Relative impacts of native and non‐native crayfish on shelter use by an indigenous benthic fish

• 1. The North American signal crayfish Pacifastacus leniusculus has been widely introduced throughout Europe where it is expanding its range and in many areas replacing the native white‐clawed crayfish Austropotamobius pallipes. There is concern with regards to the impact of this species replacement on benthic fish. Interspecific behavioural interactions and competition for shelter between the benthic fish, bullhead Cottus gobio and A. pallipes and P. leniusculus were measured to assess the comparative impact of native and non‐native crayfish.
• 2. Both white‐clawed crayfish and signal crayfish were dominant over bullhead. Bullheads moved away from approaches of crayfish, left shelters on entry of crayfish and rarely entered an occupied shelter. Signal crayfish made significantly more aggressive approaches towards bullheads than white‐clawed crayfish.
• 3. Alone, bullheads spent most of their time by day under shelter (median 96%), reflecting a highly entrained behavioural response, which was relaxed by night (median 60%). Both crayfish species reduced shelter use by bullheads although the extent of shelter sharing by bullheads was higher in trials with white‐clawed crayfish than with signal crayfish.
• 4. Sampling in the River Wharfe, northern England, where signal and white‐clawed crayfish and bullhead currently exist, demonstrated a negative relationship between the densities of signal crayfish and bullhead, with high bullhead abundance where crayfish were absent or where white‐clawed crayfish were present at low density.
• 5. Assuming that shelter is sometimes limited under natural conditions, crayfish are likely to displace bullheads from shelters, which may increase predation risk for bullheads. Although the effects of signal crayfish on bullhead shelter use were more intense, the pattern was highly evident for the native white‐clawed crayfish. The higher fecundity and densities attained by signal crayfish may be more significant than differences in the behaviour of the two crayfish species in determining the impact of crayfish on bullheads.

Copyright © 2008 John Wiley & Sons, Ltd.     

Introduction and dispersion of the bullhead, Cottus gobio L., in a sub-Arctic salmon river in northern Finland

The bullhead, Cottus gobio L., was observed in the River Utsjoki in the far north of Finland for the first time in 1979. This river is a tributary of the sub-Arctic River Teno, which flows into the Arctic Ocean and is one of the most important salmon rivers in northern Europe. The bullhead does not belong to the natural fish fauna of the Finnish river systems flowing into the Arctic. It was probably introduced by anglers as bait or accidentally during the water exchange activities as salmon fry were transferred from Finnish hatcheries to northern Norway. A viable bullhead population has dispersed through the River Utsjoki catchment. In 1995 its range extended from the lowest part of the river to a point 43 km upstream. It is highly probable that it has also entered the mainstem of the River Teno.     

Changes in the density of introduced bullhead, Cottus gobio L., and its impact on juvenile Atlantic salmon, Salmo salar L., densities in a sub-Arctic salmon river in northern Finland

A newly introduced species, the bullhead, Cottus gobio L., was observed for the first time in the River Utsjoki, a tributary of the River Teno, in 1979. The River Teno is one of the most important Atlantic salmon, Salmo salar L., rivers in Northern Europe and its tributary the River Utsjoki is an important salmon spawning and nursery area. The densities of bullhead were lowest in the areas to which the species has spread most recently and highest in the areas downstream of its introduction point. Densities were markedly lower upstream. Statistical analysis showed that the presence of the bullhead had not affected juvenile salmon densities in the River Utsjoki.     

A comparison of swimming capacity and energy use in seven European freshwater fish species

Abstract –  Migrating fish species with different swimming capacities and energy use show different capacities for passing obstacles between habitats, such as culverts and fish ladders. Here, we present an integrated study on swimming capacity and energetic use in seven European freshwater fish species with different ranges of migration (brown trout Salmo trutta L., European perch Perca fluviatilis L., roach Rutilus rutilus L., common carp Cyprinus carpio L., gudgeon Gobio gobio L., bullhead Cottus gobio L. and stone loach Barbatula barbatula L.). Critical ( U _crit), optimal ( U _opt) and maximum ( U _max) swimming speed and oxygen consumption ( M O₂) were analysed and showed values correlated to migration capacity with highest swimming capacities in trout and roach and lowest in stone loach and bullhead. The resulting data can be used to make estimates of maximum passable water speeds in culverts. In conclusion, long-distance migrators show higher swimming capacities and can potentially clear obstacles easier than short distance migrators with lower swimming capacities. Even small obstacles (<25 cm) could be a barrier for genetic exchange between populations in short-distance migrators.     

