Native Freshwater Species Research Articles

Edwarsiella ictaluri: Pathogenicity and LD50 in Pangasius nasutus

This study focuses on pathogenicity and LD50 of Pangasius nasutus against Edwardsiella ictaluri. Pangasius nasutus or ‘patin buah’ is a native freshwater species of peninsular Malaysia and can be found in Pahang River. The market price for this species is high as it tastes better compared to other catfish. Edwardsiella ictaluri is a pathogenic bacteria and the causative agent that cause enteric septicemia of catfish (ESC) in the Pangasius species. However, the prevention measures against Edwardsiella ictaluri are still unknown for Pangasius nasutus due to the lack of research and study. Therefore, the objective of this study is to identify Edwardsiella ictaluri isolated from Pangasius nasutus cultured in Pahang River using polymerase chain reaction (PCR) and to determine the pathogenicity and LD50 of Pangasius nasutus against Edwardsiella ictaluri through injection method. There are four different concentrations of Edwardsiella ictaluri (1×1010, 1×109, 1×108, 1×107) that were injected intraperitoneally including normal saline water as control to a total of 50 Pangasius nasutus. Observation of clinical signs and mortality were carried out for 30 days and LD50 was determined. The earliest clinical sign was observed at concentration of 1×1010 cfu/ml at 2 hours post-infection of Edwardsiella ictaluri where pale liver and congested kidney can be observed after dissection. Other clinical signs observed are inflammation on tail and fin, hemorrhagic fin, hemorrhagic upper mandible, discoloration, and inflammation on the lower part of body. The first mortality of Pangasius nasutus was at concentration 1×1010 cfu/ml at 2 hours of post infection. The highest cumulative mortality was recorded at concentration 1×1010 cfu/ml with 100% of mortality rate. From the result, the value of LD50 of Edwardsiella ictaluri calculated was 1×106 cfu/ml. From this study, it can be concluded that Edwardsiella ictaluri does affect the survivability Pangasius nasutus in Malaysia.

Effect of elevated embryonic incubation temperature on the temperature preference of juvenile lake (Coregonus clupeaformis) and round whitefish (Prosopium cylindraceum).

Anthropogenic impacts can lead to increased temperatures in freshwater environments through thermal effluent and climate change. Thermal preference of aquatic organisms can be modulated by abiotic and biotic factors including environmental temperature. Whether increased temperature during embryogenesis can lead to long-term alterations in thermal preference has not been explicitly tested in native freshwater species. Lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish were incubated at natural and elevated temperatures until hatching, following which, all groups were moved to common garden conditions (15°C) during the post-hatching stage. Temperature preference was determined at 8months (Lake whitefish only) and 12months of age (both species) using a shuttle box system. Round whitefish preferred a cooler temperature when incubated at 2 and 6°C compared with 0.5°C. Lake whitefish had similar temperature preferences regardless of age, weight and incubation temperature. These results reveal that temperature preference in freshwater fish can be programmed during early development, and that round whitefish may be more sensitive to incubation temperature. This study highlights the effects that small increases in temperature caused by anthropogenic impacts may have on cold-adapted freshwater fish.

Which Fish Benefit from the Combined Influence of Eutrophication and Warming in the Dnipro River (Ukraine)?

The effects of climate warming and eutrophication on aquatic organisms are well established, but we lack a deep understanding of the selective mechanisms of fish communities towards eutrophication and warming in tandem. The aim of the study was to identify fish traits that were positively related to eutrophication and ongoing warming. The research was conducted for 19 years in the Dnipro River channel and floodplain water system of the “Dnipro-Orylskiy” Nature Reserve. Both categorical and continuous fish traits were considered. The study area is characterized by a more intense warming trend than the average for Europe, which reflects an increase in the maximum summer air temperature. At the same time, the concentration of chlorophyll-a had a monotonic tendency to decrease during the study period. Phytophilic, limnophilic, and freshwater fish species are increasing in abundance, while rheophilic and lithophilic fish are decreasing due to global warming. Fish species with greater vulnerability and resilience have selective advantages in terms of global warming. Pelagic fish species are the most resistant to eutrophication, while benthopelagic and phytolithophilic fish species are the most sensitive. Brackish-water demersal self-settled species of marine origin have a competitive advantage over other native freshwater species in the face of increasing symptoms of eutrophication and a warming climate.

