Population density, growth and migration via the sea to different streams of Japanese dace Tribolodon hakonensis in lower reaches of small streams

Ecological characteristics of Japanese dace Tribolodon hakonensis were investigated in three small streams in Niigata Prefecture from 2001 to 2005 with special reference to the effect of Ayu Plecoglossus altivelis altivelis on the dace. Japanese dace were distributed in short sections below dams near the mouth of the streams flowing into the Sea of Japan. In this section, Ayu were numerically dominant from June to August, and the growth rate of dace in this period was negatively correlated with the density of Ayu. The population density of dace was high in October, but some adults stayed in the streams in June and August. When data for the five years were combined, the density of dace was negatively correlated with that of Ayu in two of the three streams. The increase in density of dace in October is considered to be due to the migration of dace from the sea. Eight dace were confirmed to migrate to different streams via the sea. Therefore, the life history of Japanese dace in the study region contained considerable individual variation.     

Seasonal variations in plasma concentrations of sex steroid hormones and vitellogenin in wild male Japanese dace (Tribolodon hakonensis) collected from different sites of the Jinzu river basin

In order to clarify the seasonal variations of plasma sex steroid hormones and vitellogenin (VTG) concentrations in the wild male Japanese dace, Tribolodon hakonensis, we measured plasma levels of testosterone (T), 11-ketotestosterone (11-KT), estradiol-17 beta (E2) and VTG, as well as spermatogenetic stages and gonadosomatic index (GSI). Wild Japanese dace were collected from different sites of the Jinzu River basin (including the Takahara River and the Itachi River). The fish from Toyama Bay were also measured the spermatogenetic stages, GSI and VTG levels. The seasonal variations of the hormone levels were discussed in the relationship with various environmental factors. In landlocked fish of the Takahara River, the plasma concentrations of T and E2 reached the highest levels in May and June. In the fish collected from the Itachi River, plasma concentrations of T, 11-KT and E2 reached the highest levels during breeding season of April and May. Sexual maturation, evaluating from GSI and the spermatogenetic stages, proceeded earlier in the fish population at Toyama Bay, and afterward it was followed in the fish population at the Takahara River, in associated with a rise of environmental water temperature at fish captured sites. In the male dace, low but detectable levels of plasma E2 were measured and there were significantly positive correlations between E2 level and the levels of GSI, VTG or T. These results suggest that E2 might be a necessary sex steroid hormone related to gonad maturation, and that circulating E2 may induce VTG production in the wild male Japanese dace.     

Predation of Japanese dace, Tribolodon hakonensis, by largemouth bass, Micropterus salmoides, in experimental aquaria

 To test the size range of prey fish that largemouth bass, Micropterus salmoides, can successfully consume, live Japanese dace, Tribolodon hakonensis, were given as prey fish to individual largemouth bass in aquaria. The ratio of maximum standard length (SL) of the Japanese dace consumed by largemouth bass was 46–69% of bass SL. The maximum length of Japanese dace consumed did not differ significantly between largemouth bass and smallmouth bass (M. dolomieu) previously studied, although largemouth bass have relatively larger mouth sizes than smallmouth bass. Largemouth bass occasionally injured and killed Japanese dace larger than the limit that could be consumed.     

Evaluating the genetic status of a Great Basin endemic minnow: the relict dace (<Emphasis Type="Italic">Relictus solitarius</Emphasis>)

The relict dace (Relictus solitarius) is an endemic minnow restricted to isolated spring systems within Butte, Goshute, Ruby and Steptoe valleys in the eastern Nevada portion of the Great Basin. It is the only native fish in these basins, but speckled dace (Rhinichthys osculus) have been introduced into some localities in Ruby Valley and, based on morphology, the two species are believed to have hybridized in those areas. We used DNA sequence data from one mitochondrial gene (cytochrome b) and one nuclear intron (S7) to determine if putative relict dace populations in Ruby Valley share mtDNA haplotypes with speckled dace, or show signs of hybridization. Results of our analyses show that 11 of 16 Ruby Valley populations sampled contain only speckled dace, and one speckled dace population exhibited signs of limited introgressive hybridization. The remaining five Ruby Valley populations that were sampled contain relict dace that remain genetically distinct from speckled dace. The integrity of the Ruby Valley relict dace populations should be actively protected, particularly in the area surrounding Ruby Lake where speckled dace have been widely introduced.     

