Cold-water Fish Species Research Articles

Genomic organization, expression and antimicrobial activity of a hepcidin from taimen (Hucho taimen, Pallas).

Hepcidin, an antimicrobial peptide, plays a crucial role in innate immune system of teleost fish. As a cysteine-rich peptide, hepcidin possesses a dual function including iron regulation and innate immunity. In the present study, a full-length hepcidin cDNA (HtHep) was cloned and characterized by RT-PCR and RACE techniques from taimen (Hucho taimen, Pallas), which is a type of rare, precious and cold-water fish species in China. The cDNA contains an open reading frame (ORF) of 267 bp encoding 88 amino acid (aa), with 170 bp located in the 5(') untranslated region (UTR) and 151 bp in the 3' UTR. The genomic sequences analysis showed that the HtHep gene consisted of three exons and two introns (with the length 94 and 251 bp, respectively). With a predicted molecular mass of 2881.4Da and a theoretical pI of 8.53, the deduced amino acid encodes a signal peptide of 24 aa, prodomain of 39 aa and mature peptide of 25 aa. The signal peptidase (SA-VP) and the motif RX (K/R)R of propeptide convertase suggested the cleavage site of signal and mature peptide. Eight conserved cysteine residues were also identified and formed four disulfide bonds. Pair-wise alignments showed that HtHep clustered together with two fish species of Salmonidae family (Salmo salar and Oncorhynchus mykiss) in HAMP1 branch. Quantitative RT-PCR analysis indicated that the mRNA levels of HtHep were detected in a wide range of tissues and the highest level was detected in the liver. Its expression was also detected early during embryonic stage and could be up-regulated in the liver when challenged with pathogenic bacteria (Yersinia ruckeri). The recombinant HtHep (rHtHep) had antimicrobial activity against both gram-positive (Micrococcus lysodeikticus and Staphylococcus aureus) and gram-negative bacteria (Escherichia coli). Our results suggested that HtHep might be involved in the innate immune defense against bacterial pathogens in taimen.

Downstream effects of hydroelectric dam operation on thermal habitat use by Brook Trout (Salvelinus fontinalis) and Slimy Sculpin (Cottus cognatus)

AbstractHydroelectric dams can alter downstream water temperatures, impacting thermal habitat available for fishes. Decreases in river water temperatures resulting from hydroelectric dam operations may be beneficial to coldwater species and could potentially offset warming resulting from climatic trends. We used two coldwater fish species, Slimy Sculpin (Cottus cognatus) and Brook Trout (Salvelinus fontinalis) to assess the impact of a cool water draw below a 15 MW hydroelectric dam on fish thermal habitat use relative to a nearby naturally flowing river. Cooler water temperatures below the dam corresponded with significantly cooler mean growth season temperature use for Slimy Sculpin, but not Brook Trout, relative to the natural river. As well, mean growing season temperature use by Slimy Sculpin was significantly cooler relative to Brook Trout in both rivers, and significantly different amongst studied sites in the regulated river. Fish condition was significantly correlated with temperature use for Slimy Sculpin in the naturally flowing river only. Our results indicate that manipulating river water temperatures through hydroelectric dam operations to benefit multiple fish species will be difficult given the complexity of riverine thermal habitat and species‐specific differences in thermal preferences and behaviour.

Effects of Climate Change on Extreme Low-Flows in Small Lowland Tributaries in the Skagit River Basin

Abstract Management of extreme low-flows requires fundamental trade-offs between water extraction for human use (e.g. for irrigation and municipal water supply) and in-stream flows to protect aquatic ecosystems. In the context of protecting endangered salmon and other cold-water fish species in small streams, extreme low-flows are one of the most important aspects of the flow regime. We quantify projected changes in low-flow magnitude and timing for several lowland tributaries of the Skagit River basin in response to regional climate change. Ten hydrologic model simulations of mid-21st century (2030–2059) streamflows are compared against a historical period (1917–2006). Each of the hydrologic simulations are forced by atmospheric variables developed from respective CMIP3 global climate model (GCM) output downscaled to 1/16th degree resolution using the Hybrid-Delta downscaling method. Baseline historical simulations are forced by historical gridded meteorological data sets of temperature and precipitation...

