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Neoergasilus japonicus, a fish ectoparasite indigenous to eastern and southern Asia, has been introduced to various regions, including Europe and North and South America, where it spreads at an alarming rate. The parasite is not host‐specific. It was also collected from the Vaal‐Orange and Limpopo river systems in South Africa. This report describes the morphology of the wound‐inflecting structures in N. japonicus and relates their morphology to the pathological effect on Tilapia sparrmanii. Host tissue with parasites attached was imbedded in resin for histological sectioning and stained with haematoxylin and eosin. Additional specimens were prepared for scanning electron microscopy. Adult female parasites attach by inserting the hooked tips of the antennae into the epidermis. The maxillulae are minute but have sharp tips. The maxillae have sharp tips on the endopod and brush‐like setae on the exopod. The mandibles are armed with sharp tips. These structures are used to remove the epidermis of the host and brush it into the buccal cavity. Host tissue in the intestine confirms that adult females consume host tissue leaving the dermis exposed to opportunistic diseases. The microscopic size of the parasite prevents casual observation, and its occurrence in Africa is, therefore, probably underreported. [ABSTRACT FROM AUTHOR]

The Lancang-Mekong River watershed has extremely high fish biodiversity. With the rapid population growth and economic development in the river basin, fish diversity and fishery resources of this river are experiencing serious threats. Basic biological information on most fish species in the Lancang River, required to improve conservation in this area, is limited. This study aimed to provide new estimates of length-weight relationships (LWRs) by using the linear regression of W = aLb for eight indigenous fish species from the Lancang River, Southwest China. From 2018 to 2021, 534 specimens belonging to 3 families and 8 genera were collected using various types of fishing techniques. Standard length (SL) and body weight (BW) of each specimen were measured to the nearest 0.1 cm and 0.1 g, respectively. This study presents the first public records of LWR parameters of Schizothorax lissolabiatus, Poropuntius huangchuchieni, Tor sinensis, Scaphiodonichthys acanthopterus, Mystacoleucus lepturus, Hemiculterella macrolepis, Glyptothorax lampris, and Schistura porthos. The range of b values for the LWRs was 2.5378–3.1732, and the r2 values for all LWRs estimates ranged from 0.9102 to 0.9952. Intraspecific difference of b values across population and/or season was observed in S. lissolabiatus, T. sinensis, P. huangchuchieni, S. acanthopterus, and M. lepturus. The range of mean condition factor (K) and mean relative weight (Wr) was 0.97–2.39 and 100.29–108.18, respectively. This study updated information for FishBase and provided new record of maximum standard length for five species, namely, S. lissolabiatus, P. huangchuchieni, T. sinensis, S. acanthopterus, and M. lepturus. The findings of this study are essential for the management and conservation of locally indigenous fish and fisheries. [ABSTRACT FROM AUTHOR]

Simple Summary: The Nile tilapia (Oreochromis niloticus) (NT) is an aggressive and omnivorous species that competes with native fishes for food resources, and it has successfully invaded much of the Pearl River basin in China. Intensive research has focused on the gut microbiota of Nile tilapia in artificial culture. However, differences in gut microbes between invasive Nile tilapia and indigenous fish are relatively less well characterized. In the present study, we chose the black Amur bream (Megalobrama terminalis) as a native omnivorous fish that shared a common habitat and partially overlapped resource usage with Nile tilapia. Here, we investigated the gut microbiomes of invasive Nile tilapia and indigenous black Amur bream (BA) in the same river section using high-throughput 16S rRNA gene sequencing. The results indicated that the gut microbiome of NT had several special characteristics, e.g., higher alpha diversity and greater niche breadth, compared with the bream. Thus, the aim of the present study was to investigate the role of gut microbiomes between an indigenous fish (black Amur bream) and invasive Nile tilapia from the low region of the Pearl River basin to better understand the microbial complexity and diversity of their gut microbiota. The gut microbiome is thought to play vital roles in host fitness and local adaptation to new environments, thereby facilitating the invasion of the host species. The Nile tilapia (Oreochromis niloticus) (NT) is an aggressive and omnivorous species that competes with native fishes for food resources, and it has successfully invaded much of the Pearl River basin in China. Here, we investigated the gut microbiomes of invasive Nile tilapia and indigenous black Amur bream (BA) in the same river section using high-throughput 16S rRNA gene sequencing. The results indicated that the gut microbiome of NT had several special characteristics, e.g., higher alpha diversity and greater niche breadth, compared with the bream. The gut microbiota of the small size of Nile tilapia (NTS) and small size of black Amur bream (BAS) groups were dominated by Proteobacteria, while those of the NTS and large size of Nile tilapia (NTL) and BAS and large size of black Amur bream (BAL). BAL and NTL were characterized by Firmicutes and Fusobacteriota, respectively. We found that Pseudomonas, Cetobacterium, Ralstonia, and Romboutsia were biomarkers of the NTS, NTL, BAS, and BAL groups, respectively. Moreover, the results collectively suggested that the clustering coefficients of BAL and NTL networks were greater than those of BAS and NTS networks, and BAS had the smallest network among the four groups. Positive interactions between two ASVs dominated the BAS, NTS, and NTL networks, while the proportion of negative interactions between two ASVs in the BAL network was remarkably increased. Low levels of interspecies competition in the NT gut microbiome would contribute to high diversity in the dietary niches and would also benefit the survival and local adaptation of the host. Our results identified specific biomarkers of gut microbial species in invasive Nile tilapia and provided useful information concerning how to monitor and manage invasive Nile tilapia populations. [ABSTRACT FROM AUTHOR]

