Determining diel variation in fish assemblages downstream of three weirs in a regulated lowland river

The diel variation in boat electrofishing catches was investigated on the lower Murray River (south-eastern Australia), downstream of three low-level weirs. Fish assemblage composition did not differ among three sites, but differed substantially between day and night. Significantly more small-bodied species ( e.g. Australian smelt Retropinna semoni , flyspecked hardyhead Craterocephalus stercusmuscarum , bony herring Nematalosa erebi and Murray rainbowfish Melanotaenia fluviatilis ) and some large-bodied predators ( e.g. golden perch Macquaria ambigua ) were caught during daytime samples. Significantly more flatheaded gudgeon Phylipnodon grandiceps , carp gudgeon Hypseleotris spp. and perch Perca fluviatilis were collected at night. The size composition of the fish assemblage also changed over the diel cycle. Significantly smaller goldfish Carassius auratus , flyspecked hardyhead, bony herring and Australian smelt were sampled during the day, while generally smaller individuals of golden perch and the common carp Cyprinus carpio were caught at night. These findings suggest that sampling during both day and night is required to adequately characterize riverine fish assemblages in the context of fish migration studies.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.     

Swimming performance and metabolic rate of three tropical fishes in relation to temperature

Oxygen consumption was measured for three tropical fishes,Exodon paradoxus, Leporinus fasciatus andLabeo erythrurus in relation to swimming speed and temperature. For each species the logarithm of oxygen consumption (mg 0₂ · g^–1 · h^–1) increased linearly with relative swimming speed (1 · s^–1) with the value of the regression coefficients varying inversely with temperature. Active metabolism and critical swimming speed ofE. paradoxus andL. fasciatus increased with temperature to a maximum at 30 and 35° C respectively. Basal metabolic rates ofE. paradoxus andL. fasciatus increased with temperature. Metabolic rates and critical swimming speed of the three fishes studied were consistent with values for polar, temperate and other tropical species over their respective thermal ranges of tolerance. Tropical fishes have lowered their metabolism and swimming performance from that expected for many temperate species at the same temperature.     

Feeding ecology of the Iberian cyprinid Barbus bocagei Steindachner, 1865 in a lowland river

Patterns of food resource utilization by Barbus bocagei in a lowland river in the central part of the Iberian Peninsula are presented and discussed. Focal points include feeding activity, diet composition and seasonal and ontogenetic diet shifts. Striking features of overall feeding pattern of barbel are its continuous feeding activity, bottom habits, high consumption of detritus and dipteran larvae and narrow diet breadth. Seasonal changes in food resource availability elicited changes in food utilization patterns, revealing a trend to more generalist feeding during spring. Barbel increase consumption of plant material and large prey during ontogeny, but overlap in prey resource utilization between size classes is high. The versatility of barbel foraging behaviour may be an important feature in its exploitation of Iberian lotic systems.     

Postembryonal growth and its variability of the three marine fishes with special reference to the mechanism of growth variation in fishes

1. To study the relation of growth variation to the behaviour pattern, newly hatched Hemiramphus sajori, Chrysophrys major and Zebrias zebra were reared in 30 litter aquaria during one month, and body length was measured four times.
2. In Hemiramphus sajori coefficient of variation of body length (CV) first increased but showed a tendency to decrease with development of schooling behaviour.
3. In Chrysophrys major CV markedly increased and mode of the distribution curve of body length inclined towards the left side, associated with appearance of aggression and cannibalism.
4. In Zebrias zebra, when behaviour pattern changed from planktonic to demersal some of the small individuals nearly ceased growing. At that time CV of body length remarkably increased and the mode of the distribution curve of body length shifted towards the right side.
5. In all the species a positive correlation was seem between specific growth rate and initial body length soon after intensive feeding began. An negative correlation was observed in most of individuals of Hemiramphus sajori after the appearance of schooling behaviour. When a conspicuous increase in CV and skewness in distribution curve took place, a separate type of correlation was seen in large and small group in the population.
6. Based on above mentioned and other materials a general mechanism of growth variation in fishes was discussed.

