Human-induced changes in the composition of fish communities in the African Great Lakes

Summary Large natural African lakes contain unique and diverse fish faunas which have evolved within each lake in a comparatively short period of time. members of the family Cichlidae are particularly diverse, although there is strong evidence to show that the haplochromines in Lake Victoria, and possibly Lake Malawi, are monophyletic. The unique faunas in Lakes Victoria and Kyoga have been subject to perturbations from the introduction of exotic fish, and the faunas in these and other lakes have been disturbed by fishing activities and other human endeavours.Factors governing the establishment of exotic species are not clearly understood. The exotic fish must be physiologically adapted to their new environment, able to compete successfully both for habitat and for food at each stage of their life history, able to avoid predation and must have a suitable reproductive potential. Although about 50 species of fish have been introduced into African inland waters, including reservoirs, only comparatively few, in particular Nile perch (Lates niloticus), various cichlids (especially tilapias) and clupeids (Limnothrissa miodon), have been successful in establishing themselves. Those that have become established have had obvious but unquantifiable impacts on the indigenous faunas.It is difficult to differentiate between the effects of fishing and of the presence of alien fish on the fish species composition of the lakes (Witte et al., 1992). Many of the lakes were overfished before introductions were made, with a resultant decline in some species, especially the larger ones, and the virtual disappearance of others. Some lake fish faunas, such as those of Lakes Kyoga and Victoria, which have been subjected to the perturbations described above, continue to change rapidly (Ogutu-Owayo, 1990b).There is a fundamental need to collect biological information on the fish communities of African lakes for effective management, resulting not only in the conservation of unique fish faunas but also the production of sustainable fish yields for the people relying on this source of protein. This information is required before any more introductions of exotic fish are made.     

Species diversity in native fish community in Japan: comparison between non-invaded and invaded ponds by exotic fish

The relationship between invasions by two exotic fishes (Micropterus salmoides and Lepomis macrochirus) and species diversity in native fish communities was studied in 14 Japanese farm ponds. We found that mean number of species in native fish communities was three times higher in the ponds without the exotic fish than in the ponds with them. Further, negative relationships were observed between abundance of the two exotic fish and the total abundance of native fish communities. Our results suggest that invasions by the two exotic fish caused serious depletion of native fish communities, although another process can also be considered , that is, that ponds with poor native fish communities were prone to colonization by these exotic fish.     

Freshwater fish biodiversity in the River Ganga (India): changing pattern, threats and conservation perspectives

The river Ganges is the largest river in India and the fifth longest in the world. Although, many studies on fish ecology and systematic have been conducted largely to improve fisheries but fish diversity and their distribution pattern from conservation point of view have never been adequately addressed in the Ganges. In this connection, current distribution and abundance of freshwater fishes of river Ganges was studied and assessed from April 2007 to March 2009. We documented and described 143 freshwater fish species in the all stretches of the river which is higher than what was reported earlier. Some species were observed with shift in their distribution ranges. First time, a total of 10 exotic fishes, including Pterygoplichthys anisitsi, which has never been reported from India found in the Ganges. Alterations of the hydrological pattern due to various types of hydro projects was seems to be the largest threat to fishes of Ganges. Indiscriminate and illegal fishing, pollution, water abstraction, siltation and invasion of exotic species are also threatening the fish diversity in the Ganges and as many as 29 species are listed under threatened category. The study advocates a need to identify critical fish habitats in the Ganga basin to declare them as conservation reserves to mitigate the loss of fish diversity from this mighty large river.     

Plectorhinchus macrolepis (Actinopterygii: Haemulidae) in the western Atlantic Ocean

Morphometric measurements, meristic counts and DNA barcoding identified the presence of a biglip grunt Plectorhinchus macrolepis in the western Atlantic Ocean. As the species is endemic to the tropical eastern Atlantic Ocean and has not previously been reported in the western Atlantic Ocean, we discuss the possible means by which it might have dispersed to the western Atlantic Ocean. Even though this species is not considered established in Paranaguá Bay, we advocate monitoring of possible new individuals and other exotic fish species.     