Diel movement of bullhead (Cottus perifretum) in a lowland stream

Abstract – Passive integrated transponder tags have been successfully applied in Cottus spp. and have enabled researchers to gather more information about the movement patterns of individual fish in the wild. In two succeeding years during springtime, a portable antenna was used to determine diel movements of bullhead (Cottus perifretum). In 2007, bullhead (N = 26) moved significantly farther distances at night (mean, 0.42 m·h^?1) and dawn (mean, 0.35 m·h^?1) than during daytime (mean, 0.11 m·h^?1; mixed model, P < 0.001, respectively; P = 0.001), which may be due to foraging activities for Gammarus spp. Irrespective of diel period, smaller fish covered significantly longer distances (P = 0.001). In 2008, similar diel movement patterns were observed, but the differentiation between daytime (mean, 0.12 m·h^?1) and night periods (mean, 0.18 m·h^?1) was not significant (mixed model, P = 0.087; N = 49 bullhead). It is discussed that longer tracking intervals used in 2008 (three times per 24‐h instead of every two hours) were not suitable to detect the sheer magnitude of distances covered during a diel period. It is shown that this may be due to ‘site fidelity’ of some individuals: after swimming several metres at night, they returned to the exact location they previously occupied during daytime. In 2008, sex and body size were not related to diel movement. The present study is the first to present a quantitative differentiation between diel distances covered in a Cottus spp.     

Physiological and behavioural responses to hypoxia in an invasive freshwater fish species and a native competitor

The spread of invasive species is one of the major environmental concerns which can have negative effects on biodiversity. While several life history traits have been identified as being important for increasing the invasiveness of introduced species, the physiological factors that allow certain species to become successful invaders remain poorly understood. It has been speculated that good invaders are thriving in disturbed environments. In unfavourable conditions, as during hypoxic events, invasive species might be better adapted in their physiological and behavioural responses towards this stressor. We compared physiological and behavioural traits between two freshwater fish species: the European bullhead (Cottus gobio), an invasive fish species in Scotland, and its native competitor the stone loach (Barbatula barbatula) over different dissolved oxygen concentrations (DO). Contrary to expectations, bullhead displayed a reduced hypoxia tolerance as compared to stone loach, indicated by a higher threshold (P_crit) for the maintenance of standard metabolism. Avoidance behaviour during progressive hypoxia was similar between bullhead and stone loach. When given a choice between an open normoxic zone and a shelter located in hypoxia, both species spent most of their time hiding under the shelter in hypoxic conditions (bullhead: 100%; stone loach: 93.93%–99.73%), although stone loach showed brief excursions into normoxic conditions under 25% DO level. These results suggest that stone loach might be more resistant to hypoxia as compared to bullhead, and thus that increased hypoxia tolerance is likely not a trait by which bullhead have been able to expand their range within the United Kingdom.     

Seasonal abundance and microhabitat use of bullhead Cottus gobio and accompanying fish species in the River Avon (Hampshire), and implications for conservation

• 1. Five side‐channels and small tributaries of the River Avon (Hampshire, UK) were examined between spring 1999 and spring 2000 using point abundance sampling by electrofishing to determine the status of fish listed in Annex II of the EC Habitats Directive prior to habitat management works to enhance spring feeding habitat of wading birds.
• 2. Seasonal patterns of abundance and microhabitat use of bullhead Cottus gobio and accompanying fish species were examined. Parr of Atlantic salmon Salmo salar were sufficiently abundant for microhabitat analysis at one site only. Only two specimens of brook lamprey Lampetra fluviatilis were observed, one at each of two sites. Bullhead was amongst the most abundant fish species at all five sites, 0+ bullhead predominating.
• 3. Bullhead microhabitat preferences were generally similar at all five sites, but seasonal variations were observed, as was the case for the accompanying fish species, which included dace Leuciscus leuciscus, chub Leuciscus cephalus, stone loach Barbatula barbatula, roach Rutilus rutilus, and threespine stickleback Gasterosteus aculeatus.
• 4. Bullhead conservation status is discussed, in particular the possible exemption of British bullhead populations, such as already granted for those of Finland, from Annex II of the Habitats Directive.

© Crown Copyright 2004 Reproduced with the permission of Her Majesty's Stationary Office. Published by John Wiley & Sons, Ltd.     