Long-Term Shifts in Faunal Composition of Freshwater Mollusks in Spring-Fed Rivers of Florida

Florida’s freshwater spring and river ecosystems have been deteriorating due to direct and indirect human impacts. However, while the conservation and restoration strategies employed to mitigate these effects often rely on faunal surveys that go back several decades, the local ecosystem shifts tend to have much deeper roots that predate those faunal surveys by centuries or millennia. Conservation paleobiology, an approach which enhances our understanding of the past states of ecosystems, allows for comparison of modern faunal communities with those prior to significant human impacts. This study examines the historical record of freshwater mollusk assemblages from two spring-fed river systems, the Wakulla and Silver/Ocklawaha Rivers. Specifically, we compared fossil assemblages (latest Pleistocene - early Holocene) and live mollusk assemblages in the two targeted river systems. Bulk sampling of the fossil record (20 sites; 70 samples; 16,314 specimens) documented relatively diverse mollusk assemblages that consist of a suite of native freshwater species that is similar across the studied systems. In contrast, sampling of live communities (24 sites; 138 samples; 7,572 specimens) revealed depauperate species assemblies characterized by the absence of multiple native freshwater species commonly found in fossil samples, the widespread presence of introduced species, and dominance of brackish-tolerant species at the lower Wakulla River sites. Unlike fossil mollusk assemblages, live mollusk assemblages differ notably between the two river systems due to differences in relative abundance of introduced species (Melanoides tuberculata and Corbicula fluminea) and the presence of brackish-tolerant mollusks in the coastally influenced Wakulla River. The diverse, exclusively freshwater mollusk associations comparable across multiple river systems documented in the fossil record provide a historical perspective on the past state of freshwater river ecosystems complementing data provided by modern surveys. The conservation paleobiology approach used in this study reinforces the importance of considering the historical ecology of an ecosystem and the utility of the fossil record in providing a historical perspective on long-term faunal changes.

Chloride Toxicity to Native Freshwater Species in Natural and Reconstituted Prairie Pothole Waters.

Oil and gas extraction in the Prairie Pothole Region (PPR) of the northern USA has resulted in elevated chloride concentrations in ground and surface water due to widespread contamination with highly saline produced water, or brine. The toxicity of chloride is poorly understood in the high hardness waters characteristic of the region. We evaluated the toxicity of chloride to two endemic species, Daphnia magna (water flea) and Lemna gibba (duckweed), exposed in field-collected waters (hardness ~ 3000mg/L as CaCO3) and reconstituted waters (hardness 370mg/L as CaCO3) intended to mimic PPR background waters. We also investigated the role of chloride in the toxicity of water reconstituted to mimic legacy brine-contaminated wetlands, using two populations of native Pseudacris maculata (Boreal Chorus Frog). Chloride toxicity was similar in field-collected and reconstituted waters for both D. magna (LC50s 3070-3788mg Cl-1/L) and L. gibba (IC50s 2441-2887). Although hardness can ameliorate chloride toxicity at low to high hardness, we did not observe additional protection as hardness increased from 370 to ~ 3000mg/L. In P. maculata exposures, chloride did not fully explain toxicity. Chloride sensitivity also differed between populations, with mortality at 2000mg Cl-/L in one population but not the other, and population-specific growth responses. Overall, these results (1) document toxicity to native species at chloride concentrations occurring in the PPR, (2) indicate that very high hardness in the region's waters may not provide additional protection against chloride and (3) highlight challenges of brine investigations, including whether surrogate study populations are representative of local populations.