     

Responses of aquatic macrophyte assemblages to nutrient enrichment in a lowland river basin of western Greece

Abstract

In Greece, as in many other Mediterranean countries, there is a lack of information enabling the use of aquatic macrophytes as biological indicators of the water trophic status. This research aimed to investigate the trophic preferences of the aquatic macrophyte assemblages encountered in selected standing water bodies of a lowland river basin of western Greece. It also aimed to assess the response of the macrophyte species that occur in the studied water bodies to different nutrient concentrations. A total of 56 macrophyte species were identified. TWINSPAN analysis distinguished four main vegetation groups potentially related to three trophic types. The Trophic Ranking Score developed in the UK was applied in order to investigate the trend in aquatic macrophytes in response to the different trophic conditions. The results indicated that TRS_UK was not in accordance to the water trophic indices. After the addition of 14 new species and the re-scoring of the plants from the UK list, the re-calculation of TRS enabled a better classification of the trophic status convergent with the information from the water trophic indices. The current study constitutes a reference document providing basic information, and must be improved by updating the plant list with new data from other sites.     

Summer co‐existence of small‐sized cyprinid and percid individuals in natural and impounded stretches of a lowland river: food niche partitioning among fishes

Due to changes of discharge regime downstream of a dam reservoir, an alluvial natural stretch of the Warta River changed to a macrophyte‐dominated ecosystem. Large patches of submersed, aquatic macrophytes appeared in summer and their effect is analysed in this study. These patches contained enriched macroinvertebrate assemblages (epiphyton and benthos) and they were refuge for both zooplankton and young fishes released from the reservoir. Despite these altered conditions in this stretch, roach Rutilus rutilus, perch Perca fluviatilis and ruffe Gymnocephalus cernua dominated, as they did in the natural backwater. Fishes were sampled every 2 weeks from June to August, together with their food resources to assess the partitioning of the diet among small individuals of the three species in both stretches (the natural and affected ones). The aim of the analysis was to answer how animal food associated with water plants was partitioned between the species. In both stretches, G. cernua were primarily benthivorous, but epiphytic fauna, zooplankton and large‐sized benthic chironomid larvae replaced lack of many large, benthic insects in the tailwater. Levins' food breath index decreased from 0·36 in the backwater to 0·29 in the tailwater. An opposite trend was observed for P. fluviatilis occurring among macrophytes. Perca fluviatilis were competitors of R. rutilus and took food not only in or on the river bed, but also in the water column. They ate zooplankton and epiphytic fauna and Levins' index increased from 0·32 to 0·44 in the tailwater. Rutilus rutilus fed on adult insects, algae and plant fragments in the natural stretch. In the tailwater, these food types were chiefly complemented by zooplankton. Despite this, the niche breadth of R. rutilus was similar at the two sites. Abundance of food associated with the macrophytes appeared to facilitate cohabitation in the abundant fish populations, but P. fluviatilis appeared to benefit the most in the altered river stretch.     

An empirical model for predicting microhabitat of 0+ juvenile fishes in a lowland river catchment

Summary Species-habitat relationships are an important aspect of fish life history, particularly in early ontogeny. To address the lack of information on the microhabitat use/requirements of European coarse fishes, particularly 0-group fishes in riverine systems, an empirical model was generated from data collected in the River Great Ouse catchment (UK). During 7 weeks in autumn 1990, data on young-of-the-year (0+) juvenile fishes and 15 environmental variables were collected at 2800 stratified, random point samples within 130 study sites (streams, rivers, side-channels, backwaters). Of 24 species of 0+ fish, only 10 were captured in 3% of non-null samples. Association analysis and canonical correspondence analysis of the samples-by-species (967×10) and samples-by-variables (967×15) data matrices revealed that the shallow, narrow, lotic, stony-pebbly channel microhabitat of riffles and runs was preferred by the progeny of substrate-spawning, substrate/plant-spawning and nest-guarding fishes. Moderately deeper and wider, sinuous channels, with slowto-moderate water velocities and medium-sized substrata were also favourable to progeny of substrate spawners. Assemblages of 0+ fish in deeper, wider, silted, trapezoidal-shaped channels with slow-to-lentic flowing water, i.e. channelised and regulated, were dominated by ubiquitous (plant/substrate) spawners.     

