Experimental differences in mortality patterns between European minnows, Phoxinus phoxinus, infected with sympatric or allopatric trematodes, Diplostomum phoxini

A factorial experiment was conducted to examine if the digenetic trematode parasite Diplostomum phoxini influences minnow growth and survival negatively and if different parasite populations differ in their effects on hosts. Juvenile full-sibling minnows from a lake located at the northern edge of the Swiss Alps were infected experimentally with D. phoxini from either their own or another lake. When exposed to sympatric parasites, the minnows survived a low and a high infection dose more or less equally, but with allopatric parasites mortality increased with infection dose. Parasites did not reduce host growth and minnows exposed to a low infection dose grew quicker than either non-infected ones or ones exposed to a high infection dose. Thus, the results show different patterns of pathogenicity between two parasite populations and suggest that (1) the observed differences are at least partially genetic and that (2) the co-evolved, sympatric host-parasite association has reached a degree of low pathogenicity. Differences between the findings presented here and those of a previously published study are discussed.     

Histopathological and ultrastructural observations of metacercarial infections of Diplostomum phoxini (Digenea) in the brain of minnows Phoxinus phoxinus

The spatial distribution and histopathological changes induced by metacercariae of the digenean trematode Diplostomum phoxini (Faust, 1918) in the brains of European minnows Phoxinus phoxinus (L.) from the River Endrick, Scotland, were studied by light and electron microscopy. Post-mortem examination of a sample of 34 minnows revealed that 50% (n = 17) of the population was infected with 13.7 +/- 2.6 (mean +/- SE; range 1 to 38) metacercariae per infected host. Serial histological sections of the infected minnow brains revealed that the metacercariae were unevenly distributed throughout the brain, with aggregations occurring in the cerebellum, the medulla oblongata and the optic lobes. In fish with highest intensities of infection, over 40% of the cerebellar area and about 30% of the medulla oblongata area were occupied by larvae. Metacercariae disrupt the integrity of brain tissue, with individuals being found in small pockets surrounded by cellular debris. Metacercariae were rarely encountered on the surface of the brain. Electron microscopic examination of infection sites revealed that the granular layer surrounding metacercariae was necrotic, exhibited nuclear degradation and was marked by vacuolation of the cytoplasm. Rodlet cells, the only inflammatory cell types recorded in this study, were found only in parasitized brains and in close proximity to the teguments of metacercariae. It is hypothesised that secretions released from the teguments of metacercariae are a counter response to protect the metacercariae from the fish brain's cellular defence mechanisms.     

Identification of extraretinal photoreceptors in the teleost Phoxinus phoxinus

The existence of cells capable of detecting changes of the photoperiod within the deep brain, the so-called deep brain photoreceptors, was proposed in the early years of the twentieth century. By using immunocytochemistry with antisera against phototransductory proteins on paraffin and vibratome sections, we have localized several positive areas in the brain of the teleost Phoxinus phoxinus. These areas were restricted to two encephalic regions: the epithalamus and the hypothalamus. Immunopositive (rod-opsin- and a-transducin-like) pinealocytes and parapinealocytes, as well as some sparse neurons in the habenula, were seen in the epithalamus. The immunoreaction of the hypothalamus was represented by a-transducin-like positive (magnocellular and parvicellular) neurons of the Nucleus Preopticus, as well as by a-transducin- and arrestin-like positive fibers corresponding to the hypothalamic-hypophyseal tract and a few fibers running towards the basal telencephalon. These findings corroborate the data published on other teleost fish and fully support the hypothesis of the presence of photosensitive cells in the encephalon of lower vertebrates. The labelling with antisera against different components of the phototransductory cascade also strengthens the idea that such cells employ a biochemical mechanism similar to that in the retinal visual photoreceptor cells, rods and cones. Although the function is still unclear, the detection of the photoperiod seems to be the most likely role for these extraretinal photoreceptors.     

The development of shoaling behaviour in the European minnow, Phoxinus phoxinus

The effects of development and disturbance on schooling and shoaling were observed in laboratory-raised minnows. Both behaviours were present at the onset of free swimming. Shoaling increased to become the most important behaviour by 3 weeks after emergence from gravel, while the main increase in schooling behaviour occurred at 4 weeks. These changes were accompanied by rises in elective group size and in the number of following responses, and by a decrease in nearest neighbour distance. The increases in social behaviour were observed at an earlier stage in the same minnows threatened by a standard net chase. The main increase in schooling in disturbed minnows took place between 3 and 4 weeks after emergence; after this time schooling became the dominant behaviour. Disturbed fish were also more likely to follow another minnow during an encounter.     

