Freshwater Fish Research Articles

Comparative pathology of (Encysted and non-encysted) trematodes in the liver of snake headed fresh water fish Channa punctatus (Bloch, 1793)

Comparative pathology of (Encysted and non-encysted) trematodes in the liver of snake headed fresh water fish Channa punctatus (Bloch, 1793)

A modified QuEChERS-based UPLC-MS/MS method for rapid determination of multiple antibiotics and sedative residues in freshwater fish

Antibiotics and sedatives are used in freshwater fish culture and transportation, and residue in freshwater fish pose potential risks to human health. Therefore, a throughput method was developed to detect antibiotic and sedative residues in fish, simultaneously quantifying 68 antibiotics and 9 sedatives in freshwater fish using a modified QuEChERS extraction method and UPLC-MS/MS. Matrix-matched calibrations demonstrated good correlation coefficients (R2 > 0.995), with a recovery range of 66.2–118.5%. The intra-day and inter-day relative standard deviation (RSD) were below 9.7% and 12.8%, respectively. The limits of detection (LOD) and quantification (LOQ) were 0.08–1.46 μg/kg and 0.25–4.86 μg/kg, respectively. 68.8% of analytes had weak matrix effects, and 13.0% had moderate matrix effects. In addition, diazepam and many types of antibiotics were detected in30 freshwater fish. The validation parameters were in agreement with the acceptable criteria of the Codex guidelines. The method was effective in analyzing antibiotic and sedative residues in freshwater fish.

Nutritional quality of fish oil extracted from selected freshwater fish species

There is increased consumer awareness of the nutritional importance of fish oil consumption in recent time, however there is paucity of information on the quality of oil obtained from freshwater fishes available in this study area. Nutritional quality of fish oil extracted from 9kg each of Chrysichthys nigrodigitatus, Synodontis membranaceous and Clarias gariepinus were investigated with the aim of providing baseline information on the nutritional quality of oil in the fish available around the study area. Wet rendering, soxhlet extraction and microwave assisted extraction methods were used. Data collected were subjected to appropriate statistical analysis using SPSS 6.0. version. S. membranaceous have the largest oil yield while C. nigrodigitatus have the lowest oil yield; wet rendering oil extraction method gave the highest oil yield. The physical quality characteristics of S. membranaceous was the best with the lowest melting point (28.73 ±0.39°C), specific gravity (0.11± 0.01) and refractive index (1.14 ±0.01) while C. gariepinus oil had the poorest physical quality characteristics. Oil of C. nigrodigitatus have better chemical qualities than the rest having the lowest saponification value (9.81±0.01 mg KOH/g), iodine value (1.59±0.01 gl/100g), acid value (1.12±0.01 mgKOH/g) and free fatty acid (0.56±0.01%) while C. gariepinus oil was the poorest. C. nigrodigitatus also have the highest polyunsaturated fatty acid (PUFA) (18.75), highest Ʃn-3 FA (23.45), highest DHA (Docosahexaenoic acid) (4.93), highest eicosapentaenoic acid EPA+DHA (7.8). The oils chemical qualities are in the order of C. nigrodigitatus> S. membranaceous> C. gariepinus and are of good quality. Oil obtained from C. nigrodigitatus is therefore recommended due to its good chemical qualities using wet rendering oil extraction method. Information provided in this study will guide industrialists and nutritionists on the best extraction method and fish that will give highest oil yield and best oil quality in the study area.

Mysis segerstralei, an unexpected but important prey for resident Arctic charr (Salvelinus alpinus) in a Svalbard lake

AbstractMysis segerstralei is distributed over a wide geographic area and in habitats with a variety of salinity conditions, including marine and brackish waters around Svalbard. The species has seldom been found in freshwater lakes, and the discovery of M. segerstralei in Lake Pulmankijärvi at the border between Northeastern Norway and Finland, may represent the single known freshwater occurrences in western Europe. Svalbard lake systems are characterized by very low water temperatures, long-term ice cover, and low levels of nutrients. Food is thus limited, and chironomids generally dominate the stomach contents in Arctic charr, the only freshwater fish species on Svalbard. Based on several surveys in more than 30 of Svalbard lakes over many decades, M. segerstralei has only been found as food for Arctic charr in Lake Vårfluesjøen. In a later fishery survey, we studied the diet of Arctic charr in this lake. The stomach contents from Arctic charr sampled in the profundal habitats were dominated by M. segerstralei, but the species was also among the most frequent prey items in the littoral and pelagic habitats. This unexpected occurrence of M. segerstralei demonstrates the high importance of mysids even in a low-productive, High Arctic lake.