Spawning strategies in cypriniform fishes in a lowland river invaded by non-indigenous European barbel Barbus barbus

Spawning strategies of lowland river fishes include single spawning, where reproduction generally occurs in early spring to provide 0+ fish with an extended growth season through the summer, but with a high risk of stochastic mortality events occurring, such as early summer floods. This risk can be reduced by multiple or protracted spawning strategies, where 0+ fish are produced over an extended period, often into mid-summer, but with the trade-off being a shorter growth season. The spawning strategies of cypriniform fish were explored in the River Teme, a spate river in Western England, which has non-indigenous European barbel Barbus barbus present. Sampling 0+ fish in spring and summer and across three spawning periods, B. barbus, chub Squalius cephalus and minnow Phoxinus phoxinus always revealed multiple spawning events, with 0+ fish of < 20 mm present in samples collected from June to August. Fish below 20 mm in August remained relatively small by the end of their growth season (October). For dace Leuciscus leuciscus, only single spawning events were evident, but with 0+ dace always being relatively large. Therefore, multiple spawning appears to be a common strategy that provides resilience in 0+ fish against stochastic mortality events in lowland rivers.

     

Temporal variation in river nutrient and dissolved lignin phenol concentrations and the impact of storm events on nutrient loading to Hood Canal, Washington, USA

Rapid rainfall events can be responsible for a large proportion of annual nutrient and carbon loading from a watershed. The bioavailability of organic matter during these rapid loading events increases, suggesting that storms play a relevant role in the mobilization of potentially labile terrestrial carbon. A high correlation between river discharge rates and dissolved and particulate nutrient and carbon concentrations during autumn and winter storms was observed in several temperate Pacific Northwest rivers. Dissolved and particulate lignin concentrations also increased with river discharge; for example, in October 2009 dissolved lignin concentrations increased roughly 240% with a 200% increase in river discharge. During these storms a unique phenolic composition was observed for dissolved lignin that was rapidly mobilized from surface soils relative to the base flow of dissolved lignin. The observed increase in Ad/Al ratios with discharge indicates that rapidly mobilized dissolved lignin is more degraded than the base flow of dissolved lignin. Similarly, a marked increase in C/V ratios and decrease in the S/V ratio of dissolved lignin phenols with increasing river discharge was observed. These results may indicate a difference in source between mobilized and base flow pools, or, more likely, preferential degradation and mobilization/retention of specific lignin phenols. The cumulative results from this year-long data set indicate that a shallow nutrient-rich pool of particulate and dissolved organic matter accumulates in watersheds during periods of soil-saturation deficiency (summer). Autumn and winter storms mobilize this pool of accumulated nutrients from surface soils, which is exhausted with successive winter storms.     

In situ nutrient assays of periphyton growth in a lowland Costa Rican stream

Nutrient limitation of primary production was experimentally assessed using an in situ bioassay technique in the Quebrada Salto, a third-order tropical stream draining the northern foothills of the Cordillera Central in Costa Rica. Bioassays employed artificial substrata enriched with nutrients that slowly diffuse through an agar-sand matrix (Pringle & Bowers, 1984). Multiple comparisons of regression coefficients, describing chlorophyll-a accrual through time for different nutrient treatments, revealed positive micronutrient effect(s). Micronutrient treatment combinations (Fe, B, Mn, Zn, Co, Mo, EDTA), supplemented with and without nitrate and phosphate, exhibited significantly greater chlorophyll-a accrual over all other treatments (P < 0.05), supporting over three times that of the control after 14-d of substratum colonization. Neither of the major nutrients (N or P) produced a significant stimulation, although the N treatment displayed 50% more chlorophyll-a than the control after 14-d. Similarly, Si, EDTA, and Si + N + P treatments did not exhibit chlorophyll-a response curves that were significantly different from the control. During the experiment, mean NH₄-N and (NO₂ + NO₃)-N concentrations in the Salto were 2.0 µM (28.6 µg · l^–1) and 7.2 µM (100.2 µg · l ^–1), respectively. High concentrations of PO₄-P ( = 2.0 µM; 60.9 µg · l^–1) and TP ( = 3.0 µM; 94.0 µg · l^–1) were also found, and consequently low molar N:P ratios = 4.7). Despite the potential for N limitation in the system, both N and P appear to be at growth saturating levels. This may be due to micronutrient limitation and/or light limitation of periphyton growth in densely shaded upstream portions of the stream.     