The parasitic communities of the minnow (Phoxinus phoxinus L>)

Phoxinus phoxinus being a widely distributed through Palaearctic and ecologically specialised species is a good model to study parasite communities. 72 specimens of P. phoxinus from 5 localities of the Siberia and Mongolia has been studied by the author and 651 specimens--from 5 localities in Kola Peninsula by the other researches. 595 specimens were studied by B. S. Shulman (1983) year around. To describe infra- and component parasite communities the Brillouin, Shannon, Berger-Parker indexes were used. Communities within individual fish were compared within, and between localities with quantitative percentage similarity index (Esch e. a., 1988). The Brillouin, Shannon and Berger-Parker indexes can be calculated based on abundance or total number of parasites of each species for component or compound communities. Intensity cannot be used. Significant negative correlation was observed between the Brillouin and Berger-Parker dominance indexes (r = -0.984, p < 0.01, n = 66) in infracommunities. The Brillouin index was significant positive correlated with the number of parasites in infracommunity (r = 0.407, p < 0.01, n = 66) and with the number of species in infracommunity (r = 0.92, p < 0.01, n = 66). Berger-Parker dominance index was significant negative correlated with the number of parasite in infacommunity (r = -0.815, p < 0.01, n = 66) and with the number of species in infracommunity (r = -0.268, p < 0.05). Total number of parasites and the number of species in infracommunity was positive correlated significantly (r = 0.565, p < 0.01, n = 66). These correlations remain the same at the component community level for the Shannon/Berger-Parker indexes (r = -0.965, p < 0.01, n = 10) and total number of parasites/number of species (r = 0.789, p < 0.01, n = 10) only. Similarity index was not correlate with any other indexes and parameters. No significant correlation was found between the Brillouin, Berger-Parker indexes and geographical characters of localities (longitude, latitude, altitude above sea-level). Weak correlation (r = 0.551, p < 0.098, n = 10) was observed only between the Berger-Parker dominance index and the latitude. 37 metazoan parasites have been found in all localities (specialists--40%, allogenic species--22%, rare species--40%). Allogenic generalist species of the genus Diplostomum (D. phoxini in most cases) were dominant in 60% of the component communities and 36% of infracommunities on average. 20% of the component communities were dominant by autogenic specialists Gyrodactylus magnificus and only 12% of the infracommunities were dominated by this species. Trematode and nematode larvae were core species in most localities. Frequency distribution of infracommunity richness varied from locality to locality being overdispersed in combine sample. Parasite communities at least on the infracommunity level demonstrate high variability of all parameters. Some tendency to decrease the diversity seems to be present depending on remoteness from prospective centre of origin of the genus Phoxinus.     

CSF-contacting and other somatostatin-immunoreactive neurons in the brains of Anguilla anguilla,Phoxinus phoxinus,and Salmo gairdneri (Teleostei)

Summary A system of somatostatin-immunoreactive neurons was demonstrated in the brains of the eel, Anguilla anguilla, the European minnow, Phoxinus phoxinus, and the rainbow trout, Salmo gairdneri, by means of the light-microscopic indirect immunoperoxidase technique.In the anterior periventricular nucleus, somatostatin-immunoreactive cerebrospinal fluid (CSF)-contacting neurons display intensely stained intraventricular dendritic protrusions, perikarya, and axonal processes. The latter taper into a somatostatin-immunoreactive fiber plexus extending to the infundibulum, the proximal neurohypophysis, and the lateral and mammillary recesses.In addition, somatostatin-immunoreactive neurons were demonstrated in the magnocellular preoptic, entopeduncular and dorsolateral thalamic nuclei, further in the pretectal area and the ventrolateral tegmentum. Somatostatin-immunoreactive fiber bundles project via the stria medullaris toward the habenular nucleus; they also course in the dorsomedial-ventrolateral direction at the level of the pretectal-tegmental area, and within the ventral and dorsal tegmentum.The presence of somatostatin in a variety of different neurons of the teleost brain is discussed in connection with their tentative inhibitory function. The CSF-contacting neurons of the anterior periventricular nucleus are supposed to function as sensors that pass information from the CSF to the somatostatin system of the hypothalamus and/or other components of the neuroendocrine apparatus.Dedicated to Professor Helmut Leonhardt, Kiel, on the occasion of his 65^th birthdayThis investigation was supported by grants from the Deutsche Forschungsgemeinschaft to A.O. (Ok 1/25-3) and H.W.K. (Ko 758/2-2)On leave of absence from the second Department of Anatomy, Semmelweis OTE, Budapest, Hungary     

The problem of sexual inversion in the minnow, Phoxinus phoxinus (L.)

