Interspecific competition between stream-dwelling brown trout and Alpine bullhead

Density and composition of benthic invertebrates and the diet of brown trout Salmo trutta and Alpine bullhead Cottus poecilopus were studied at two sites in one Norwegian stream. The sites were separated by an impassable waterfall, and brown trout density was five to 10 times higher at the upper, allopatric site than downstream where it lived in sympatry with the Alpine bullhead. Benthic invertebrate communities did not differ between sites; however, the size distribution of chironomids and trichopterans were skewed towards lighter individuals at the sympatric site. Diet composition suggested that sympatric brown trout foraged more on invertebrate drift and from the surface than allopatric brown trout. Alpine bullhead diet did not differ significantly from brown trout diet, except that the Alpine bullhead fed on heavier individual prey within a few taxa and did not consume chironomid pupae or surface insects. The collected data support the hypothesis that brown trout living in sympatry with Alpine bullhead feed at locations with higher predation risk, which is a probable explanation for their lower population density.     

Habitat degradation and trout stocking can reinforce the impact of flash floods on headwater specialist Alpine bullhead Cottus poecilopus – A case study from the Carpathian Mountains

In freshwater streams, flooding is a typical source of natural disturbance that plays a key role in the dynamics of animal populations and communities. However, habitat degradation and fish stocking might increase the severity of its impact. We tested the effects of a flash flood on the abundance of three size classes of headwater dwelling Alpine bullhead, Cottus poecilopus, in the streams of the Carpathian Mountains in the Czech Republic, that are stocked with hatchery‐reared brown trout, Salmo trutta. We showed that the overall abundance of Alpine bullhead was highest at the sites with the least degraded habitat (i.e., natural habitat) and we caught almost no Alpine bullhead at the sites with the most degraded habitat. The flash flood had a strong negative effect on the abundance of the largest individuals of Alpine bullhead. Abundance of small and medium size Alpine bullhead was negatively affected by the abundance of adult stocked brown trout before as well as after the flash flood. However, negative effect of adult brown trout abundance on abundance of large Alpine bullhead was not significant before the flash flood, and it became significant after the flash flood. This could indicate an accumulation of negative impacts of trout stocking and flash flood on this size class. Overall, our results suggest that stocking of hatchery trout and habitat degradation can reinforce the impact of flash floods on the population of Alpine bullhead in the streams of the Carpathian Mountains.     

The buffering power of plasma in brown bullhead (Ameiurus nebulosus)

Brown bullhead (Ameiurus nebulosus) blood plasma was found to exhibit an unusually high non-bicarbonate buffer capacity (beta) in relation to that of other teleost fish. In brown bullhead, the non-bicarbonate buffer capacity of plasma (beta(plasma)), at -5.72 +/- 0.34 mmol l(-1) pH unit(-1) (mean +/- S.E.M., N=30), constituted 37% of whole blood beta and was 2.5 times higher than beta(plasma) in rainbow trout (-2.33 +/- 0.42 mmol l(+/-1) pH unit(-1); N=7). The strong buffering power of bullhead plasma was not the result of unusually high plasma protein levels. Size separation chromatography in conjunction with a spectrophotometric assay for buffering capacity were used to isolate a plasma fraction of high buffering power. SDS-polyacrylamide gel electrophoresis revealed that this fraction contained four proteins, but was dominated by a protein of approximately 68-70 kDa molecular mass. On the basis of the amino acid composition of this fraction, the dominant protein was identified as albumin. In comparison to other fish albumins, bullhead albumin appears to be histidine-rich (6.7%). Thus, the unusually high non-bicarbonate buffer capacity of bullhead plasma appears to stem from the presence in the plasma of a histidine-rich albumin.     