Morphological and molecular data establishes Clinostomum dolichorchum n. sp. (Digenea: Clinostomidae) in the great blue heron Ardea herodias L. and American bullfrog Rana catesbeiana Shaw.

Clinostomum is a cosmopolitan genus of trematodes that infect piscivorous birds, freshwater molluscs, freshwater fish and amphibians. Herein, a novel species of Clinostomum is described based on morphological and molecular data from an adult in the oral cavity of the great blue heron Ardea herodias and metacercariae collected from the gills and skin of American bullfrog tadpoles Rana catesbeiana. The novel species shares similar qualitative and quantitative morphological features with a congener, Clinostomum marginatum, which has overlap in host and geographic distribution. The most notable morphological difference when compared to C. marginatum is the greater posterior testis length of the novel species. Molecular data resolved similarities with morphological comparisons to nominal species and supports the establishment of a novel species. Molecular data include partial small ribosomal subunit (18S rRNA gene), ribosomal internal transcribed spacer regions (ITS1, 5.8S rRNA gene, and ITS2), partial large ribosomal subunit (28S rRNA gene), cytochrome c oxidase subunit 1 gene (cox1), and nicotinamide adenine dinucleotide dehydrogenase subunit 1 gene (nad1) sequences. Phylogenetic analyses place the novel species in a sister clade to C. marginatum. Morphological and molecular data, combined with phylogenetic analyses support the establishment of Clinostomum dolichorchum n. sp.

Taxonomic Status of Diplectanum robustitubum Wu & Li, 2003 (Monogenoidea: Diplectanidae) from the Purple-Spotted Bigeye Priacanthus tayenus (Priacanthidae) and the Description of Platycephalotrema parile n. sp. (Monogenoidea: Dactylogyridae) from the Bartail Flathead Platycephalus indicus (Platycephalidae), in the Arabian Gulf.

The present paper represents the third installment concerning the monogenoids collected during surveys to explore their diversity on the marine and freshwater fishes of Iraq. Previous installments on the monogenoids emanating from the surveys included the dactylogyrid and gyrodactylid species parasitizing mugilid fishes. The purpose of this paper is to further document the diversity of monogenoids infecting the fishes of Iraq. Marine fishes were necropsied for parasites, and standard procedures for collecting, mounting, drawing, and measuring of monogenoids were employed. Oliveriplectanum robustitubum n. comb. (Diplectanidae) and Platycephalotrema parile n. sp. (Dactylogyridae) were collected. The occurrence of O. robustitubum in the Arabian Gulf represented a new locality record for the species. The recorded presence of O. robustitubum and P. parile n. sp. suggests that the diversity of monogenoids in Iraq is under estimated in the literature.

Lunar-linked biorhythms in the immune system of freshwater three-spined stickleback

Abstract Immune responses are widely accepted to be under circadian regulation via a molecular clock, with many practical consequences, but much less is known of how other biorhythms could affect the immune system. In this study we search for lunar rhythms (circalunar, circasemilunar and circatidal cycles) in the immune expression of the recently marine-derived freshwater fish, the low-plate morph of the three-spined stickleback. We employed time series of immune expression (mRNA) measurements for 14 immune-associated genes, representing a variety of immunological pathways. Times series measurements were taken on fish populations in the wild, in seminatural outdoor mesocosms and in the laboratory, according to sampling regimens originally designed to study circannual variation but with the additional potential to provide information about lunar variation. Our evidence best supported the existence of a very small endogenous tidal rhythm. This is consistent with previous suggestions of the existence of a primordial tidal endogenous clock, some elements of which may be conserved in animals evolving outside the marine environment.

Studies on Morphological Effect of Some Pesticides on Fresh Water Fish, Labeo rohita in Sai River of Jaunpur District, Uttar Pradesh, India

Pesticides are one of the potentially harmful toxic chemicals introduced into the aquatic environment. Fish serve as important bio-indicators for aquatic life. Widely used pesticides formulation two investigate possible chemical biological and toxicological effects of pesticides that may enter into our eco-system. Effects of pesticides (herbicides insecticides, rodenticides and fungicides) to loss protein content of the liver gill and intestinal tissue of the fresh water fish, Labeorohita.The Recent study is aimed two assess the toxicological impacts of treated and untreated effluents on aquatic fresh water fish, Labeo rohita. The Most common edible fish having diverse characters includes difference in morphology, food and feeding etc. Symptoms were nearly identical on various host spp (Labeo rohita. with respect to behaviour of the infected fish. The toxicity of pesticides to an organism is usualy expressed in terms of the LD50 (lethal dose 50 percent) and LC50 (50 percent lethal concentration) observed the behavioural studies of exposed to Labeorohita. Therefore, the protection and prevention of aquatic ecosystem will be possible only with the appropriate and rationalized application of pesticides.

