The aquarium hobby: can sinners become saints in freshwater fish conservation?

The aquarium hobby is popular worldwide, but it has positives and negatives for freshwater fish conservation. The most damaging impacts of the aquarium trade on ecosystems are overharvesting and invasive species. Consequently, many conservationists and academics have the perception that aquarium hobbyists are generally harmful to species conservation. Without overlooking these major drawbacks of the aquarium hobby, we aim to establish common ground between hobbyists and conservationists by correcting some misconceptions and showing the benefits of serious aquarium hobbyists in the conservation of freshwater fishes and their habitats. Our overview illustrates that the aquarium hobby is not insensitive to the pernicious effects of this enduring hobby on natural systems and that serious aquarists and their associations can directly assist and fund scientific research, increase conservation awareness among the general public and even participate in ex situ and in situ conservation programmes for native fish species at national or international levels. Whilst the relationship between conservationists and the aquarium hobby has often been antagonistic in recent years, ultimately most biologists and aquarists share a love of the species they study or maintain, and this common interest could be the basis for a more positive and productive relationship.     

Predation on native fish eggs by invasive round goby revealed by species‐specific gut content DNA analyses

1. Conservation of riverine fish often aims to improve access to spawning grounds and restore longitudinal connectivity by removing migration barriers, and involves substantial investments. However, these investments also enable non‐native predators to invade upstream into spawning areas and potentially adversely affect the recruitment of threatened freshwater fish through egg or fry predation.
2. Detecting egg predation is often challenging. Visual inspections of fish gut contents may underestimate predation of soft materials such as eggs and fry, which limits the discovery of predators preying upon these life‐stages. DNA‐based detection assays may offer a more sensitive tool to assess predation of soft materials.
3. A conservation issue was confirmed by developing and applying a species‐specific DNA‐based detection assay: invasive round goby (Neogobius melanostomus) prey on the eggs or fry of the threatened common nase (Chondrostoma nasus) in Switzerland.
4. DNA‐based detection assays were also developed for five other valuable native fish species, including endangered salmonid and cyprinid river spawners. The applicability of the assays was confirmed in a series of laboratory and field feeding experiments involving eggs and fish tissue. In addition, this work provides a guiding framework for conservation managers regarding the use and applicability of different DNA‐based detection approaches for gut content analysis.
5. The results of this study could inform local conservation measures – such as temporary reductions in the density of round goby at spawning sites prior to spawning – and demonstrate how targeted application of species‐specific molecular markers may advance freshwater fish management.

     

Invasive gobies in the Danube: invasion success facilitated by availability and selection of superior food resources

Abstract –  We investigated somatic condition, growth rate, diet and food resources of the native (lower Danube) and non-native (upper Danube) populations of invasive bighead goby Neogobius kessleri and round goby N. melanostomus within the Danube River to answer the question whether prey availability and type may have facilitated successful goby invasion to the upper Danube. The non-native populations of both species were in better somatic condition and grew faster. The biomass of nonmollusc macrozoobenthos, dominated by Amphipoda, was markedly higher in the non-native range while molluscs were recorded frequently in both the native and non-native ranges. Amphipods were far the most consumed prey by non-native fish, whereas native fish combined two main prey types – amphipods and fish (bighead goby) and amphipods and bivalves (round goby). A laboratory experiment was conducted to reveal whether the low consumption of bivalves by the round goby in the non-native range reflects prey encounter rates or alternatively prey selectivity. When bivalves and amphipods were offered simultaneously in excess to the experimental fish, round goby showed strong preference towards amphipods. Molluscs are hypothesised to be an alternative rather than the most preferred prey for the round goby. Rich food resources utilised by the non-native bighead and round goby contribute to their invasive success in the upper Danube.     