Gonadal morphology, enzyme histochemistry and plasma steroid levels during the annual reproductive cycle of male and female brown bullhead catfish, Ictalurus nebulosus Lesueur

The annual reproductive cycle of the brown bullhead catfish, Ictalurus nebulosus Lesueur, was investigated over a two-year period. In females, GSI increased in the spring as follicles enlarged and the granulosa became hypertrophied, dropped during spawning in August, then rose in the autumn as follicles enlarged slightly. 3β-Hydroxysteroid dehydrogenase (3β-HSD) activity was limited to thecal nests of large, vitellogenic follicles. Plasma testosterone and estradiol-17β levels increased in parallel with GSI. Levels of both steroids dropped prior to the spawning period, although a peak in estradiol-17β was evident during the spawning period. No 11-ketotestosterone was detected in female plasma. In males, GSI increased in the spring as spermatogenesis proceeded, and dropped during spawning. 3β-HSD activity was confined to Leydig cells and was most intense prior to spawning. Plasma testosterone and 11-ketotestosterone peaked during the pre-spawning period, dropped prior to spawning, then rose slowly during the autumn. A peak in estradiol-17β occurred during the spawning period. Significant differences in GSI and plasma steroid levels during the pre-spawning and spawning periods were observed between the two yearly cycles; they may be related to differences in rainfall during these periods.     

Olfactory discrimination of amino acids in brown bullhead catfish

Olfactory discrimination of amino acids was investigated in brown bullhead catfish (Ameiurus nebulosus). Based on the magnitude of the observed food search activity of catfish conditioned to single amino acids, the tested compounds were classified as being detected by the catfish as equal to, similar to, or different from the conditioned stimulus. L-Proline (L-Pro)-conditioned brown bullhead catfish discriminated all amino acids from L-Pro, but catfish conditioned to L-valine (L-Val) and L-isoleucine (L-Ile) did not discriminate L-Val from L-Ile nor L-Ile from L-Val; however, all other amino acids tested were always discriminated from these two compounds. Catfish conditioned to L-alanine (L-Ala) discriminated basic, acidic and several neutral amino acids with long side-chains (LCNs) from L-Ala; however, they did not always discriminate L-Ala from all neutral amino acids with short side-chains (SCNs). The L-norleucine (L-nLeu)-conditioned fish responded to L-norvaline (L-nVal), L-methionine (L-Met) and L-Ala similarly to L-nLeu, indicating that these amino acids are detected as similar or identical to L-nLeu. L-nLeu was, however, discriminated from L-Ala in L-Ala-conditioned catfish. Interestingly, L-leucine (L-Leu) was discriminated from the conditioned stimuli, L-Ala, L-Ile and L-Val, indicating independent receptors for L-Leu. Although conditioned catfish discriminated other amino acids from L-arginine hydrochloride (L-Arg), in some tests they were unable to discriminate L-Arg from L-lysine hydrochloride (L-Lys). These results imply the existence of independent olfactory receptive pathways for: (i) L-Pro; (ii) basic amino acids (L-Arg and L-Lys); (iii) L-Leu; (iv) other neutral amino acids with branched side-chains (L-Ile and L-Val); (v) neutral amino acids with long linear side-chains (L-nLeu, L-nVal and L-Met); (vi) neutral amino acids with short side-chains; and (vii) amino acids with sulfhydryl groups (L-Cys and L-homoCys).     

Characterization of benzo[a]pyrene metabolites formed by 3-methylcholanthrene-induced goldfish, black bullhead and brown bullhead

Metabolites of BaP formed by 3-MC-induced goldfish (Carassius auratus), black bullhead (Ictalurus melas), brown bullhead (Ictalurus nebulus) and rat have been separated by HPLC. The main metabolites in both bullhead species and the rat were 3-hydroxy-BaP and BaP 9,10- and 7,8-dihydrodiols, whereas BaP 1,6- and 3,6-diones and 9- and 3-hydroxy-BaP predominated in the goldfish. Induced rat formed over 10 times as many total metabolites as the fish. No induction was observed in the 3-MC-treated brown bullheads kept at 7 degrees C. TCPO and alpha-naphthoflavone decreased metabolite production by 50 and 30%, respectively.     