The aquatic macrophytes of an English lowland river system: assessing response to nutrient enrichment

Assessment of the effects of nutrients in running water upon macrophytes is compounded by the variety of additional environmental factors which influence their growth. Some classification schemes have been effective in detecting eutrophication on a national or regional scale, and also downstream changes in large single catchments. However, in lowland rivers with naturally nutrient-rich geologies, detection of change at smaller spatial scales has been difficult. This study examined the macrophyte community at 44 sites on the river Welland, a small lowland catchment rising below 150 m in Leicestershire, England. The community at 23 of these sites was adequate for further analysis. The data show that the clearest effect on community composition is caused by watercourse size. However, sites below sewage works, even small village works, did show a reduction in Mean Trophic Rank, (MTR – an assesment system introduced into the UK over the last three years using a 10–100 scale based upon scores and cover value of indicator species). Overall there was a slight but significant correlation of MTR with soluble phosphate and nitrate. The effectiveness of the MTR method is limited at full catchment scale by low numbers of the indicator taxa at small upstream sites. Catchment-scale assessment of the plant community is probably best served by more detailed phytosociological analysis and by the further development of the habitat templet approach.     

Distribution of chromobacteria in a lowland river

A selective medium was used to estimate the numbers of purple pigmented bacteria in the River Wey. Chromobacteria were never isolated from the springs at the source of the river, but they appeared within a short distance and their numbers generally increased over the first 30 km. Counts were always low but were much higher during the winter than during the summer.Records of water temperature and turbidity, as well as daily rainfall, were maintained during the sampling period. An unweighted multiple regression analysis of some of the results has shown that much of the variability in the counts of chromobacteria was correlated with turbidity (r=0.67,P<0.001). After turbidity was allowed for, a significant inverse correlation with temperature (r=0.60,P < 0.001) became apparent and these two factors together accounted for 64.7% of the variation in counts. Allowing for these two factors revealed a significant correlation with rainfall during the previous 4 days (r=0.27,P<0.05), and the three factors together accounted for 67.2% of the variability in counts.In an attempt to discover the source of chromobacteria, samples of silt, soil, and storm overflow effluents were studied. In general, chromobacteria were present in highest numbers in soil or silt containing substantial quantities of organic material.     

Bioenergetics of growth of a cyprinid, Phoxinus phoxinus (L.): the effect of ration and temperature on growth rate and efficiency

Growth of minnows, Phoxinus phoxinus , weighing 1-5.5 g was studied experimentally at five ration levels from starvation to ad libitum and four temperatures ranging from 5 to 15°C. The relationship between specific growth rate (SGR) and ration was a decelerating curve. SGR at maximum rations increased with increased temperature, but at restricted rations it decreased with increased temperature. Predictive models for the specific growth rates were developed using multiple regression. Maintenance rations and optimum rations both increased with increased temperature. Maintenance rations were less sensitive to temperature than optimum rations and mostly lay between 1 and 2% of body weight per day. Conversion efficiencies increased with increased ration from zero value at the maintenance ration to a peak at the optimum ration, then decreased with further increases in ration. At a given restricted ration level, conversion efficiencies generally decreased with increased temperature. At maximum rations, conversion efficiencies were relatively insensitive to temperature. Growth in wet weight, dry weight and energy content showed similar responses to ration, temperature and body weight.     

The influence of temperature on the embryonic development of three cyprinid fishes, Abramis brama, Chalcalburnus chalcoides mento and Vimba vimba

The influence of temperature on the embryonic development of three European cyprinid fishes, Abramis brama, Chalcalburnus chalcoides mento and Vimba vimba , was studied with respect to hatching efficiency and the functional relationship with the duration of development. The functional dependance of the duration of development on temperature is well described by a power function with a correcting constant for temperature. Comparison with published data for other cyprinids shows that the response of embryos to temperature, together with the various temperature controlled responses of adult fishes, is a valuable aid for the ecological characterization of the different species.     