Fish assemblage response to removal of a low‐head dam in the lower reach of a tropical island river

Abstract Dams are often removed from rivers to restore habitat connectivity for biota such as fish. Removal of inland dams is well studied in temperate mainland rivers but this approach has been little studied in fish assemblages in islands, tropic systems, or for dams near the mouth of the river. In Puerto Rico, one of the most intensively dammed territories in the world, all native river fishes migrate between fresh water and the sea, and previous work shows that these movements are impeded or blocked by dams. Fish assemblages were compared before and after removal of the Cambalache dam, a porous, low‐head structure near the mouth of the Río Grande de Arecibo, as well as in two other rivers in western Puerto Rico, one with a similarly sized and positioned dam, and one reference river without artificial barriers. Fish were sampled using backpack electrofishing on 39 occasions during 2017–2019, including seven samples collected after removal of the Cambalache dam, at four to six sites per river. Fish assemblages upstream from dams were poorer in species, and species richness showed a marginal tendency (p = 0.0515) to increase upstream of the Cambalache dam 3 months after its removal. The two small lowland dams studied herein limited the upstream extent of marine species, which recolonised upstream sites of the Río Grande de Arecibo after removal of the Cambalache dam. An estimate of relative density (catch per unit effort) of common native freshwater species was higher above these two dams, and decreased at upstream sites after removal of the Cambalache dam. The estimated relative density of a native freshwater species that is of conservation concern, the American eel (Anguilla rostrata), was reduced above dams, and increased upstream of the former Cambalache dam after its removal. In extensive surveys conducted previously in Puerto Rico, sampling was concentrated higher in the catchment, and native fishes were more common and abundant below than above dams. The present work was conducted near the river mouth, and opposite results were observed. These contrasting results suggest that the effects of dams (or dam removal) on fish assemblages vary along the river gradient, although data from other systems are needed to confirm this. The present results suggest low‐head dam removal to be a viable method of restoring connectivity in fish assemblages in lower reaches of rivers in Puerto Rico and, potentially, other tropical islands. Removal of dams near the mouth of the river appears to be of particular benefit to marine fish species that use lower river reaches.

Morphological Variations of Wild Populations of Brycon dentex (Characidae, Teleostei) in the Guayas Hydrographic Basin (Ecuador). The Impact of Fishing Policies and Environmental Conditions.

Simple SummaryThe conservation status of a native fish species is often a key indicator of the state of habitat alteration, which supports strong anthropogenic disturbance. Ecuador contains the Guayas basin, the largest basin in the Pacific Ocean, which is a biodiversity reserve. However, there is little information regarding the morphometric characterization of Brycon dentex and its variations within this basin, although its plasticity has been proposed as an indicator of the maintenance of biodiversity. The goal of this study was to analyze the effects of anthropogenic activity and habitat modification on the morphological variation of Brycon dentex and to determine the usefulness of discriminant analysis in the morphometric differentiation of three populations of Brycon dentex in Ecuador. The Brycon dentex morphometric model could be used as a framework in conservation and, thus, an indicator of habitat status by quickly detecting changes in fish shape.The Guayas, located in Ecuador, is the largest basin in the Pacific Ocean and has an inventory of 123 native freshwater species. Most of these are endemic species that are threatened or at-risk due to anthropogenic activity and the modification, fragmentation, and destruction of habitats. The aim of this study was to determine the morphometric variation in three wild populations of Brycon dentex in the Guayas basin rivers and their connections to fishing management and environmental conditions. A total of 200 mature fish were captured, and 26 morphometric parameters were measured. The fishing policies (Hypothesis 1) and environmental conditions (Hypothesis 2) were considered fixed factors and were validated by t-tests. The morphological variation among the three populations (Hypothesis 3) was validated through a discriminant analysis. Fishing policies and resource management were found to generate morphological differences associated with body development. In addition, the environmental conditions were found to influence the size and structure of Brycon dentex populations. The analyzed populations were discriminated by the generated morphometric models, which differentiated Cluster 1 (Quevedo and Mocache rivers) with high fishing pressure from Cluster 2 (Pintado river) with medium–low fishing pressure. Morphometric differentiation by discriminant analysis is a direct and economic methodology that can be applied as an indicator of diversity maintenance.

