Primary Freshwater Research Articles

Broad-scale sampling of primary freshwater fish populations reveals the role of intrinsic traits, inter-basin connectivity, drainage area and latitude on shaping contemporary patterns of genetic diversity.

Background. Worldwide predictions suggest that up to 75% of the freshwater fish species occurring in rivers with reduced discharge could be extinct by 2070 due to the combined effect of climate change and water abstraction. The Mediterranean region is considered to be a hotspot of freshwater fish diversity but also one of the regions where the effects of climate change will be more severe. Iberian cyprinids are currently highly endangered, with over 68% of the species raising some level of conservation concern.Methods. During the FISHATLAS project, the Portuguese hydrographical network was extensively covered (all the 34 river basins and 47 sub-basins) in order to contribute with valuable data on the genetic diversity distribution patterns of native cyprinid species. A total of 188 populations belonging to 16 cyprinid species of Squalius, Luciobarbus, Achondrostoma, Iberochondrostoma, Anaecypris and Pseudochondrostoma were characterized, for a total of 3,678 cytochrome b gene sequences.Results. When the genetic diversity of these populations was mapped, it highlighted differences among populations from the same species and between species with identical distribution areas. Factors shaping the contemporary patterns of genetic diversity were explored and the results revealed the role of latitude, inter-basin connectivity, migratory behaviour, species maximum size, species range and other species intrinsic traits in determining the genetic diversity of sampled populations. Contrastingly, drainage area and hydrological regime (permanent vs. temporary) seem to have no significant effect on genetic diversity. Species intrinsic traits, maximum size attained, inter-basin connectivity and latitude explained over 30% of the haplotype diversity variance and, generally, the levels of diversity were significantly higher for smaller sized species, from connected and southerly river basins.Discussion. Targeting multiple co-distributed species of primary freshwater fish allowed us to assess the relative role of historical versus contemporary factors affecting genetic diversity. Since different patterns were detected for species with identical distribution areas we postulate that contemporary determinants of genetic diversity (species’ intrinsic traits and landscape features) must have played a more significant role than historical factors. Implications for conservation in a context of climate change and highly disturbed habitats are detailed, namely the need to focus management and conservation actions on intraspecific genetic data and to frequently conduct combined genetic and demographic surveys.

Phylogenetic relationships among Neotropical freshwater crabs of the Pseudothelphusidae (Decapoda, Brachyura) and the taxonomic position of Ptychophallus and related genera

The primary freshwater crab family Pseudothelphusidae is distributed with almost 300 described species from northern Mexico to the southern tributaries of the Amazon, including most of the Greater and Lesser Antilles. Its systematic grouping is solely based on morphological characters. The most recent and commonly applied classification distinguishes two subfamilies, the Epilobocerinae on the Greater Antilles, and the Pseudothelphusinae on the mainland of Central and South America and the Lesser Antilles (Rodríguez, 1982). In addition, several tribes are recognized based on the morphology of the first pair of male pleopods, the so called gonopods: the Pseudothelphusini, the Potamocarcinini, the Hypolobocerini, the Kingsleyini, and the Strengerianini. Here, we present the first molecular phylogeny of the Pseudothelphusidae, including representatives of all the subfamilies and tribes. The generaAchlidon,Allacanthos, andPtychophallusform a strongly supported monophyletic unit, clustering independently of the tribi where they have been classified so far. We present preliminary suggestions for a possibly derived taxonomy of the family.

Development and Application of an Integrated Hydrological Model for Singapore Freshwater Swamp Forest

As Singapore's only remaining patch of primary freshwater swamp forest, the conservation of the Nee Soon Swamp Forest (NSSF) is of utmost importance if a large proportion of the flora and fauna in Singapore is to be conserved. An integrated hydrological model for the NSSF is developed, with the objectives to numerically model the hydrological variations, to assess the impact of future climate change as well as to facilitate future eco-hydrology management. The numerical model considers the hydrological processes in a holistic manner, which includes the rainfall-runoff, the evapotranspiration, and the interactions between surface water and groundwater etc. Due to the constraints imposed from setting up monitoring stations in the protected forest, a combined approach is adopted to develop the numerical model which makes use of the field survey data and the alternative remote sensing data. With the climate projection inputs from the Regional Climate Model (RCM), the numerical model is applied to run future scenarios to assess the climate change impact. A few management strategies are also proposed in order to maintain favourable hydrological conditions for conserving the local ecosystem.