DNA barcoding of Schizothorax species from the Neelum and Jhelum Rivers of Azad Jammu and Kashmir

The mitochondrial Cytochrome Oxidase 1 gene is used as a standardized, authenticated, and reliable genetic marker for a global species-level bio-identification system. The present study was conducted to determine whether barcoding can help accurate species identification in fishes. The overall base composition of Schizothorax species was 29.6% of T, 25.5% of C, 26.5% of A, and 18.4% of G, A + T content 56.1% and G + C content 43.9%. The Ts/Tv bias (R) was 2.51. Complete COI gene was amplified using PCR and sequenced from 17 samples collected from river Neelum and Jhelum, and identification of species were done by following Mirza (1991), Jhingran (1991) classification and also through BOLD (99.3 to 99.9%) and NCBI (99.6 to 99.9%) reference sequences of those species. Multiple alignments of CO1 mtDNA gene resulted in a range of 1535–1551 base pairs. Out of 1535 consensus sites, 1490 were constant, 61 characters were variable, in which 54 were parsimony informative, and 7 variables were parsimony uninformative. This is the very first study reported from a reservoir of cold water bodies of Azad Kashmir which have a great potential for conservation of cold water fish species. We emphasized that, DNA barcoding is an accurate, reliable and has the great potential for identification of freshwater fish species.

Recovery of Edwardsiella piscicida from farmed whitefish, Coregonus lavaretus (L.), in Finland

Bacterial pathogens, preliminary identified as Edwardsiella sp., were isolated from farmed whitefish, Coregonus lavaretus (L.), in Finland during disease outbreaks in 2000, 2002 and 2013. The diseased fish exhibited clinical and histopathological signs of general septicemia. Bacterial diagnostics were initially performed with conventional biochemical tests and the API50 CH rapid diagnostic system, followed by a species-specific PCR assay. Antimicrobial susceptibility profiles, enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), multilocus sequence analysis (MLSA) and biofilm formation were used to characterize the bacterial isolates. For comparison, two reference strains Edwardsiella piscicida ET883T (NCIMB 14824) and Edwardsiella tarda ATCC 15947T were included in the analyses. Biochemical and antimicrobial analysis displayed the same profile for all isolates from whitefish and this was similar to both reference strains. Molecular assays including PCR and ERIC-PCR demonstrated that all whitefish isolates were genetically different from the E. tarda reference strain. MLSA analysis revealed that the whitefish isolates and ET883T are in a separate clade distinct from ATCC 15947T; they are not genetically identical. It is concluded that whitefish is susceptible to infection with E. piscicida a bacterial species with a wide geographical distribution and adaptability to different hosts. It is postulated that in the future E. piscicida might pose a serious threat to farmed whitefish especially in recirculating aquaculture systems. Statement of relevanceEdwardsiella piscicida was recently described and separated from the species Edwardsiella tarda. E. tarda/piscicida is a well-known fish pathogen infecting mainly warm water species. However, during recent years the pathogen has also been isolated from cold water fish species, mainly salmonids. It is not known if this is due to an adaptation of the pathogen to lower temperatures or due to farming of these fish in higher temperatures. In the present study E. piscicida was isolated and described for the first time from disease outbreaks of whitefish (salmonid species) in different freshwater farms in Finland.Farming of whitefish is increasing in Finland, especially in recirculating systems. The examined isolates were all obtained from farmed whitefish and it is hypothesized that this pathogen could be an increasing threat for the future farming of whitefish.