Conservation genetics of the vulnerable stone crayfish using DNA barcoding and microsatellites

The stone crayfish Austropotamobius torrentium is a native European freshwater species with significant population declines caused by anthropogenic pressure onto its habitats, climate change and spreading of non-native invasive crayfish and their pathogens. Large-scale DNA barcoding based on sequencing a short fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene revealed this species represents a highly divergent taxon whose evolutionary heritage is preserved in genetically divergent mtDNA phylogroups, with majority of them having restricted distribution ranges. Guarding in mind vanishing populations trends and potential loss of genetic diversity, effective conservation planning and monitoring are needed for ensuring the persistence and long-term survival of this endangered species. Since genetic data are often critical for defining populations for conservation and management purposes, along with DNA barcoding, we employed microsatellites to examine samples of more than 400 individuals from 17 populations across its entire distribution range in Croatia, known as the stone crayfish diversity hot spot. Microsatellite analyses revealed high level of genetic diversity and differentiation among studied populations that grouped according to their geographical position and mtDNA phylogroup. Almost all sampled populations represent a distinct genetic cluster, showing high level of differentiation and reflecting long periods of isolation. Results of genetic characterisation enabled selection of suitable donor populations for future restocking and reintroduction programs. Combination of DNA barcoding and microsatellites provided good insight into genetic diversity and population structure as well as enabled sound conservation programs for this threatened species in Croatia.

Hydrological alterations enhance fish invasions: lessons from a Neotropical coastal river

With the aim of assessing whether hydrological alterations differently affect non-native and native fish species in coastal systems, we investigated fish assemblages along the fluvio-estuarine ecotone of the Neotropical Sao Joao River, Brazil. During a year, samplings with standardized efforts and limnological parameter records were carried out bimonthly at 15 sampling points in the last 50 km of the Sao Joao River, representing natural (meandering riverine and estuarine) and modified (reservoir, channelized and drained floodplain) stretches. We recorded 48 marine and 51 freshwater fish species, with 12 non-native species among the latter. Several native species were exclusively found within natural stretches, whereas non-native species presented significantly higher biomass catches in modified stretches. Only three species occurred in the entire study area, all of which were non-native species. Non-native species were associated with low dissolved oxygen and pH levels below the dam, whereas native freshwater species responded negatively to water transparency, and marine species responded positively to water conductivity at the hydrologically unaltered points. The hydrological alterations disrupted the fluvio-estuarine ecotone of the lower Sao Joao River, which plays the role of a dispersion source for non-native species and where invasive species are favored.

Triggers for the Impoverishment of the Macroinvertebrate Communities in the Human-Impacted Rivers of Two Central European Ecoregions

Human activity triggers negative alternations in river habitats, including changes to the physical and chemical parameters of the water, its hydromorphological features and the introduction and spread of invasive alien species. These modifications are expected to be intensified by climate change. Eight rivers in one of the most urbanised and industrialised regions in Europe, i.e. the Upper Silesian Coal Basin, were surveyed in order to explain the impact of anthropopressure on the distribution of macroinvertebrates. Conductivity, altitude, hydromorphological transformations, hardness, the organic matter content and certain fractions of benthic sediments significantly affect (p < 0.01) the occurrence of macroinvertebrates in Central European rivers. Our results proved that the hydromorphological transformation of watercourses, which is expressed by the relevant indices, is one of the most predictive factors that contribute to the distribution of macroinvertebrates. Anthropogenic inland waters that have been salinised by the discharge of hard coal mine waters create new habitats for brackish and marine species that replace native freshwater species. An increase in salinity causes an impoverishment of macroinvertebrate biodiversity therefore all possible actions should be taken to reduce the anthropogenic salinity of inland waters. Secondary saline rivers may prove to be prescient for climate-induced changes to river macroinvertebrates.

Usefulness of Discriminant Analysis in the Morphometric Differentiation of Six Native Freshwater Species from Ecuador.