INDICATORS OF INFLUENCE OF SALINITY IN THE RESISTANCE AND RESILIENCE OF FISH COMMUNITY IN A TROPICAL COASTAL LAGOON (SOUTHEASTERN BRAZIL)

The effects of a disturbance by sandbank opening on the sh fauna community were evaluated through a long-term study in the Imboassica coastal lagoon, Rio de Janeiro State, Brazil. The sh and salinity samples were conducted between 1993 and 2004, with the goal of characterizing the structure and effects of four sandbank openings on this community, such as resilience and resistance measurements. During three sandbank openings, between the years of 1993 and 1996, the resilience time of the sh community could not be identied due to the short time period between openings, their magnitude and the discontinuity of the sh sampling. Monitoring studies previously conducted between 1993 and 2004, indicated that factors structuring the sh fauna of Imboassica lagoon are due to salinity !uctuations, in!uenced by the sandbank openings to which this environment is subjected. These events were indicated by the recolonization of primary freshwater species, oligohaline salinity values, and small variations in the composition and abundance on the sh community. Due to the magnitude and frequency of the disturbance, the ichthyic populations available that enter the lagoon from the adjacent ocean plus the resistance of this environment to salinity variations, determined the resilience and resistance of the sh fauna in the Imboassica lagoon. Thus, the resilience of the sh fauna in this lagoon was indicated in groupings of: a) Spearman probability values lower than 0.05 between the pairs of communities pre and post-disturbance; b) presence of freshwater species that indicate resilience; c) salinity values varying between 0 and 5; and d) small alterations in the abundance of sh populations.

Fishes of the Grijalva River basin of Mexico and Guatemala

The Grijalva River basin is one of the largest hydrological systems in Central America. Despite its importance, an inventory of its ichthyofauna remains incomplete. We provide a systematic checklist of fishes recorded in the Grijalva River basin based on surveys performed from 2002 to 2015. The systematic list includes 92 species, belonging to 13 orders, 25 families and 50 genera, of which 83 species are native and nine are exotics. This checklist includes three range expansions (Profundulus hildebrandi, Poecilia sphenops and Paraneetroplus hartwegi). Fifteen species are endemic to the basin. The most diverse families are Cichlidae and Poeciliidae with 25 and 23 species, respectively. Secondary freshwater fish diversity is high with 65.1%, the remaining species are primary freshwater (13.3%) and peripheral (21.7%) fishes.

Fish faunal provinces of the conterminous United States of America reflect historical geography and familial composition

Although the conterminous USA has a long history of ichthyological exploration, the description of biogeographical provinces has been ad hoc. In this study we quantitatively determined fish faunal provinces and interpreted them in the context of the geological history of North America. We also evaluated influences of major river basin occupancy and contemporary environmental factors on provincial patterns. Our data set comprised 794 native fishes, which we used to generate a presence and absence matrix for U.S. Geological Survey (USGS) four-digit hydrologic units. Three nested data sets were analysed separately: primary freshwater families, continental freshwater families (including primary and secondary families) and all freshwater families (including primary, secondary and peripheral families). We used clustering analysis to delimit faunal breaks and one-way analysis of similarity (ANOSIM) to determine significance among clusters (i.e. provinces). We used an indicator-species analysis to identify species that contributed most to province delineations and a similarity-percentage (SIMPER) analysis to describe the relative influence of representatives from each category (i.e. primary, secondary, peripheral) on provincial boundaries. Lastly, we used a parsimony redundancy analysis to determine the roles of historical (i.e. major river basin) and contemporary environmental factors in shaping provinces. Analysis of the nested data sets revealed lessening provincial structure with inclusion of more families. There were 10 primary freshwater provinces, 9 continental freshwater provinces and 7 all freshwater provinces. Major basin occupancy, but not contemporary environmental factors, explained substantial variance in faunal similarities among provinces. However, provincial boundaries did not conform strictly to modern river basins, but reflected river-drainage connections of the Quaternary. Provinces represent broad-scale patterns of endemism and provide a starting point for future studies. Relative malleability of province boundaries in the continental interior highlights this region as biogeographically diverse and dynamic. Interior-core provinces of this region (Central Gulf Coastal Plains, Northern Interior) have not been recognized previously and warrant further study.

