The presence of anadromous twaite shad (Alosa fallax) in the Ebro River (western Mediterranean,Spain): an indicator of the population's recovery?

Although the Ebro River is one of the largest Mediterranean rivers, the presence of anadromous fish species was near to complete extirpation since the second half of the 20th century. However, many mature twaite shads (Alosa fallax) were captured at the lower reaches of this river (Xerta's weir site, 63 river km) in spring 2005, suggesting a natural recovery of this population. In this study, the first biological data on twaite shad from the Ebro River are presented, and their significance for the species conservation and recovery are discussed. The historical reasons for the decline of this species are reviewed, and data supports the proposal for urgent construction of a proper fish passage for anadromous species at the Xerta's weir. This action would allow fish access to a further 60 km of river upstream of the weir, representing a 200% increase in the amount of freshwater habitat and potential spawning areas. Improved access together with restrictive fishery regulations will assist with renewed interest in the fishery and conservation of the species.     

Prioritising the rehabilitation of fish passage in a regulated river system based on fish movement

Environmental rehabilitation budgets are often limited, and management actions need to be prioritised to achieve the best outcomes. Prioritisation can best be done when evidence informs the decision‐making process. We acoustically tagged twenty Golden Perch (Macquaria ambigua) in the Loddon River, Australia, and tracked their movements to gain an understanding on the requirements for fish passage at a major regulating structure, the Box Creek regulator. The movements of these fish were monitored through a network of receivers located throughout the lower Loddon River and Pyramid Creek system. Five fish moved 50–120 km upstream, four of which reached the Box Creek regulator before moving back downstream to the entrance of the Kerang Lakes system. Most long distance upstream movements were associated with an increase in river discharge. The remaining 15 fish moved <20 km, with all fish being detected at least once. This pilot study indicates that Box Creek regulator is acting as a barrier for some fish within the Loddon River system. Movement data also indicate that Golden Perch migration pathways may be influenced by river discharge. The management implications of this work includes the need to reinstate fish passage at Box Creek regulator and the potential use of environmental flows to enhance colonisation of native fish species throughout the Murray Darling Basin.     

Comparing the fish assemblages and food‐web structures of large floodplain rivers

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A mark-recapture population estimate for invasive silver carp (<Emphasis Type="Italic">Hypophthalmichthys molitrix</Emphasis>) in the La Grange Reach,Illinois River

Invasive silver carp (Hypophthalmichthys molitrix) populations have expanded greatly in the Upper Mississippi River System (UMRS) since their introduction in the early 1970s. We conducted a Chapman-modified, continuous Schnabel mark-recapture population and biomass estimate for silver carp (106–901 mm) in the La Grange reach, Illinois River during 2007–2008. We estimated a total of 328,192 (95% CI 231,226–484,474) silver carp (2,544 per river km 1,792–3,756) comprising 705 (95% CI; 496–1,040) metric tons of biomass (5.5 metric tons per river km 3.8–8.1). Long Term Resource Monitoring Program (LTRMP) data from the La Grange reach showed an exponential increase in silver carp catches since 1998, with an intrinsic rate of increase approaching 84%. In 2008, silver carp comprised about 51% of the total LTRMP annual fish collection. To our knowledge, this large river reach may contain the greatest ambient densities of wild silver carp in the world. Our findings provide a target for reduction efforts and also emphasize the importance of the La Grange reach as a source population for potential expansion of the species to the Laurentian Great Lakes.     

SOME OBSERVATIONS ON THE FISH LIFE IN A SEASONAL SAND RIVER

Summary

Five fish species were collected in a seasonal sand river that had migrated upstream more than 150 km from the permanent Limpopo River. The population structure indicated that mainly juveniles had taken part in this colonisation. No fish were collected in the winter when the river was dry. Information was obtained of fish surviving underground in the dry river bed.     