Simple SummaryEcuador is among the 25 highest fish producers in the world and the fishing sector contributes 7% to the national consumption of animal proteins. This country has a high number of native freshwater species, some of which are endangered due to the modification, fragmentation and destruction of habitats; introduction of foreign species; overfishing with illegal gear; environmental pollution; development of large-scale intensive forestry practices; loss of ecological continuity between different rivers; and climate change. The Guayas, the largest basin (CHG) in the Pacific Ocean located in Ecuador, constitutes an important biodiversity reserve of native freshwater. Most part of these 125 species are endemic and threatened or in an at-risk situation. It would be useful to analyze the morphological differences among six existing species in the CHG, and to select a reduced number of direct, simple and low-cost measurements to be applied in marginal communities. In this work, the usefulness of discriminant analysis was proven in the differentiation of six native freshwater species. Results represent a new step in the development of breeding and conservation plans for this native zoogenetic resource.The aim of this research was to find out the morphometric differentiation of six native freshwater species in the Guayas Hydrographic Basin (Ecuador) by means of discriminant analysis. A total of 1355 mature fishes (Cichlasoma festae, Andinoacara rivulatus, Dormitator latifrons, Bryncon dentex, Hoplias microlepis and Leporinus ecuadorensis) were captured and 27 morphometric measurements and 20 landmarks were used. Two-way analysis of variance with species and sex as fixed factors and discriminant analysis were applied. The selection of the most discriminant variables was made applying the F of Snedecor, Wilks’-Lambda and the 1-Tolerance. While sex within species had no significant effect on the morphology, differences among species were significant. Twenty-seven morphological variables showed highly significant differences among six native freshwater species. Nine biometric variables with high discriminant power were selected. The six species analyzed were discriminated by the morphometric models generated, thus showing that discriminant analysis was useful for differentiating species. The morphometric differentiation by discriminant analysis is a direct, simple and economic methodology to be applied in situ in rural communities. It favors the implementation of a livestock development program and it could be used with other native freshwater species in the Guayas Hydrographic Basin.

Suckermouth armoured catfish (Pterygoplichthys spp.) menace in freshwater aquaculture and natural aquatic systems in Andhra Pradesh, India

Suckermouth armoured catfish (Pterygoplichthys spp.) which is popularly called “Devil fish” in Andhra Pradesh, was recorded in 93.33% of fish ponds out of 600 ha surveyed in Krishna and West Godavari districts including mesohaline ponds wherein salinity ranges from 2 to 20‰. Pterygoplichthys spp. have ranged from 150 to 600 kg/ha that accounts to 2.01-7.50% of total biomass of fish harvested in aquaculture ponds leading to escalation of feed conversion ratio by 25.76%. Consequently, carp production has diminished by 18.88% to 22.92% leading to economic losses to fish farmers up to 13.40%. Food chain disruption by this alien fish is not only confined to benthic algae and periphyton but also foraging on supplementary feeds leaving primary fishes deprived from availing feed. Abundance of Pterygoplichthys spp populations in culture ponds as also in canals was high in monsoon season when compared to winter. Invasion and abundance of Pterygoplichthys spp in various river systems in Andhra Pradesh has become major concern for fishers causing extensive damage to nets and gears as also retarded catch per unit effort resulting in minimization of their income by 30%. Efforts to extract fish hydrolysate from Pterygoplichthys spp were futile due to intense bony skeleton and poor recovery rate which projected utilization of this fish for allied activities to minimum. Abundance of Pterygoplichthys spp is increasing in confined and open water bodies due to their tolerance and ability to grow and breed in variety of aquatic habitats including polluted environments as also lack of effective predators thus poses a high risk and threat to native freshwater species in any ecosystem in which they get established.

Fish distribution pattern and environmental influence in the Bandama River estuary (West Africa)

The structure and distribution of the fish population were investigated from March 2019 to February 2020 in relation to environmental variables in the Bandama River estuary. Overall, the estuary showed environmental homogeneity outside of the conductivity and width of the study area. A total of 52 species of fish were recorded, belonging to 48 genera, 28 families and 12 orders. This ichthyofauna was composed of 24 native freshwater species, 27 brackish and marine species and a hybrid (Coptodon guineensis x Coptodon zillii). The species defined a distribution according to their ecological category in the Bandama estuary. Redundancy analysis (ARD) indicated that salinity and bed width are the main variables that influence the fish species distribution in the Bandama River estuary.

