Synchrony in the downstream migration of smolts and upstream migration of adult Atlantic salmon in the subarctic River Utsjoki

Seasonal and diel migration timing of wild Atlantic salmon Salmo salar smolts and adults were investigated annually (2001–2004) in the subarctic River Utsjoki, a tributary of the large River Teno (70° N), using underwater video monitoring. Submerged video cameras provided information on the exact timing and intensity of both migrations in a natural river channel, without disturbing the fish. In contrast to the mainly nocturnal migration pattern described from temperate rivers, the River Utsjoki smolts and adults migrated throughout the day. Smolts migrated most intensively during hours of rising (0300–0900 hours) and high sun (0900–1500 hours), while adults favoured the period of low sun (2100–0300 hours). Smolt migrations started in June and lasted on average 42 days. Adults usually ascended the site 2–3 weeks before the first descending smolts were observed and the adult migrations extended to the end of August. Seasonal synchrony was observed between smolt and adult migrations in years of slowly warming water, whereas in a year of exceptionally warm early summer (2002), smolts migrated earlier than adults. Thus, water temperature seemed to be an important environmental factor triggering the smolt migration, while the migration of adults was probably more fixed to a certain season. Weak positive correlations between fish counts and water temperature were observed, indicating that increasing water temperature may have promoted both smolt and adult migrations. The influence of discharge was negligible, although increasing discharge late in the season may have activated the remaining individuals in both groups.     

Climatic and biotic controls on annual carbon storage in Amazonian ecosystems

• 1 The role of undisturbed tropical land ecosystems in the global carbon budget is not well understood. It has been suggested that interannual climate variability can affect the capacity of these ecosystems to store carbon in the short term. In this paper, we use a transient version of the Terrestrial Ecosystem Model (TEM) to estimate annual carbon storage in undisturbed Amazonian ecosystems during the period 1980–94, and to understand the underlying causes of the year‐to‐year variations in net carbon storage for this region.
  • 2 We estimate that the total carbon storage in the undisturbed ecosystems of the Amazon Basin in 1980 was 127.6 Pg C, with about 94.3 Pg C in vegetation and 33.3 Pg C in the reactive pool of soil organic carbon. About 83% of the total carbon storage occurred in tropical evergreen forests. Based on our model’s results, we estimate that, over the past 15 years, the total carbon storage has increased by 3.1 Pg C (+ 2%), with a 1.9‐Pg C (+2%) increase in vegetation carbon and a 1.2‐Pg C (+4%) increase in reactive soil organic carbon. The modelled results indicate that the largest relative changes in net carbon storage have occurred in tropical deciduous forests, but that the largest absolute changes in net carbon storage have occurred in the moist and wet forests of the Basin.
    • 3 Our results show that the strength of interannual variations in net carbon storage of undisturbed ecosystems in the Amazon Basin varies from a carbon source of 0.2 Pg C/year to a carbon sink of 0.7 Pg C/year. Precipitation, especially the amount received during the drier months, appears to be a major controller of annual net carbon storage in the Amazon Basin. Our analysis indicates further that changes in precipitation combine with changes in temperature to affect net carbon storage through influencing soil moisture and nutrient availability.
      • 4 On average, our results suggest that the undisturbed Amazonian ecosystems accumulated 0.2 Pg C/year as a result of climate variability and increasing atmospheric CO₂ over the study period. This amount is large enough to have compensated for most of the carbon losses associated with tropical deforestation in the Amazon during the same period.
        • 5 Comparisons with empirical data indicate that climate variability and CO₂ fertilization explain most of the variation in net carbon storage for the undisturbed ecosystems. Our analyses suggest that assessment of the regional carbon budget in the tropics should be made over at least one cycle of El Niño–Southern Oscillation because of interannual climate variability. Our analyses also suggest that proper scaling of the site‐specific and subannual measurements of carbon fluxes to produce Basin‐wide flux estimates must take into account seasonal and spatial variations in net carbon storage.