Stocking strategies for a pre-alpine whitefish population under temperature stress

Cold-water fish stocks are increasingly affected by steadily increasing water temperatures. The question arises whether stock management can be adapted to mitigate the consequences of this climatic change. Here, we estimate the effects of increasing water temperatures on fisheries yield and population dynamics of whitefish, a typical cold-water fish species. Using a process-based population model calibrated on an empirical long-term data set for the whitefish population (Coregonus lavaretus (L.) species complex) of the pre-alpine Lake Irrsee, Austria, we project density-dependent and temperature-dependent population growth and compare established stock enhancement strategies to alternative stocking strategies under the aspect of increasing water temperatures and cost neutrality. Additionally, we contrast the results obtained from the process-based model to the results from simple regression models and argue that the latter show qualitative inadequacies in projecting catch with rising temperatures. Our results indicate that increasing water temperatures reduce population biomass between 2.6% and 7.9% and catch by the fishery between 24% and 48%, depending on temperature scenario and natural mortality calculation. These reductions are caused by accelerated growth, smaller asymptotic size and lower annual survival of whitefish. Regarding stocking strategies under constant temperatures, we find that stocking mostly whitefish larvae, produces higher population biomass than stocking mostly one-summer-old whitefish, while catch remains almost constant. With increasing temperatures, stocking one-summer-old fish is more beneficial for the angling fishery. Adaption to climate change by changing stocking strategies cannot, however, prevent an overall reduction in catch and population size of this cold-water fish species.

The mitochondrial genome of Schizothorax esocinus (Cypriniformes: Cyprinidae) from Northern Pakistan

The mitochondrial DNA sequence represents a mainstay of phylogenetics. It allows biologists to elucidate the evolutionary relationships among species. It also permits an examination of the relatedness of populations, hence got importance in the field of biology. The current study was designed to know the mitochondrial sequence of Schizothorax esocinus, a delicious fish belonging to family Cyprinidae. In this study, the complete mitochondrial genome of S. esocinus from Northern Pakistan was determined. The mitogenome of S. esocinus was found to be 16 591 bp in length and consisted of 13 protein coding genes, 22 tRNA genes, two rRNA genes, and one control region. All genes were encoded on heavy strain except ND6 and few tRNA genes. The overall base composition was T 25.5%, C 27.0%, A 29.8% and G 17.7%, A + T content 55.3% and G + C content 47.7%. The length of control region (CR) was 938 bp and contained putative termination-associated sequence (TAS) and several conserved sequence blocks (CSB) and control region also contained a microsatellite region (TA). This is the very first study reported from a reservoir of large cold water bodies in Pakistan which have a great potential for conservation of cold water fish species. This mitogenome sequence would be useful to know the phylogenetic status of the fish.

InSTREAM-Gen: Modelling eco-evolutionary dynamics of trout populations under anthropogenic environmental change

Current rates of environmental change are exceeding the capacity of many populations to adapt to new conditions and thus avoid demographic collapse and ultimate extinction. In particular, cold-water freshwater fish species are predicted to experience strong selective pressure from climate change and a wide range of interacting anthropogenic stressors in the near future. To implement effective management and conservation measures, it is crucial to quantify the maximum rate of change that cold-water freshwater fish populations can withstand. Here, we present a spatially explicit eco-genetic individual-based model, inSTREAM-Gen, to predict the eco-evolutionary dynamics of stream-dwelling trout under anthropogenic environmental change. The model builds on a well-tested demographic model, which includes submodels of river dynamics, bioenergetics, and adaptive habitat selection, with a new genetic module that allows exploration of genetic and life-history adaptations to new environments. The genetic module models the transmission of two key traits, size at emergence and maturity size threshold. We parameterized the model for a brown trout (Salmo trutta L.) population at the warmest edge of its range to validate it and analyze its sensitivity to parameters under contrasting thermal profiles. To illustrate potential applications of the model, we analyzed the population's demographic and evolutionary dynamics under scenarios of (1) climate change-induced warming, and (2) warming plus flow reduction resulting from climate and land use change, compared to (3) a baseline of no environmental change. The model predicted severe declines in density and biomass under climate warming. These declines were lower than expected at range margins because of evolution towards smaller size at both emergence and maturation compared to the natural evolution under the baseline conditions. Despite stronger evolutionary responses, declining rates were substantially larger under the combined warming and flow reduction scenario, leading to a high probability of population extinction over contemporary time frames. Therefore, adaptive responses could not prevent extinction under high rates of environmental change. Our model demonstrates critical elements of next generation ecological modelling aiming at predictions in a changing world as it accounts for spatial and temporal resource heterogeneity, while merging individual behaviour and bioenergetics with microevolutionary adaptations.