Length-weight relationships of 37 freshwater fish species from the Lefini river,middle Congo River basin (Republic of the Congo)

The present study reports on length-weight relationships (LWRs) for 37 of the most abundant fish species in the Lefini River basin, one of the largest right bank tributaries of the Congo River in the Republic of the Congo. The study area comprised 12 stations along 103 km of the river. Each station was sampled during March 2007 to August 2008 following standardized methods utilizing five monofilament gill nets of 10, 12, 15, 20 and 30 mm mesh size. Sample size, lengths, weights, LWRs, 95% confidence intervals of a and b, coefficient of correlation r² and growth type are provided for each species. Values of allometric coefficient b of the LWRs (W = aSL^b) ranged from 2.556 for Synodontis nigriventris to 3.363 for Brycinus poptae. These results represent the first study of length-weight relationships for fish species in a large affluent of the Congo basin as a whole.     

Length-weight relationship of fish species captured around an artificial offshore reef (northern Rio de Janeiro,Brazil)

The present work provides length-weight relationships (LWRs) for fish species captured around artificial offshore reef deployed 5 km from Guaxindiba Port, northern Rio de Janeiro, Brazil. The fish were captured during two sampling periods each year between 1996 and 2017 using bottom gill nets (25 m_length × 3 m_depth; 30 mm mesh). The fish were kept on ice and the biometric data, including total length (cm) and total wet weight (g) were determined in the laboratory. A total of 16 species belonging to 10 families were analyzed with Sciaenidae being the species richest family (5 spp) in the samples. The new value of LWRs for Sphyraena guachancho and new maximum sizes recorded for seven species highlight the scarcity of information on biological aspects of South America coastal fishes. These LWRs should assist fisheries scientist and managers to complement their further studies of population parameters to improve management decisions.     

The Invasion of the Chinese Mitten Crab (<Emphasis Type="Italic">Eriocheir sinensis</Emphasis>) in the United Kingdom and Its Comparison to Continental Europe

Owing to its catadromous lifestyle, the Chinese mitten crab, Eriocheir sinensis, allows comparison between a coastal and an inland biological invasion of the same species. Information about the distribution of this species in the United Kingdom has been collected from sightings made by governmental agencies, The Natural History Museum (London) collection, literature, and from the general public. This information indicated that the range of the species has expanded since the species’ arrival in 1973. The spread has been most marked along the east coast northwards to the river Tyne, on the south coast westwards to the river Teign. The expansion range was quantified and compared using geographic information software, and then compared to recorded spread in Europe. Mitten crabs dispersed along the coast at an average rate of 78 km per year (1976–1999), with a recent sharp increase to 448 km per year (1997–1999). These values are comparable with the historic outbreak in continental Europe where the average rate of dispersion along the Baltic Sea coast (1928–1935) was 416 km per year. Comparable figures for the North Sea coast (1923–1954) were 75 km per year with a peak of 168 km per year in 1927–1937. The upstream spread along rivers in the United Kingdom was 16 km per year in 1973–1998 with a marked increase since 1995 to 49 km per year (1995–1998). These data, in combination with population data published for the river Thames, indicate that the population has been increasing since the early 1990s, causing further range expansion into previously uninvaded river systems. The comparison of the spreading behaviour of the ongoing invasion in the United Kingdom with the historic invasion in northern Europe suggests that E. sinensis in future has the potential to establish itself in all major UK estuaries.     

Length–weight relationships (LWRs) of 12 Indian freshwater fish species from an un‐impacted tropical river of Central India (River Ken)

The length–weight relationships (LWRs) were studied of 441 fish individuals covering six families, eight genera and 12 freshwater species (L. dyochilus, L. calbasu, L. gonius, L. fimbriatus, P. sarana, L. boggut, C. mrigala, W. attu, B. bagarius, E. vacha, N. notopterus and S. aor) captured in the River Ken (tributary of the Yamuna River) from December 2007 to January 2009. The b value ranged from 3.52 for Cirrihinus mrigala, to 2.11 for Labeo gonius, with a mean of 3.03 at p < 0.001 for all species. The present observations are significant for conservation and management because the Ken River has been approved under India’s first interlinking plan with the River Betwa. The objective was to evaluate the LWRs of the freshwater fish species of an unimpacted and understudied river, which serves as a baseline for comparison to other relatively altered tropical Indian rivers.     