     

Downstream migration of juvenile fish in the Krasnaya River (Vietnam)

The first material is presented on downstream migration of fish juveniles in the Krasnaya River, one of the largest rivers in South-East Asia. The spatial-temporal structure of distribution of downstream-migrating fish juveniles in the Krasnaya River has traits usually characteristic of migration in rovers with turbid water. Concentration of fish was extremely variable by the time of the day, river length, and depth. In length-wise distribution, there was a tendency to increasing concentration of downstream migrants from the upper stretches to the downstream stretch. In the upper reaches, Perciformes prevailed, in the middle part, Cypriniformes prevailed, and in the lower reaches of the river Clupeiformes prevailed. During 24 h, Clupeiformes and Perciformes migrated more intensively at night and Cypriniformes migrated more in the daytime. By depth horizons, Clupeiformes made downstream migration predominantly at the surface and Cypriniformes and Perciformes did at the bottom. These differences may be caused by species differences in fish biology, local specific traits of stream hydraulics, anthropogenous factors, etc.     

Use of trehalose in the semen cryopreservation of Amazonian catfish Leiarius marmoratus

The current study assessed a semen cryopreservation protocol in the Amazonian catfish Leiarius marmoratus, a freshwater fish, of rheophilic behavior, and of great importance for Brazilian fish farming. Eight males (n = 8) were stripped and the semen was cryopreserved if total motility in fresh semen was higher than 80%. The external cryoprotectant Trehalose was then diluted in Beltsvile Thawing Solution (BTS) extender in the following concentrations: 50, 100, 150, and 200 mM. Semen samples were diluted in the media (1:9 v/v) being tested, then frozen in a container with nitrogen vapor (dryshipper), and stored in liquid nitrogen at −196 °C. Motility parameters assessed post-thawing were performed by CASA-system and sperm cell integrity analyses (membrane integrity, DNA integrity, and mitochondrial function) were performed through fluorescence microscopy. As a result, no significant statistical difference was observed between treatments, independently of Trehalose concentrations tested in the following post-thawing analysis: membrane integrity, DNA integrity, mitochondrial functionality, and sperm motility duration. As of total and progressive motilities, the treatment containing 50 mM trehalose (15.6 and 9.5%, respectively), exhibited inferior results when compared to treatments with 150 mM (22.9 and 17.7%, respectively) and 200 mM (31.4 and 26.3%, respectively) trehalose concentrations (P < 0.05); however, it did not differ from the treatment with 100 mM trehalose (18.6 and 15.3%, respectively). Therefore, treatments with trehalose at higher concentrations exhibited superior results when compared to other treatments in in vitro motility parameters for L. marmoratus.     

Genetic structure in the Amazonian catfish Brachyplatystoma rousseauxii: influence of life history strategies

The Dorado or Plateado (Gilded catfish) Brachyplatystoma rousseauxii (Pimelodidae, Siluriformes) is a commercially valuable migratory catfish performing the largest migration in freshwaters: from the Amazonian headwaters in the Andean foothills (breeding area) to the Amazon estuary (nursery area). In spite of its importance to inform management and conservation efforts, the genetic variability of this species has only recently begun to be studied. The aim of the present work was to determine the population genetic structure of B. rousseauxii in two regions: the Upper Madera Basin (five locations in the Bolivian Amazon) and the Western Amazon Basin (one regional sample from the Uyucalí–Napo–Marañon–Amazon basin, Peru). Length polymorphism at nine microsatellite loci (284 individuals) was used to determine genetic variability and to identify the most probable panmictic units (using a Bayesian approach), after a significant departure from Hardy–Weinberg equilibrium was observed in the overall dataset (Western Amazon + Upper Madera). Bayesian analyses revealed at least three clusters in admixture in the five locations sampled in the Bolivian Amazon, whereas only two of these clusters were observed in the Western Amazon. Considering the migratory behaviour of B. rousseauxii, different life history strategies, including homing, are proposed to explain the cluster distribution. Our results are discussed in the light of the numerous threats to the species survival in the Madera basin, in particular dam and reservoir construction.     