Assessment and control of non‐indigenous brown bullhead Ameiurus nebulosus populations using fyke nets in shallow ponds

In order to evaluate fyke nets as a tool for population assessment and mass removal of brown bullhead Ameiurus nebulosus populations, small, shallow ponds were sampled during late summer in 1999 and 2000. Catch efficiency, species and size selectivity of fyke nets were investigated with the mark‐recapture method. Two different strategies were applied: (1) on six occasions, the mark‐recapture method was applied to entire populations, and (2) in six other cases, sampling was done in two replicated enclosed areas (625 m²). When applied to entire populations, fyke nets were found to be size selective, and capture efficiency significantly increased with standard length. Conversely, no size selectivity of fyke nets was found in enclosed areas. Sampling in replicated enclosures yielded reproducible estimates of population density and biomass. The results suggest that double fyke nets, when combined with the mark‐recapture technique, are a very useful tool for the efficient and reliable assessment of brown bullhead populations. The results of the study also suggest that double fyke nets may potentially be a cost‐effective tool for the mass removal of non‐indigenous brown bullhead populations.     

Predator Generalization Decreases the Effect of Introduced Predators in the San Marcos Salamander,Eurycea nana

The introduction of novel predators into an environment can have detrimental consequences on prey species, especially if these species lack the ability to recognize these predators. One such species that may be negatively affected by introduced predators is the federally threatened San Marcos salamander (Eurycea nana). Previous research found that predator‐naïve (captive‐hatched) salamanders showed decreased activity in response to the chemical cues of both a native fish predator (Micropterus salmoides) and an introduced fish predator (Lepomis auritus), but not to a non‐predatory fish (Gambusia geiseri). We tested the hypothesis that E. nana recognized the introduced Lepomis (and other non‐native Lepomis) because they share chemical cues with other native congeneric Lepomis predators in the San Marcos River. We examined the antipredator response of predator‐naïve E. nana to chemical cues from (1) a sympatric native sunfish (Lepomis cyanellus; Perciformes: Centrarchidae); (2) a sympatric introduced sunfish (L. auritus); (3) an allopatric sunfish (Lepomis gibbosus); (4) a sympatric non‐native, non‐centrarchid cichlid (Herichthys cyanoguttatum; Perciformes: Cichlidae); and (5) a blank water control to determine whether individuals make generalizations about novel predators within a genus and across a family. Exposure to chemical cues from all fish predator treatments caused a reduction in salamander activity (antipredator response). Additionally, there were no differences in the antipredator responses to each predatory fish treatment. The similar responses to all sunfish treatments indicate that E. nana shows predator generalization in response to novel predators that are similar to recognized predators. Additionally, the antipredator response to H. cyanoguttatum indicates that predator generalization can occur among perciform families.     

Comparative metabolism of benzo[f]quinoline by liver microsomes from brown bullheads and rats

1. Liver microsomes from rats were considerably more active in metabolizing benzo[f]quinoline (B f Q) than those from brown bullheads (Ictalurus nebulosus). 2. The main B f Q metabolites formed by both rat and brown bullhead liver microsomes were qualitatively similar and included B f Q-7,8-dihydrodiol, B f Q-9,10-dihydrodiol, B f Q-N-oxide, 7-hydroxy B f Q, and 9-hydroxy B f Q. 3. The liver microsomes from control brown bullheads and rats metabolized B f Q primarily at the 7,8-and 9,10-positions, respectively, whereas in the case of microsomes from 3-methylcholanthrene (3-MC)-treated rats or brown bullheads, the major site of metabolic attack was the 7,8-position. 4. A 3-MC-type of cytochrome P-450 appears to be primarily responsible for the oxidation of B f Q by control brown bullhead liver microsomes, whereas a phenobarbital-inducible type of cytochrome P-450 seems to be involved in the metabolism of B f Q by control rat liver microsomes.     