Molecular Characterization and In Silico Analysis of Defensin From Tor putitora (Hamilton).

Antimicrobial peptides (AMPs) are vital constituents of innate immune system. In fish, one of the most important AMP is β-defensin that has a potential to activate the adaptive immune system. β-defensin is a cysteine-arginine-rich cationic AMP with broad spectrum activity against microbes. In this study, we identified cloned and characterized β-defensin 1 from Tor putitora, a cold water fish species also known as mahseer. An open reading frame of β-defensin 1 was amplified, cloned and sequenced which encodes a peptide of 67 amino acid residues. The pro-peptide includes a signal peptide comprising 24 amino acids as predicted by Signal P along with a mature peptide of 43 amino acid residues. Tor putitora β-defensin 1 (TP-βdf1) has a molecular weight of 4.6kDa with a pI of 8.35. Six cysteine residues are present in the mature peptide which is a characteristic feature of defensins. All six cysteine residues are involved in the formation of three intra-molecular disulfide bonds. Three-dimensional modeling of mature peptide of TP-βdf1 was carried out using Modeller 9.10, and validated TP-βdf1 model revealed three β-sheets. The cysteine residues form three disulfide bonds in the pattern of Cys(1)-Cys(5), Cys(2)-Cys(4), Cys(3)-Cys(6) stabilizing the β-sheet. Structural analysis revealed three β-strands and an α-helix at the N terminus. Phylogenetic analysis revealed that the β-defensin 1 of Tor putitora was close to Megalobrama amblycephala which possibly suggests that TP-βdf1 peptide sequence is quite similar to β-defensin peptide sequences of carps and minnows.

Modeling climate change impacts on the thermal dynamics of polymictic Oneida Lake, New York, United States

The thermal dynamics of lakes are affected by climate change, and in turn affect most aspects of lake ecology, including primary and secondary production, biogeochemistry, and biodiversity. These effects may be particularly large in polymictic lakes which have variable durations and degrees of thermal stratification. A one-dimensional model, the Dynamic Reservoir Simulation Model (DYRESM), was used to evaluate the impacts of predicted climate change on temperature and stability in Oneida Lake, a 207km2 shallow, polymictic lake in central New York State. Field data were collected on stream temperature and discharge, weather, and lake temperatures at varying depths to calibrate and validate the model for Oneida Lake. Modeled temperatures at 2m and 10m were generally within ±1°C of observed values, but only after wind speeds from a nearby airport were decreased by 25%. Downscaled climate data from three general circulation models and two emissions scenarios were used to assess the impacts of different anticipated climate scenarios on the lake for 2041–2050 and 2090–2099. By 2050, under the higher emissions scenario, water temperatures (April–November) at 2m and 10m depths indicated an increase of 1.36°C and 1.43°C, respectively; however, 2011 simulation temperatures already aligned with mid-century predictions. By the end of the century, the prediction of the higher emissions scenario indicated an increase in 2m and 10m water temperatures (April–November) of 3.70°C and 3.37°C, respectively, and an increase of 61 consecutive days of stratification in Oneida Lake. These impacts would lead to increased periods of lack of oxygen in the bottom waters of this lake and changes in the biotic species composition, including extirpation of a coldwater fish species, burbot (Lota lota). This study contributes to our understanding of the thermal regime of polymictic lakes in a warmer world.

Seasonal dynamics of ichthyodiversity in a hill stream of the Darjeeling Himalaya, West Bengal, India

The small torrential spring-fed hill-stream Relli in the Darjeeling Himalaya of West Bengal was studied from March 2007 to February 2009 to assess seasonal dynamics and diversity of fish populations. The study revealed that the stream sustained 25 rheophilic cold water fish species from 15 genera and five families having ornamental, food and sport value. Seven omnivorous species were abundantly found, and the array of juveniles and sub adults suggests this stream is used as a breeding and nursery ground for some species. The stream harboured fish with unique modifications such as adhesive structures. Analysis of monthly data indicate that abundance and diversity indices increased slightly during April–May and sharply during October–November, indicating significant seasonal variations with the low diversity observed during monsoon months reflecting environmental stresses. Evenness was high in all sampling sites, and inversely related to the dominance index of ichthyofauna. The density and diversity of fish assemblages along the gradient of the stream may be interrupted due to anthropogenic disturbances. Our study provides baseline data which may be helpful for conservation and management of fish species, and in formulating fishery policy.