Assessment of fish communities using environmental DNA: Effect of spatial sampling design in lentic systems of different sizes

Freshwater fish biodiversity is quickly decreasing and requires effective monitoring and conservation. Environmental DNA (eDNA)‐based methods have been shown to be highly sensitive and cost‐efficient for aquatic biodiversity surveys, but few studies have systematically investigated how spatial sampling design affects eDNA‐detected fish communities across lentic systems of different sizes. We compared the spatial patterns of fish diversity determined using eDNA in three lakes of small (SL; 3 ha), medium (ML; 122 ha) and large (LL; 4,343 ha) size using a spatially explicit grid sampling method. A total of 100 water samples (including nine, 17 and 18 shoreline samples and six, 14 and 36 interior samples from SL, ML and LL, respectively) were collected, and fish communities were analysed using eDNA metabarcoding of the mitochondrial 12S region. Together, 30, 35 and 41 fish taxa were detected in samples from SL, ML, and LL, respectively. We observed that eDNA from shoreline samples effectively captured the majority of the fish diversity of entire waterbodies, and pooled samples recovered fewer species than individually processed samples. Significant spatial autocorrelations between fish communities within 250 m and 2 km of each other were detected in ML and LL, respectively. Additionally, the relative sequence abundances of many fish species exhibited spatial distribution patterns that correlated with their typical habitat occupation. Overall, our results support the validity of a shoreline sampling strategy for eDNA‐based fish community surveys in lentic systems but also suggest that a spatially comprehensive sampling design can reveal finer distribution patterns of individual species.     

Historical DNA documents long‐distance natal homing in marine fish

The occurrence of natal homing in marine fish remains a fundamental question in fish ecology as its unequivocal demonstration requires tracking of individuals from fertilization to reproduction. Here, we provide evidence of long‐distance natal homing (>1000 km) over more than 60 years in Atlantic cod (Gadus morhua), through genetic analysis of archived samples from marked and recaptured individuals. Using a high differentiation single‐nucleotide polymorphism assay, we demonstrate that the vast majority of cod tagged in West Greenland and recaptured on Icelandic spawning grounds belonged to the Iceland offshore population, strongly supporting a hypothesis of homing. The high degree of natal fidelity observed provides the evolutionary settings for development of locally adapted populations in marine fish and emphasize the need to consider portfolio effects in marine fisheries management strategies.     

Genetic structure analysis of Girella laevifrons populations in central Chile

Connectivity among most marine species depends of their life cycles, and the main phase that can regulate dispersal is the larval stage of an organism. Girella laevifrons (Girellidae) is an omnivore fish inhabiting in intertidal pools as juveniles and subtidal reefs as adults from northern to central Chile. It has a pelagic larval duration for approximately 69 days. In this study, we used eight molecular markers (microsatellites) to explore the genetic structure of their populations along 400 km of the central Chilean coast.20 juveniles were sampled from four different populations. Microsatellite loci did not detect a genetic structure within a 400 km scale along the coast of Central Chile. There is evidence (F_st = ?0.0038, p = 0.8954) suggesting that populations between Coquimbo and Littoral Central behave as a single whole population. This could be an estimate that may define future management units for the species.     

Finding Nemo’s Genes: A chromosome‐scale reference assembly of the genome of the orange clownfish Amphiprion percula

The iconic orange clownfish, Amphiprion percula, is a model organism for studying the ecology and evolution of reef fishes, including patterns of population connectivity, sex change, social organization, habitat selection and adaptation to climate change. Notably, the orange clownfish is the only reef fish for which a complete larval dispersal kernel has been established and was the first fish species for which it was demonstrated that antipredator responses of reef fishes could be impaired by ocean acidification. Despite its importance, molecular resources for this species remain scarce and until now it lacked a reference genome assembly. Here, we present a de novo chromosome‐scale assembly of the genome of the orange clownfish Amphiprion percula. We utilized single‐molecule real‐time sequencing technology from Pacific Biosciences to produce an initial polished assembly comprised of 1,414 contigs, with a contig N50 length of 1.86 Mb. Using Hi‐C‐based chromatin contact maps, 98% of the genome assembly were placed into 24 chromosomes, resulting in a final assembly of 908.8 Mb in length with contig and scaffold N50s of 3.12 and 38.4 Mb, respectively. This makes it one of the most contiguous and complete fish genome assemblies currently available. The genome was annotated with 26,597 protein‐coding genes and contains 96% of the core set of conserved actinopterygian orthologs. The availability of this reference genome assembly as a community resource will further strengthen the role of the orange clownfish as a model species for research on the ecology and evolution of reef fishes.     