Catching sharks: recreational saltwater angler behaviours and attitudes regarding shark encounters and conservation

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Aquatic macroinvertebrates from littoral vegetated lakes in arid Patagonia: The influence of fish introduction on community structure

1. Wetlands in arid regions are characterized by their great heterogeneity, often including endemic species that contribute to regional aquatic biodiversity. In the Patagonian steppe, most lakes are naturally fishless and sustain a rich aquatic biodiversity, including endemics; however, many of these lakes have been stocked with Oncorhynchus mykiss (rainbow trout) during recent decades. The introduction of predatory fish into aquatic ecosystems naturally devoid of these organisms can produce profound alterations in the structure of the original communities and in the configuration of their biotic assemblages.
2. Aquatic invertebrates play important roles in both the structure and functioning of freshwater ecosystems, including their contribution to global biodiversity and their cascading effects across ecosystem boundaries.
3. The aim of this study was to assess the effect of introduced non-native fish on the pleustonic macroinvertebrate assemblage. Samples were taken from 10 shallow Patagonian lakes (five fishless and five stocked with fish) in two consecutive warm periods.
4. Lakes with fish had higher conductivity and phosphate values. Higher inter-annual differences were also observed in lakes with fish for phytoplanktonic chlorophyll a, nitrate, phosphate, conductivity, and water temperature.
5. The community structure (relative abundance of different taxa, species composition, and diversity index) was affected by the presence of rainbow trout, with the differences mainly driven by the relative abundance of Ostracoda, Hyalella, Chironomidae, and Haliplus species.
6. This approach can be used to assess the required conservation actions in shallow Patagonian steppe lakes, which have been listed as priority areas for waterbird conservation. Specifically, this study provides a baseline for monitoring future trends of the macroinvertebrate communities and for evaluating conservation and management efforts over time.

     

Abiotic and biotic associations between the round goby Neogobius melanostomus and tubenose goby Proterorhinus marmoratus with the endangered northern madtom Noturus stigmosus in Canada

1. Quantifying habitat associations and threats to the persistence of imperilled species is a fundamental step for initiating species recovery efforts, but the traits associated with species imperillment (e.g. rarity and vulnerability to stressors) also limit the ability to empirically inform recovery strategies. Novel sampling designs and modelling approaches are therefore needed to quantitatively assess habitat associations and the threats to species persistence.
2. To improve the understanding of habitat associations and threats for one of the rarest endangered freshwater fish species in Canada, northern madtom (Noturus stigmosus), two‐species occupancy models were developed with two invasive gobies: round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus marmoratus). Models were parameterized with data from a multi‐year benthic trawling survey of two large Great Lakes tributaries in southern Ontario, Canada, and subsequently used to evaluate the need for reducing measurement error with future sampling efforts.
3. The probability of detecting northern madtom in the St. Clair (0.163) and Thames (0.194) rivers was low compared with round goby (St. Clair, 0.827; Thames, 0.833) and tubenose goby (St. Clair, 0.297). The best occupancy models indicated a negative association between northern madtom and round goby in the St. Clair River and the importance of gravel substrate for northern madtom.
4. Up to 16 repeated non‐detections using benthic trawls are needed to be 95% confident that northern madtom is absent at a site, indicating that current sampling approaches are likely inadequate.
5. Despite low detection probabilities, intensive trawling surveys combined with the two‐species occupancy modelling framework provided vital information for describing habitat associations for northern madtom and identified a significant negative association with round goby. Nonetheless, alternative sampling methods to improve the detection probability of northern madtom would allow a more robust evaluation of habitat associations and would provide more information on the negative association with round goby.

     

Conservation of fish communities: Extending the ‘research life cycle’ by achieving practical effects