Production of trans-fat-free margarine prepared using catfish oil and palm stearin with the addition of avocado waste oil for tocopherol enrichment

Catfish oil (CFO) is rich in unsaturated fatty acids (UFA) which are potentially produced into margarine through the blending method with palm stearin (PS) addition. The high UFA content of CFO causes margarine to be susceptible to oxidative damage, which can also trigger the formation of trans fatty acids (TFA). An antioxidant compound in the form of avocado waste oil (AWO) that contains tocopherol is added during margarine production to inhibit oxidative damage and TFA formation in the final product. Thus, the temperature and duration of CFO extraction, avocado peel and seed ratio of AWO extraction, and CFO:PS:AWO ratio of margarine production were analyzed for their effect on CFO, AWO, and margarine characteristics. This study was conducted by several stages; CFO extraction with temperature (50, 70 and 90oC) and duration (1 and 2 hrs) treatment, AWO extraction with avocado peel and seed ratio treatment (100:0, 75:25, 50:50, 25:75, 0:100), and margarine production with CFO:PS:AWO ratio treatment (41:40:0, 36:40:5, 31:40:10, 26:40:15, 21:40:20). The results showed that the increasing extraction temperature and duration caused the decrease of CFO hydrolytic-oxidative stability. The best CFO extraction treatment was 50oC and 1 hr of extraction. The increasing avocado peel ratio in AWO extraction led to the increase of AWO antioxidant potential. The best AWO extraction treatment was the ratio of peel:seed = 75:25. The addition of AWO in margarine production for tocopherol enrichment was proven to suppress oxidative damage and TFA formation. The best margarine production treatment was the 3rd formulation (10% of AWO) with UFA-rich and trans-fat-free margarine characteristics. It was selected as the most preferred color, taste and flavor of margarine. These studies’ results are beneficial for the product development of UFA-rich and transfat-free margarine with good oxidative stability prepared using freshwater fish oil and plant byproduct oil.

A review of arsenic speciation in freshwater fish: Perspectives on monitoring approaches and analytical methods

Arsenic accumulation in fish poses concerns for subsistence and recreational fishers worldwide. However, the toxicity of arsenic to consumers strongly depends on the chemical forms, or species, present. Risk assessments often rely on total arsenic concentrations ([As]), adjusting for assumed small percentages of the most harmful inorganic species. While studies on arsenic speciation in marine fish are widespread, and commonly report less toxic arsenobetaine (AsB) as the dominant form, fewer studies have been conducted on freshwater fish, where arsenic speciation may be more variable. To assess these findings, we conducted a systematic literature review on arsenic speciation in freshwater fish using Covidence© review management software. From over 1100 screened studies, 41 were selected for inclusion based on predefined criteria. These studies reported highly variable arsenic speciation patterns in freshwater fish, calling into question the assumption that AsB is the dominant form present. Sites with suspected or known arsenic contamination issues were prominent, with >50% of data reviewed originating from a contaminated river or lake, but the effect of contamination on arsenic speciation was variable. Although AsB and other organic forms typically dominated, some studies (6/41; 15%) identified fish with elevated concentrations of inorganic arsenic (>1 mg/kg dry wt.), most often corresponding to over 20% of total arsenic. Furthermore, arsenic speciation results accounted for a highly variable proportion of total [As] in fish, often less than 50%. Assuming 20% inorganic arsenic appears to be a poor approximation that cannot be applied to all fish. Based on this considerable variability, we recommend the direct measurement of arsenic species whenever possible, especially when total [As] is elevated above relevant guidelines for the most toxic species (e.g., 0.1-2 mg/kg inorganic arsenic wet wt.). We also recommend future works communicate their results in more detail, including complete description of QAQC protocols, to improve the potential for future meta-analyses. Additional work is needed to characterize arsenic speciation in freshwater fish and assess the toxicity of various arsenic species to accurately evaluate the environmental and human health risks associated with arsenic in fish.

DyFish-DETR: Underwater Fish Image Recognition Based on Detection Transformer

Due to the complexity of underwater environments and the lack of training samples, the application of target detection algorithms to the underwater environment has yet to provide satisfactory results. It is crucial to design specialized underwater target recognition algorithms for different underwater tasks. In order to achieve this goal, we created a dataset of freshwater fish captured from multiple angles and lighting conditions, aiming to improve underwater target detection of freshwater fish in natural environments. We propose a method suitable for underwater target detection, called DyFish-DETR (Dynamic Fish Detection with Transformers). In DyFish-DETR, we propose a DyFishNet (Dynamic Fish Net) to better extract fish body texture features. A Slim Hybrid Encoder is designed to fuse fish body feature information. The results of ablation experiments show that DyFishNet can effectively improve the mean Average Precision (mAP) of model detection. The Slim Hybrid Encoder can effectively improve Frame Per Second (FPS). Both DyFishNet and the Slim Hybrid Encoder can reduce model parameters and Floating Point Operations (FLOPs). In our proposed freshwater fish dataset, DyFish-DETR achieved a mAP of 96.6%. The benchmarking experimental results show that the Average Precision (AP) and Average Recall (AR) of DyFish-DETR are higher than several state-of-the-art methods. Additionally, DyFish-DETR, respectively, achieved 99%, 98.8%, and 83.2% mAP in other underwater datasets.