Early life stages of exotic gobiids as new hosts for unionid glochidia

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Temporal and spatial macrofaunal community changes along a salinity gradient in seagrass meadows of Akkeshi-ko estuary and Akkeshi Bay,northern Japan

Changes in water clarity (secchi disc transparency) in relation to the presence/absence of introduced, exotic fish, including rudd (Scardinius erythrophthalmus), tench (Tinca tinca), perch (Perca fluviatilis), brown bullhead catfish (Ameiurus nebulosus), goldfish (Carassius auratus), and koi carp (Cyprinus carpio) were determined for 49 small, North Island, New Zealand lakes. There was a negative association between water clarity and the presence of exotic fish independent of lake depth. Moreover, a ‘before-and-after’ comparison and examination of case-studies indicated that introductions of exotic fish reduce water clarity. The number of species introduced affected the relationship between lake depth and water clarity but the specific role of each species could not be distinguished because most of the lakes (83%) contained more than one exotic fish species. A model incorporating the known mechanisms by which planktivorous, benthivorous and herbivorous fish can influence water clarity in lakes showed that control over just one species or feeding guild may not result in an improvement in water clarity because of the additive and synergistic effects of different species on lake trophic processes. Handling editor J. Cambray     

Alien fish species in Indian inland wetlands: current status and future challenges

Although wetlands are well-recognized for their biological, ecological, cultural, hydrological, recreational, socio-economic and educational values, still they are facing severe anthropogenic pressure in the form of habitat destruction, pollution, overexploitation of resources and the invasion of alien species. India is bestowed with several natural and man-made wetlands which support rich aquatic biodiversity with high degree of endemism, especially fish diversity. Zoological Survey of India reported that, inland wetlands alone support 1027 species of fishes with more biological, nutritional and economic values. However, for the past three centuries Indian wetlands are witnessing continuous introduction of exotic fishes. According to available reports, 31 aquaculture species, 600 ornamental varieties and 2 species of larvicidal fish have been introduced. Surfacing reports confirmed that among the introduced fishes nearly 55 fish species established a sustainable reproductive population in several inland wetlands (i.e. wild) including in the biodiversity hotspots. Among the 55 the National Biodiversity Authority of India has declared 14 species as invasive. Though, there are no comprehensive studies available in India about the impacts of invasive alien species on its ecosystem and food security. In addition, researchers are of the opinion that the ongoing climate change, river linking projects, Genetically Improved Farmed Tilapia (GIFT) project and ornamental trade will exacerbate the invasive issues in future. India is thus in a position to develop new robust policy and research guidelines on the exotic species issues. Cooperation among different stakeholders and common public is the need of the hour, else India will lose its unique aquatic diversity and also face huge socio-economic problems.

     

澜沧江西双版纳段鱼类组成和物种多样性

根据2018-2020年澜沧江西双版纳段5次鱼类资源调查数据,结合相关文献资料,对该流域鱼类组成及物种多样性进行了分析。结果显示：澜沧江西双版纳段此次共调查到鱼类119种,隶属于11目28科79属,而历史记录鱼类共179种,隶属于12目34科106属。随着调查的不断深入,土著鱼类种数逐渐增多,但占比却逐渐下降,外来鱼类种数逐渐增多,占比也逐渐升高;本次调查到土著鱼类92种,占鱼类种数的77.31%,占比进一步下降;外来鱼类27种,占鱼类种数的22.69%,占比进一步升高。该区域鱼类优势种为云南吻孔鲃Poropuntius huangchuchieni和少鳞舟齿鱼Scaphiodonichthys acanthopterus,常见种为长臀鲃Mystacoleucus marginatus和宽额鳢Channa gachua。有《国家重点保护野生动物名录》（2021年）鱼类5种,《中国生物多样性红色名录脊椎动物卷》（2015年）受威胁鱼类8种。相对于我国其他江河,澜沧江西双版纳段有极高水平的鱼类物种多样性,其中澜沧江干流鱼类物种多样性相对于左、右岸支流较低,左岸支流鱼类多样性高于右岸,罗梭江鱼类多样性高于其他一级支流。虽然澜沧江西双版纳段鱼类物种多样性维持在较高水平,但土著鱼类占比下降趋势明显,仍面临着严重威胁,本文分析了受威胁因素,并提出了保护建议。     

Tilapia (Teleostei: Cichlidae) status in Nicaraguan natural waters

We surveyed the watersheds covering more than 80% of the surface area of Nicaragua, and review the history of deliberate introductions and unintentional invasion of tilapias, Oreochromis spp., into the freshwater of Nicaragua. The species have become widely established, with a range of negative consequences for the rich natural fish fauna of this Central American country. Tilapias compete directly with native cichlids in a number of ways, and have also supplanted native species as food fish in local markets. We suggest that introduced tilapias may have been responsible for the outbreak of blindness in native cichlids. We make recommendations on the management of these exotic species and on further introductions. An erratum to this article can be found at     