Ichthyological investigations were performed at 11 sampling sites in the Krupinica stream basin in the period of 2020 and 2021. In total, 22 fish species of 6 families (Balitoridae, Cobitidae, Cyprinidae, Gobiidae, Lotidae, Salmonidae) were recorded in the study area. The ichthyocenosis composition varied in the longitudinal profile from source to mouth. Upper sections of the watercourses were dominated by typical rhithral species, such as Eurasian minnow (Phoxinus phoxinus), stone loach (Barbatula barbatula) and brown trout (Salmo trutta m. fario). The fish community is to some extent influeneced by human activity (stocking of indigenous fish species, water reservoir). In the middle section rheophilic fish species were in dominant position and the share of rhithral species decreased. The lower section near the mouth to Ipeľ proved to be important for the occurrence of several protected species of European importance, such as Sabanejewia bulgarica and Kessler's gudgeon (Romanogobio kesslerii). This part of the river also plays a significant role as a nursery habitat of the 0+ rheophilic species such as common nase (Chondrostoma nasus), barbel (Barbus barbus), ide (Leuciscus idus) and asp (Leuciscus aspius). [ABSTRACT FROM AUTHOR]

Infection of non-indigenous pumpkinseed (Lepomisgibbosus, Centrarchidae) with the bothriocephalidean cestode Bothriocephalusclaviceps (Cestoda: Bothriocephalidae) was confirmed at several sites in the lower Oder river basin in Poland. The preferred host for this cestode species is the European eel (Anguillaanguilla), with a wide range of other fish species serving as paratenic hosts. The pumpkinseed showed a relatively high prevalence and abundance of larvae, along with several mature and gravid specimens, thereby confirming development of B.claviceps to the adult stage in an alternative host. As such, the pumpkinseed may represent an additional definitive host for this cestode, in addition to its role as a paratenic host, as previously recorded in other European regions. Our results indicate that inclusion of pumpkinseed as an additional definitive host in the cestode's life cycle, high infection of pumpkinseed with B.claviceps larvae and inclusion of pumpkinseed in the eel's diet could potentially lead to increased parasite pressure on native fish hosts. Further comparative studies or experimental testing will be required to confirm this. [ABSTRACT FROM AUTHOR]

River systems globally are experiencing social-ecological changes that often impact Indigenous fishing practices, including climate change and resource developments. We explore the relationship between access to fish and well-being, and the determinants of access to fish amidst changing social-ecological conditions through interviews with 29 individuals across four Gwich'in First Nation communities in Canada's Northwest Territories. Our interviews show that socioeconomic and environmental barriers are making it harder to access fish and that this has negative implications for well-being. Despite these barriers, access to fish continues to make positive, diverse contributions to well-being in Gwich'in communities through socioeconomic factors such as sharing networks and adaptive practices that are often part of ecological monitoring and land-based education and facilitate access to fish. Increasing our understanding of the relationship between access to fish and well-being, and determinants of access to fish, can contribute to land-based programs, land-use planning, and decision-making in Gwich'in territory and other river systems. [ABSTRACT FROM AUTHOR]

This study provides new length‒weight (LWR) and length‒length relationships (LLR) for 25 indigenous fish species from Xingu River basin. Overall specimens were collected in different aquatic habitats in the Xingu River basin in quarterly collections between 2012 and 2018. The collections were carried out using distinct fishing gears, such as gill nets (20 to 180 mm mesh), seines (3 mm mesh), sieves (1 mm mesh), and casting nets (20 to 60 mm mesh). The present study shows the LWRs for 25 species, and the LLRs for 23 species. In addition, presents the new maximum total lengths for 20 species. [ABSTRACT FROM AUTHOR]

Local fishers often claim that cage culture practices in reservoirs result in high fish catches as fish cages attract a diverse variety of wild fish, which mainly aggregate to forage on waste from the practices. Previous studies have focused on fish aggregation effects brought about by fish cages. In the present study, we explored the responses of wild fish assemblages to fish cages and increased fishing pressure in the vicinity of cage farms in the Geheyan reservoir (110.80°-111.22° E, 30.35°-30.48° N) which located on the middle reaches of the Qingjiang River of the Yangtze River basin. Seasonal hydroacoustic surveys were conducted between April 2016 and January 2017 using a Simrad EY60 echosounder to determine the changes of fish assemblages along the density gradient of fish cages in the reservoir. Significant negative correlations between wild fish density and the density of fish cages were observed in April 2016 and January 2017. In other two seasons, we also found analogous trends. In general, the abundance of wild fish assemblages around fish cages declined resulting from increased fishing pressure in the reservoir. This study suggests that the commercial capture of indigenous fish around cage farms should be limited to protect the indigenous fish resources in reservoirs. • The consequences of increased fish pressure on wild fish assemblages around fish cages are severe. • Restrictions for capture of wild fish in the vicinity of cage farms may avoid fish cages acting as ecological traps. • Wild fish provide an ecosystem service by reducing environmental impact. • Fish cage culture did not deteriorate water quality significantly in this study. [ABSTRACT FROM AUTHOR]