The incidence of sexual inversion in Phoxinus phoxinus has been studied by examining histologically (a) the gonads of 406 adult specimens caught from the wild during a period of 16 months, (b) the gonads of 168 adults kept in captivity in groups with an experimentally altered sex-ratio, and (c) the differentiation of the gonads in the fry.
All the adults had either testes or ovaries and no case of intersexuality was observed. For both testis and ovary, we recognized two phases, depending on the seasonal cycle: an active spring-summer phase, corresponding with the period of reproduction, and a quiescent autumn-winter phase. The ovaries showed an asynchrony in oocyte development, which is typical of species that spawn many times during the breeding season.
In P. phoxinus the ovaries are easily recognizable just one month after hatching and testes are well differentiated in 2-month-old fingerlings. Differentiation is, therefore, precocious and follows a pattern typical of gonochoristic species in which hermaphroditism never occurs.     

Temperature-dependent development of cardiac activity in unrestrained larvae of the minnow Phoxinus phoxinus

The minnow (Phoxinus phoxinus) was raised up to the stage of swim bladder inflation at temperatures between 10 degrees C and 25 degrees C, and the time of development significantly decreased at higher temperatures. Accordingly, initiation of cardiac activity was observed at day 2 in 25 degrees C animals and at day 4 in 12.5 degrees C animals. Only a minor increase in body mass was observed during the incubation period, and, at the end of the incubation period, animals raised at 25 degrees C did not have a significantly lower body mass compared with animals raised at 15 degrees C. Metabolic activity, determined as the rate of oxygen consumption of a larva, increased from 3.3 to 19.5 nmol/h during development at 15 degrees C and from 5.6 to 47.6 nmol/h during development at 25 degrees C. Heart rate showed a clear correlation to developmental stage as well as to developmental temperature, but at the onset of cardiac activity, diastolic ventricular volume and also stroke volume were higher at the lower temperatures. Furthermore, stroke volume increased with development, except for the group incubated at 12.5 degrees C, in which stroke volume decreased with development. Initial cardiac output showed no correlation to incubation temperature. Although metabolic activity increased severalfold during development from egg to the stage of swim bladder inflation at 15 degrees C and at 25 degrees C, weight-specific cardiac output increased only by approximately 40% with proceeding development. At 12.5 degrees C, cardiac output remained almost constant until opening of the swim bladder. The data support the notion that oxygen transport is not the major function of the circulatory system at this stage of development. The changes in heart rate with temperature appear to be due to the intrinsic properties of the pacemaker; there was no indication for a regulated response.     

The life history of the minnow Phoxinus phoxinus (L.) in a productive stream

SUMMARY. 1. In the River Frome, Dorset, this small cyprinid spawned from mid-April to early August and consequently some 0 group minnows did not develop scales until the following spring.
2. Most I group fish formed a summer hyaline band on their otoliths in a edition to the normal winter band.
3. Life-span was short with a winter age-structure of 67% 0 group, 32% I group and 1% II group fish with mean fork lengths of 29, 55 and 73 mm respectively.
4. In June, substantial numbers of I group fish reached reproductive size (50mm) and thereafter progressively replaced II group fish in the spawning shoals. Few II group males survived beyond June, few females beyond August.
5. Only half of I group minnows reached matutity. These were usually fish which had reached 30mm by the previous winter. Very few of these large I group fish survived to spawn the following year.
6. This differential mortality, together with the loss of condition and disappearance of II group fish during spawning, may indicate the cost of an extended high level of reproductive effort.
7. In this productive environment the life history of the minnow more closely resembles that of the small sympatric species Cottus gobio and Noemacheilus harhatulus than it does that of sympatric cyprinids.     

The effect of exercise on the survival of Phoxinus phoxinus L. in sodium cyanide solutions

Summary Minnows (Phoxinus phoxinus) exercised moderately or severely in an apparatus lost their sense of balance in a shorter time than controls in moderately low and high concentrations of sodium cyanide. This loss of equilibrium was also proportional to the duration of exercise.     