Effects of experimental duration and density of Japanese dace <Emphasis Type="Italic">Tribolodon hakonensis</Emphasis> on the strength of trophic cascades on benthic algae

To analyze density-mediated indirect effects through trophic cascades caused by Japanese dace Tribolodon hakonensis on the algal biomass and growth of ayu Plecoglossus altivelis altivelis, (freshwater fish belonging to Salmoniformes), I introduced zero, five, ten, and 20 dace with and without ayu into experimental pools. Ayu fed predominantly on benthic algae, whereas dace fed on both invertebrates and algae. The percentage of algae in the food content of dace was correlated with the number of dace in a pool. In the experiment lasting 8 days, trophic cascades on algae were not clear. In contrast, when the experimental duration was extended to 20 days, the number of gastropods and ephemeropteran nymphs was negatively correlated with the number of dace, consequently increasing the algal biomass and ayu growth through trophic cascades. Compared with pools with five dace, the presence of ten and 20 dace had similar gross effects on the number of algivorous invertebrates and algal biomass and greater gross effects on the ayu growth. The significant increase in ayu growth in pools with ten and 20 dace strongly suggests that small positive effects on algal growth by dace accumulated and extended to ayu during a 20-day experimental period. These results indicate the importance of analyzing interactions between the density and behavior of the top predator and the experimental duration on the intensity of trophic cascades.     

Long-term changes in the size of the Pomphorhynchus laevis (Acanthocephala) population in the River Avon

Samples of Gammarus pulex and dace, Leuciscus leuciscus , taken from the River Avon, Hampshire, at intervals over a period of 9 years were examined for the presence of the acanthocephalan. Pomphorhynchus laevis. Changes in the incidence and intensity of infection of P. laevis in dace and in G. pulex and in the frequency distribution of P. laevis in dace were used as indicators of the population size of the parasite. Throughout the period of observation, the parasite showed a similar pattern of distribution along the length of the river, although at some sites its abundance varied from year to year. Levels of both incidence and intensity of infection of P. laevis in both hosts at one specific locality remained fairly constant over the 9-year period, and the annual variations fell within the natural range of monthly variation over any 12-month period. The frequency distribution of P. laevis in dace also exhibited a similar pattern throughout the period. It was thus concluded that the population size of P. laevis had not changed to any great extent over the 9 years. The factors responsible for this constancy are discussed in the light of conclusions drawn from earlier work.     

Isolation and characterization of polymorphic microsatellite loci for the dace complex: Leuciscus leuciscus (Teleostei: Cyprinidae)

Ten novel polymorphic microsatellites were isolated from the dace complex (Leuciscus leuciscus), which is a European cyprinid species. Four multiplex polymerase chain reaction sets were optimized in order to genotype 26 polymorphic loci in all, including 16 previously published cyprinid-specific loci. The level of genetic diversity was assessed in 142 dace individuals. We also successfully applied 26 of the microsatellites to 10 related species. These primers thus will be useful to assess population structure of the dace and other cyprinid species, with application for conservation issues and phylogeographical approaches.     

Characterization of microsatellite loci in longnose dace (Rhinichthys cataractae) and interspecific amplification in five other Leuciscinae species

The longnose dace (Rhinichthys cataractae) appears as a relevant model to address environmental and ecological issues in an evolutionary perspective. Eleven microsatellite markers were characterized for this species. Eight of these loci were highly polymorphic for populations of this species. Between four to 10 loci were also successfully amplified in five closely related species. These markers are believed to be valuable tools for genetic analysis of populations of longnose dace and other Leuciscinae species.     

