Exotic Fish Research Articles

Alien fish species in open waters of India: Appearance, establishment and impacts

The diverse germplasms pool already available in the vast and varied water resources of India has potential to cater to the need of the fisheries and aquaculture sector, but introduction of fish species for different purposes is still continuing. The exotic fishes introduced into India for different purposes covers nearly 13.6% of total fish diversity. Due to wider tolerance limit and generalist nature, some alien fish species have acclimatised to diverse eco-climatic conditions. Some of these introduced fishes are now established in the open water bodies including rivers, wetlands and reservoirs and some others are in the process of establishment. Degraded open waters and wanton destruction of fishery resources in the rivers have resulted in depletion of the sensitive fish species and appearance of exotic fishes. The potential risk areas for appearance of the alien species are mushrooming fish culture units in different parts of the country, porous boundaries, farming of alien fishes in flood prone areas, rapid expansion of aquaculture and ornamental fish trade. Eradication of an introduced species is usually difficult or impossible once it is established in open water bodies. Therefore, there is an urgent need to regulate the import of alien fish species, based on their merit and likely impacts on open waters.

​A Study on Fish Diversity, Marketing and Economics in Fish Markets at Kharagpur, West Bengal, India

Background: There is no previous published record regarding different fish species found in fish markets of Kharagpur town. The place is internationally renowned due to first Institute of Technology of India. Due to largest railway establishment in Kharagpur town, an influx of population is always here from different states. As such their food preference and cultural practice is different. Present survey is relevant to depicts fish preference of the town dwellers and socio-economic status of market associated people. Methods: The study have been conducted from November 2018 to January 2020 thoroughly from 13 fish markets of Kharagpur town, West Bengal, India. Fish specimens collected, identified and preserved. Market related data have been collected from different agents, wholesaler etc. through questionnaire interviews. Result: During the study period it has been observed that 28 freshwater inland fish species; 6 freshwater exotic fish species; 19 marine fish species and 4 crustacean species are available in the Kharagpur town. Some marine molluscs like Loligo sp and Sepia sp are also sold here. There are different peoples, those belong from different districts of West Bengal and involved in fish marketing activities. Therefore, a marketing chain is being established which is interdependent to each other with a socio-economic framework. Some measures have been highlighted towards improvement of infrastructure, hygienic conditions.

Amphibian occurrence and abundance patterns across a modified floodplain ecosystem

AbstractAmphibian populations have experienced unprecedented decline over the past few decades. River regulation, water diversions and reductions in the frequency of reconnections between rivers and floodplains have contributed to decreased floodplain inundation and overall wetland degradation, contributing to regional declines in amphibians. Hydrological modifications coupled with invasive exotic fish also have had a significant impact on inland floodplain frog communities. Using an eight‐year study of 21 wetlands across a nationally important inland floodplain system, we quantified occurrence and abundance patterns in six frog species (adults and tadpoles) to a range of landscape‐scale and site‐scale hydrological and vegetation‐related variables. Occurrence and abundance models for adult frogs and tadpoles were characterised by different suites of predictor variables and effect directions for each species. The occurrence of some frog species, such as the inland banjo frog (Limnodynastes interioris), was negatively related to distance to the main river and area of inundation, whereas the abundance of most species was positively related to mean daily discharge. Tadpoles of species such as the plains froglet (Crinia parinsignifera) had contrasting relationships to introduced common carp (Cyprinus carpio) and eastern gambusia (Gambusia holbrooki). Our findings suggest factors that lead to a particular species occurring at a wetland may differ from those that make them abundant once conditions necessary for occurrence have been met. Thus, management interventions to improve amphibian diversity across inland floodplain systems will need to consider watering actions that benefit a range of frog species, particularly endangered species, across their developmental stages.