Fishes from the Tusubres River basin, Pacific coast, Costa Rica: checklist, identification key and photographic album

A checklist of the fishes of the Tusubres River basin, Pacific coast of Costa Rica, compiled from field and museum surveys is herein presented. A total of 54 species, representing 47 genera and 27 families, were recorded. Peripheral species were dominant (64.8%), followed by secondary freshwater fishes (20.4%); primary freshwater fishes accounted only for 14.8% of the total fish diversity. Eleotridae (6 spp.), Gobiidae (6 spp.), Poeciliidae (5 spp.) and Characidae (4 spp.) were the most diverse. Two species (Caranx sexfasciatus, Carangidae; and Opisthonema libertate, Clupeidae) were new records for Costa Rican freshwaters, and two species (Gymnotus maculosus, Gymnotidae; and Lebiasina boruca, Lebiasinidae) was found to have expanded ranges. An identification key and a complete photographic album of all fish species recorded in the basin are presented. The results of this investigation provide a framework for future studies on biogeography, ecology and conservation on fishes from this area.

A natural history museum as a platform for accumulating verifiable information on non-native fishes: a Japanese example

Natural history museums provide permanent storage for specimen collections, including non-native species. We extracted the records for specimens and photographs of exotic non-native fishes collected in Japan by experts and citizens at the Kanagawa Prefectural Museum of Natural History, Japan. The museum began operation in 1994. The records of alien species known to be established in Japan (FSAK) consisted of 1756 specimens (789 lots) belonging to 29 species and 611 photographs (494 lots) of 25 species. Additionally, there were records of alien species that were introduced to Japan but not known to be established (FSUK) consisting of 23 specimens (23 lots) belonging to 11 species and of 46 photographs (31 lots) of 17 species. The FSAK could be classified as 22 primary freshwater, six diadromous, and one marine species, whereas the FSUK were classified as 12 primary freshwater, one diadromous, and six marine species. We identified a significant difference in the life-cycle types of FSAK and FSUK suggesting that fluvial species are established more easily than marine species, which reflects the biogeography of Japan. In addition, the records of FSUK were probably caused by an increase of aquarium fish introductions due to dereliction of pet fish, ejectment for pleasure, or crime by traders. The museum collections were mostly provided by experts, followed by citizens and other institutions. We also discussed the functions of a public museum of natural history for accumulating information and for citizen participation.

Vertebrate microfossils from the Upper Freshwater Molasse in the Swiss Molasse Basin: Implications for the evolution of the North Alpine Foreland Basin during the Miocene Climate Optimum

Abstract The older part of the Upper Freshwater Molasse (OSM) in the Swiss and South German Molasse Basin records the extended warm period known as the Miocene Climate Optimum. However, dating and global correlation of fossils and palaeoclimatic data from OSM sediments remains challenging, because sections are often incomplete and biostratigraphic data sometimes ambiguous. Here we present the rare case of a fossiliferous OSM section that can be securely dated to the late Early Miocene and early Middle Miocene ( c . 16.1–15.7 Ma). Vertebrate microfossils have been recovered from three levels in superposition. Fish teeth document primary freshwater fishes (Cyprinidae, Channidae), but otoliths found in the middle level indicate dominance of euryhaline fishes (Cyprinodontiformes, Gobiiformes). The herpetofaunal assemblages largely consist of taxa that were widely distributed in Central Europe during the Miocene Climate Optimum and fragments of turtle eggshells assignable to the Oofamily Testudoolithidae Hirsch, 1996. The small-mammal fauna is dominated by the cricetid Megacricetodon bavaricus Fahlbusch, 1964. The fossil biota implies that the lowermost level (late Early Miocene, c . 16.1 Ma) represents a palaeo-soil that formed under humid conditions, while the levels above it (early Middle Miocene, c . 15.7–15.8 Ma) record a warm freshwater pond subject to evaporation (middle level), and mean annual temperature ≥ 17 °C in the vicinity of a river with an open hinterland (upper level). Our results, together with previous data, suggest that the palaeoclimate of the North Alpine Foreland Basin of Switzerland and Southwest Germany was humid during the late Early Miocene and earliest Middle Miocene, and that the Middle Miocene onset of seasonality and low mean annual precipitation occurred by c . 15.7–15.8 Ma. We conclude that global climate change and the 100-kyr orbital eccentricity minimum at 15.75 Ma may have triggered the decrease in humidity in the North Alpine Foreland Basin.