Observations on the age, growth, reproduction and food of the dace, Leuciscus leuciscus (L.), in two rivers in southern England

Scales of 497 dace from the river Stour and 573 from the river Frome were used for age determinations. Annuli were laid down in late May to early June at the start of the growth period. Minimal growth occurred from November to April. Male dace grew minimally faster than females; Frome dace faster than those from the Stour. Growth rates in the two rivers were similar to those published for most other European waters. Variation in growth rates in different years was not great, but there were marked differences in recruitment success. Spawning occurred in the second half of March and elaboration of the gonads between September and March. Immature dace have an annual cycle in condition with a maximum in June and a minimum during the winter months. The condition of the mature females is affected by the gonad cycle. The fecundity of Stour dace is represented by the formula:

and for Frome dace by:

Most dace were mature by age IV, but there were more mature II and III group fish in the Frome population. Molluscs and Trichoptera larvae comprised the bulk of the winter diet of Stour dace, and Ephemeroptera nymphs, Simulium and chironomid larvae were the principal constituents during the summer.     

Distribution and variation in the growth of roach, Rutilus rutilus (L.), and dace, Leuciscus leuciscus (L.), in a river catchment in south-west England

The distribution and growth of roach and dace in the R. Exe catchment was studied. Distribution conformed to the classic theories of zonation, although human interference extended or reduced the range of species. Distinct differences were found in the growth rates of roach and dace between different regions of the catchment. Both species achieved their fastest growth in zones where the river topography portrayed their 'preferred' habitat characteristics, i.e. the fast-flowing middle and slow-flowing lower reaches for dace and roach, respectively. Female roach were found to grow considerably faster than male fish, whilst no sexual differentiation in growth rates was found in dace. Considerable fluctuations in year class strength were observed in both species.     

Respiratory metabolism of Utah chub, Gila atraria (Girard) and speckled dace, Rhinichthys osculus (Girard)

Measurements of active, standard and routine oxygen consumption were made for 207 Utah chub at 6°, 9°, 12°, 18° and 22° C; and 123 speckled dace at 4°, 8°, 12° and 18° C. These were expressed as mathematical functions of water temperature and size of the fish. The mean slopes of log_e oxygen consumption (mg O₂/h) and log_e wet weight (g) were 0.771, 0.526, and 0.619 for active, standard, and routine rates respectively for Utah chub, and 0.943, 0.486, and 0.683 respectively for speckled dace.     

Environmental correlates, plasticity, and repeatability of differences in performance among blacknose dace (Rhinichthys atratulus) populations across a gradient of urbanization

Urbanization alters stream and watershed hydrology so that fish from urban stream systems are confronted with extreme flows during storms and runoff events. To test whether residence in urban streams is associated with altered swimming ability, we compared sprint and endurance swimming performances of eight populations of blacknose dace (Rhinichthys atratulus) from different watersheds along an urban/rural gradient. Watershed impervious surface cover, a measure of urbanization, was significantly correlated with sprint performance in dace from all stream types and endurance swimming performance (U(crit)) when only fish from urban streams were analyzed. Three estimators of water flow in a stream system, watershed area, mean annual discharge, and base-flow current speed, were all related to U(crit) in fish from nonurban streams. The U(crit) was significantly repeatable after 6 mo in the laboratory, but dace populations with exceptional U(crit) values lost ability under no-flow, "detraining" conditions. Sprint performance changed substantially in individual dace after 10 wk under no-flow conditions and was a significant function of the animal's original performance. Animals with high sprint performance tended to lose ability, whereas those with poor performance gained ability. Interpopulation differences in both sprint and endurance swimming were robust over multiple years of collection from the same sites.     