Do exotic poeciliids affect the distribution or trophic niche of native fishes? Absence of evidence from Hong Kong streams

Abstract Exotic poeciliids have been reported to reduce abundance and richness of native fishes and, more generally, constrain the trophic niches of native counterparts. However, understanding of the consequences of poeciliids on native fishes in tropical streams is limited. We conducted a survey of lowland streams in Hong Kong during 2018–19 to document the prevalence of poeciliids and look for signs that they had affected the distribution of native fishes. Overall, 31 native and 15 exotic fishes were recorded during the survey. Exotics occurred at 37 out of 45 survey sites, with poeciliids present at 35 sites. Richness of poeciliids or other exotic fishes had no correlation with the number of native species at each site. Moreover, native fish assemblages appeared unaffected by poeciliids, which might reflect a legacy of stream pollution. By comparing nine streams where the presence and composition of poeciliids varied, we investigated whether the mosquitofish (Gambusia affinis) alone, and in combination with the guppy (Poecilia reticulata), swordtail (Xiphophorus hellerii), and variable platy (Xiphophorus variatus), affected the trophic niche of native half‐banded barb (Puntius semifasciolatus: Cyprinidae) which has a similar body size to the poeciliids, as quantified by gut content and stable‐isotope analysis. We also tested whether the trophic niche of the mosquitofish was affected by the three other poeciliids. Gut‐content analysis indicated that the half‐handed barb fed on aquatic invertebrates, while the mosquitofish ate mainly terrestrial insects. The three other poeciliids were predominately primary consumers. The mosquitofish, alone or in combination with other poeciliids, had no detectable effects on the dietary or isotopic niche of the barb, nor was the niche of the mosquitofish influenced by the presence of other poeciliids. Limited dietary overlap and differences in microhabitat use were likely to account for the absence of a detectable niche shift by the barb where poeciliids were present.

Ecosystem vulnerability of floodplain wetlands of the Lower Brahmaputra Valley to climatic and anthropogenic factors

Abstract This study assessed the vulnerability of 16 floodplain wetlands (beels) of the Lower Brahmaputra Valley, Assam, India, in relation to a range of natural and anthropogenic factors including climate change. The total water-spread area of the selected beels varied widely (8–50 ha), with 68.75% of the beels showing a reduction in water-spread area over the past 30 years. High levels of siltation and encroachment and detachment of marginal areas through the construction of roads were the major factors responsible for the reduction in the water-spread area of the beels. The reduction was observed to be in the range of over 33% in three beels (Raghunath Sora, Chulkani, and Dudua beel) to 83% in Bhoishpuri beel. In addition, one beel (Chulkani) experienced reduction in its deep pool area, which is an important wetland area that provides shelter to brood fishes during the dry season. Only 12.5% of the beels studied practiced enclosure (pen) culture for rearing fish. None practiced cage culture. Our study showed that only two beels (Bhoishpuri and Tariachora) were free from exotic fishes; the remaining surveyed beels reported exotic species such as, Cyprinus carpio (Common Carp), Ctenopharyngodon idella (Grass Carp), Hypophthalmichthys molitrix (Silver Carp), H. nobilis (Bighead Carp) and Piaractus brachypomus (Pacu). The prevalence of exotic fishes in the majority of the beels (due both to escape from nearby aquaculture ponds during floods and intentional stocking in certain beels) would have adversely affected the diversity of indigenous fishes in those wetlands. From discussion with the fishers, 50% of the beels surveyed experienced a reduction in the number of fish species from that recorded 10–20 years ago. In addition to climate change-related factors (e.g. abnormal rains, floods, or drought-like situations), other factors – both natural (e.g. hyper-nutrification) and anthropogenic (e.g. construction of roads, houses, and other structures) – also adversely affected the studied wetlands. To help cope with these factors and increase the adaptive capacity of fishers, four measures aimed at mitigation are suggested. These are: the practice of enclosure aquaculture in beels; the construction of floating macrophyte refuges (katal); deep pool refuges; and stock enhancement programmes with climate-resilient indigenous fishes.