Snakeheads of Sri Lanka: A Taxonomic and Biogeographic Review

Purpose : Fish species of the family Channidae, commonly known as snakeheads, represent biggest and most caught native freshwater species in Sri Lanka. Despite importance for biodiversity and fisheries in Sri Lanka, members of this family are one of the least studied on taxonomic status and geographic distribution.Research Method : As an initial step of a study to revise the taxonomy and biogeography of freshwater fish in the family Channidae based on molecular phylogenetic and morphological relationships and biogeographical affinities, authors reviewed all the available published information and examined the specimens available at the National Museum of Sri Lanka.Findings : Six valid species have been recorded; Channa ara (Deraniyagala, 1945), C. marulius (Hamilton, 1822) C. kelaartii (Gunther,1861), C. orientalis Bloch and Schneider 1801 C. punctata (Bloch, 1794) and C. striata (Bloch, 1793). Current review suggests the exiting knowledge on the phylogeny and biogeography of Channidae in Sri Lanka is far from complete, identifying specific gaps to be prioritized in future research.Limitations : Current regional studies on the family Chanidae highlight the importance of a complete systematic revision of Sri Lankan species with an integrative approach. Literature review shows the necessity of a fresh analysis on the distribution data with ecological niche modeling and molecular phylogenetic studies to understand biogeographical and evolutionary history of the family.Originality / Value : Provides a consolidated account of the current knowledge on the taxonomy and biogeography of the Sri Lankan members of the family Channidae.

Responses of five naturalised ornamental freshwater plant species to elevated carbon dioxide concentration and nutrient enrichment

Ongoing global environmental changes such as rising atmospheric CO2 concentration ([CO2]) and eutrophication are in some parts thought to facilitate exotic plant species invasions in freshwater systems. Although an increasing number of studies have documented the impacts of these factors on native and invasive freshwater plant species, relatively little is known about how they might interact to affect naturalised exotic species. We investigated the growth and biomass allocation responses of five naturalised ornamental freshwater plant species (Ludwigia palustris, Mentha aquatica, Mentha pulegium, Nasturtium officinale and Zantedeschia aethiopica) to varied levels of CO2 (ambient and elevated) and nutrient (low and high) concentrations. We found limited evidence that these factors interacted to affect plant growth and biomass allocation. However, the relative growth rate (RGR) of most of the species was enhanced under elevated [CO2] and/or nutrient enrichment. These results suggest that most of the tested study species will likely be of management concern under future global environmental change conditions. However, it is important that future research efforts test the potential shifts in the competitive interactions between native and exotic naturalised freshwater species in response to global environmental changes in order to determine community-level consequences of these changes.

Crayfish plague in Japan: A real threat to the endemic Cambaroides japonicus

Global introductions of aquatic species and their associated pathogens are threatening worldwide biodiversity. The introduction of two North American crayfish species, Procambarus clarkii and Pacifastacus leniusculus, into Japan in 1927 seems to have negatively affected native Japanese crayfish populations of Cambaroides japonicus. Several studies have shown the decline of these native populations due to competition, predation and habitat colonization by the two invasive North American crayfish species. Here, we identify an additional factor contributing to this decline. We report the first crayfish plague outbreaks in C. japonicus populations in Japan, which were diagnosed using both histological and molecular approaches (analyses of the internal transcribed spacer region). Subsequent analyses of the mitochondrial ribosomal rnnS and rnnL regions of diseased specimens indicate that these outbreaks originated from a P. clarkii population and identify a novel haplotype of Aphanomyces astaci, d3-haplotype, hosted by P. clarkii. Overall, our findings demonstrate the first two cases of crayfish plague in Japan, and the first case in a non-European native crayfish species, which originated from the red swamp crayfish P. clarkii. This finding is a matter of concern for the conservation of the native freshwater species of Japan and also highlights the risk of introducing crayfish carrier species into biogeographic regions harboring species susceptible to the crayfish plague.

21. Invasion of Asian Carp in the Great Lakes

A recent threat posed to the Great Lakes and adjoining waterways is the Asian Carp. This large bodied fish originated from Asia and was first imported to the North American between 1960 to 1970. Their migration northward through the Mississippi River eliminated native freshwater species through competition of habitat and food resources. It is imperative to focus on the potential invasion of the Asian Carp because the risk assessment is high that the carp would eliminate all native species. Currently the carp are at the border of entering Lake Michigan, which would then provide access to the rest of the freshwater regions in the surrounding area. Ultimately, the loss of lake biodiversity is the fundamental problem and is coupled with economic issues. Bowfin Environmental Consulting INC and various invasive species awareness programs have been utilized to provide guidance on undertaking a project that involves an aggressive invasive species. The challenge faced will be to determine a method in which to prevent the invasion of Asian Carp. Examining their migration patterns, importation laws of live fish, and the policies of invasive species, will provide insight on the approach that should be taken to eliminate the threat of Asian Carp. It is also important to analyze which native species are most susceptible to becoming extinct. Overall, the intention is not only to increase government, scientific, and public awareness of this issue, but also to provide methods that can be implemented to prevent and eradicate the spread of Asian Carp in North American waterways.

