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Concept: Freshwater fish


This paper focuses on an overview of radioactive cesium 137 (quasi-Cs137 included Cs134) contamination of freshwater fish in Fukushima and eastern Japan based on the data published by the Fisheries Agency of the Japanese Government in 2011. In the area north and west of the Fukushima Nuclear plant, freshwater fish have been highly contaminated. For example, the mean of active cesium (quasi-Cs137) contamination of Ayu (Plecoglossus altivelis) is 2,657 Bq/kg at Mano River, 20-40 km north-west from the plant. Bioaccumulation is observed in the Agano river basin in Aizu sub-region, 70-150 km west from the plant. The active cesium (quasi-Cs137) contamination of carnivorous Salmondae is around 2 times higher than herbivorous Ayu. The extent of active cesium (quasi-Cs137) contamination of Ayu is observed in the entire eastern Japan. The some level of the contamination is recognized even in Shizuoka prefecture, 400 km south-west from the plant.

Concepts: Chernobyl disaster, Japan, Freshwater fish, Prefectures of Japan, Government of Japan, Honshū, Shizuoka Prefecture, Ayu


The prevalence of foodborne trematode (FBT) metacercariae was investigated in fish from 2 localities of northern Vietnam in 2004-2005. Freshwater fish (9 species) were collected from local markets in Hanoi City (n=76) and Nam Dinh Province (n=79), and were examined for FBT metacercariae using the artificial digestion technique. Adult flukes were obtained from hamsters experimentally infected with the metacercariae at day 8 post-infection. Three (Haplorchis pumilio, Centrocestus formosanus, and Procerovum varium) and 6 (Haplorchis taichui, H. pumilio, C. formosanus, P. varium, Stellantchasmus falcatus, and Heterophyopsis continua) species of FBT metacercariae were detected in the 2 regions, respectively. Overall, among the positive fish species, H. pumilio metacercariae were detected in 104 (80.0%) of 130 fish examined (metacercarial density per infected fish; 64.2). C. formosanus metacercariae were found in 37 (40.2%) of 92 fish (metacercarial density; 14.7). P. varium metacercariae were detected in 19 (63.3%) of 30 fish (Anabas testudineus and Mugil cephalus) (metacercarial density; 247.7). S. falcatus metacercariae were found in all 10 M. cephalus examined (metacercarial density; 84.4). H. continua metacercariae (2 in number) were detected in 1 fish of Coilia lindmani. Morphologic characteristics of the FBT metacercariae and their experimentally obtained adults were described. The results have demonstrated that various FBT species are prevalent in northen parts of Vietnam.

Concepts: Prevalence, Anabas testudineus, Freshwater fish, Vietnam, Hanoi, Nam Dinh Province, Red River Delta, Ngo Dinh Diem


Mercury pollution poses risks for both human and ecosystem health. As a consequence, controlling mercury pollution has become a policy goal on both global and national scales. We developed an assessment method linking global-scale atmospheric chemical transport modeling to regional-scale economic modeling to consistently evaluate the potential benefits to the United States of global (UN Minamata Convention on Mercury) and domestic [Mercury and Air Toxics Standards (MATS)] policies, framed as economic gains from avoiding mercury-related adverse health endpoints. This method attempts to trace the policies-to-impacts path while taking into account uncertainties and knowledge gaps with policy-appropriate bounding assumptions. We project that cumulative lifetime benefits from the Minamata Convention for individuals affected by 2050 are $339 billion (2005 USD), with a range from $1.4 billion to $575 billion in our sensitivity scenarios. Cumulative economy-wide benefits to the United States, realized by 2050, are $104 billion, with a range from $6 million to $171 billion. Projected Minamata benefits are more than twice those projected from the domestic policy. This relative benefit is robust to several uncertainties and variabilities, with the ratio of benefits (Minamata/MATS) ranging from ≈1.4 to 3. However, we find that for those consuming locally caught freshwater fish from the United States, rather than marine and estuarine fish from the global market, benefits are larger from US than global action, suggesting domestic policies are important for protecting these populations. Per megagram of prevented emissions, our domestic policy scenario results in US benefits about an order of magnitude higher than from our global scenario, further highlighting the importance of domestic action.