Chemical-free ion exchange and its application for desalination

In some coastal areas, the primary freshwater obtained through seawater desalination has been widely used as the feed water in high purity-water production. Due to its high conductivity, however, further lowering ionic species load is needed before the final polishing process such as the mixed bed ion exchange and electrodeionization. In this work, a new process called as chemical-free ion exchange (CFIE) was proposed to replace the conventional two-bed (cation–anion) ion exchange for the purpose above. Results demonstrated that the mixed resin regeneration was achieved mainly by electrically enhancing water split. After regeneration, the resins could resume their ability to desalinate. The conductivities of purified water were 0.8–1.5μS/cm, and the energy consumption and water recovery were 0.29–1.04kWh/m3 water and 81.8–94.7%, respectively. The neutral concentrate collected during regeneration could be returned to a pretreatment unit for recovery. No chemical was needed and no wastewater was produced. Repetitive experimental results showed that the CFIE system could run stably.

Erratum to: The genetic legacy of lower sea levels: does the confluence of rivers during the last glacial maximum explain the contemporary distribution of a primary freshwater fish (Pseudobarbus burchelli, Cyprinidae) across isolated river systems?

Erratum to: The genetic legacy of lower sea levels: does the confluence of rivers during the last glacial maximum explain the contemporary distribution of a primary freshwater fish (Pseudobarbus burchelli, Cyprinidae) across isolated river systems?

Complete mitochondrial DNA genome of Metzia mesembrinum (Cypriniformes: Cyprinidae)

In this study, we sequenced the complete mitochondrial genome of Metzia mesembrinum (Cypriniformes, Cyprinidae), an Endangered pelagic primary freshwater fish distributed in South China. This mitochondrial genome, consisting of 16,611 base pairs (bp), encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a noncoding control region as those found in other vertebrates, with the gene synteny identical to that of typical vertebrates. Control region (D-Loop), of 936 bp long, was located between tRNAPro and tRNAPhe. The overall base composition of the heavy strand shows T 26.83%, C 25.48%, A 32.01% and G 15.68%, with a slight AT bias of 58.84%.

Gorgona, Baudó y Darién (Chocó Biogeográfico, Colombia): ecorregiones modelo para los estudios ecológicos de comunidades de quebradas costeras

This paper summarizes the available information on the geology, hydrology, and biota of coastal streams located in the Gorgona National Natural Park (GNNP), and the Baudó and Darién ecoregions within the Biogeographic Chocó (Colombia). Despite of the scant number of studies, we hypothesized that these streams are consistent with the typology observed in volcanic oceanic islands in the Caribbean and the Pacific that do not conform to the tenets of the River Continuum Concept. Coastal streams in the Biogeographic Chocó are short (100-101km) and steep and waterfalls and cascades are frequent due to tectonic origin. Step-and-pool sequences are common in montane reaches, while cobble-bed glides and riffles dominate in coastal plain reaches. Flow regimes are flashy in Pacific drainages (annual rainfall: <7000mm), but seasonally dry in the Caribbean drainages (<3500mm). Therefore, floods and droughts are important drivers of communities and ecosystem processes. Canopies are closed in low-order streams discharging directly to the ocean, thus contributing large amounts of litter. Diadromous fish and shrimp dominate consumer assemblages and various species are shared with streams in the Central America and the Antilles. These species play ecological roles probably equivalent to those found in other regions. These coastal streams are unique in terms of the number of primary freshwater fishes found (some endemics), and the functionally absence of diadromous gastropods. Rev. Biol. Trop. 62 (Suppl. 1): 43-64. Epub 2014 February 01.