Climate change and stream temperature projections in the Columbia River basin: habitat implications of spatial variation in hydrologic drivers

Abstract. Water temperature is a primary physical factor regulating the persistence and distribution of aquatic taxa. Considering projected increases in air temperature and changes in precipitation in the coming century, accurate assessment of suitable thermal habitats in freshwater systems is critical for predicting aquatic species' responses to changes in climate and for guiding adaptation strategies. We use a hydrologic model coupled with a stream temperature model and downscaled general circulation model outputs to explore the spatially and temporally varying changes in stream temperature for the late 21st century at the subbasin and ecological province scale for the Columbia River basin (CRB). On average, stream temperatures are projected to increase 3.5 °C for the spring, 5.2 °C for the summer, 2.7 °C for the fall, and 1.6 °C for the winter. While results indicate changes in stream temperature are correlated with changes in air temperature, our results also capture the important, and often ignored, influence of hydrological processes on changes in stream temperature. Decreases in future snowcover will result in increased thermal sensitivity within regions that were previously buffered by the cooling effect of flow originating as snowmelt. Other hydrological components, such as precipitation, surface runoff, lateral soil water flow, and groundwater inflow, are negatively correlated to increases in stream temperature depending on the ecological province and season. At the ecological province scale, the largest increase in annual stream temperature was within the Mountain Snake ecological province, which is characterized by migratory coldwater fish species. Stream temperature changes varied seasonally with the largest projected stream temperature increases occurring during the spring and summer for all ecological provinces. Our results indicate that stream temperatures are driven by local processes and ultimately require a physically explicit modeling approach to accurately characterize the habitat regulating the distribution and diversity of aquatic taxa.

A new aquareovirus causing high mortality in farmed Atlantic halibut fry in Norway.

A new aquareovirus was isolated from cultured Atlantic halibut (Hippoglossus hippoglossus) fry at a facility where massive mortalities had occurred during the start-feeding phase. The same virus was also detected in juveniles (about 10 grams) of the 2013 generation at two other production sites, but not in larger fish from generations 2007–2012. The virus replicated in BF-2 and CHSE-214 cell cultures and produced syncytia and plaque-like cytopathic effects. This Atlantic halibut reovirus (AHRV) was associated with necrosis of the liver and pancreas, syncytium formation in these tissues, and distinct viroplasm areas within the syncytium in halibut fry. Transmission electron microscopy revealed that the viroplasm contained virions, non-enveloped, icosahedral particles approximately 70 nm in diameter with a double capsid layer, amorphous material, and tubular structures. The RNA-dependent RNA polymerase (RdRp) gene from the AHRV isolates showed the highest amino acid sequence identity (80 %) to an isolate belonging to the species Aquareovirus A, Atlantic salmon reovirus TS (ASRV-TS). A partial sequence from the putative fusion-associated small transmembrane (FAST) protein of AHRV was obtained, and this sequence showed the highest amino acid sequence identity (46.8 %) to Green River Chinook virus which is an unassigned member of the genus Aquareovirus, while a comparison with isolates belonging to the species Aquareovirus A showed <33 % identity. A proper assessment of the relationship of AHRV to all members of the genus Aquareovirus, however, is hampered by the absence of genetic data from members of several Aquareovirus species. AHRV is the first aquareovirus isolated from a marine coldwater fish species and the second reovirus detected in farmed fish in Norway. A similar disease of halibut fry, as described in this paper, has also been described in halibut production facilities in Canada and Scotland.