Lower sensitivity of cyprinid fishes to three acetylcholinesterase inhibitor pesticides: an evaluation based on no-effect concentrations

Researchers have suggested that cyprinid fishes are less sensitive to chemical stress than comparable fish families, yet few empirically based evaluations of this hypothesis have been conducted. In this study, we developed a generalized linear mixed model in which the no-effect concentrations (NECs; threshold concentration below which no effect on survival is predicted during prolonged exposure) of 29 fish species from 13 families exposed to an acetylcholinesterase inhibitor pesticide (carbaryl, chlorpyrifos, or malathion) were used as the response variable. The corresponding specific somatic maintenance (SSM) rates, as a size-independent proxy for fish metabolism and a categorical variable regarding whether the species is a cyprinid, were used as the predictor variables. We included SSM rates in the analysis because previous work demonstrated that they are negatively correlated with NECs. Our results indicate that the NECs for cyprinid fishes were significantly higher than those for other fishes, suggesting that cyprinids are indeed less sensitive to the three studied pesticides. Although the SSM rates were negatively related with the NECs, the actual relationship between the two was not clear, implying that the importance of SSM rates may depend on the taxonomic group tested.     

Seasonal and interannual variation in nutrient fluxes from tributary inputs, consumer recycling and algal growth in a eutrophic river impoundment

We measured tributary inputs, algal nutrient demand and excretion rates of consumers (gizzard shad and zooplankton) at a eutrophic river impoundment. During two summers with contrasting flow regimes, tributary inputs accounted for 38% (1998) and 3% (1999) of algal N demand and 95% (1998) and 17% (1999) of algal P demand. Gizzard shad contributions averaged 14% and 20% of algal demand for N whereas P contributions were 31% and 58% (1998, 1999; respectively). Zooplankton recycling accounted for a comparable fraction of algal P demand (47%) but a larger fraction of N demand (43%) because their excretia were N rich (N:P = 13:1) compared to fish (7:1). Nutrient release by one of the consumers (gizzard shad) was compared with tributary loading over a nine-year period to assess inter-annual variation in their relative importance. Historical records of inflow chemistry, discharge and gizzard shad biomass showed that variation in tributary inputs was the primary determinant of seasonal and inter-annual variation in nutrient loading. Consumer-derived nutrients were important in late-summer and during years when tributary inputs were low. We propose a conceptual model in which primary production is regulated by external nutrient loading and consumer recycling acts to stabilize and sustain production during periods of diminished external inputs.     

Contribution of photosynthetic rate to growth and reproduction in Amaranthus hybridus

While it is known that genetic variation for photosynthetic and growth traits exists in natural populations, the functional significance of this variation remains unclear, particularly for photosynthetic traits. To test the hypothesis that photosynthetic rate has direct effects on reproduction as well as contributing indirectly to reproduction through effects on growth, we compared wild-type Amaranthus hybridus families to those with a single gene mutation that confers a lower photosynthetic rate. Wild-type and photosynthetic-mutant families were grown in competitive and non-competitive environments and we compared size, biomass allocation, architecture, and reproduction at three developmental stages. To assess the contributions of individual growth traits to reproduction, we calculated covariances between standardized traits and relative fitness (selection differentials), and compared selection between the two biotypes. Finally, we used path analysis to calculate the indirect effects of photosynthetic rate on fitness through growth. The size, allocation, and architecture of photosynthetic mutants did not differ from those of the wild type in either the competitive or non-competitive environment, with the exception that they were taller by the last developmental stage. However, the reproductive biomass of the photosynthetic mutants was significantly reduced compared to the wild type. In the competitive environment, the wild type achieved greater fitness because, while similar in size to the mutants, at any given size it produced more reproductive biomass. This suggests that photosynthetic rate affected the linkage between plant size and reproduction and is evidence of an indirect contribution to fitness. In the non-competitive environment, there were fewer differences in selection differentials between the two plant genotypes, suggesting fewer indirect effects. Path analysis showed that variation in photosynthetic biotype had indirect effects on reproductive biomass, via growth traits, and that there were no direct effects. Photosynthetic rate appears to have fitness consequences primarily through multiple contributions to growth throughout development. Received: 27 March 1998 / Accepted: 28 August 1998