1. This article highlights the practical impact of our 2018 Aquatic Conservation: Marine and Freshwater Ecosystems publication, ‘Importance of peripheral basins: Implications for the conservation of fish assemblages’, which described fish communities in a Polish river.
2. Data on the fish assemblages of the Dniester River (Black Sea basin) are scarce; however, evidence indicates that the assemblages have declined. In our 2018 study, we hypothesized that the peripheral basin (the small basin on the edge) of the larger Upper Dniester River basin (the Strwi?? River) could maintain good ecological status and contained unique fish assemblages.
3. To examine the influence of historical factors and assess the role of peripheral basins on fish conservation, data from the Strwi?? basin were compared with the adjacent but unconnected Wiar basin (the Vistula basin; Baltic Sea basin). The Strwi?? River fish assemblages featured higher species richness and a greater number of native Ponto–Caspian species that function near the edge of their ranges.
4. This article focuses on four impacts of the 2018 publication: increasing awareness by various groups and organizations of the unique character of the surveyed river basin; highlighting important issues in assessing the ecological status of European rivers; driving the red‐listing of species and the development of stream fish conservation strategies; and identifying possible future impacts.
5. Our 2018 publication demonstrated the value of studying peripheral basins, which may affect conservation strategy development and encourage study of the importance of other peripheral basins and their role in aquatic resources conservation. Our article influenced the interpretation of fish‐based biotic indices and the conduct of monitoring work and its evaluation. It also strongly emphasized the native origin of the racer goby (Babka gymnotrachelus) in the Strwi?? River, which was important for subsequent works seeking to change the legal status of the species in Poland.

     

Non‐indigenous fish in protected spaces: Trends in species distribution mediated by illegal stocking

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Do non-native ornamental fishes pose a similar level of invasion risk in neighbouring regions of similar current and future climate? Implications for conservation and management

1. Global trade in non-native ornamental species coupled with high connectivity among countries is well known to result in worldwide biological invasions, which pose challenges for the conservation and management of biodiversity.
2. There are few studies aimed at implementing management strategies that have examined differences in the potential invasiveness of non-native species between neighbouring political regions within the same ecoregion.
3. To compare the potential risk of invasiveness of non-native ornamental fishes with high commercial value in the river basins of two neighbouring regions of East and Southeast Asia, 32 extant and horizon species were screened with the aquatic species invasiveness screening kit (as-isk ) for the lower Pearl River basin (South China) and the Chao Phraya River basin (Thailand). Both regional (i.e. basin level) and combined risk-ranking thresholds were determined by receiver operating characteristic curve analysis.
4. Of the 32 species screened, 14 were categorized as posing a high risk and seven were categorized as posing a medium risk of being invasive in both regions, under current and future climate conditions. These species have a history of invasiveness and the climate of their native ranges is similar to that of the two study regions. Pterygoplichthys pardalis received the highest risk score in both regions. The risk ranks of 11 species differed between the two regions, based on either the combined or regional thresholds, and this was partly related to the different risk of invasiveness between the two regions, coupled with cognitive subjectivity among the assessors.
5. The results of the present study suggest that the invasion of non-native ornamental fish species could pose similar threats to biodiversity in neighbouring regions. This will serve to inform policy makers of neighbouring countries in the development of coordinated, mutually beneficial regulations and management strategies to enhance the conservation of native species.

     

Do protected areas mitigate the effects of fisheries‐induced evolution on parental care behaviour of a teleost fish?

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Dams in the Amazon: The importance of maintaining free-flowing tributaries for fish reproduction

1. Free-flowing tributaries are important for the maintenance of fish diversity in dammed systems. In relation to the reproduction of fish species, the role of a free-flowing tributary was evaluated and compared with that of a dammed tributary downstream of large dams in the Madeira River, one of the main tributaries of the Amazon River.
2. Two hypotheses were tested: (i) the densities of the ichthyoplankton differ between the dammed and the free-flowing tributaries; and (ii) the free-flowing tributary contributes a greater diversity of fish larvae species to the assemblage structure of the main stem than the dammed tributary.
3. Fish eggs and larvae were sampled at five sites: one in each tributary (Jamari – dammed – and Machado – free-flowing) and three in the main stem (Madeira River), upstream and downstream from the mouth of each tributary.
4. Fitted Bayesian models showed that the densities both of eggs and larvae were more than twice as high in the free-flowing tributary than in the dammed tributary. The results also indicated that the free-flowing tributary makes a major contribution to the fish assemblage structure of the Madeira River, whereas the dammed tributary does not have a significant influence on the main stem assemblage structure.
5. The results demonstrate the importance of conservation and maintenance not only of the Machado River but also of other free-flowing tributaries in dammed basins, especially those basins with high biodiversity, such as the Amazon. Moreover, this study helps inform the decision-making process regarding the location of new dams, which is critical in fish diversity conservation.