Hypolimnetic oxygenation in Twin Lakes, WA. Part II: Feeding ecology of a mixed cold- and warmwater fish community

Line-diffuser hypolimnetic oxygenation (HO) was initiated in North Twin Lake, Washington, in 2009 to mitigate loss of coldwater fishery habitat due to temperature–dissolved oxygen “habitat squeeze” and to reduce internal phosphorus cycling. Active tracking, net-captures, and hydroacoustic analyses demonstrated that trout populations rapidly expanded into increased hypolimnetic habitat within the first few years of oxygenation; however, long-term fishery benefits and many basic ecological aspects of HO have yet to be established. Diet and food web analyses indicate significant changes in feeding ecology of principal coldwater fish species in North Twin in 2012 compared to preoxygenation (2005) and to unoxygenated South Twin in 2012. North Twin rainbow trout (Oncorhynchus mykiss) consumed significantly more large-bodied Daphnia during midsummer 2012 than in South Twin, where rainbow trout fed primarily on littoral amphipods. Additionally, relative gut weight for brook trout (Salvelinus fontinalis) in August 2012 was significantly higher in North Twin compared to South Twin, apparently due to increased access to hypolimnetic zooplankton. Golden shiner (Notemigonus crysoleucas) diets also seem to include more zooplankton in oxygenated North Twin. Littoral-focused largemouth bass (Micropterus salmoides) diets were not altered by HO. Observed changes in feeding ecology following HO have significant implications for future fishery management in the Twin Lakes.

Impacts of the warming of the continental shelf in spring 2012 on acoustic propagation conditions and fish distributions north of Cape Hatteras

During May 2012, we conducted hydrographic surveys in conjunction with studies of acoustic scattering from fish schools north of Cape Hatteras. The waters of the continental shelf were greater than 4° Degrees C. warmer than prior observations during typical spring-time conditions in May 1996. In addition, the temperature gradients which normally exist across the shelfbreak front were absent, leading to intensification of the shelfbreak frontal jet. We relate the warming to large-scale atmospheric shifts and also report on the absence of cold water fish species, which were expected to be abundant in the study area.

The complete mitochondrial genome of Schizothorax prenanti (Tchang) (Teleostei, Cyprinidae, Schizothoracinae)

The ya-fish, Schizothorax prenanti, is a well-known commercial cold-water fish species with the hexaploid karyotype distributed in the upper reaches of the Yangtze River and its tributaries on the western Sichuan Plateau in China. The complete mitogenome of S. prenanti is 16,587 bp in length, containing 37 genes of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a control region (D-loop). The gene nucleotide composition of S. prenanti is 29.6% A, 25.4% T, 27.1% C and 17.9% G, with a slight AT bias of 55.0%. The complete mitogenome sequence of S. prenanti could provide useful data for further studies on genetic structure and diversity, as well as the artificial cultivation and breeding of S. prenanti.

Comparative Phylogenetic Study of Four Coldwater Fishes (Family Cyprinidae) Based on Targeted 16S RNA Mitochondrial Gene

S. richardsonii, T. putitora, B. Bendelisis and G. Gotyla are commercially important coldwater fish, widely used as a food fish, game fish and ornamentally fish in the Uttarakhand region of India. The present study examined the phylogenetic relationship within and between four coldwater fish species from Kumaun and Garhwal region of Uttarakhand. The mitochondrial 16S ribosomal DNA were used to elucidate phylogeny of the family Cyprinids. Analysis of 34 sequences of 16S rRNA gene (550 bp) revealed 12 haplotypes for both regions. The 16S rRNA dataset contained 93 and 94 variable site found for Garhwal and Kumaun region respectively. Rate of transition were higher than transversion for both region. The nucleotide diversity was lowest between the T. putitora and S. richardsonii and highest between the B. bendelisis and G. gotyla for both regions. The phylogenetic tree, constructed unweighted pair group average (UPMGA) methods revealed similar results suggesting that T. putitora and S. richardsonii have a close relationship to each other while maximum divergence was observed in B. bendelisis , which was also confirmed by the genetic distance data. The understanding of genetic variations of coldwater fishes will play a key role in conservation and management of this endangered fish species.