Repeat swimming performance and its implications for inferring the relative fitness of asexual hybrid dace (Pisces: Phoxinus) and their sexually reproducing parental species

While theories explaining the evolution and maintenance of sex are abundant, empirical data on the costs and benefits of asexual relative to sexual reproduction are less common. Asexually reproducing vertebrates, while few, provide a rare opportunity to measure differences in fitness between asexual and sexual species. All known asexually reproducing vertebrates are of hybrid origin, and hybrid disadvantage (i.e., reduced hybrid fitness) is thought to facilitate long-term coexistence between asexual and sexual species. We used repeat swimming performance as a proxy for fitness to compare the fitness of asexual hybrid dace (Pisces: Phoxinus) and their sexually reproducing parental species, finescale dace (Phoxinus neogaeus) and northern redbelly dace (Phoxinus eos). We tested the prediction that, given the widespread coexistence of these hybrid and parental dace, the parental species should show equivalent and perhaps superior repeat performance relative to hybrids. A repeat constant acceleration test (U(max)) was conducted at both acclimation temperature (16 °C) and at an elevated temperature (25 °C) to simulate the combined influence of a repeat swim and acute temperature change that fish might experience in the wild. The asexual hybrids performed more poorly than at least one of the parental species. There was a negative effect of temperature on repeat swimming performance in all fish, and the repeat performance of hybrids was more severely affected by temperature than that of finescale dace. No difference in the effect of temperature on repeat performance was detected between hybrids and northern redbelly dace. These results suggest that hybrids suffer physiological costs relative to the parentals or at least that the hybrids do not gain advantage from hybrid vigor, which probably contributes to the coexistence of asexual and sexual species in this system.     

Genetic divergence of Far Eastern dace species belonging to the genus Tribolodon (Pisces,Cyprinidae) and closely related taxa

Based on a biochemical-genetic approach, heterozygosity and divergence of structural genes of 30 enzyme loci were analyzed in six dace species. In addition, intra- and interspecific divergence of gene expression was analyzed based on a sample of 12 to 15 loci. Mean heterozygosities per individual varied as follows: Tribolodon species, Hobs = 0.007 +/- 0.007 and Hexp = 0.007 +/- 0.007; T. ezoe, Hobs = 0.045 +/- 0.016 and Hexp = 0.067 +/- 0.029. Several variants of genetic distances were estimated. Standard Nei's distances (DN) varied from 0.145 to 0.284 in four dace species studied. As related to Tribolodon dace species, the following genetic distances were obtained for two members of other genera: Pseudaspius leptocephalus, DN = 0.269; Leuciscus waleckii, DN = 0.769. Based on the distance matrices, different clustering algorithms were realized. The main feature shared by different dendrograms was a separate position of the cluster joining Far-Eastern dace species, to which P. leptocephalus and L. waleckii are successively added. Among the species studied, the proportion of loci similar by expression (E) varied from 87 to 100%. The greatest difference was found between anadromous and nonanadromous ecotypes of T. hakonensis, E = 67%. The following conclusions can be made: (1) Four studied species of the genus Tribolodon are rather well genetically differentiated. Diagnostic loci are available. (2) A nominal dace species, T. species, should be considered the fourth isolated species of this genus, which is confirmed by its recent zoological acceptance of this species. (3) The origin and divergence of dace species belonging to the genus Tribolodon are relatively late (1 to 3 Myr ago) historical events. (4) Taxonomically, the genus Tribolodon belong to the tribe Pseudaspinini together with P. leptocephalus, which is confirmed by genetic data. (5) Data on heterozygosity and the divergence of structural and regulatory elements of genome, along with the proposed scheme of speciation types, suggest the following speciation modes for the species studied: for four species, adaptive divergence and for two species, genetic transformation.     

Juvenile migration of Japanese dace Pseudaspius hakonensis revealed in a tributary of Lake Biwa with seasonal changes in abundance and stable isotope ratios

Ichthyological Research - Migration patterns of Japanese dace Pseudaspius hakonensis in and around Lake Biwa, Japan are unknown, although fluvial–lacustrine life history has been known in...     

Populational structure of three fish species (Cypriniformes: Cyprinidae) living in rivers of the Ob-Irtysh basin,by the data of isoenzyme analysis

Data are presented on genetic subdivision of populations of roach Rutilus rutilus lacustris, ide Leuciscus idus, and dace L. leuciscus baicalensis living in rivers of West Siberia. These fish species have comparable levels of variation of allozyme loci and similar populational structure which well agrees with geography of the river network of the Ob-Irtysh basin. The populational differentiation is more expressed in ide than in roach and dace.     