Phylogeography ofRhinichthys cataractae(Teleostei: Cyprinidae): pre-glacial colonization across the Continental Divide and Pleistocene diversification within the Rio Grande drainage

The longnose dace, Rhinichthys cataractae, is a primary freshwater fish inhabiting riffle habitats in small headwater rivers and streams across the North American continent, including drainages east and west of the Continental Divide. The mitochondrially encoded cytochrome b gene (1140 bp) and 2298–2346 bp of the nuclear-encoded genes S7 and RAG1 were obtained from 87 individuals of R. cataractae (collected from 17 sites throughout its range) and from several close relatives. Phylogenetic analyses recovered a monophyletic R. cataractae species-group that contained Rhinichthys evermanni, Rhinichthys sp. ‘Millicoma dace’, and a non-exclusive R. cataractae. Within the R. cataractae species-group, two well-supported lineages were identified, including a western lineage (containing R. evermanni, R. sp. ‘Millicoma dace’ and individuals of R. cataractae from Pacific slope drainages) and an eastern lineage (containing individuals of R. cataractae from Arctic, Atlantic, and Gulf slope drainages). Within the eastern lineage of R. cataractae, two well-supported groups were recovered: a south-eastern group, containing individuals from the Atlantic slope, southern tributaries to the Mississippi River, and the Rio Grande drainage; and a north-eastern group, containing individuals from the Arctic slope and northern tributaries to the Mississippi River. Estimates of the timing of divergence within the R. cataractae species-group, combined with ancestral area-reconstruction methods, indicate a separation between the eastern and western lineages during the Pliocene to early-Pleistocene, with a direction of colonization from the west of the Continental Divide eastward. Within the southern portion of its range, R. cataractae likely entered the Rio Grande drainage during the Pleistocene via stream capture events between the Arkansas River (Mississippi River drainage) and headwaters of the Rio Grande. A close relationship between populations of R. cataractae in the Rio Grande drainage and the adjacent Canadian River (Mississippi River drainage) is consistent with hypothesized stream capture events between the Pecos (Rio Grande drainage) and Canadian rivers during the late-Pleistocene. The population of R. cataractae in the lower Rio Grande may have become separated from other populations in the Rio Grande drainage (upper Rio Grande and Pecos River) and Canadian River during the late-Pleistocene, well before initiation of recent and significant anthropogenic disturbance within the Rio Grande drainage. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 317–333.

Median Lethal Salinity (MLS96 h) of Two Small Indigenous Fish Species Amblypharyngodon mola and Pethia ticto from Indian Sundarban

Amblypharyngodon mola and Pethia ticto are small indigenous fish species belonging to family cyprinidae and considered as primary freshwater fish widely distributed in Indian subcontinent including Sundarban region. The 96-h median lethal salinity (MLS96 h) level of these fish was found out by exposing to saline water (0-10 ppt) in direct transfer method. The 96-h median lethal salinity for A. mola was found to be 6.20 ppt with 95% confidence intervals of 4.38-7.09 ppt where as for P. ticto it was 6.12 with 95% confidence intervals of 3.67-7.07 ppt. The Probit showed that at 6.12-6.20 ppt, 50% of the both test species shows sensitivity to salinity that leads to mortality. The regression analysis indicated that the mortality rate is positively correlated with salinity concentration having a regression coefficient close to 1.0 in each case. Various levels of external stress responses were noticed at 8 and 10 ppt salinity. The study suggests that these fish can potentially be used as a candidate species for aquaculture in slight brackishwater areas of Sundarban. However, further studies are required to understand the ecosystem based adaptation processes at higher salinity levels.

Freshwater crabs occupying tropical north Queensland coastal creeks

Balancing coastal urban development with species conservation and habitat protection can be challenging for managers especially where good quality ecological data is lacking. Primary freshwater crabs (Austrothelphusa species) of the family Gecarcinucidae (formerly Parathelphusidae) that occupy inland creek systems are also present in small coastal areas. In coastal regions, habitat loss in response to urbanisation and transformation of natural water channels to concrete drainage lines is a major threat to coastal crab populations. We provide data showing that one species, A. transversa, still exists in natural creek lines in Townsville, but not in engineered creek channels a little further downstream in some cases. Continued urbanisation means that populations will be under threat as the city continues to expand, transforming further natural creek lines to engineered concrete channels. Whether the absence of crabs in urban channels is due to increased predation from fish present in the permanent water (including noxious Oreochromis mossambicus), water chemistry differences, increased competition for food and shelter, or simply because this species cannot burrow in concrete channels to complete important lifecycle stages, warrants further investigation. Evidence is also provided that A. transversa coexists in natural waters with another freshwater crab species, the varunid, (Varuna litterata). The importance of management strategies for both species is discussed, particularly under continuing habitat squeeze with expanding coastal development.