Dietary Exposure to Organochlorine Compounds in Tarragona Province (Catalonia,Spain): Health Risks

The human health risks due to the dietary exposure to organochlorine compounds (OC) were assessed in the Catalan stretch of the Ebro River (Spain). The concentrations of various persistent organic pollutants (POPs): polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), pentachlorobenzene (PeCB), various hexachlorocyclohexanes (HCHs), as well as dichloro-diphenyl-trichloroethane (DDT) and derivatives, were determined in samples of fish and seafood, vegetables, fruits, and rice, acquired in localities of the zone under evaluation. In general terms, pollutant concentrations were similar to recent levels reported in the literature. With the exception of the consumption of fish and seafood by children, and due to the presence of PCBs (Aroclor 1254), food intake from local sources does not pose non-carcinogenic risks for all population groups examined. The presence of OC in foods of local origin in the Catalan basin of the Ebro River would not increase the health risks for the area's consumers.     

Length-weight relationships of eight fish species from the Hailang river,China

The present study reports the length-weight relationships (LWRs) for eight fish species sampled in Hailang River, a left-bank tributary of the Mudan River in Northeast China. The fishes were collected from April to October bimonthly 2017 by electrofishing (fishing 2 kilometers along the river and within 5 meters from the bank) and netting (drift gillnet: mesh size 2 cm × 3 cm; 200 m net length). The specimens were weighed (nearest 0.1 g) and measured (nearest 0.1 cm) in the laboratory. This study provides an update in maximum lengths for five species.     

The Meuse river as a corridor for range expansion of the exotic plant species <Emphasis Type="Italic">Sisymbrium austriacum</Emphasis>: evidence for long-distance seed dispersal

Riparian habitats are particularly prone to invasion of non-indigenous plant species and several species have been shown to rapidly expand their range along river networks, possibly mediated by the occurrence of frequent long-distance seed dispersal events. However, there is still relatively little empirical evidence for long-distance seed dispersal along river networks and most studies to date are inconclusive with regards to the direction (upstream vs. downstream) of seed movement. Using assignment analyses based on dominant AFLP markers, we provide empirical evidence that downstream long-distance seed dispersal has facilitated range expansion of the exotic plant Sisymbrium austriacum along the Meuse River. Of 242 sampled individuals, 13 (5.4%) were allocated to a population other than the one from which it was sampled. Of these, nine (3.7%) individuals were assigned to a known population within the area, the furthest being more than 20 km away from the population from which it was sampled. All putative source populations were located upstream, thus providing strong evidence for downstream migration of propagules. These results support the general view that river systems may serve as efficient transport vectors of plant species and thus may play an important role in increasing the spatial spread and range expansion of exotic plant species.     

Microsatellite analysis reveals genetic differentiation between year-classes in the icefish <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis> at South Shetlands and Elephant Island

Chaenocephalus aceratus is one of the most abundant Antarctic icefish species in the Atlantic sector and has been a by-catch species in the fishery for mackerel icefish, Champsocephalus gunnari, between the mid-1970s and mid-1980s at South Georgia, South Orkney, and South Shetland Islands. The species became the target of the fishery in particular seasons, such as at South Georgia in 1977/78. In our paper, we report results on genetic differentiation for 11 microsatellite loci in C. aceratus samples collected at the South Shetlands and Elephant Island. This study represents the first report on microsatellite variability of an icefish species. Our results support the evidence from previous studies on differences in infestation patterns of parasites that a single panmictic population of C. aceratus exists, spanning the two sampling sites separated by about 100 km. Moreover, our study indicates the presence of a significant genetic differentiation between individual year-classes pointing out the existence of dynamic processes acting at the population genetic level, according to recent results for broadly distributed marine species. Both small effective population size and immigration from unsampled differentiated stocks may be at the base of the differentiation found in C. aceratus. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Restoration of naturally reproducing and resident riverine lake sturgeon populations through capture and transfer