Not all lineages are equally invasive: genetic origin and life-history in Atlantic salmon and brown trout acclimated to the Southern Hemisphere

Salmonids are fish from the Northern Hemisphere which have been introduced and acclimated to many regions in the Southern Hemisphere for commercial (aquaculture) and recreational (sport fishing) purposes. In some cases a species like brown trout Salmo trutta rapidly spread across the host ecosystem and became invasive, threatening local fauna, and even outcompeting other exotic fish. We have analyzed life-history traits in combination with genetic variation of Atlantic salmon and brown trout adapted to the lake systems of the Argentinean Patagonia (South America). We have identified two main characteristics that conferred invasive capacity to those exotic species: undomesticated status and lifelong growth. Stocks originated from wild populations adapted better than long-term domestic lineages, and their geographic origin seems to be less important for adaptation to exotic environments. We propose that considering these characteristics in future planning of commercial aquaculture projects by selecting non-invasive lineages will minimise the impact of accidental escapes.     

Non-native fish species in Slovak waters: origins and present status

Freshwater fishes recorded in the territory of Slovakia include 95 fish species. As many as one third of these are allochthonous fish species belonging to 14 families, among which several have not occurred in Slovakia recently. Historically, there were three main periods of introduction: the first is the beginning of the 20^th century, the second includes two decades between 1955 and 1975 and the third period is from the year 1990 up to the present time. The origins of the exotic species seen in Slovakia are the four continents — Africa (3), North America (7), Central America (3), and Asia (13) and ten of them are from different regions in Europe. The purpose of intentional introductions of non-native species was to occupy vacant ecological niches in the ecosystems reshaped by human activities, fish stocking, angling or fish farming. Some of these species spread from their original ranges or they penetrated spontaneously from the adjacent countries via the river network system. At the present time, 76 fish species in total form populations in Slovakia. There are 54 autochthonous and 22 allochthonous species, 14 of them are exotic fishes. The invasive characters in 13 fish species were considered, the recent native/total fish ratio is 0.71.     

A comparison of passage efficiency for native and exotic fish species over an artificial baffled ramp

This study used an experimental approach to compare the passage success of native and exotic fish species from the temperate Southern Hemisphere over an artificial baffled fish ramp designed for overcoming low-head (≤1.0 m) fish migration barriers. Passage efficiency was, on average, lower for the exotic species [koi carp (Cyprinus carpio), rudd (Scardinius erythrophthalmus) and rainbow trout (Oncorhynchus mykiss)] compared to the native species [inanga (Galaxias maculatus), redfin bully (Gobiomorphus huttoni) and common bully (Gobiomorphus cotidianus)]. Nonetheless, there was considerable variation between individual species, with rainbow trout outperforming common bully and juvenile inanga, but koi carp and rudd failing to pass any of the ramps. The differences in predicted probability of passage success between the native and exotic fish species in this study were sufficient in some cases to indicate the potential for the baffled fish ramps to operate as a selective migration barrier. Nonetheless, further testing is required to validate these results across a broader range of conditions before deployment.     

Measuring ecosystem degradation through half a century of fish species introductions and extirpations in a large isolated lake

The introduction of exotic species and the extirpation of native species that occurred during the past two centuries have strongly modified the structure of most plant and animal assemblages across the globe. Such a biotic change is particularly marked in isolated environments such as islands or isolated lakes. Most studies reported drastic changes between before and after human disturbances, but the dynamics of change in assemblage structure through the invasion and extirpation processes are rarely reported. Here we measured the aquatic ecosystem degradation through exotic species introduction and native species extirpation experienced by Lake Erhai (China) during the last 50 years using structural, functional and taxonomic distinctness biodiversity indices. Structural diversity (species richness) did not varied monotonically along the temporal gradient, due to an opposite trend between exotic species increase and a concomitant decline of native species richness. Functional diversity displayed unclear ascending trends driven by the introduction of exotic species having distinct functional traits than natives. Taxonomic distinctness indices exhibited an increase of the average taxonomic distinctness (Δ⁺), but a decrease of the variation in taxonomic distinctness (Λ⁺) through time. Structural, functional and distinctness indices providing complementary information on ecosystem degradation, we here proposed a new multifaceted degradation index integrating these three facets of biodiversity. Such an index provided an accurate representation of the faunistic changes experienced by Lake Erhai and might constitute a comprehensive way to measure ecosystem degradation through exotic fish species introductions and native fish species extirpations.     