Feeding ecology and habitat preferences of the catfish genus Trichomycterus in low‐order streams of the Colombian Andes

Six lower order streams in the south‐west of Colombia were sampled on a monthly basis in order to determine the status of Trichomycterus species in relation to their food supply (macroinvertebrates), and physico‐chemical habitat. Fishes were sampled by electrofishing and samples taken for dietary analysis. Macroinvertebrates were collected using a Surber sampler. Trichomycterus spp. populations were present in all streams in habitats ranging from soft to hard substrata and from relatively stagnant waters to fast flowing streams. The average density of the fishes ranged from 0·06 to 1·14 individuals m⁻² with peaks in population corresponding to recruitment of individuals of <1 g. Trichomycterus spp. were found to be benthic carnivores with a diet mostly of aquatic insects. The index of relative importance for the dietary items was 35·0, 10·5, 1·9 and 7·8% for Chironomidae, Trichoptera, Ephemeroptera and Oligochaeta respectively. Combined with physical habitat data, ordinations of fishes and macroinvertebrate data suggested that differences in abundance among sites were driven by stream size and flow regime, indicating dominance of the physical habitat, although a high correlation between Trichomycterus spp. and Chironomidae abundances ( r  = 0·81, P  = 0·049) was also recorded.     

Impact of ocean barriers, topography, and glaciation on the phylogeography of the catfish Trichomycterus areolatus (Teleostei: Trichomycteridae) in Chile

We examined the role of several earth history events on the phylogeographic distribution of the catfish Trichomycterus areolatus in Chile using the cytochrome b gene. We explored three biogeographic hypotheses: that sea level changes have resulted in the isolation of populations by drainages; that glaciation has impacted genetic diversity; and that ichthyological subprovince boundaries correspond to phylogeographic breaks in our focal species. We found seven well-supported clades within T. areolatus with high levels of genetic divergence. The strongest signal in our data was for an important role of sea level changes structuring populations. Five of the seven clades mapped cleanly to the geographic landscape and breaks corresponded closely to areas of narrowest continental shelf. In addition, few haplotypes were shared between rivers within clades, suggesting that only limited local movement of individuals has occurred. There was no relationship between the levels of genetic diversity and the proportion of individual drainages covered by glaciers during the last glacial maximum. Two phylogeographic breaks within T. areolatus did match the two previously identified faunal boundaries, but we found three additional breaks, which suggests that faunal breaks have only limited utility in explaining phylogeographic patterns. These results imply that the narrow continental shelf coupled with sea level changes had a strong influence on the obligate freshwater fishes in Chile.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 876–892.     

First description of color variations in the annual killifish Millerichthys robustus,and preliminary observations about its geographical distribution

Millerichthys robustus is the only annual killifish distributed in America with phenotypic color variations, not yet described. Accordingly, we first describe the color pattern in both sexes to define its phenotypical variations. We then analyze the frequency of these phenotypes on a geographical scale, in four localities that represent opposite points of Millerichthys’s distribution in the Mexican southeast. Color analysis based on the RGB system allowed us to define five-color phenotypes in males continuously distributed in various perceptual units between two extreme colors (yellow-red): yellow, moderate orange, dark orange, strong orange and red. These color patterns found in M. robustus could be attributed to melanin, carotenoid, and pteridine pigments. The orange phenotypes was present in all localities studied. The yellow phenotype was present only in northeastern and northwestern locations, and the red phenotype was present only in northern populations. Female color variations were observed in the number of ocelli (from 1 to 15) at the base of the caudal peduncle and dorsal region. Ocelli have been associated with anti-predator functions because they resemble the eyes of vertebrates, thus shifting the target of predator attacks to less vital body parts. Females with 3 ocelli were the most frequent phenotype, and females with 13–15 ocelli occurred only in the northern populations. We concluded that male and female of M. robustus are not randomly distributed along their distribution range, which suggest that color phenotypes may react differently to biotic and abiotic factors that probably determine their distribution and frequency within the studied population.