Impacts, control and perception of introduced Crayfish in Thailand

To gain more scientific understanding regarding Crayfish in a tropical climate since its first introduction in 1987, this research focused on perceptions of non-native species trading and invasive species as it relates to management. Pet store owners and farmers were interviewed. There are two Crayfish species in Thailand—Procambarus clarkii and Cherax quadricarinatus and the Crayfish trade is expanding due to high demand. The results demonstrated that respondents had a basic knowledge of Crayfish biology, primarily related to farming production. However, most respondents lacked understanding of the negative impact and invasiveness of Crayfish and, therefore, the potential risk of invasion. Respondents suggested: (1) controlling invasive species by the government using stringent law enforcement and prohibition of the release of nonnative species into the wild and harsher legal penalties for those who do not comply with the law; and (2) an educational campaign, especially on the negative impacts of Crayfish, should be publicized targeting both traders and pet owners. We further examined Crayfish biology and behavior using a laboratory experiment. The study considered the impact of different densities of Crayfish in captivity on survival rates and tolerance of Crayfish to different environmental conditions. The potential effects of native freshwater species as control agents for Crayfish were also determined. Results revealed that stocking Crayfish at a high density tended to achieve higher growth and survival rates than at a low density, as Crayfish reared at a high density were unable to exhibit agonistic (fighting) behavior in a very confined area. It was also revealed that Crayfish are sensitive to polluted water conditions (dissolved oxygen 2.55 ± 0.25 mg l−1; biological oxygen demand 8.45 ± 0.04 mg l−1) and could not survive there very long. This intolerance limits the potential of Crayfish to spread further to other water bodies in Thailand. Biological control agents demonstrated that Anabus testudineus, or the Climbing Perch, appeared to be the most effective predator and may help resist invasion of exotic Crayfish in the wild.

Native freshwater species get out of the way: Prussian carp (Carassius gibelio) impacts both fish and benthic invertebrate communities in North America.

Prussian carp (Carassius gibelio) are one of the most noxious non-native species in Eurasia. Recently, Prussian carp, a non-native freshwater fish species, were genetically confirmed in Alberta, Canada and have been rapidly expanding their range in North America since establishment. Given their rapid range expansion, there is an increasing need to determine how Prussian carp may impact native species. We assessed the severity of the Prussian carp invasion by (i) determining their impact on fish communities, (ii) assessing their impact on benthic invertebrate communities, (iii) evaluating if Prussian carp alter abiotic conditions, and (iv) identifying where we find higher abundances of Prussian carp. When Prussian carp were established, we found significant changes to the fish community. Correspondingly, the degree of impact to benthic invertebrate communities was related to the stage of invasion (none, early or recent), where changes in fish communities were significantly concordant with changes in benthic invertebrate communities. Finally, we found that higher abundances of Prussian carp were significantly associated with lower abundances of a majority of native fish species. Altogether, using three lines of evidence, we determine that Prussian carp can have wide-ranging impacts on freshwater ecosystems in North America, pressing the need for management intervention.

First Scientific Records of the Invasive Red Swamp Crayfish, Procambarus clarkii (Girard, 1852) (Crustacea: Cambaridae) in Malta, a Threat to Fragile Freshwater Habitats

This study reports the first records of the invasive fresh water red swamp crayfish, Procambarus clarkii in Malta, first spotted in the wild in summer 2016. In spring 2017, 26 specimens of P. clarkii were collected, sexed, measured and identified both morphologically and genetically. The distribution and density of the species along the same valley were investigated at Fiddien Valley and Chadwick Lakes. As these two locations are associated with one of the major valley systems that cross the island, the presence of this prolific, aggressive and opportunistic feeding crayfish species increases the vulnerability of native freshwater species.