Evaluation of toxicity of cryoprotectant to the sperm of mohashol fish, Tor tor (Hamilton) at various concentrations of the salt solution

Cryogenic gene banking is a prime necessity for conserving the genetic constitutes of vulnerable, endangered and critically endangered native and exotic fish species. Cryogenic freezing of fish gametes is the first step to develop such a gene bank. In the study, attempts have been taken to develop a cryogenic freezing protocol of spermatozoa of Mohashol, Tor tor as it is considered as a critically endangered fish species by IUCN. Juvenile and brood fish of Tor tor were collected from the Someshwari River of Netrokona district and domesticated in captive condition at Bangladesh Agricultural University campus. During breeding season, sperms were collected from hormone induced males by stripping. The milt was very sticky. The concentration of sperm was 4.47x1010 cells per ml and pH was 8.6±0.5. To evaluate the toxicity of cryoprotectant, sperm was incubated with DMSO and methanol at 5, 10 and 15% concentrations for a period of 5 to 55 min. The motility of sperm decreased with the increase of cryoprotectant concentration (5, 10 and 15%) and 10% DMSO with Alsever’s solution could be the best combination for cryopreservation of T. tor. sperm at 10 min (83.0±2.74).

Production Trends, and Challenges for Biodiversity Conservation and Sustainable Fisheries Management of Kaptai Lake, the Largest Reservoir in Bangladesh

Kaptai Lake (KL), the largest artificial lake in Bangladesh, supports an important inland open water fishery. Nevertheless, detailed studies on its fish diversity and environmental threats are still limited. Hence, a study was conducted to evaluate the current fish management scenarios, fish production, relative abundance to improve the production and biodiversity of KL. Data were collected from stakeholders through personal observation, focus group discussions, and cross-check interviews from September 2018 to July 2019. The fish production of KL increased from 1,200 metric tons (MT) in 1965–1966 to 10,577 MT in 2018–2019. The output of the lake was dominated by small fish remarkably, Gudusia chapra (Hamilton, 1822), Gonialosa manmina (Hamilton, 1822), and Corica soborna Hamilton, 1822, accounting for 64 % of the total production in 2018–2019. A total of seventy-six fish species were observed under ten orders, including seven exotic fish species. According to the IUCN Bangladesh, 14 % of total species were identified as vulnerable, 11 % as endangered, 3 % as critically endangered, 11 % as near threatened and 51 % as least concern. The study also identified that climate change and various human-driven causes threaten the fish production and biodiversity of this lake. These findings suggest that community-based fisheries management, protection of natural breeding grounds of carps, control of pollution, amendment of existing fishing laws, and collaborative research would be a necessary approach for mitigating the negative environmental impact of this lake. The overall practical knowledge of this investigation could assist in policymaking and further research.

Changes in an Exotic Fish Community Assemblage of a Thermal Spring in Central Idaho

Barney Hot Springs is a thermal spring in the headwaters of the Little Lost River drainage in central Idaho. Tropical fish have been released into Barney Hot Springs, and several species have established self-sustaining populations. The objectives of this study were to determine the current community assemblage of tropical fish in Barney Hot Springs and to assess species composition and extent of downstream distribution of tropical fish in Barney Creek. The composition in 2017 consisted of Amelanic Convict Cichlids Amatitlania nigrofasciata, Mozambique Tilapia Oreochromis mossambicus, Zebra Mbuna Maylandia zebra, and Green Swordtails Xiphophorus hellerii. Total abundance of all fish species was estimated at 12,043 fish (95% CI 9807–15,600), with Green Swordtails making up 68% of the population, Zebra Mbuna 20%, Convict Cichlids 9%, and Mozambique Tilapia 3%. In Barney Creek, fish were collected within 800 m of Barney Hot Springs. In March 2018, a rain-on-snow event occurred that resulted in a fish kill. In fall 2018 after this event, Convict Cichlids, Green Swordtails, and Goldfish Carassius auratus were collected. Overall abundance was estimated at 1972 fish (95% CI 1757–2227), with Green Swordtails and Goldfish each composing 50% of the population; no Convict Cichlids were recaptured, so abundance could not be estimated. In Barney Creek, fish were collected within 400 m of Barney Hot Springs. We documented current changes to the fish community assemblage of Barney Hot Springs and Barney Creek that were driven by colonization (i.e., introduction of aquarium fish) and by local extinction through species interactions and stochastic events. Currently, we do not know the impact that the introduced fish fauna of Barney Hot Springs may have on native species or ecosystem function.