     

Occupancy dynamics of rare cyprinids after invasive fish eradication

1. The eradication of invasive species is a management strategy implemented to eliminate adverse impacts of invaders on native species communities. After eradications, follow‐up studies are done to confirm eradication of the invasive species and the short‐term recovery of the native species, but long‐term monitoring to confirm full population recovery and stability is often not completed.
2. In this study, long‐term monitoring of native fishes was carried out over 5 years after the eradication of an invasive fish from the Rondegat River, South Africa. Forty‐six sites distributed along four river sections were sampled for presence/absence using underwater cameras and snorkel surveys. Density data were collected by snorkel surveys.
3. Using multi‐season occupancy models, the annual probability of colonization and local extinction of the native fishes and annual rate of change in occupancy along the river were estimated. Changes in native fish densities across time and across the control and treatment sections were analysed using Kruskal–Wallis analysis, followed by Dunn's post‐hoc test.
4. Probability of colonization and local extinction differed for each native fish species and may have been affected by extrinsic factors, such as rainfall, and intrinsic density‐dependent factors, hypothesized from the density data. The occupancy rates of change revealed that the two Near Threatened fish species have reached an occupancy dynamic equilibrium but the Endangered fish has not, suggesting that other conservation efforts may be needed.
5. Long‐term monitoring of native fishes after an eradication programme has confirmed the successful removal of the invader and the recovery and stability of the community. However, successful eradication was not sufficient for full recovery of all species; additional conservation management strategies are needed to secure the population stability and persistence of endangered fishes. We recommend that eradication programmes, regardless of locality, should employ long‐term monitoring to ensure full recovery of a native fish community.

     

Selecting areas with rare and restricted fish species in mountain streams of Southern Brazil

1. The delimitation of conservation units may be supported by information on compositional (taxonomic), functional, and phylogenetic diversity of a given locality or region. In this context, systematic conservation planning and key biodiversity areas are promising approaches for biodiversity protection.
2. Factors such as species representativeness and exclusivity may be used to identify geographical distribution patterns and select relevant areas for conservation at a local scale.
3. This study aims to identify areas with rare and restricted fish species in mountain streams in Southern Brazil, using a method that unites ecological and biogeographical approaches.
4. Seven river basins and 152 mountain streams in Southern Brazil were sampled to obtain data on the occurrence and abundance of 115 fish species. The rarity status of each species was determined and endemicity analysis was used to find areas of restricted species (ARS) with three cell sizes.
5. Using larger cells, continuous areas were identified and supported by a higher proportion of rare fish species. Using smaller cells, discontinuous areas were identified within each of the river basins, where rare and endemic fish species occur. Most of the smaller areas relevant for protecting fish fauna were located outside of conservation units.
6. Fundamental areas were selected for the protection of fish species in mountain streams in Southern Brazil. Both the method proposed and the areas with rare and restricted fish species identified may be used to support systematic conservation planning and to delimit new priority areas for conservation.

     

Modelling the potential distribution of two tropical freshwater fish species under climate change scenarios

1. Climate change is causing shifts in the distribution patterns of freshwater fish at various spatio-temporal scales. Tropical freshwater fish are vulnerable, especially in areas where a high impact of climate change is predicted; thus, there is an increasing need to predict these shifts to determine conservation and adaptation strategies.
2. Ecological niche models offer a reliable way to predict the effects of climate change on species distribution. Potential shifts in the distribution of tropical fish were tested under two scenarios (4.5 – moderate and 8.5 – extreme) with three general circulation models for years 2050 and 2070 using maximum entropy software using as models two predatory species – the tropical gar Atractosteus tropicus and the giant cichlid Petenia splendida.
3. The potential distribution of both species was associated with warm and humid–sub-humid conditions. Future projections showed a higher availability of suitable areas for both species resulting from the expansion of warmer conditions in the middle and upper basins of the Central American mountain range and centre of the Yucatan Peninsula.
4. Ecological niche models of keystone or umbrella species such as A. tropicus and P. splendida could be useful to support conservation plans of protected areas. The potential distribution of both species covers areas of high suitability including six important biosphere reserves in Mexico, three protected areas in Guatemala and part of the Mesoamerican biological corridor.
5. Despite the potential expansion of the present distribution range suggested by the models, it is important to consider the biological and ecological requirements of the species and the ecological implications of these potential shifts in distribution. Both scenarios could have several implications at genetic, population, and ecosystem levels.