The Winnebago System, Wisconsin, is home to one of the largest Lake Sturgeon Acipenser fulvescens populations in North America. Although there are >50 known spawning sites utilized by Lake Sturgeon in the 200 km of the lower Wolf River upstream of Lake Winnebago, the construction of two dams >90 years ago eliminated the ability of Lake Sturgeon to access 18.5 km of river up to their ancestral spawning grounds below Keshena Falls. Given the cultural importance of sturgeon to the Menominee Indian Tribe of Wisconsin, expanded efforts aimed at restoring Lake Sturgeon spawning and a resident population to the upper Wolf River commenced in 2011. To meet these objectives, 100 or more Lake Sturgeon per year were captured below the dams, and transferred upstream to the Wolf River within the Menominee Reservation. All transferred fish were PIT tagged and 245 fish were surgically implanted with 10 year acoustic transmitters to determine spawning locations and monitor post‐release movement. The first five transfer cohorts contained 621 Lake Sturgeon, with spawning activity observed below Keshena Falls each spring following release. Gravid fish transferred within 3 weeks of spawning exhibited higher spawning rates above the upstream dam (70.2% females; 73.9% males) than gravid fish transferred in late fall (41.8% females; 41.2% males). Spawning documented below Keshena Falls and within the Red River represent the first spawning activity at these locations in >100 years. Lake Sturgeon transferred in early fall displayed higher retention rates, 2‐5 years post‐tagging, in the pool upstream of both dams (10.4%) compared to the late fall (3.1%) and spring transfers (7.4%). Natural reproduction was documented through capture of larval Lake Sturgeon immediately below Keshena Falls in 2013. These results demonstrate that capture and transfer can be utilized as a cost‐effective and biologically‐effective tool for Lake Sturgeon spawning stock and population restoration.     

Influence of habitat dynamics on the distribution and abundance of the federally threatened Santa Ana Sucker, <Emphasis Type="Italic">Catostomus santaanae</Emphasis>, in the Santa Ana River

Habitat degradation affects native stream fish populations worldwide. We examined the impact of fluctuation in environmental variables on the population dynamics of the federally threatened Santa Ana sucker, Catostomus santaanae, in the Santa Ana River, California through: 1) annual quantitative surveys of C. santaanae abundance and habitat at three 100-m sites between 2001 and 2008 and 2) annual surveys of habitat composition within a 30-km stretch of the Santa Ana River between 2006 and 2008. We used Akaike’s Information Criterion (AIC) to evaluate competing models that used environmental variables to explain variation in C. santaanae abundance among sites and years. The most plausible model identified a positive relationship between C. santaanae abundance and both the amount of coarse substrate (i.e., gravel and cobble) and rate of discharge among site-years. Surveys at the 30-km scale indicated that the prevalence of coarse substrate declined in a downstream direction in each year and that the total amount of this habitat type varied annually. Specifically, cobble/gravel habitat was mostly confined to the upstream 4 km, 9.6 km, and 5.1 km of the survey area in 2006, 2007, and 2008, respectively. Fine sediment comprised the bulk of downstream habitat every year. This large-scale flux in the distribution of coarse sediment likely has a large effect on the population dynamics of C. santaanae in the Santa Ana River. Our results underscore the need to maintain and enhance suitable C. santaanae habitat to ensure its long-term persistence in the Santa Ana River.     

Exposure to Metals through the Consumption of Fish and Seafood by the Population Living Near the Ebro River in Catalonia,Spain: Health Risks

The health risks due to metal exposure from consuming various fish and seafood species were assessed for the Catalan population living near the Ebro River (Spain). The concentrations of arsenic, cadmium, chromium, copper, mercury, manganese, nickel, and lead were determined in samples of mussel, clam, hake, sole, cuttlefish, sardine, and anchovy randomly acquired in various localities of the zone under evaluation. In general terms, metal concentrations were similar or lower than the levels recently reported in the literature. The current dietary intake of metals is analogous to that recently estimated for the non-exposed population of Catalonia. Metal exposure through fish and seafood consumption would only mean a slight increase of noncarcinogenic and carcinogenic risk for arsenic, whereas the remaining elements showed risk values below the corresponding threshold levels.