Icthyofauna of Madhumati River at Mohammadpur, Magura

The investigation was conducted on the present situation of fish biodiversity and abundance of fish fauna at two different points of Madhumati River at Mohammadpur upazilla under Magura district from October 2018 to September 2019. A total of 83 species of fresh water fish species were recorded belonging to 58 genera of 28 families under 11 orders. Cypriniformes was recorded as the dominant order comprising 26 species constituting 31% of the total. According to IUCN 59% of fish species were Least Concern, 12% were Vulnerable, 11% were Endangered, 9% were Near Threatened, 1% of each were Data Deficient and Critically Endangered locally, and 7% Exotic fish species were also enlisted. Annual value of Shannon diversity index (H) was 1.974 and Sipmson diversity index (λ) was 0.272 which indicate highest diversity of fish was in March. Annual Margalef’s richness index (D) was 6.654 and Pielou’s evenness index (E) was 0.447 denote highest richness was in November and evenness was in March. The river was found to have moderate type of diversity in terms fish species composition. Bangladesh J. Zool. 49(1): 19-34, 2021

Rotenone for exotic trout eradication: nontarget impacts on aquatic communities in a mountain lake

Beaulieu J, Trépanier-Leroux D, Fischer JM, Olson MH, Thibodeau S, Humphries S, Fraser DJ, Derry AM. 2021. Rotenone for exotic trout eradication: nontarget impacts on aquatic communities in a mountain lake. Lake Reserv Manage. 37:323–338. Rotenone is widely used in lake and reservoir management for the eradication of exotic fish. However, nontarget effects of rotenone on freshwater organisms such as zooplankton and macroinvertebrates are of concern because of the ecological importance of these organisms in aquatic food webs as a resource base for fish, especially when rotenone is applied to lakes prior to native fish reintroduction. The objective of our study was to determine the effects of rotenone on nontarget zooplankton and macroinvertebrate species assemblages in a headwater mountain lake where rotenone was applied to remove exotic brook trout (Salvelinus fontinalis; Banff, AB Canada). We found strong negative rotenone impacts on the community structure and density of crustacean zooplankton, and to a lesser extent on macroinvertebrates, lasting for at least 1 yr after the rotenone treatment. Our study offers 2 unique insights that differentiate from rotenone studies on other lakes: (1) the persistent and almost complete eradication of crustacean zooplankton in the following summers, 11 months after rotenone treatment, and (2) a considerable shift in the macroinvertebrate community composition, likely resulting from combined effects of both nontarget rotenone effects on taxon density and trophic interactions associated with the eradication of brook trout from the lake. We advocate that assisted recolonization in the restoration of aquatic food webs could play an important role in facilitating nontarget aquatic community recovery following lake rotenone treatment.

Remazol reactive dye degrading Bacteria from freshwater fish of River Cauvery, Pallipalayam of Namakkal District, South India

BackgroundAzo dye effluents cause severe pollution problems in soil and water and affect their flora and fauna throughout the world. The combination of dye degrading bacteria in the gut of freshwater fish has been considered a prospective approach towards the development of a sustainable environment. In the southernmost part of India, especially in the Namakkal District of Tamil Nadu state, urbanization and industrial development lead to various environmental issues. In lieu, most of the earlier works were carried out on the bacterial dye degradation from soil and water sources, least concentration on the dye degradation from fish gut flora. The objective of this study was to analyze the role of dye degrading bacteria in the gut of freshwater fish collected from the study area.ResultsWe have studied the aerobic degradation of remazol yellow reactive dye by bacteria forming the gut flora of exotic fish Oreochromis mossambica from river Cauvery at Pallipalayam of Namakkal District, India. Eight dye degrading gut isolates viz. Pseudomonas sp. AD1, Bacillus sp. AD2, Staphylococcus sp. AD3, Staphylococcus AD4, Enterobacter sp. AD5, Escherichia coli AD6, Streptococcus sp. AD7 and Clostridium sp. AD8 were obtained capable of growing in azo dye incorporated in Basic mineral medium (BMM) medium. Optimization study was carried out for various parameters for the selected isolates. Based on the growth, maximum growth was seen in Pseudomonas sp. AD1 (in 0–24 h) and minimum in Escherichia coli.AD 6 (in 72–96 h). Pseudomonas sp. AD1, Enterobacter sp.AD5, and Bacillus sp. AD 2 exhibited efficient dye degradation during 0–96 h analysis which was confirmed by FTIR analysis. Loss of azo group stretch at 1572–76 cm−1 and 1429 cm−1 and presence of primary (–NH2–) and secondary amides (–NH2–), aliphatic –C–N– stretching and confirmed –C–S– stretching in FTIR analysis confirms the breaking down of the azo bond.ConclusionThis study showed that there is a platform for using the bacterial flora of fish gut that paves a prominent way in the degradation of Azo dye.