     

Improving the detection of rare native fish species in environmental DNA metabarcoding surveys

1. The presence of threatened or endangered species often strongly influences management and conservation decisions. Within the Murray–Darling Basin (MDB), Australia, the presence of threatened native fish affects the management and allocation of water resources. In New South Wales, these decisions are currently based on traditional fisheries data and a predictive MaxEnt model. However, it is important to verify the model's predictive power given the implication it may have, but this requires methods with a high detection sensitivity for rare species.
2. Although the use of environmental DNA (eDNA) monitoring, in particular eDNA metabarcoding, achieves a higher detection sensitivity compared with traditional methods, earlier surveys in the MDB have shown that the highly abundant and invasive common carp (Cyprinus carpio) can reduce detection probabilities for rare species. Consequently, a polymerase chain reaction (PCR) blocking primer designed to block the amplification of carp eDNA could increase the detection probabilities for rare native species while simultaneously reducing the required sampling effort and survey costs. Although PCR blocking primers are often used in ancient DNA and dietary studies, no aquatic eDNA metabarcoding study to date has evaluated the potential benefits of using PCR blocking primers.
3. A laboratory and field-based pilot study was used to address this knowledge gap and assess the impact of a blocking primer, targeting cyprinid fishes (including carp), on the detection probabilities of native species and the minimum sampling effort required.
4. Results showed that the inclusion of the blocking primer increased the detection probabilities for native species by 10–20% and reduced the minimum required sampling effort by 25–50%. These findings provide important insights into possible methods for optimizing eDNA metabarcoding surveys for the detection of rare aquatic species.

     

Historical distribution of freshwater fishes and the reference conditions concept in a large Mediterranean basin

1. The European Water Framework Directive 2000/60/EC (WFD) defines the ecological status of aquatic systems as the deviation between their present biological state and that which would be expected in the absence of any major human disturbance, referred to by the WFD as the ‘reference condition’ (RC). It assumes that their biotic composition should remain balanced and constant over time. This study tested both assumptions against an analysis of the historical distribution of the fish fauna in a large and highly disturbed Mediterranean basin. If fish communities change substantially over time, it will mean that the validity of the RC concept comes into question.
2. Using presence/absence data for historical native fish fauna from the Guadalquivir Basin, distribution changes among sub-basins were quantified by mapping between the nineteenth century and today.
3. The range of two native species (Anguilla anguilla and Salmo trutta) has changed significantly. In addition, the diadromous species assemblage has almost become locally extinct, with the exception of the eel. Finally, most Guadalquivir sub-basins (94.7%) have suffered major changes in the composition of their fish communities, either by losing native species or by adding new non-native species.
4. These results render the definition of any RC unlikely. In Mediterranean areas, the WFD objective of ‘good ecological status’ recovery based on the integrity of aquatic communities is a theoretical rather than a real goal. Nonetheless, the WFD provides an ecological guiding principle that can also be transferred to the conservation of freshwater ecosystems.
5. As an alternative to the RC concept in Mediterranean lotic ecosystems, specific multimetric indices can be used, based on expert criteria, the metrics of which can also relate to the conservation value of water bodies, and not only to their ecological status.

