Use of terrestrial arthropod prey by a stream-dwelling cyprinid fish

Synopsis The spatio-temporal availability to, and use of terrestrial (allochthonous) prey by, a subset of the fish assemblage of a Virginia piedmont stream were investigated during spring and summer. Terrestrial invertebrates were most abundant in drift nets, but least common in fish stomachs, during April. In contrast, during August, terrestrial prey dominated the diet of the major cyprinid fish,Notropis ardens, even though terrestrial prey availability in the stream declined by an order of magnitude. Several other co-occurring fishes only rarely consumed prey of terrestrial origin. Drifting terrestrial invertebrates, were concentrated at the surface near the thalweg, compared to stream margin or substrate locations. This study suggests that morphologial and behavioral constraints of individual fish taxa, including predator avoidance responses, regulate the use of terrestrial prey within a given fish assemblage.     

Reproduction compromises adaptive immunity in a cyprinid fish

Vertebrates differ in their ability to mount an adaptive immune response to novel antigens. Bioenergetic resources available to an organism are finite; investment in reproduction compromises immune function and may therefore affect critical life history trade-offs. We tested whether reproduction impairs the ability to produce an antibody response against a novel antigen in roach (Rutilus rutilus). The antigen approach has rarely been used in fish studies, and the ability to produce an antibody response during reproductive season has never been tested in cyprinid fish before. The fish in an experimental group were injected with a Brucella abortus (BA) antigen, while the fish in a control group were injected with an isotonic saline solution. Blood samples were extracted from all the fish to obtain the total number and proportion of blood cells such as lymphocytes, neutrophils and antioxidant glutathione. The groups were tested during the spawning season and one week after it had ended. The roach were unable to mount an immune response during spawning but produced a robust response after it. We conclude that reproduction is costly in roach, as indicated by the increased concentration of neutrophils in fish injected with BA during spawning, as well as the negative associations between neutrophil counts and glutathione levels. This study demonstrates the potential of BA antigen as a research tool in experimental research on fish ecological immunology.     

Dry-season spawning in a cyprinid fish of southern India

Synopsis A population of the S. Indian cyprinid fishBarbus melanampyx was sampled monthly through 24 months. Seasonal cycles of the gonado-somatic index (GSI), ovarian stages, male breeding tubercles, spawning behaviour and population structure were assessed. These fish breed strictly seasonally during the main dry period: December/January through April. Comparison with other Barbus species of the same general region led to the conclusion that the patterns of reproductive investment ofB. melanampyx are similar to those of perennial species, and different from those of wet-season spawners. The reasons for this rather unexpected result were found in the more constant conditions prevailing during a dry season as compared to the monsoon. It was argued thatB. melanampyx and the species spawning perennially are in effect small-brood spawners, rather than partial spawners.     

Invasive cyprinid fish in Europe originate from the single introduction of an admixed source population followed by a complex pattern of spread

The Asian cyprinid fish, the topmouth gudgeon (Pseudorasbora parva), was introduced into Europe in the 1960s. A highly invasive freshwater fish, it is currently found in at least 32 countries outside its native range. Here we analyse a 700 base pair fragment of the mitochondrial cytochrome b gene to examine different models of colonisation and spread within the invasive range, and to investigate the factors that may have contributed to their invasion success. Haplotype and nucleotide diversity of the introduced populations from continental Europe was higher than that of the native populations, although two recently introduced populations from the British Isles showed low levels of variability. Based on coalescent theory, all introduced and some native populations showed a relative excess of nucleotide diversity compared to haplotype diversity. This suggests that these populations are not in mutation-drift equilibrium, but rather that the relative inflated level of nucleotide diversity is consistent with recent admixture. This study elucidates the colonisation patterns of P. parva in Europe and provides an evolutionary framework of their invasion. It supports the hypothesis that their European colonisation was initiated by their introduction to a single location or small geographic area with subsequent complex pattern of spread including both long distance and stepping-stone dispersal. Furthermore, it was preceded by, or associated with, the admixture of genetically diverse source populations that may have augmented its invasive-potential.     