The adenohypophysis of the flounder,Pleuronectes flesus,and the minnow,Phoxinus phoxinus

Summary The pituitary gland of the flounder, Pleuronectes flesus, showed several unusual cytological features. Between the RPD and the PPD was a zone of cells that stained purple with Alcian blue—PAS—orange G. Many of these cells were apparently degenerating. In the PPD the strands and coils of presumptive STH cells showed a tremendous variation in both size and staining properties. In the PI there were two cell types, the PAS-positive one bordering the neurohypophysis. Around the periphery of the PI was a zone of chromophobic cells, and throughout the PI were numerous intracellular and extracellular acidophil spheres.No well defined ACTH cells were found in the RPD of the minnow (Phoxinus phoxinus). The Alcian blue—PAS—orange G technique distinguishes between blue TSH cells and purple GTH cells in the RPD and PPD. GTH cells from animals collected in the winter were vacuolated. The PI contained two cell types whose staining reactions and ultrastructure were extremely variable. Intra- and extra-cellular acidophil spheres were present.I should like to thank Dr. T. Kerr of the Zoology Department, Leeds University, for his help and encouragement, and Mr. J. Dingley of the Department of Zoology, Aberystwyth, for collecting the flounders.     

Acquired Recognition of Predator Odour in the European Minnow (Phoxinus phoxinus)

Naive European minnows (Phoxinus phoxinus) do not show a fright reaction when they first encounter the odour of a natural predator (the pike: Esox lucius) or the odour of a non-piscivorous exotic (tilapia: Tilapia mariae). A conditioned fright response to both these odours will however develop if minnows experience them in a potentially dangerous situation, for example, in conjunction with Schreckstoff, the ostariophysian alarm pheromone. Although minnows respond to both odours the reaction to the tilapia odour is reduced. This suggests that a constraint on learning is involved. Olfactory recognition is particularly valuable for detecting predators that hunt in conditions where visibility is poor.     

The genetic structure and microdistribution of shoals of Phoxinus phoxinus, the European minnow

Efficient foraging and a reduction in predation risk have been proposed as reasons for shoal formation. Some behaviours in cyprinid shoals are at first sight altruistic (e.g. predator inspection behaviour, reactions to alarm substance), such that kin selection may have been involved in their evolution. If shoaling behaviour does evolve through kin selection, then genetic differentiation is expected to be greater between shoals than within shoals. Such a hypothesis was tested here by examining shoal integrity and the relatedness of individuals within and between shoals in the European minnow, Phoxinus phoxinus , using nuclear and mitochondrial DNA markers. The breeding structure of 13 minnow shoals collected from Dorset and North Wales, U.K., was examined using allozymes. Genetic affinity within and between shoals was tested using mitochondrial DNA and multi-locus DNA fingerprinting. Shoals consisted of a random assortment of allozyme genotypes, shoal members did not share the same maternal mtDNA lineages and DNA fingerprint profiles were as varied within shoals as between them. The data indicate that it is unlikely that kin selection occurs in P. phoxinus and there is no apparent relationship between shoaling behaviour and genotype distribution in this species.     

Male Ornamentation in the European Minnow (Phoxinus phoxinus) Signals Swimming Performance

The association between male secondary sexual ornamentation and male quality has been under intensive study for decades. It has been shown that male ornaments in fish indicate a variety of physical and genetic qualities. However, only few studies have investigated whether male ornaments signal locomotor performance, a trait that is expected to be vital for individual fitness in the nature. In this study, we sampled two populations of European minnow (Phoxinus phoxinus), a cyprinid fish species with spectacular and colourful male breeding ornamentation, and examined the association between male ornaments (tubercle number, lateral darkness and abdominal redness), swimming performance, and three fitness‐related traits, body length (L_T), condition factor (K) and gonadosomatic index (GI). We found that male tubercle number and abdominal redness were positively correlated with their swimming performance. In addition, these two ornaments were correlated with male fitness‐related traits, which in turn were also directly associated with the swimming performance. In general, these results suggest that in the European minnow male ornamentation may act as an honest signal of several fitness‐related traits and locomotor performance in the nature.     

The colour change of the minnow, Phoxinus phoxinus with particular reference to the effect of spinal lesions

An account is given of the anatomy of the spinal cord of the minnow, Phoxinus phoxinus L., and comparisons are made with the spinal cords of other teleosts. The effects on the rapid, neurally controlled colour responses of complete transection of the spinal cord at different levels indicated that, in the particular fish used for this work, the sympathetic pigmento-motor fibres had a localized outflow from the spinal cord around vertebra 13. Partial lesions of the spinal cord at vertebrae 3, 4, 10 and 11 and their effects on the colour responses indicated that, at these spinal levels, the pigmento-motor fibres were dorsomedially located within the dorsal horns. Complete and partial transection of the spinal cord at any single level between vertebrae 12 and 14 and partial transection of the dorsomedial spinal tissues at vertebrae 3, 4, 10 and 11 resulted in differential paling of the entire dorsolateral skin of the fish in response to a change of background from black to white. It would appear that in both cases this differential response of the melanophores was the result of transecting a proportion of the spinal pigmento-motor fibres.     