     

Sex-specific metabolic changes in the annual reproductive cycle of a freshwater catfish

Sex-specific enzymatic and other biochemical changes were studied in the annual reproductive cycle of the freshwater catfish, Clarias batrachus. Citrate synthase (CS) activity of brain, liver and skeletal muscle was maximum in spawning and minimum in postspawning showing a sharp decline in aerobic capacity after spawning. Similar CS activity in remaining phases of the annual reproductive cycle reflects similar energy need during regressed, preparatory and prespawning phases. Glucose 6-phosphate dehydrogenase (G6-PDH) activity declined in spawning and postspawning indicating a possible decrease in lipid and nucleic acid syntheses. The subsequent increase in G6-PDH activity with onset of resting and maintenance of the increased level throughout preparatory and prespawning phases shows restoration of biosynthetic activity. Higher activity of G6-PDH in female than male may be to satisfy a greater biosynthetic need of female reproduction and breeding. The decreased RNA content of tissues showed reduction in protein synthesis capacity during spawning and subsequent increase through postspawning until resting phase. The RNA content of brain and liver was higher in female than male during preparatory and prespawning, which may be associated with higher protein synthesis requirement of female for preparation of reproductive activities. The requirement based sex related changes in metabolism of catfish may be enzyme, tissue or reproductive phase-specific.     

Hitchhiking behaviour in the obligatory upstream migration of amphidromous snails

Migratory animals endure high stress during long-distance travel in order to benefit from spatio-temporally fluctuating resources, including food and shelter or from colonization of unoccupied habitats. Along with some fishes and shrimps, nerite snails in tropical to temperate freshwater systems are examples of amphidromous animals that migrate upstream for growth and reproduction after a marine larval phase. Here I report, to my knowledge, the first example of ‘hitchhiking’ behaviour in the obligatory migration of animals: the nerite snail Neritina asperulata appears to travel several kilometres as minute juveniles by firmly attaching to the shells of congeneric, subadult snails in streams of Melanesian Islands, presumably to increase the success rate of migration.     

Some observations on salmon smolt migration in a chalkstream

Observations on smolt migration in a chalkstream over a period of four years indicate a relationship between number of fish migrating during the day and maximum afternoon water temperature. Few fish move below an apparent threshold temperature. This threshold appears to be different each year, varying with the general water temperature of the period proceeding the main run. Tests made with dummy telemetry tags indicate that their use to observe natural migratory behaviour may be justified.     

Diurnal and seasonal behaviour of adult and juvenile European catfish as determined by radio-telemetry in the River Berounka, Czech Republic

The first telemetry study analysing behaviour of the largest freshwater predator in European rivers, Silurus glanis , was performed bimonthly during the years 2002–2004. Movement of juveniles and adults occurred mostly in the same time intervals. The only statistical differences occurred for nocturnal activity in spring and autumn. In spring and winter, activity was low with the peaks during daylight, and in autumn, maximal movement was recorded during dusk. In summer, the European catfish were active across the whole 24 h even during high-flow conditions. During all other seasons, movement was inversely related to flow rate. Maximal home ranges occurred in summer, being larger for adults. Juveniles and adults were spatially segregated. With increasing flow, fish were displaced, and individuals from both groups got closer to each other. Only juveniles migrated downstream from the upstream isolated river stretch suggesting a negative impact of lateral obstructions on the fish population structure.     

Visual constraints on migration behavior of juvenile French grunts

Synopsis Retinomotor movements of three size classes of juvenile French grunts, Haemulon flavolineatum, are characterized during the periods of their daily evening and dawn migration. Differences in the extension and withdrawal of the cones correlate with the earlier departure and later return to the daytime schooling sites of the smallest juveniles as compared to the larger juveniles. For each size class changes in the dimensions and retinal distribution of the cone cells and optical properties of the eye are used to estimate differences in photosensitivity under conditions of equal radiant intensities. For a target subtending any given angle, calculation indicates that the largest juveniles should be capable of discrimination at one-thousandth the light intensity of the smallest juveniles. The differences in potential photosensitivity correlate with the different intensities at which they migrate. The likely trigger to initiate their daily migrations probably involves circadian factors at dawn and extension of the single cones from the focal region of the retina prior to the evening migration.This paper is dedicated to the memory of John Lythgoe, whose insight served as inspiration for this study.     

