without fortification of spirulina and wolffia. T2 diet was prepared with spirulina as supplement of carotenoids. Similarly, T3, T4, T5 and T6 diets were prepared by substituting 25, 50, 75 and 100 g/kg of CP from spirulina with wolffia, respectively. Significant differences (p < .05) in final mean weight, mean weight gain, body weight gain and specific growth rate were observed. 100 percent survivability was recorded in T4 and T5. Final carotenoids content (μg/g) in skin (166.39 ± 2.71) and muscle (10.67 ± 0.32) was recorded highest in T5 and in whole fish in T6 (13.03 ± 0.95 μg/g). Redness, yellowness and whiteness found to have no significant differences (p > .05). Thus, it can be concluded that diet containing 100 g/kg spirulina can be effective for better growth while diet containing 25 g/kg spirulina and 150 g/kg wolffia can be effective for higher survival and pigmentation in Botia dario.     

The influence of physical watercourse parameters on the degree of anadromy in different lake populations of Arctic charr (Salvelinus alpinus (L.)) in northern Norway

The influence of physical watercourse parameters on the degree of anadromy was studied in 15 lake populations of Arctic charr (Salvelinus alpinus (L.)) in northern Norway. The anadromy of the different populations was scored based on the following criteria; marine parasites. fish length and length at maturity. There were significant negative correlations between the anadromy scores and both the length of the outlet rivers of the different lakes and a migration barrier index for the different watercourses (combining migration distance and water velocity). It is hypothsized that these correlations were due to differences in energy expenditure for charr during upstream migration and/or differences in predation pressure on charr during river migration. Short rivers with relatively high water velocity seem to be the most preferable conditions for the anadromous life-history strategy. There were no correlations between the degree of anadromy and mean river slope or minimum summer water discharge.     

Variation in DVM behaviour of juvenile and adult pearlside (Maurolicus muelleri) linked to feeding strategies and related predation risk

In the Norwegian fjord Masfjorden, different developmental stages of the mesopelagic planktivore Maurolicus muelleri form vertically separate sound scattering layers (SSLs) and in late autumn display different diel vertical migration (DVM) behaviour. Post‐larvae and juvenile fish perform normal crepuscular DVM, whereas the large majority of adults remain at depth throughout the diel period. In this study we examined the stomach contents of juvenile and adult fish caught at different times and depths during a 24‐h period in autumn. The different DVM behaviour of these two SSLs in addition to a shallow layer believed to be composed of post‐larvae is explained with a model for visual foraging in aquatic environments that uses gradients in vertical light intensity and copepod density and size as input variables. Field data revealed that vertically migrating juveniles distributed at a higher ambient light intensity and on average consumed 25 times more copepods than non‐migrating adult fish. The model showed that juveniles experienced a 15 times higher prey encounter rate and a higher level of predation risk than non‐migrating adults, and that the energetic benefits for post larvae and juveniles from prolonged feeding in a nearly constant and brighter environment outweigh the associated predation risk. The model also suggests that the visual detection range of piscivore predators is relatively more limited by the turbid surface water than that of their prey, which provide the post‐larva and juvenile life‐stages of M. muelleri a window of reduced visual predation near the surface.     

The effects of winter ice cover on the trophic ecology of whitefish (Coregonus lavaretus L.) in subarctic lakes

Lakes in Arctic and subarctic regions display extreme levels of seasonal variation in light, temperature and ice cover. Comparatively little is known regarding the effects of such seasonal variation on the diet and resource use of fish species inhabiting these systems. Variation in the diet of European whitefish Coregonus lavaretus (L.) during periods of ice cover in this region is often regarded as ‘common knowledge’; however, this aspect of the species' ecology has not been examined empirically. Here, we outline the differences in invertebrate community structure, fish activity, and resource use of monomorphic whitefish populations between summer (August–September) and winter (February–March) in three subarctic lakes in Finnish Lapland. Benthic macroinvertebrate densities did not exhibit measurable differences between summer and winter. Zooplankton diversity and abundance, and activity levels of all fish species (measured as catch per unit effort) were lower in winter. The summer diet of C. lavaretus was typical of a generalist utilising a variety of prey sources. In winter, its dietary niche was significantly reduced, and the diet was dominated by chironomid larvae in all study sites. Pelagic productivity decreases during winter, and fish species inhabiting these systems are therefore restricted to feeding on benthic prey. Sampling time has strong effect on our understanding of resource utilisation by whitefish in subarctic lakes and should be taken into account in future studies of these systems.     

The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), on insect emergence and benthic invertebrate abundance in experimental ponds

Abstract The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), predation on the production of insects emerging at the water surface and the autumn biomass of benthic macro-invertebrates were assessed in a series of experimental ponds. The study attempted to discover whether fish affect food availability for diving and dabbling ducks in freshwater habitats. Ten ponds (bisected by fine netting) were used for the study: one was left totally fish-free, whilst one half of each of three groups of three ponds was stocked with either perch, bream or perch plus bream. The relative abundance of emerging insects (mainly Chironomidae) was significantly reduced in two perch ponds, two perch + bream ponds and two bream ponds. The autumn standing crops of benthic macroinvertebrates were significantly reduced in one perch pond, three bream ponds and one perch plus bream pond. These results support findings of a contemporaneous large bio-manipulation experiment carried out in two adjacent lakes. During the biomanipulation studies, aquatic invertebrate standing stocks greatly increased after the removal of fish and decreased following restocking.