Trophic overlap between non‐native brown bullhead (Ameiurus nebulosus) and native shortfin eel (Anguilla australis) in shallow lakes

We quantified trophic overlap between the invasive, non‐native catfish brown bullhead (Ameiurus nebulosus) and the New Zealand native shortfin eel (Anguilla australis) in four peat and riverine lakes using stable isotope (δ¹³C and δ¹⁵N) and gut content analyses. Across all lakes and fish sizes over the austral spring–summer period, shortfin eel guts were dominated numerically by fish prey (57% occurrence cf 42% in brown bullhead), while Diptera larvae were most commonly encountered in guts of brown bullhead (45% cf 14% in eels). Significant differences in % composition of animal contents in guts were detected between fish species and sampling occasions (n = 4) but not between lakes. In contrast, stable isotope signatures of brown bullhead and shortfin eel did differ significantly between lakes but not between sampling occasions, indicating enduring sources of nutrition despite apparently differing ingestion patterns over time. The R mixing model MixSIAR indicated that shortfins likely assimilated higher proportions of fish prey carbon compared to brown bullheads, which appeared to show greater assimilation of invertebrates, consistent with the results of gut content analyses. Isotopic niche regions, calculated in nicheROVER using probabilistic ellipses, indicated that shortfin eels occupied at least c.60% of brown bullhead trophic niche, which occupied less than 30% of eel trophic niche in all but one lake. These estimates suggest that brown bullhead has higher potential to influence shortfin eel nutrition than vice versa, or that a broad trophic niche occupied by eels provides resilience to the effects of overlapping consumption patterns with invasive omnivores.     

Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish

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A potential biomarker of androgen exposure in European bullhead (Cottus sp.) kidney

The aim of this study was to identify a signal that could be used as an androgen exposure indicator in the European bullhead (Cottus sp.). For this purpose, the ultra-structure of the kidney was characterized to identify normal structure of this organ, and histological changes previously described in the kidney of breeding male bullheads were quantified using the kidney epithelium height (KEH) assay previously developed and validated for the stickleback. In the next step, the effect of trenbolone acetate (TbA), a model androgen, was assessed to identify potential androgenic regulation of bullhead kidney hypertrophy. Measurement of KEH performed on adult non-breeding male and female bullheads exposed for 14 and 21 days to 0, 1.26 and 6.50 μg/L showed that kidney hypertrophy is induced in a dose-dependent manner, confirming the hypothesis that the European bullhead possesses a potential biomarker of androgen exposure. Combined with the wide distribution of the European bullhead in European countries and the potential of this fish species for environmental toxicology studies in field and laboratory conditions, the hypothesis of a potential biomarker of androgen exposure offers interesting perspectives for the use of the bullhead as a relevant sentinel fish species in monitoring studies. Inducibility was observed with high exposure concentrations of TbA. Further studies are needed to identify molecular signals that could be more sensitive than KEH.     

Diet of the Eurasian otter (Lutra lutra) on the River Gradac,Serbia: Predation in a brown trout‐dominated stream

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Glochidial infestation by the endangered mollusc Unio crassus in rivers of north‐eastern France: Phoxinus phoxinus and Cottus gobio as primary fish hosts

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River modification reduces climate resilience of brown trout (Salmo trutta) populations in Ireland

This study investigated interactions between eco‐hydromorphological state, riparian vegetation cover, water temperature and fish community composition in lowland rivers in Ireland. Physical habitat modification of study sites corresponded with degraded eco‐hydromorphological state (degree of ecological and physical modification) and reduced thermal buffering capacity (greater temperature fluctuation and increased frequency of extreme temperature events). This impact was reflected in the fish community, with a shift from a brown trout‐dominated (Salmo trutta L.) fish assemblage to predominance of the more thermally plastic minnow, Phoxinus phoxinus (L.), and stone loach, Barbatula barbatula (L.). Eco‐hydromorphological state may be a central factor affecting the ability of temperate rivers to resist temperature change in a warming climate and to maintain suitable conditions for salmonids and other cold‐water biota. Strategies aimed at climate change proofing of temperate rivers should focus on preserving or re‐establishing the eco‐hydromorphological processes that create habitat complexity and buffer stream temperature.     