Development and characterization of 16 polymorphic microsatellite loci for the Alaska blackfish (Esociformes: Dallia pectoralis)

Blackfishes (Esociformes: Esocidae: Dallia), small fishes with relictual distributions, are unique in being the only primary freshwater fish genus endemic to Beringia. Although the number of species of Dallia is debated, disjunct populations and distinct mitochondrial divisions that predate the end of the last glacial maximum are apparent. We developed sixteen polymorphic microsatellites from the Alaska blackfish (Dallia pectoralis) to study genetic diversity in Dallia. Genotypes from two populations, Denali (n = 31) and Bethel (n = 35), demonstrated the usefulness of the loci for population-level investigation. Observed and expected heterozygosity averaged 18.6 and 19.8 % in Denali and 61.1 and 63.7 % in Bethel. Number of alleles at each locus averaged 3.50 in Denali and 9.63 in Bethel. The observed signature of variability and structuring between populations is consistent with mitochondrial data.

The genetic legacy of lower sea levels: does the confluence of rivers during the last glacial maximum explain the contemporary distribution of a primary freshwater fish (Pseudobarbus burchelli, Cyprinidae) across isolated river systems?

The primary freshwater fish Pseudobarbus burchelli (Smith 1841) occurs across four presently isolated river systems in the south-western cape floristic region of South Africa. Mitochondrial DNA cytochrome b (701 base pairs) and control region (601 base pairs) genes were sequenced to assess the evolutionary history of P. burchelli and evaluate the role of climatic and landscape changes in shaping patterns of genetic variation in this species. We identified three historically isolated lineages in P. burchelli: a widespread lineage that occurs across three isolated river systems and two geographically restricted lineages. The results were evaluated against predictions of the confluence of river systems during low sea levels of the last glacial maximum. Occurrence of the widespread Breede lineage in the Duiwenhoks River system is consistent with reconstructed palaeoriver systems. However, the occurrence of this lineage in the Goukou river system that formed part of the eastern Gourits–Goukou palaeoriver system can only be explained by translocation or a recent river capture or episodic inundation of low drainage divides. Extreme ecological gradients or the potential presence of instream physical barriers could have prevented an exchange of lineages between the Breede and Heuningnes river systems.

Fishes of River Bharathapuzha, Kerala, India: diversity, distribution, threats and conservation

We present here a comprehensive account of the diversity, distribution, threats, and suggest conservation measures for the fishes of Bharathapuzha, the largest west flowing river in the southern Indian state of Kerala. A total of 117 species under 43 families and 81 genera were recorded from the river, of which 98 were primary freshwater and 19 were secondary freshwater and/or diadromous species. Six species of non-native fish were also recorded, of which three were exotic to the country and three were transplanted from the gangetic plains. Twenty-eight percent (S = 33) of species that occur in the Bharathapuzha are endemic to the Western Ghats, while three species (Balitora jalpalli, Mesonoemacheilus remadevii and Pseudolaguvia austrina) are restricted in their distribution to the river system. A little more than one-tenth (11%; S = 13) of species that occur in the river are listed under various threatened categories on the IUCN Red List. As part of this study, we also extend the distribution range of Osteochilichthys longidorsalis to the Bharathapuzha River system, based on its collection from the Thoothapuzha tributary. Several anthropogenic stressors including deforestation and loss of riparian cover, dams and other impoundments, pollution, sand mining, non-native species and destructive fishing practices are threatening the rich ichthyofaunal diversity and endemism in the Bharathapuzha. There is hence an urgent need to develop and implement conservation plans, some of which are discussed.

Annotated checklist of the freshwater fishes of continental and insular Costa Rica: additions and nomenclatural revisions

Based on a combination of intensive literature review, electronic database searches, re-identification of museum specimens and fieldwork, we hereby provide an updated checklist of the freshwater fishes of continental and insular Costa Rica. This checklist, systematically arranged at the ordinal and familial level, includes nomenclatural revisions, distributional information, and when appropriate, cross-references on the basis of Bussing (1998). According to our results, the native Costa Rican freshwater fish fauna is composed by 250 species, divided into 119 genera, 49 families and 19 orders; increasing in 108 the number of species originally reported by Bussing (1998). By far, the vast majority of these species, according to their supposed tolerance to salinity, are peripheral (63.2%), followed by secondary freshwater fishes (23.6%); only 13.2% are primary freshwater fishes. 24 species in this checklist appear to be endemic to Costa Rica. In addition to the native fauna 8 exotic species are reported.