Concepts: United States, Million, U.S. state, Ratio, Freshwater fish, Nazi Germany, Minamata disease, United States dollar


Freshwater fishes are highly vulnerable to human-caused climate change. Because quantitative data on status and trends are unavailable for most fish species, a systematic assessment approach that incorporates expert knowledge was developed to determine status and future vulnerability to climate change of freshwater fishes in California, USA. The method uses expert knowledge, supported by literature reviews of status and biology of the fishes, to score ten metrics for both (1) current status of each species (baseline vulnerability to extinction) and (2) likely future impacts of climate change (vulnerability to extinction). Baseline and climate change vulnerability scores were derived for 121 native and 43 alien fish species. The two scores were highly correlated and were concordant among different scorers. Native species had both greater baseline and greater climate change vulnerability than did alien species. Fifty percent of California’s native fish fauna was assessed as having critical or high baseline vulnerability to extinction whereas all alien species were classified as being less or least vulnerable. For vulnerability to climate change, 82% of native species were classified as highly vulnerable, compared with only 19% for aliens. Predicted climate change effects on freshwater environments will dramatically change the fish fauna of California. Most native fishes will suffer population declines and become more restricted in their distributions; some will likely be driven to extinction. Fishes requiring cold water (<22°C) are particularly likely to go extinct. In contrast, most alien fishes will thrive, with some species increasing in abundance and range. However, a few alien species will likewise be negatively affected through loss of aquatic habitats during severe droughts and physiologically stressful conditions present in most waterways during summer. Our method has high utility for predicting vulnerability to climate change of diverse fish species. It should be useful for setting conservation priorities in many different regions.

Concepts: Conservation biology, Animal, Future, Endangered species, Freshwater fish, Invasive species, Introduced species, Biogeography


Tropical wetlands are highly threatened socio-ecological systems, where local communities rely heavily on aquatic animal protein, such as fish, to meet food security. Here, we quantify how a ‘win-win’ community-based resource management program induced stock recovery of the world’s largest scaled freshwater fish (Arapaima gigas), providing both food and income. We analyzed stock assessment data over eight years and examined the effects of protected areas, community-based management, and landscape and limnological variables across 83 oxbow lakes monitored along a ~500-km section of the Juruá River of Western Brazilian Amazonia. Patterns of community management explained 71.8% of the variation in arapaima population sizes. Annual population counts showed that protected lakes on average contained 304.8 (±332.5) arapaimas, compared to only 9.2 (±9.8) in open-access lakes. Protected lakes have become analogous to a high-interest savings account, ensuring an average annual revenue of US$10,601 per community and US$1046.6 per household, greatly improving socioeconomic welfare. Arapaima management is a superb window of opportunity in harmonizing the co-delivery of sustainable resource management and poverty alleviation. We show that arapaima management deserves greater attention from policy makers across Amazonian countries, and highlight the need to include local stakeholders in conservation planning of Amazonian floodplains.

Concepts: Poverty, Lake, River, Amazon River, Sustainability, Freshwater fish, Limnology, Oxbow lake


Arapaima gigas, a fresh water fish found in the Amazon Basin, resist predation by piranhas through the strength and toughness of their scales, which act as natural dermal armour. Arapaima scales consist of a hard, mineralized outer shell surrounding a more ductile core. This core region is composed of aligned mineralized collagen fibrils arranged in distinct lamellae. Here we show how the Bouligand-type (twisted plywood) arrangement of collagen fibril lamellae has a key role in developing their unique protective properties, by using in situ synchrotron small-angle X-ray scattering during mechanical tensile tests to observe deformation mechanisms in the fibrils. Specifically, the Bouligand-type structure allows the lamellae to reorient in response to the loading environment; remarkably, most lamellae reorient towards the tensile axis and deform in tension through stretching/sliding mechanisms, whereas other lamellae sympathetically rotate away from the tensile axis and compress, thereby enhancing the scale’s ductility and toughness to prevent fracture.