Effects of a flow-gauging weir on the migratory behaviour of adult barbel, a riverine cyprinid

Barbel Barbus barbus exhibited substantial movements in the River Nidd between March and July 1994, with some individuals moving nearly 20 km upstream, although there was considerable individual variation. Most upstream movement occurred during May. Fifteen of the 23 fish tracked attempted to pass the weir, and of these six were successful. Barbel tended to approach the weir around dusk and dawn, reflecting observed patterns of localized activity, or at night, but crossed the weir only at night. Those fish which crossed the weir moved substantial distances upstream to spawn, while those that were unsuccessful moved down-stream. The weir delayed the net upstream progress of all adult barbel. Successful traversal was not closely related to flow or water temperature conditions. The study emphasizes the impact of relatively minor obstructions on the natural migrations of barbel.     

Mechanics of the feeding action of a cyprinid fish

The pressures in the buccal cavities of Golden orfe (Idus idus) have been recorded as the fish took food from a tube connected to a pressure transducer. Pressures 50–105 cm water below the pressure of the surrounding water were recorded as the buccal cavity expanded to suck the food in. Calculations based on the dimensions of the muscles lead to the conclusion that the levatores hyoidei, sternohyoideus, rectus abdominis, epaxial trunk muscles and obliquus internus probably all had to exert almost their maximum isometric tensions, to produce the largest reductions of pressure. These muscles seem nicely balanced in strength for their functions in feeding.     

Behavioural asymmetry affects escape performance in a teleost fish

Escape performance is fundamental for survival in fish and most other animals. While previous work has shown that both intrinsic (e.g. size, shape) and extrinsic (e.g. temperature, hypoxia) factors can affect escape performance, the possibility that behavioural asymmetry may affect timing and locomotor performance in startled fish is largely unexplored. Numerous studies have found a relationship between brain lateralization and performance in several cognitive tasks. Here, we tested the hypothesis that behavioural lateralization may affect escape performance in a teleost, the shiner perch Cymatogaster aggregata. Escape responses were elicited by mechanical stimulation and recorded using high-speed video (250 Hz). A number of performance variables were analysed, including directionality, escape latency, turning rate and distance travelled within a fixed time. A lateralization index was obtained by testing the turning preference of each subject in a detour test. While lateralization had no effect on escape directionality, strongly lateralized fish showed higher escape reactivity, i.e. shorter latencies, which were associated with higher turning rates and longer distances travelled. Therefore, lateralization is likely to result in superior ability to escape from predator attacks, since previous work has shown that escape timing, turning rate and distance travelled are among the main determinants of escape success.     

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

Ecological applications of stable isotope data require knowledge on the isotopic turnover rate of tissues, usually described as the isotopic half-life in days (T _0.5) or the change in mass (G _0.5). Ecological studies increasingly analyse tissues collected non-destructively, such as fish fin and scales, but there is limited knowledge on their turnover rates. Determining turnover rates in situ is challenging, with ex situ approaches preferred. Correspondingly, T _0.5 and G _0.5 of the nitrogen stable isotope (δ¹⁵N) were determined for juvenile barbel Barbus barbus (5.5 ± 0.6 g starting weight) using a diet-switch experiment. δ¹⁵N data from muscle, fin and scales were taken during a 125 day post diet-switch period. Whilst isotopic equilibrium was not reached in the 125 days, the δ¹⁵N values did approach those of the new diet. The fastest turnover rates were in more metabolically active tissues, from muscle (highest) to scales (lowest). Turnover rates were relatively slow; T _0.5 was 84 (muscle) to 145 (scale) days; G _0.5 was 1.39 × body mass (muscle) to 2.0 × body mass (scales), with this potentially relating to the slow growth of the experimental fish. These turnover estimates across the different tissues emphasise the importance of estimating half-lives for focal taxa at species and tissue levels for ecological studies.     

Abnormal meiosis in fertile and sterile triploid cyprinid fish

Meiosis is the key process for producing mature gametes.A natural fertile triploid Carassius auratus population (3nDTCC) and an artificially derived sterile tri...     