     

Interspecific competition between the round goby,Neogobius melanostomus,and the logperch,Percina caprodes,in the Duluth‐Superior Harbour

The Laurentian Great Lakes have been the site of numerous aquatic invasive species such as the sea lamprey, zebra mussel and round goby. To further understand interactions between invasive and native species in situ, competitive interactions between native logperch (Percina caprodes) and invasive round goby (Neogobius melanostomus) were examined using submerged enclosures in the Duluth‐Superior Harbour. Experiments were conducted on rocky or sandy substrate throughout the spring and summer months. Trials consisted of single fish, paired conspecifics or round goby/logperch pairs with weight change determined after 28 days. The round gobies were able to outcompete and/or negatively affect logperch on rocky substrates as a direct result of round goby/logperch interactions, as logperch fared well when round gobies were excluded from the enclosures. Although there is evidence that round gobies exclude logperch from rocky substrates, the logperch population remains close to pre‐invasion levels in the predominantly soft‐bottomed harbour. The continued coexistence of the logperch with the round goby is attributed to the vastly greater area of soft‐bottom vs. rocky substrate in the harbour, with the round gobies in the soft bottom younger and smaller than those in the rocky substrate. Recent evidence suggests that the round goby population is declining on the soft substrates indicating that the two populations will continue to coexist in the harbour.     

Recreational angling markets to advance the conservation of a reach of the Western Ramganga River,India

• 1. Mahseer fishes of the genus Tor are ‘iconic species’ in Indian rivers, representing ‘flagship’ species for conservation purposes but with additional exploitable, cultural and economic values. Conservation action is required to address their vulnerability to numerous pressures on multiple habitats, and connections between them, across the extended aquatic ecosystems supporting different life stages.
• 2. Recreational angling for mahseer, along with associated wildlife and cultural tourism, is a growth industry dependent upon healthy river ecosystems.
• 3. A cyclic, ecosystem‐based model in which local people can benefit economically from sustainable mahseer exploitation through catch‐and‐release fisheries can form a basis for conservation of both mahseer and the wider river ecosystem.
• 4. Experience on the Western Ramganga River in the vicinity of the town of Bikhyasen, Uttarakhand State (in the Himalayas in northern India), demonstrates the importance of involving local people in the benefits associated with angling, wildlife and cultural tourism. This creates local incentives for river protection, and may be the most effective means for preventing destructive over‐exploitation in poor rural communities.
• 5. Recognition of this value and its recirculation to local people can form the basis for a ‘paying for ecosystems services’ (PES) market. This will benefit river ecosystems, local people, tour operators and visiting anglers, provided that local people benefit to a greater extent than through the killing of fish for non‐renewable consumption or sale.
• 6. This is the basis for a potentially transferable model which may support regional development through involving local people in markets for iconic species. Copyright © 2010 John Wiley & Sons, Ltd.

     

The role of anglers' perceptions and habits in biological invasions: perspectives from the Iberian Peninsula

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Angling for endangered fish: conservation problem or conservation action?

Recreational angling has been implicated in population declines of some marine and freshwater fish, but this activity is rarely considered as a threat or even halted when endangered species are targeted. Indeed, in some cases, anglers are drawn to fish for rare or endangered species. Conservation‐oriented behaviours such as catch‐and‐release are often practiced voluntarily due to the ethics of anglers, yet even in these cases, some fishing mortality occurs. Nonetheless, there are many indirect conservation benefits associated with recreational angling. Here, we present a series of case‐studies and consider whether catch‐and‐release angling for endangered fish is a conservation problem or a conservation action. If recreational angling activities contribute to population‐level consequences that are contrary to recovery strategies, then angling for endangered species would seem to be a poor option. However, as revealed by several case‐studies, there is much evidence that anglers are vocal and effective proponents of fish and habitat conservation, and for endangered species, they are often the only voice when other stakeholders are not engaged. Anglers may contribute directly to conservation actions via user fees (e.g. licences), philanthropic donations or by volunteering in research, education and restoration activities. However, it is important to quantify post‐release mortality as well as understand the full suite of factors influencing a given population or species to know the potential risks. A risk assessment approach outlined in the paper may be used by managers to determine when the benefits of angling for endangered species outweigh the risks.