Genetic Diversity in Four Species of Coldwater Fishes (Family Cyprinidae) Using Random Amplified Polymorphic DNA Markers and Implication for their Conservation

Information on the genetic profile of cultivable fish species is essential for studying molecular systematic and optimizing fisheries management and fish farming. In the Kumaun and Garhwal regions of Uttarakhand Himalayas, coldwater fish species (Cyprinidae) is widespread and endemic in the natural water bodies. The usefulness of random amplified polymorphic DNA (RAPD) was examined as a potential tool to test the genetic relationship among four predominant fish species, viz., Tor putitora, Schizothorax richardsonii, Garra gotyla and Barilius bendelisis (Cyprinidae: Pisces). The samples were collected from two different geographical region of Kumaun and Garhwal of Uttarakhand. Species specific markers were observed using 10 mer random primers through RAPD-PCR assay. The statistical analysis of RAPD was performed with the software POPGENE version 1.31. The phylogenetic trees based on RAPD-PCR, by using 15 random primers, showed a consistent result of forming two separate monophyletic groups consisting of T. putitora with S. richardsonii and Garra gotyla with B. bendelisis. The present investigation concluded that these methods could be a valuable tool for studying molecular systematic and establishing the taxonomic position among cyprinids coldwater fish species of India.

Thermal Carrying Capacity for a Thermally-Sensitive Species at the Warmest Edge of Its Range

Anthropogenic environmental change is causing unprecedented rates of population extirpation and altering the setting of range limits for many species. Significant population declines may occur however before any reduction in range is observed. Determining and modelling the factors driving population size and trends is consequently critical to predict trajectories of change and future extinction risk. We tracked during 12 years 51 populations of a cold-water fish species (brown trout Salmo trutta) living along a temperature gradient at the warmest thermal edge of its range. We developed a carrying capacity model in which maximum population size is limited by physical habitat conditions and regulated through territoriality. We first tested whether population numbers were driven by carrying capacity dynamics and then targeted on establishing (1) the temperature thresholds beyond which population numbers switch from being physical habitat- to temperature-limited; and (2) the rate at which carrying capacity declines with temperature within limiting thermal ranges. Carrying capacity along with emergent density-dependent responses explained up to 76% of spatio-temporal density variability of juveniles and adults but only 50% of young-of-the-year's. By contrast, young-of-the-year trout were highly sensitive to thermal conditions, their performance declining with temperature at a higher rate than older life stages, and disruptions being triggered at lower temperature thresholds. Results suggest that limiting temperature effects were progressively stronger with increasing anthropogenic disturbance. There was however a critical threshold, matching the incipient thermal limit for survival, beyond which realized density was always below potential numbers irrespective of disturbance intensity. We additionally found a lower threshold, matching the thermal limit for feeding, beyond which even unaltered populations declined. We predict that most of our study populations may become extinct by 2100, depicting the gloomy fate of thermally-sensitive species occurring at thermal range margins under limited potential for adaptation and dispersal.

Observations on morphology of post-embryonic development and histology of sensory organs in larval and juvenile Siberian sturgeon, Acipenser baerii

Siberian sturgeon,Acipenser baerii,one of the oldest extant cold-water fish species in the world,are of considerable research and economic value.We documented the postembryonic development of the Siberian stur-geon by monitoring morphological characteristics and cell types in retina,taste buds,olfactory sac,and ampullary organs in the larvae.The stages of postembryonic development were defined based on both the external morphol-ogy and the internal organ characteristics.Larvae were reared at a water temperature of(18.0±1.0)℃ and a pH of 7.0?7.5.The newly hatched larvae(day 0) were(9.05±0.14) mm long.During the early-stages of development(days 0–7),the larvae were nurtured by a large yolk sac and the eye was the primary sense organ.The late-stage larvae(day 8?–22) were characterized by the disappearance of the yolk sac and initiation of active feeding,the formation of fins and fin rays,a shift in habitat use towards the bottom of the water column,and the completion of organ differentiation.As larvae reached the juvenile stage(day 23–57),the scutes begin to form,the organs tended to become fully developed,and the external morphology and body color pattern gradually matured into the adult pattern.We observed some differences in the development characteristics of the primary sensory organs in Sibe-rian sturgeon relative to other teleosts.Our observations suggest that Siberian sturgeon is an ancient species that occupy a unique position during the evolution of teleosts.