Species segregation during predator evasion in cyprinid fish shoals

SUMMARY. 1. When a predator attacks a mixed-species group, individual prey arc faced with a conflict between retaining the advantages of large group size and the disadvantages of remaining among aliens. Experiments were designed to show how this conflict is resolved in fish shoals.
2. Simulated attacks with a model predator were made upon mixed and single species shoals of three cyprinid species under semi-natural conditions in a fluvarium.
3. Measurements of elective group size, neighbour identity and distance, and encounters within and between species revealed behaviour which sorted fish into species at the onset of predator attack.
4. A control experiment demonstrated the same effect for fish of matched size.
5. The value to the individual of segregative behaviour in response to predator threat is discussed.     

Behavioural crypsis in a South African galaxiid fish induced by predatory and non-predatory heterospecifics

This study investigated recognition of, and behavioural responses to, predatory and non-predatory heterospecifics by a small cryptically coloured fish species, Galaxias ‘nebula’. Nebula recognised and differentiated between predatory and non-predatory heterospecifics and altered its behaviour facultatively. With both predatory and non-predatory fishes, the proportion of time spent motionless increased, whereas refugia use was affected only by predators and neither heterospecific affected the time spent active. Although nebula appeared to face no conflict, in that their responses to predatory and non-predatory heterospecifics varied in the same direction and differed only in intensity, the presence of both heterospecifics together induced responses midway between those for each heterospecific separately. Non-predatory heterospecifics thus modified nebula's responses towards predators, potentially making time available for other essential activities such as foraging. This modified predator response may aid its survival in an increasingly threatened habitat.     

Outcomes of a pilot fish telemetry workshop for developing countries

Fisheries management is a crucial issue worldwide, but it is proportionally more crucial in developing countries that rely heavily on inland fisheries. Management requires proper knowledge of fish behaviour and habitat use, as can be achieved through telemetry techniques, although these are most rarely used in tropical regions. Here we report briefly on the outcomes of a pilot workshop and training course aiming at improving technology transfer and capacity building, laying the stress on strengths and weaknesses of this approach, as evaluated by trainees.     

Bioturbation by cyprinid fish affecting the food availability for predatory water mites

Summary Field observations suggested that benthivorous fish, causing bioturbation, are able to effect the food availability for predacious water mites feeding on bottom dwelling chironomid larvae. This hypothesis was tested in the laboratory. In an undisturbed situation the predation rate exercised by the water mites on the tube dwelling chironomid Cladotanytarsus mancus was very low. However, when the sediment was disturbed, the predation rate increased substantially. The relevance of this for the field situation is discussed.     

Persistence and heterogeneity in habitat selection studies using radio telemetry

Biologists attach radio transmitters to animals so that the animals' movements through their preferred habitats can be followed. To analyze the resulting sequences of visited habitat classes, McCracken, Manly, and Vander Heyden (1998, Journal of Agricultural, Biological, and Environmental Statistics 3(3), 268-279) proposed an independent multinomial selections (IMS) model. Two issues that arise when using this approach are: (i) serial dependence possibly affects measures of uncertainty; and (ii) individual animals from the population studied may exhibit heterogeneity in their selection patterns. We develop two single-parameter extensions of the IMS model to address these issues. A Markov chain model allows for persistence in the habitat class previously visited. Heterogeneity is modeled by assuming the population of animal selection patterns follows a Dirichlet distribution, from which the study animals are a random sample. We show that these persistence and heterogeneity characteristics are present in the study by McCracken et al. (1998) of bear movements. Simulations demonstrate that failure to account for persistence or heterogeneity when either is present can seriously misrepresent measures of uncertainty.     

Behavioural thermoregulation in two freshwater fish species

In the presence of a vertical thermal gradient, juvenile three‐spined sticklebacks Gasterosteus aculeatus and minnows Phoxinus phoxinus positioned themselves higher in the water column compared with adult conspecifics. This result was consistent regardless of whether age cohorts were tested separately or together. Furthermore, juveniles but not adult fishes positioned themselves higher in water column in the presence of a thermal gradient compared with those in the absence of a thermal gradient. Juvenile G. aculeatus and adult fish of both species did opt to position themselves higher in the water column in the hours immediately following a feeding event relative to their positions in the same gradient when they had not fed.