Growth‐rate variation in brown trout in small neighbouring streams: evidence for density‐dependence?

The within- and among-population variation in individual growth rate of brown trout Salmo trutta L. was studied in five small neighbouring streams (seven isolated populations) within a distance of 70 km in east Norway. Observed growth rate was only weakly correlated with predicted maximum growth rate based on laboratory models, and there was a significant interaction with site. A generalized linear model showed that growth rate was positively correlated with temperature, but also that growth rate decreased as the summer season progressed. This might indicate either a seasonal decline in food availability or appetite, or a change in energy allocation strategy. Growth rate decreased with increasing fish age, probably as an effect of sexual maturation of older fish, and differential allocation of protein and lipid among different size-groups of brown trout. After adjusting for variation in temperature, season, and fish mass, there was still significant among-site variation in growth rate. A significant part of this variation was due to variation in brown trout density and the presence or absence of Alpine bullhead Cottus poecilopus . Growth rate decreased with increasing brown trout density, and was lower in the presence than in the absence of Alpine bullhead after correcting for variation in brown trout density. This last result may indicate the presence of interspecific competition.     

High plasma buffering and the absence of a red blood cell beta-NHE response in brown bullhead (Ameiurus nebulosus)

The high non-bicarbonate buffer capacity of brown bullhead (Ameiurus nebulosus) plasma was postulated to function as an alternative mechanism for the protection of red blood cell (RBC) intracellular pH (pHi) in the absence or attenuation of a RBC adrenergic response. The requirement for protecting RBC pHi arises from the presence of a Root effect haemoglobin in bullhead. In support of this hypothesis, bullhead RBCs incubated in vitro with isoproterenol (10(-8)-10(-5) mol l(-1)) or forskolin (10(-4) mol l(-1)) exhibited significant cyclic AMP accumulation, but failed to exhibit cell swelling or significant Na(+) or Cl(-) accumulation; plasma pH (pHe) was also unaffected. Similarly, no significant effect on RBC water content, Na(+) or Cl(-) concentration, or pHe was detected in bullhead blood incubated with 8-bromo cyclic AMP (10(-4)-10(-2) mol l(-1)) in vitro. These results suggest that while bullhead RBCs possess a beta-adrenoreceptor linked to cyclic AMP formation, stimulation of this adrenergic receptor does not result in measurable activation of a Na(+)/H(+) exchanger.     

Vertical distribution and movements of brown bullhead (Ameiurus nebulosusLesueur 1819) in Motuoapa Bay,southern Lake Taupo,New Zealand

Ultrasonic telemetry was used to determine the swimming depths of brown bullhead (Ameiurus nebulosus) in Motuoapa Bay at the southern end of Lake Taupo, New Zealand. Sonic transmitters equipped with a pressure sensor were surgically implanted in 12 adult fish (295–345 mm FL). Three automatic receivers recorded a total of 61335 data points on swimming depth between 26 November 1998 and 7 November 1999. Brown bullheads swam in water from 0 to 17 m deep but showed some seasonal variations. They were more active at night when they used shallow water extensively, especially during the winter months. They were most mobile in spring when they left Motuoapa Bay, suggesting migratory behaviour. During winter the fish remained more stationary, only moving around inside the bay. The results of this study provide guidance for establishing a brown bullhead control program should it become necessary.     

Within-stream variation in early life-history traits in brown trout

Significant additive genetic variance for most early life-history traits was found in brown trout Salmo trutta living in both allopatry above an impassable waterfall and sympatry (below the waterfall in the same stream) with alpine bullhead Cottus poecilopus. These traits included length, mass and yolk sac volume at hatching, and size at'button-up' (the time when yolk is enclosed within the body cavity). There were small differences in size at hatching and size at button-up among populations (adjusted for egg size). However, sympatric fry grew more rapidly and experienced lower mortality rates during the period of first feeding than allopatric fry. This might indicate behavioural differences between brown trout from the two populations. It is suggested that these phenotypic differences may be a result of adaptation to living in sympatry with alpine bullhead.     