Physiological characterization of juvenile Chinook salmon utilizing different habitats during migration through the Columbia River Estuary

Although off-channel habitats in the estuaries of large rivers impart many benefits to fish that rear within them, it is less clear how these habitats benefit migrating anadromous species that utilize these habitats for short periods of time. We evaluated the physiological correlates (nutritional condition, growth, and smoltification) of habitat utilization (main-channel vs. off-channel) by juvenile Chinook salmon Oncorhynchus tshawytscha during emigration. Fish from the off-channel had higher condition factor scores and relative weights than fish from the main-channel throughout the study period. Plasma triglyceride and protein concentrations were significantly different between habitat types and across the sampling period, suggesting that fish utilizing the off-channel habitats were compensating for energy losses associated with emigration as compared to main-channel fish. Growth potential (RNA to DNA ratio) did not vary by habitat or sampling period, presumably due to short residency time. There were no differences in osmoregulatory capacity (gill Na(+), K(+)-ATPase activity) based on habitat type. Our results indicate that short-term off-channel habitat use may mitigate for energy declines incurred during migration, but likely does not impart significant gains in energy stores or growth.     

The distributions of larval and juvenile fishes in Amazonian rivers of different nutrient status

1. Previous work has indicated, at least in two river systems, that some Characiformes species migrate from nutrient‐poor rivers to spawn in nutrient‐rich rivers. In the present work, larval and juvenile fish were surveyed to index spawning activity in order to determine whether this spawning pattern is repeated in nine major tributaries of the Amazon basin. 2. Adult Mylossoma aureum, M. duriventre, Colossoma macropomum, Anodus elongatus, Triportheus elongatus, Brycon cephalus, Semaprochilodus insignis, S. taeniurus and Prochilodus nigricans were recorded in nutrient‐poor and nutrient‐rich rivers. However, larval and juvenile individuals of these species were found in nutrient‐rich rivers only, indicating that spawning activity was restricted to that river type. 3. Concentration of suspended solids in the river was correlated with total ichthyoplankton density and related to species composition of juvenile characiform assemblages. 4. Our findings reinforce the hypothesis that nutrient‐rich rivers and associated floodplains function as spawning and nursery grounds, and suggest that they function as source habitats for these species in the Amazon Basin.     

Annual dynamics variation of a landlocked Galaxias maculatus (Jenyns 1842) population in a Northern Patagonian river: occurrence of juvenile upstream migration

Galaxias maculatus, broadly distributed in the southern hemisphere, presents both diadromic and landlocked populations. The upstream migration of larvae and juveniles from the sea to freshwater habitats is a characteristic phenomenon of diadromous populations, but upstream migration has never been reported in those that are landlocked. The objective of this study was to establish the population dynamics of a peculiar riverine landlocked population that presents an upstream migration at the larvae–juvenile transition from the Piedra del Águila Reservoir to the Caleufú River (Argentina). A spawning season from September to November and the arrival of shoals of metamorphic larvae and juveniles from February to April to the adult habitat were coincidental with lacustrine landlocked populations, but not with diadromous populations. Growth rate and age at migration, 147 ± 22.6 days, were also similar to other landlocked and diadromous populations. The arrival of these shoals produced a 20‐fold increase in fish density while the two cohorts of G. maculatus overlapped in time and space. No significant differences in morphology or vertebrae number were detected when riverine and reservoir adults were compared. The great life history plasticity of G. maculatus, shown to be even greater in our results, could be the key to explain the wide distribution of this species in the southern hemisphere. Likewise, discovering this juvenile potamodromous behaviour in a landlocked population will provide a new view for the analysis of the ways of this species’ dispersion in continental waters.     

First records of the North American catfish Ameiurus melas in Portugal

The North American catfish Ameiurus melas is recorded for the first time in Portugal. Its presence in the Tagus River Basin is probably due to natural spread of individuals from Spanish populations, while episodic translocation could explain its occurence in the previously non-invaded Guadiana and Sado River basins.     

First record of the white catfish Ameiurus catus in Great Britain

The North American catfish Ameiurus catus is recorded for the first time in Great Britain. An albino variety of 620 mm fork length and 4550 g was believed to have been an ornamental fish that was introduced subsequently into the wild.