Concepts: Continuum mechanics, Tensile strength, Amazon River, Freshwater fish, Amazon Basin, Work hardening, Deformation, Plastic deformation in solids


Paracellular permeability characteristics of the fish gill epithelium are broadly accepted to play a key role in piscine salt and water balance. This is typically associated with differences between gill epithelia of teleost fishes residing in seawater versus those in freshwater. In the former, the gill is ‘leaky’ to facilitate Na(+) secretion and in the latter, the gill is ‘tight’ to limit passive ion loss. However, studies in freshwater fishes also suggest that varying epithelial ‘tightness’ can impact ionoregulatory homeostasis. Paracellular permeability of vertebrate epithelia is largely controlled by the tight junction (TJ) complex, and the fish gill is no exception. In turn, the TJ complex is composed of TJ proteins, the abundance and properties of which determine the magnitude of paracellular solute movement. This review provides consolidated information on TJs in fish gills and summarizes recent progress in research that seeks to understand the molecular composition of fish gill TJ complexes and what environmental and systemic factors influence those components.

Concepts: Lung, Fish, Epithelium, Freshwater fish, Lamprey, Gill, Shark, Osteichthyes


In this study, we explore the feasibility of using bioinspired robotics to influence the behaviour of mosquitofish (Gambusia affinis), a social freshwater fish species that is extensively studied for the ecological issues associated with its diffusion in non-native environments. Specifically, in a dichotomous choice test, we investigate the behavioural response of small shoals of mosquitofish to a robotic fish inspired by mosquitofish in its colouration, shape, aspect ratio, and locomotion. Our results indicate that the swimming depth and the aspect ratio of the robotic fish are both determinants of mosquitofish preference. In particular, we find that mosquitofish are never attracted by a robotic fish whose colouration and shape are inspired by live subjects and that the degree of repulsion varies as a function of the swimming depth and the aspect ratio.

Concepts: Psychology, Aspect ratio, Degrees of freedom, Freshwater fish, Poeciliidae, Mosquitofish, Gambusia, Live-bearing fish


An endoparasitic copepod is reported from the urinary bladder of a fish for the first time. Endoparasitic copepods on fish hosts are extremely rare and the impact of colonization of this novel microhabitat on the biology of the parasite is discussed. This curious association was reported from two different host families of Neotropical freshwater fishes, Erythrinidae and Cichlidae, collected from the Cristalino River, a tributary of the Araguaia River, in Brazil. The copepod is fully described using light and scanning electron microscopy. Urogasilus brasiliensis n. g., n. sp. represents a new genus and species of the family Ergasilidae and can be distinguished from other genera by its unique tagmosis, in which the fourth and fifth pedigerous somites and the genital double-somite are all fused to form an elongate trunk. The anal somite is the only free abdominal somite present. The pattern of leg segmentation is also unique, with legs 1 to 3 each having a 2-segmented endopod and leg 4 reduced to a single seta. The discovery of ovigerous female ergasilids in the urinary bladder of a fish is novel and this discovery represents a good model for further studies on the adaptations to an endoparasitic life style.

Concepts: Kidney, Biology, Species, Fish, Freshwater fish, Copepod, Maxillopoda, Poecilostomatoida


We investigated the efficacy of praziquantel (PZQ) and fenbendazole (FBZ), each administered by bath and orally, against the monogenean Lepidotrema bidyana Murray, a gill parasite of the freshwater fish silver perch, Bidyanus bidyanus (Mitchell). PZQ and FBZ were each administered by bath at 10 mg L(-1) for 48 h and on surface-coated feed pellets at 75 mg kg(-1) per body weight (BW) per day for 6 days. Bath treatments of PZQ and FBZ had an efficacy of 99% and 91%, respectively, against adult L. bidyana. Oral treatments of PZQ and FBZ had an efficacy of 79% and 95%, respectively, against adult L. bidyana. Fish rejected feed pellets surface-coated with PZQ, suggesting that palatability of surface-coated PZQ-medicated feed is poor, which undermined efficacy. In all trials, some juvenile parasites were present on fish after treatment during efficacy assessment, indicating that efficacy may be lower against juvenile parasites or that recruitment occurred post-treatment, demonstrating that repeat treatments are necessary to effectively control L. bidyana in aquaculture.

Concepts: Fish, Parasitism, Freshwater fish, Murray River, Anthelmintic, Freshwater fish of Australia, Terapontidae, Silver Perch