Rapid population increase of the threatened Australian amphibian Litoria aurea in response to wetlands constructed as a refuge from chytrid-induced disease and introduced fish

Amphibians have declined due to multiple impacts including invasive fish and the disease chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). Wetland restoration can be used to increase amphibian populations. However the design of created wetlands must account for threats such as Bd and introduced fish. There have been no attempts on a landscape level to manage these threats with habitat design. Here we monitored the green and golden bell frog (Litoria aurea) in 2.6 ha of constructed wetlands designed to enhance breeding and increase survival through passive mitigation of Bd and exotic fish. We compared the fecundity, adult population sizes, introduced fish occupancy, Bd prevalence and survival rates of frogs in created wetlands (CW) to three control sites to determine if and why the habitat design was successful. Monitoring involved weekly capture-recapture during the austral spring and summer for three L. aurea breeding seasons. We hypothesised that (1) if the CWs were successful in passively limiting fish colonisation, a larger number of breeding events would be detected compared to control sites which are known to be widely colonised by introduced fish. (2) If the wetlands were successful in passively mitigating Bd, then we would observe an equal or greater survival rate and equal to or lower Bd prevalence compared to control wetlands. We observed a 3.3-fold increase in adult population size in CW from season 1 to 2, and the population increased further in season 3.We found strong support for hypothesis (1) and weak support for (2). Based on these results, we conclude that this design was beneficial shortly after their formation primarily due to fish exclusion, but further study is required to determine if these benefits extend long-term. Future amphibian restoration studies are needed to improve the design of wetlands to enhance suppression of Bd.

David W. Schindler—Icon and Iconoclast

David W. Schindler—Icon and Iconoclast

A regional study of the zoonotic broad tapeworm Dibothriocephalus spp. in Northwestern Patagonia (Argentina): origin of fishes and coastal cities as factors affecting infection in fishes.

Diphyllobothriosis was first recorded in humans in Argentina in 1892 and in introduced salmonids in 1952. The aim of this work is to assess factors influencing the values of prevalence and abundance of plerocercoids in fishes that could increase the risk of transmission of Dibothriocephalus spp. in Andean Patagonian lakes. We analysed two key issues potentially related to the occurrence of tapeworms in fish: the presence of cities on coastlines (as potential sources of eggs to nearby lakes) and the difference between native and exotic fishes in susceptibility to infection. We investigated the probability of finding parasites in fish, the variation in parasite abundance in different environments and the relationship between host length and occurrence of plerocercoids. A total of 3226 fishes (belonging to six autochthonous and four introduced species) were analysed between 2010 and 2019 in eight environments. Plerocercoids were counted, and a subset was determined molecularly to species level. Two species, Dibothriocephalus latus and Dibothriocephalus dendriticus, were identified from both salmonids and native fishes, this being the first molecular confirmation of these tapeworm species parasitizing native South American fishes. Salmonids had higher levels of infection than native fishes, and these levels were higher in aquatic environments with a city on their coastline. Transmission to humans seems tooccur mainly through Oncorhynchus mykiss, which showed the highest infection values and is the species most captured by fishers. Based on previous data and the present results, eggs shed by humans, dogs and gulls in cities could be the principal factors in maintaining the life cycle of this parasite in surrounding aquatic environments.