Summer use of a small stream by fish and crayfish and exchanges with adjacent lentic macrohabitats

1. Movements between a stream reach and two adjacent lentic macrohabitats, a beaver pond and a lake, were followed for the Appalachian crayfish and two fish species, brook charr and brown bullhead, over an 85‐d period from early June to late August, and were analysed in relation to water level, maximum water temperature, photoperiod length, lunar luminosity, and age, by use of time‐series regressions. 2. Brook charr showed strong net immigration to the stream reach for underyearling (age class 0+) fish but net emigration for 1+ fish. Both immigration and emigration were positively related to water level and temperature; migratory responses to temperature were age‐specific. 3. Brown bullhead used the stream primarily as a corridor for downstream migration from the beaver pond to the lake. As with brook charr, water level and temperature had a positive effect on movement and responses were stronger in younger individuals. 4. Crayfish emigrated from the stream during the summer. Movements were positively related to increases in water level and temperature, with responses of 1+ crayfish much stronger than those of older individuals. 5. The results indicate that the stream tributary played different roles for brook charr (nursery), brown bullhead (dispersal corridor) and Appalachian crayfish (early summer refuge), and suggest that variation in water level or temperature resulting from climatic change or local anthropogenic activities might modify connectivity between macrohabitats, particularly for younger individuals.     

The populations of fish in the River Tees system on the Moor House National Nature Reserve, Westmorland

The age, growth, population densities and annual production of an isolated population of brown trout ( Salmo trutta L.) and bullhead ( Coitus gobio L.) were investigated over a 5 year period in Trout Beck in the northern Pennines. Additional data were obtained from two other sites; Great Dodgen Pot Sike and the River Tees.
Trout growth rates were low, particularly in Dodgen Pot Sike, but ages up to VIII were recorded. Bullhead growth rates were similar to those in the Tees at Cow Green (Crisp et al. , 1974), though the Moor House bullheads had a higher survival rate. Population densities of trout ranged from 0.10–0.22/m², with a fry contribution of 0.80%. The bullhead population in Trout Beck was sparse, generally 0.1/m², though an 0 group value of 0.46/m^a was estimated in 1967. At Tees Bridge values ranged from 2.5–7/8/m². Most trout matured by age III, though in Great Dodgen Pot Sike only half of the females were mature at age IV.
Annual production was estimated from Allen graphs. Trout production ranged from 1.02–3.50 g/m²/year, the fry contributing up to 51.5% of the total. A value of 0.48 g/m²/year was obtained for bullheads in the Trout Beck system in a year of good recruitment, whilst bullhead production at Tees Bridge was 7.43 g/m²/year, with fry and I group contributing 48.7 and 37.5% respectively. The high survival rate, irregular recruitment, and poor growth of these high altitude populations is discussed. Growth and reproductive peculiarities of the Great Dodgen Pot Sike trout are also discussed.     

Ameiurus melas (black bullhead): morphological characteristics of new introduced species and its comparison with Ameiurus nebulosus (brown bullhead)

In the present study we examined and compared external morphology as well as osteological characters of two species of the genus Ameiurus (Teleostei, Ictaluridae): the black bullhead (Ameiurus melas) and brown bullhead (Ameiurus nebulosus), two catfish species that are invasive to Europe. In total 83 (53 and 30) individuals were captured in the Czech Republic and the Slovak Republic and further analysed. For genetic screening of both Ameiurus species were chosen three DNA regions: part of nuclear Recombination activating gene 1 (RAG-1), mitochondrial gene for cytochrome b (cyt b) and mitochondrial sequence which includes 12S and 16S ribosomal RNA genes. The results presented in this paper concern specific osteological characteristics (original scheme of pectoral spine and pectoral girdle) used for the determination purposes and also verification that mathematical multivariate methods for external morphology analysis can be used for the determination of Ameiurus species. The summary of 80 out of 83 fish (96.4 %) was correctly classified using the discriminant analysis.     