Patterns in the distribution of fish assemblages in Río Amacuzac,Mexico: influence of abiotic factors and biotic factors

Patterns in spatial and seasonal distribution of fish communities were analyzed in the Río Amacuzac, Mexico, and their relationship to environmental variables and habitat characteristics. The PCA biplot of the study sites and environmental factors showed the first two axes accounting for 52.93% of the variance. The diagram showed the study sites ordination in environmental gradients. The first axis explained variables related to habitat characteristics and temperature (36.30%) and second axis arranged the sites in physicochemical and water quality environmental gradients (conductivity, dissolved oxygen, orthophosphates, ammonium, pH) displaying seasonal variation. Fifteen species were recorded, eight of them are exotic. One new record appeared for the Río Amacuzac: Pterygoplichthys disjunctivus is exotic. Study sites with highest species richness were: 5, 7 and 9 (twelve species each one); while the study sites with low species richness were 1, 2, 3 and 6 (eight species each one). Six of the species were distributed throughout the whole river. Based on the composition of the fish fauna, the study sites form two groups and the analysis of fish species displays three groups according to the Bray–Curtis index. The diagram of the canonical correspondence analysis relates environmental parameters to the abundance of fish species and showed that the first two axes exhibit 78.31% of the explained variance. Species richness had a spatial pattern associated to the introduction of exotic species for ornamental uses. According to the results of the importance value index (IVI), the dominant species were the poecilids Poeciliopsis gracilis and Heterandria bimaculata, small fishes that were introduced in the river. Río Amacuzac has a biotic alteration in the structure of fish communities due to the invasion of exotic species, representing risks to the integrity of the native fish fauna.     

Do Exotics Homogenize or Differentiate Communities? Roles of Sampling and Exotic Species Richness

It is commonly asserted that exotic species promote the homogenization of biological communities. However, theoretical evidence implies that exotic species may often have the opposite effect, of differentiating biological communities where different exotic species become established in different areas. Furthermore, few empirical studies have directly measured the homogenizing effects of exotics. In this study, I used the plant inventories of 20 localities in the United States to measure whether exotic plant increased the similarity of those localities. I calculated Jaccard's index of similarity (JI) for exotic species and then for native species to see if the exotic JI was consistently higher when comparing two localities. I found that JI for both exotic and native species decline exponentially with increasing distance and latitude separation between localities so that localities that share many native species also tend to share many exotic species. More importantly, in nearly half of the pairwise locality comparisons (87 of 190), the (JI_exotic/JI_native) ratio is less than one, indicating a slight tendency for exotic species to differentiate rather than homogenize the localities analyzed. Also, the pattern of differentiation versus homogenization is strongly related to exotic species richness. When both localities have relatively few exotics, there is a clear tendency for exotics to produce biotic differentiation (JI_exotic/JI_native < 1). Much of this pattern seems related to the right-skewed frequency distribution of the geographic ranges of exotic species. As with native species, most exotics occur in few localities so there is a high probability that localities with low numbers of exotic species will share very few, if any, of those exotics. As exotic richness increases, the homogenizing effects become increasingly pronounced.     

Non‐lethal predator effects on the performance of a native and an exotic crayfish species