Establishment and impact of exotic Cyprinus carpio (Common Carp) on native fish diversity in Buxar stretch of River Ganga, India

Abstract The catch pattern of the exotic Common Carp (Cyprinus carpio) and their relationship with water quality along with maturity status of fishes were assessed during 2017-2019 to understand overall establishment and impact of the species in Buxar stretch of River Ganga in West Bihar, India. A total of 64 fish species were recorded including two exotic fishes (C. carpio and Oreochromis niloticus) from the river stretch during the study period. The annual production data depicted Cyprinus carpio to be the most dominating fish species encountered from the study area sharing 57.07% (by weight) during the period 2017-19. Calculated average ‘Invasion coefficient index (Ix)’of 0.25 in entire three-year study period revealed that the invasion has moderately impacted the indigenous fish diversity. Landing of Indian Major Carp (IMC) indicated severe decline (76.4 - 95.6%) in comparison to the catch data recorded earlier from Buxar. Data generated on sex structure of Common Carp indicated that the overall sex ratio showed positive recruitment within the smaller size range of 282-307 mm and thus avails a competitive breeding advantage over other carp fishes. Gut content of Common Carp from the stretch observed major share of phytoplankton (81.04%) and zooplankton (17.18%) and thus there are significant dietary overlap of Common Carp with other valuable species. The stretch has been impacted with anthropogenic loading as identified through significantly higher water specific conductivity (580 µScm-1), Biochemical Oxygen Demand (3 mgl-1), etc. in drastically reduced water discharge regime. Among different water parameters, river flow, Biochemical Oxygen Demand and Total Phosphate showed positive whereas specific conductivity showed negative correlation with Common Carp seasonal abundance. Future conservation management measures may be formulated keeping in view of the identified factors through the present study for reducing the impending risks of the invasive fish species in Buxar stretch of River Ganga.

Management strategies to regulate the introduction of exotic ornamental fish, the silent invaders of freshwater ecosystems in India

Abstract Ornamental fish culture and aquarium keeping have become a booming sector worldwide. It has been observed that a number of stakeholders are involved in introducing exotic ornamentals in India as well, as the takers are interested on variants and new species. Most of the exotic ornamental fishes are also being domesticated in India, since the demand is readily fulfilled through adequate supply to the hobbyists. This sector provides livelihood option to many people and helps to earn millions of dollars to our country every year, however, the invasion of exotic ornamentals in our natural water bodies needs to be assessed, monitored and controlled with due attention as it is a staid menace to our biodiversity. Around 400 species / variants of exotic freshwater ornamentals and around 100 exotic marine ornamental species including invertebrates are found to have introduced in the trade. It is significant to note that an apparent violation in the trade is taking place by concealing the Government of India approval, which is given only for 92 species / variants of fishes for import. Further, as some of the freshwater ornamental fishes currently available in the aquarium trade have invaded through natural water bodies, their impacts need to be studied in detail. To deal with the situation, the proper precautionary approach should be implemented by adopting measures after having proper quarantine, meticulous risk analysis and strategic prevention methods as well. Combined efforts of industry stakeholders with different government agencies, academic and research institutions is required and a suitable protocol has to be formulated for permissible import, sustainable production, supply and management.

MaxEnt distribution modeling for predicting Oreochromis niloticus invasion into the Ganga river system, India and conservation concern of native fish biodiversity

Abstract In order to assess the distribution pattern and understand the prevailing factors for predicting further expansion of an exotic fish Oreochromis niloticus, this study was undertaken in the Ganga river flowing through the state of Uttar Pradesh using MaxEnt model. The authors report the distribution pattern of O. niloticus and prevailing causative factors mounting the expansion of O. niloticus in the Ganges based on MaxEnt modeling technique. The presence only occurrence data-set for this invasive species was prepared from the field data and also from data collated from the authenticated publications of different fisheries researchers. The data-set was analyzed with environmental and topographical variables typically incorporating seasonal and temporal variability using MaxEnt, a maximum entropy algorithm which showed that the area under curve was much closer to 1 ( 0.999). The model predicted elevation as the most influential predictor variable with permutation importance of 69.2% followed by slope_steepness (10.1%), Tmax_1 (7.3%) and Srad_5 (6.8%). The findings from the results suggest that invasive O. niloticus tend to spread in rivers where elevation is lower as well as slope_steepness of the river is higher and thus indicated that invasion might be higher in the downstream of the river. The model suggests that topography and its derived variable are the most significant predictors for distribution of invasive O. niloticus. The results of this study also confirm that the water qualities of the Ganga river are suitable for O. niloticus and if the model is supplemented with water quality variables data, the influential predictor variable in water quality can be well investigated with permutation importance.