Underwater evaluation of habitat partitioning in a European river between a non‐native invader,the racer goby and a threatened native fish,the European bullhead

We conducted underwater surveys using SCUBA gear to examine habitat and microhabitat competition between the Ponto‐Caspian racer goby Babka gymnotrachelus and native European bullhead Cottus gobio to assess the potential for competitive displacement of the native species by the invading species. In summer, 88 surveys were made in a tributary of the River Vistula within defined benthic areas across the entire width of the river bed. The occurrence of fish by total length class (small: <6 cm; large: >6 cm) and environmental conditions (depth, water velocity, substratum type, plant cover, shelter type) was recorded. We found a substantial separation between the species and size classes in relation to substratum, shelter type and water velocity. European bullheads were limited to lotic areas with stony bottoms, whereas racer gobies also occupied lentic areas over sand or mud. European bullheads usually took refuge under stones in contrast to a wider range of shelters used by racer goby, including tree roots and rubbish. In general, the breadth of habitat used by the racer goby was wider than that of the European bullhead, although habitat overlap between the species was not statistically significant except for the type of shelter occupied by small fish, selecting smaller stones. An inverse relationship was observed between small European bullheads and all racer gobies in areas where they co‐occurred, suggesting that invader may be having an adverse effect on the distribution and habitat use of small native bullheads, particularly in areas of moderate water velocities over small stones and gravel.     

Adiposity and growth of post-smolt Atlantic salmon Salmo salar L.

The long‐term adipose homeostasis seen in mammals gives rise to a ‘lipostatic’ model in which signals produced in proportion to fat stores serve to regulate energy intake. An extension of this predicts an impact of these signals on growth; downregulation of feeding in animals with increased adiposity should result in reduced growth. This was tested by monitoring fat deposition and growth in Atlantic salmon Salmo salar L. provided with feeds that differed in fat content. Salmon parr (mass c. 20 g) were fed either high‐ (H: 34%) or low‐fat (L: 22%) feeds, based on either fish (F) or vegetable (V) oils for 6 months to create groups of fish that differed in adiposity (10–12% and 5–7% body fat) at parr–smolt transformation (mass c. 130 g). Fish fed the high‐fat feeds deposited more body fat, and this was confirmed by measurement of fat concentrations in the fillet, viscera and remaining carcass. The fish were then grown‐on in sea water (c. 35 g L^?1, 8 °C, 24L:0D) for 14 weeks while being fed either high‐ or low‐fat feed formulated with fish oil to give the following treatments: HF→ H, HF→ L, LF→ L, LF→ H, HV→ H, HV→ L, LV→ L, LV→ H. Although fish exposed to the various feed treatments did not differ markedly in growth rate (SGR range 1–1.14% day^?1) over the 14 weeks of rearing in sea water, the results were in general agreement with predictions from the ‘lipostatic’ model, i.e. fish with the greatest fat reserves after the parr–smolt transformation grew more slowly than fish that were ‘leaner’ at this time. This suggests that adiposity, or ‘fatness’, may exert a negative feedback on feeding in salmon, thereby having an influence upon growth.     

Effect of fish size and temperature on the utilization of different protein sources in two catfish species

Two sets of feeding trial were conducted to determine the effect of size and temperature on the utilization of different protein sources in two catfish species. In both the experiments, the fish were fed to apparent satiation daily at 08.00 and 18.00 hours, and faecal matter collected through slow siphoning. The first experiment was designed to study the effect of fish size on apparent digestibility coefficients for plant and animal proteins in the African catfish, Clarias gariepinus (Burchell, 1822). Three size classes (105–109 g; 780–830 g; 1250– 1300 g) of fish were stocked in triplicate sets of 600‐L plastic pools fitted with a flow‐through system (2 L min^?1). Within each size class, the apparent digestibility coefficient (ADC) for protein varied significantly with the source and quality of protein used. Soybean meal and fishmeal protein were utilized with greater efficiency, whereas rice bran protein was least digestible. An increase in ADC protein was apparent with increase in fish size for high protein sources such as soybean meal, full‐fat soybean, laboratory‐prepared fishmeal, steam‐cooked brown fishmeal and dried fish. ADC protein for other ingredients decreased with increase in size. In the second experiment, the influence of varying temperature on ADC for protein was determined in the catfish, Heteropneustes fossilis (Bloch) (6–8 g). Triplicate groups of 25 fish were kept at three different ambient temperatures (18, 28 and 38 °C), in 70‐L polyvinyl indoor flow‐through (1–1.5 L min^?1) circular tanks (water volume = 55 L). The trend in utilization of protein from different sources remained similar at the three temperatures. For each ingredient, digestibility values obtained at 18 °C were significantly lower than those obtained at 28 °C and 38 °C. Optimal protein utilization in H. fossilis was measured at 28 °C.     