Analysis of fish bile with HPLC — fluorescence to determine environmental exposure to benzo(a)pyrene

Brown bullhead from the Black River, Ohio, have a high incidence of liver neoplasia which is associated with elevated concentrations of polynuclear aromatic hydrocarbons (PAHs) in the sediment. We evaluated the use of biliary concentrations of benzo(a)pyrene [B(a)P] equivalents as a means for determining PAH exposure. Bile was collected from 16 brown bullheads and 8 common carp taken from each of two Lake Erie tributaries in Ohio, the industrialized Black River and the non-industrialized Old Woman Creek. Hatchery bullhead (n = 8) were used to determine base levels of PAHs. A high performance liquid chromatography (HPLC) — fluorescence technique was used to determine the concentration of B(a)P equivalents in the bile samples. The area of all peaks fluorescing at 380/430 nm was summed to give a single value for B(a)P equivalents in each sample. Concentrations of B(a)P equivalents generally reflected concentrations of PAH in sediment where fish were collected. Bile taken from Black River carp contained the highest concentration of B(a)P equivalents and was significantly different from all other groups. The value obtained for Black River bullhead was also high and was found to be significantly different from hatchery bullhead. B(a)P equivalents varied between carp and bullhead from the same habitat possibly because of differing food habits or metabolic pathways. However, our results indicate that relative levels of B(a)P equivalents in the bile of fish correspond well to B(a)P levels in sediment and may offer a means of determining environmental exposure of fish to the parent compound.     

Diagnostic criteria for proliferative hepatic lesions in brown bullhead Ameiurus nebulosus

Brown bullhead Ameiurus nebulosus is used as indicator species for contaminant effects at areas of concern (AOC) in the Great Lakes and other areas. One of the beneficial use impairments at numerous AOC is 'fish tumors and other deformities'. An impairment occurs when the prevalence of fish tumors and other deformities exceeds those at unimpacted or control sites or when survey data confirm the presence of neoplastic or preneoplastic liver lesions in bullhead or white sucker Catostomus commersonii. Numerous surveys have been conducted over the years assessing neoplasia in these fishes, both liver and skin tumors. However, a major problem in comparing the results has been a lack of consistent criteria for evaluating histological changes in bullhead livers. As individual AOC develop and implement remedial action plans, realistic and attainable delisting targets need to be specified. For this to occur and be consistent from site to site there must be standardization of the criteria being used to evaluate specific impairments. In this report, specific diagnostic criteria are provided for both non-neoplastic and neoplastic proliferative hepatocellular and biliary lesions. These criteria should assist fish pathologists in describing and categorizing proliferative liver lesions from brown bullhead.     

Metabolism of benzo[a]pyrene and persistence of DNA adducts in the brown bullhead (Ictalurus nebulosus).

1. The in vitro metabolism of [3H]benzo[a]pyrene (BP) and [14C]benzo[a]pyrene-7,8-dihydrodiol (BP-7,8-diol) by liver of brown bullhead (Ictalurus nebulosus) was characterized, as was the formation and persistence of BP-DNA adducts in vivo. 2. Compared to rat liver microsomes, bullhead liver microsomes produced relatively larger amounts of BP-7,8-diol (predominantly the [-] enantiomer) and smaller amounts of of BP-7,8-diol (predominantly the [-] enantiomer) and smaller amounts of BP-4,5-diol. 3. BP phase I metabolites were efficiently converted by freshly isolated bullhead hepatocytes to conjugates, predominantly glucuronides. 4. BP-7,8-diol was metabolized by hepatocytes 4-fold more rapidly than was BP and was converted to approximately equal amounts of glucuronides, glutathione conjugates and sulfates. 5. BP-DNA adducts formed in bullhead liver with a lag time of several days and maximum adduct formation at 25-30 days. The major adduct was anti-BPDE-deoxyguanosine.