Changing foodwebs of Indian aquatic ecosystems under the threats of invasive species: An overview

Abstract Biological invasions are a worldwide threat to the aquatic systems and have the potential to homogenize entire foodwebs and shift species abundance distributions to more skewed ones. Invasion impacts include effects on the foodweb structure and ecosystem functioning leading to a loss in native fish biodiversity and commercially important fisheries in many open water systems. The impacts of invasives are generally devastating as they spread in the foodweb with each species potentially interacting with multiple species. The foodweb modeling studies conducted in different inland aquatic ecosystems show that not all exotics cause a detrimental effect on the resilience of an ecosystem. Information on the foodweb structure and ecosystem properties is a prerequisite for formulating management protocols for conserving biodiversity, enhancement programmes and sustaining fisheries. The present paper reviews the impacts of invasive fishes in Indian aquatic ecosystems in the context of a changing foodweb scenario due to exotic fish species invasions. The information generated here could be applied for future research on similar ecosystems for deducing management actions.

Habitat based fish assemblage and distribution pattern in a large reservoir of peninsular India

The pattern of a fish assemblage of a large reservoir, Stanley (also called as Mettur) in Peninsular India was studied to derive various management protocols, specifically fish enhancement. The investigation was carried out in the spatial and temporal scale of the reservoir during 2017–2019. A total of 52 species belonging to 35 genera were recorded indicating high species richness. Simpson (0.17), Shannon (0.17), dominance (0.104), and evenness (0.52) indices did not show significant differences among zones whereas there was a significant difference during different seasons. On a temporal scale, maximum species were recorded in monsoon (47) followed by post-monsoon (43) and pre-monsoon season (33). On a spatial scale, it represented that riverine (47) and transitional zone (37) showed more species richness compared to lacustrine zone (30). Based on the catch structure of this reservoir, it is evident that exotic fishes play a major role in the recent past. One species under critically endangered and endangered, three species under near threatened, and two under vulnerable species were observed in the catch during this study period. The trophic guild of fishes showed the dominancy of planktivores. Abiotic factors such as temperature, pH, and chlorophyll were found directly influencing the species abundance. The study suggested management measures, including observation of closed fishing season, protection of breeding grounds, use of fish aggregating devices, mesh size regulation, and fish seed stocking in the reservoir.

The presence of rainbow trout reduces drift of aquatic insects in Yungas streams (Tucumán, Argentina)

The drift or transport of individuals downstream is an important phenomenon of rivers and streams, since most aquatic organisms participate in it at some period of their life cycle. This work describes the assemblage of macroinvertebrate drift from ten sites in eight mountain streams of Tucumán, and evaluates the effect of the presence of rainbow trout (Oncorhynchus mykiss Walbaum), an exotic fish and visual predator, on this fraction of the community. Thirty-one (31) families of drifting aquatic invertebrates were identified, mainly immature insects and to a lesser extent water mites (Acari: Hydrachnidia), oligochaetes (Annelida: Oligochaeta) and nematodes (Nematoda). The richness and diversity of the sites with trout did not differ from the others, except when comparing lower and upper reaches of a same stream. Samples from rivers without trout or with low density of trout did not show significant changes in drift density of macroinvertebrates. In contrast, in rivers with high trout densities, a notable decrease in insect taxa was observed (those with large sized individuals): Baetidae (Ephemeroptera), Gripopterygidae (Plecoptera) and Leptoceridae (Trichoptera). On the contrary, the density of small Diptera, water mites, oligochets and nematodes increased in trout-streams