1. I tested the hypothesis that the potential for non‐lethal effects of predators are more important for overall performance of the fast‐growing exotic signal crayfish (Pacifastacus leniusculus Dana) than for the slower growing native noble crayfish (Astacus astacus L.). I further tested if omnivorous crayfish switched to feed on less risky food sources in the presence of predators, a behaviour that could reduce the feeding costs associated with predator avoidance. 2. In a 2 month long outdoor pool experiment, I measured behaviour, survival, cheliped loss, growth, and food consumption in juvenile noble or signal crayfish in pools with either a caged predatory dragonfly larvae (Aeshna sp.), a planktivorous fish that do not feed on crayfish (sunbleak, Leucaspius delineatus Heckel), or predator‐free controls. Crayfish had access to multiple food sources: live zooplankton, detritus and periphyton. Frozen chironomid larvae were also supplied ad libitum outside crayfish refuges, simulating food in a risky habitat. 3. Crayfish were mainly active during hours of darkness, with signal crayfish spending significantly more time outside refuges than noble crayfish. The proportion of crayfish outside refuges varied between crayfish species, time and predator treatment, with signal crayfish spending more time in refuges at night in the presence of fish. 4. Survival in noble crayfish was higher than in signal crayfish, and signal crayfish had a higher frequency of lost chelipeds, indicating a high level of intraspecific interactions. Crayfish survival was not affected by the presence of predators. 5. Gut‐contents analysis and stable isotope values of carbon (δ¹³C) and nitrogen (δ¹⁵N) indicated that the two crayfish species had similar food preferences, and that crayfish received most of their energy from feeding on invertebrates (e.g. chironomid larvae), although detritus was the most frequent food item in their guts. Signal crayfish guts were more full than those of noble crayfish, but signal crayfish in pools with fish contained significantly less food and fewer had consumed chironomids compared with predator‐free controls. Length increase of signal crayfish (35%) was significantly higher than of noble crayfish (20%), but signal crayfish in pools with fish grew less than in control pools. 6. This short‐term study indicates that fish species that do not pose a lethal threat to an organism may indirectly cause reductions in growth by affecting behaviour and feeding. This may occur even though prey are omnivorous and have access to and consume multiple food sources. These non‐lethal effects of predators are expected to be particularly important in exotic crayfish species that show a general response to fish, have high individual growth rates, and when their feeding on the most profitable food source is reduced.     

Length–weight and length–length relationships for common fish and crayfish species in the Everglades,Florida, USA

Length–weight and length–length relationships are reported for 18 species of fish and two species of crayfish within the Everglades, FL, USA. This study provides updated relationships for native species, as well as initial relationships for established exotic species in this region. Additionally, 14 length–weight and two length–length relationships are presented to FishBase for the first time.     

Size of the local species pool determines invasibility of a C4-dominated grassland

The size of the local species pool (i.e., species surrounding a community capable of dispersal into that community) and other dispersal limitations strongly influence native plant community composition. However, the role that the local species pool plays in determining the invasibility of communities by exotic plants remains to be evaluated. We hypothesized that the richness and abundance of exotic species would be greater in C4‐dominated grassland communities if the local species pool included a larger proportion of exotic species. We also predicted that an increase in the exotic species pool would increase the invasibility of sites thought to be resistant to invasion (annually burned grassland). To test these hypotheses, study plots were established within two long‐term (>20 yr) fire experiments at a tallgrass prairie preserve in NE Kansas (USA). Study plots were surrounded by either a small pool of exotic species (small species pool (SSP) plots; six species) or a larger exotic species pool (large species pool (LSP) plots; 18 species). We found that richness and absolute cover of exotic species was significantly (P<0.001) lower (～70 and 90%, respectively) in annually burned compared to unburned plots, regardless of the size of the exotic species pool. As predicted, exotic species richness was higher (P<0.001) for LSP plots (3.9 per 250 m2) than for SSP plots (0.7 per 250 m2); however, absolute cover was unaffected by the size of the exotic species pool. In the absence of fire, plots with a LSP had four times as many exotic species than SSP plots. An increase in the local exotic species pool also increased the invasibility of annually burned grassland. Indeed, richness of exotic plant species in annually burned LSP plots did not differ from unburned plots with a SSP, indicating that a larger pool of exotic species countered the negative effects of fire. These findings have important implications for predicting how the invasion of plant communities may respond to human‐induced global changes, such as habitat fragmentation. Community characteristics or factors such as frequent fires in grasslands may impart resistance to invasions by exotic species in large, intact ecosystems. However, when a large pool of exotic species is present, frequent fire may not be sufficient to limit the invasions of exotic plants in fragmented landscapes.     

The alien flora of Europe: a taxonomic and biogeographic review

Abstract. A geographic and taxonomic overview of the non-indigenous plant species of Europe, based on the ‘Flora Europaea’ is given. The flora of Europe includes 1568 species which have either expanded their ranges within Europe under human influence (naturalized European species) or are of non-European origin (exotic species). The latter group consists of 580 species (37%) which form a diverse group in terms of their taxonomic composition and geographic origin. The exotics are represented by 113 families, of which the Compositae, Rosaceae and Gramineae are most important. The ratio of species to families is low. Most exotic species in Europe originate from the Americas and Asia. Countries of southern Europe have a higher relative number of exotics in their non-native flora than northern ones. The species-range size distribution differs between naturalized European and exotic species; the latter are on average more widespread than the naturalized.