Small founding number and low genetic diversity in an introduced species exhibiting limited invasion success (speckled dace, Rhinichthys osculus)

Molecular evaluations of successful invaders are common, however studies of introduced species that have had limited invasion success, or have died out completely, are rare. We studied an introduced population of speckled dace (Rhinichthys osculus) from northern California, USA that has rapidly increased in abundance but remained restricted to a 25-km stretch of river since its introduction in the mid-1980s. Field and laboratory analyses indicate that invasion success of speckled dace is constrained by the combined effects of multiple predators. The role of bottleneck effects associated with the introduction has not been studied. We assayed variation in seven microsatellite loci and one mitochondrial DNA gene in the introduced population and nine putative source populations to identify the source population and evaluate bottleneck effects. The Trinity River system was supported as the source owing to its genetic similarity and geographic proximity to the introduced population. Consistent with a bottleneck, the introduced population exhibited reduced allelic and haplotype richness in comparison to source populations. Estimates of the genetically effective number of individuals founding the introduced population using nuclear coalescent analyses and a mitochondrial simulation procedure were highly concordant in suggesting that the initial colonizing group was comprised of about 10 individuals. A bottleneck effect in an exotic species exhibiting limited invasion success has rarely been documented and thus introduction of speckled dace represents an important model system for future investigation. Establishing a relationship between genetic diversity and factors limiting invasion success in this system (e.g., predator avoidance) will help determine the extent to which genetic diversity loss has constrained invasion success in speckled dace.     

Changes in the species composition of anglers' catches in the River Trent (England) between 1969 and 1984

Data on anglers' catches on the River Trent were collected for the seasons 1969/70 to 1983/84 using postal questionnaires. During this period 60.4t of fish were caught during a total fishing effort of 526 871 man-h or 60.15 man-years, and more than 20 species of fish were recorded. The percentage of anglers making a catch (70–80%) and the catch per unit effort, mean 114.7g man-h ⁻¹, were comparable with those reported for other waters.
Roach and gudgeon were the most commonly captured species with chub, bleak, bream, eels and dace also forming major components of anglers' catches. Since 1969 chub, bream, eels and perch have made an increasingly greater contribution to catches, coupled with a decline in numbers of roach and dace. It is suggested that improvement in water quality and its implication on interspecific competition was the most likely cause of the changes.     

Ontogenetic Changes in the Response of Largemouth Bass (Micropterus salmoides, Centrarchidae, Perciformes) to Heterospecific Alarm Pheromones

Juvenile largemouth bass ( Micropterus salmoides ) undergo an ontogenetic niche shift from invertebrate feeding members of the cyprinid prey guild to piscivory during their first year of growth. We conducted laboratory and field trials to determine whether juvenile bass show a similar ontogenetic shift in their response to the alarm pheromone of finescale dace ( Phoxinus neogaeus , Cyprinidae). When exposed to dace skin extract (with alarm pheromone), juvenile bass exhibited a significant positive relationship between standard length and horizontal and vertical area use and time spent moving. Small bass (< 50 mm standard length) tended to reduce area use and time spent moving (indicative of an anti-predator response), while larger bass (> 50 mm standard length) increased area use and time spent moving (indicating a foraging response). Bass exhibited no change in behaviour when exposed to swordtail ( Xiphophorus helleri ) skin extract, which lacks Ostariophysan alarm pheromone. During field trials, small (30–45 mm standard length) and medium (46–60 mm standard length) bass actively avoided areas labelled with dace alarm pheromone and exhibited a significant increase in dashing behaviour. Large bass (61–80 mm standard length) were attracted to such areas and exhibited a significant increase in approach behaviour. These data suggest that largemouth bass undergo an ontogenetic shift in response to heterospecific chemical alarm signals.