Genetic variability in the European minnow,Phoxinus phoxinus (L.)

An electrophoretic study of genetic variation at 11 loci was performedfor a population of European minnows, Phoxinus phoxinus (L.). Ten loci, EST-1 ^*, EST-2 ^* EST-3 ^*,GPD-1 ^*,GPD-2 ^*,GPI-1 ^*,GPI-2 ^*,MPI ^*,6PGD ^* and PGM ^* were polymorphic. IDH ^*wasmonomorphic. The mean number of heterozygotic loci over all 176 fish was 3.05 ± 0.104(SE). Observed mean heterozygosity was 0.28±0.058(SE) and expected mean heterozygosity was 0.27±0.054(SE). EST-2 ^*, EST-3 ^* andPGM ^* were not in Hardy-Weinberg equilibrium. Length,condition, parasite numbers or male breeding characters, i.e. red colorationand tubercles, were not influenced by single enzyme loci.     

Intracellular responses from the photosensitive pineal organ of the teleost,Phoxinus phoxinus

Summary Intracellular potentials from the isolated dark-adapted pineal organ ofPhoxinus phoxinus were recorded by using glass microelectrodes. The majority of cells had resting potentials of 20 to 35 mV and responded to light with intensitygraded hyperpolarizations. Voltage intensity curves of responses to brief flashes followed the hyperbolic tangent functionV/V _max=Iⁿ/(I ⁿ + ⁿ ).The latency of onset for responses to light stimuli near threshold was 400 ms and decreased with saturating flashes to about 50 ms. The membrane resistance decreased during the hyperpolarization. Spectral sensitivity measurements for these cells exhibited curves with _max=530 nm. Intracellular dye injection unequivocally identified this cell type as a photoreceptor cell.A second cell type with resting potentials between 30 to 40 mV exhibited a biphasic response pattern to light stimulation. The cell depolarized with dim light flashes and hyperpolarized with bright flashes. The amplitude of the hyperpolarizing component showed no saturation over an intensity range of 5 log units. Latencies and rise times were comparable to those of photoreceptor potentials. Spectral sensitivity curves peaked at longer wavelengths ( _max=550 nm) than the action spectra of photoreceptors ( _max=530 nm). It is assumed that this rare cell type represents a small class of pineal interneurons.     

Avoidance experiments with homing shoals of minnows, Phoxinus phoxinus in a laboratory stream channel

In a laboratory stream channel consisting of two tributaries joining to form a 'river' it proved possible to establish three populations of minnows in separate home ranges. Minnows in the apparatus avoided water with low concentrations of dissolved oxygen but returned to the home range when aerated water was re-established. Concentrations of 4, 8 and 10 mg 1⁻¹ of phenol did not cause avoidance behaviors, in fact the highest concentration killed some fish, but activity levels were severely depressed and shoaling behaviors was also affected.     

Variability of functional traits and their syndromes in a freshwater fish species (Phoxinus phoxinus): The role of adaptive and nonadaptive processes

Functional traits can covary to form “functional syndromes.” Describing and understanding functional syndromes is an important prerequisite for predicting the effects of organisms on ecosystem functioning. At the intraspecific level, functional syndromes have recently been described, but very little is known about their variability among populations and—if they vary—what the ecological and evolutionary drivers of this variation are. Here, we quantified and compared the variability in four functional traits (body mass, metabolic rate, excretion rate, and boldness), their covariations and the subsequent syndromes among thirteen populations of a common freshwater fish (the European minnow, Phoxinus phoxinus). We then tested whether functional traits and their covariations, as well as the subsequent syndromes, were underpinned by the phylogenetic relatedness among populations (historical effects) or the local environment (i.e., temperature and predation pressure), and whether adaptive (selection or plasticity) or nonadaptive (genetic drift) processes sustained among‐population variability. We found substantial among‐population variability in functional traits and trait covariations, and in the emerging syndromes. We further found that adaptive mechanisms (plasticity and/or selection) related to water temperature and predation pressure modulated the covariation between body mass and metabolic rate. Other trait covariations were more likely driven by genetic drift, suggesting that nonadaptive processes can also lead to substantial differences in trait covariations among populations. Overall, we concluded that functional syndromes are population‐specific, and that both adaptive and nonadaptive processes are shaping functional traits. Given the pivotal role of functional traits, differences in functional syndromes within species provide interesting perspectives regarding the role of intraspecific diversity for ecosystem functioning.