Fish pass effectiveness for bullhead (Cottus gobio), perch (Perca fluviatilis) and roach (Rutilus rutilus) in a regulated lowland river

Abstract –  The effectiveness of a pool-and-weir fish pass in the regulated river Laarse Beek (Belgium) was assessed for bullhead ( Cottus gobio ), perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ) from August 2002 to April 2003. Fish were caught by electrofishing downstream, within and upstream of the fish pass. They were marked with visible implant elastomer tags and released downstream of the fish pass. Our results suggest that the fish pass is ineffective for the bullhead because none of the 1270 tagged bullheads were recaptured in the upstream study area. Passage failure most likely resulted from excessive water velocities in the fish pass. On the contrary, 8% of the tagged perch and 29% of the tagged roach were recaptured in the upstream study area. Several management strategies are proposed to allow free upstream passage of the endangered bullhead at the fish pass under study.     

Nitrogen and phosphorus digestibility and excretion of different-sized groups of milkfish (Chanos chanos Forsskal) fed formulated and natural food-based diets

This study determined the digestibility of nitrogen and phosphorus, and the excretion rate of different‐sized groups of milkfish fed a commercial diet, a SEAFDEC formulated diet or lab‐lab (natural food‐based diet). Fish (31.2–263.0 g) were stocked in 12 units of 300‐L fibreglass tanks filled with aerated seawater. The postprandial total ammonia‐nitrogen (TAN) and phosphate (PO₄‐P) excretion of fish were estimated from changes in TAN and PO₄‐P concentrations in water for 24 h. Digestibility was determined from the nitrogen, phosphorus and Cr₂O₃ content of the diets, and pooled faeces after the fish had been fed diets marked with chromic oxide. TAN excretion rate (mg TAN kg^?1 fish day^?1) was significantly lowest (P < 0.05) in medium to very big fish fed the lab‐lab diet (60.8–124.4) and highest in small and medium fish fed the SEAFDEC diet (333.3–331.6) and small fish fed the commercial diet (280.1). Regardless of size, fish fed lab‐lab excreted (mg PO₄‐P kg^?1 fish day^?1) significantly lower PO₄‐P (36.2) but did not differ with fish fed the commercial diet (64.8). Excretion rates decreased exponentially as fish weight increased but positively increased with feed ration. Excretion pattern of milkfish revealed two peaks: the first peak occurred 6 h after feeding and the second peak at 18 h for TAN and 21 h for PO₄‐P, coinciding with the start of the daylight hours. TAN and PO₄‐P excretion accounted for 20.5–34.6% of total N consumed and 18.7–42.6% of P consumed respectively. Approximately 27.9–42.5% of N consumed and 47.2–58.5% of P consumed were lost as faeces. Total nutrient losses were lower using the lab‐lab diet (0.31 g N and 0.14 g P kg^?1 fish) compared with the formulated diets (0.47–0.48 g N and 0.17–0.19 g P kg^?1 fish); the losses decreased per kg of fish as fish size increased. Results suggest that the diet and size of fish influence wastage of N and P to the environment with greater losses in small fish and when artificial diets are used. Such measurements will provide valuable information for the preparation of N and P budgets for milkfish in grow‐out systems.     

Accuracy of snorkelling counts in assessing spawning stock of Atlantic salmon,Salmo salar,verified by radio‐tagging and underwater video monitoring

Abstract The accuracy of underwater snorkel counts of adult Atlantic salmon, Salmo salar L., was analysed in a small tributary of the River Teno before and during the spawning period using two independent verification methods (video counts and radio‐tagged fish) with known numbers of fish. The observation efficiency of snorkelling crews was generally high, but that of an inexperienced crew (65–72%) was significantly lower than an experienced crew (81–82%). Habitat type affected the accuracy of snorkelers, especially those of the inexperienced crew. The efficiency of snorkelers was high in pool‐type habitats (75–100%) but decreased considerably in faster flowing turbulent habitats (43–82%), where the inexperienced crew provided the lowest estimates. Thus, snorkel counting is a valid method for estimating Atlantic salmon spawning population densities in small rivers with adequate underwater visibility and with a sufficiently experienced snorkelling crew.