Gut Microbial Composition of Cyprinella lutrensis (Red Shiner) and Notropis stramineus (Sand Shiner): Insights from Wild Fish Populations

The gut microbiome is a highly intricate ecosystem that exerts a pivotal influence on the host’s physiology. Characterizing fish microbiomes is critical to understanding fish physiology and health, but little is known about the ecology and colonization dynamics of microorganisms inhabiting fish species. In this study, we investigated the bacterial communities of two small-bodied fish species, Cyprinella lutrensis (red shiner) and Notropis stramineus (sand shiner), two fish species where gut microbiomes have not been investigated previously and surrounding waters, collected from rivers in Nebraska, USA. Our study focused on evaluating microbial diversity in small-bodied fish and identifying autochthonous microbes present within these species irrespective of location to better understand bacterial community composition and possible roles of such bacterial species. Our results revealed that both red shiner and sand shiner exhibited gut bacterial communities dominated by typical bacterial phyla found in freshwater fish. The phylum Bacteroidota was minimally abundant in both species and significantly lower in relative abundance compared to the surrounding water microbial community. Furthermore, we found that the gut microbiomes of red shiner and sand shiner differed from the microbial community in the surrounding water, suggesting that these fish species contain host-associated bacterial species that may provide benefits to the host such as nutrient digestion and colonization resistance of environmental pathogens. The fish gut bacterial communities were sensitive to environmental conditions such as turbidity, dissolved oxygen, temperature, and total nitrogen. Our findings also show bacterial community differences between fish species; although they shared notable similarities in bacterial taxa at phyla level composition, ASV level analysis of bacterial taxa displayed compositional differences. These findings contribute to a better understanding of the gut bacterial composition of wild, freshwater, small-bodied fish and highlight the influence of intrinsic (host) and environmental factors on shaping the bacterial composition.

Convergence of aquatic products consumption: A disaggregated analysis in European countries

Several benefits of consuming fishery and aquaculture products have been documented by the extant literature. However, the literature has been largely silent on few dimensions of aquaculture products, including the convergence of aquatic products consumption. An importance of investigating the convergence of aquatic products is that it provides hindsight on which countries should be the focus of exporters of the products. Convergence analysis of aquatic products consumption provides information that is relevant to the need to boost local production of aquatic products, and to conserve foreign exchange earnings. The aim of this study is to investigate the convergence of total aquatic products consumption per capita in 27 European Union countries plus United Kingdom, during 1993–2019. We have further considered the convergence of the components of total aquatic products consumption, which include aquatic animals, cephalopods, crustaceans, demersal fish, freshwater fish, marine fish, molluscs, and pelagic fish. Additionally, we have examined conditional convergence by evaluating the determinants of convergence of total aquatic products consumption. Using recently introduced unit root tests that provide for both smooth and sharp breaks, the results provide support for stochastic convergence of total aquatic products consumption per capita. Using a new conditional convergence approach, the analysis demonstrates that population growth rate, real gross domestic product, and prices of aquatic products are factors that enable the convergence of total aquatic products. The results are not materially different across the components of total aquatic products consumption. The implications of the results are discussed in the paper.

Evaluating the effectiveness of joint species distribution modeling for fresh water fish communities within large watersheds

Accurately predicting species’ distributions is critical for the management and conservation of fish and wildlife populations. Joint Species Distribution Models (JSDMs) account for dependencies between species often ignored by traditional species distribution models. We evaluated how a JSDM approach could improve predictive strength for stream fish communities within large watersheds (the Chesapeake Bay Watershed, USA), using a cross-validation study of JSDMs fit to data from over 50 species. Our results suggest that conditional predictions from JSDMs have the potential to make large improvements in predictive accuracy for many species, particularly for more generalist species where single species models may not perform well. For some species there was no added explanatory effect from conditional information, most of which already exhibited strong marginal predictive ability. For several rare species there were significant improvements in occurrence predictions, while the results for two invasive species considered did not show the same improvements. Overall, the optimal number of species to condition upon, as well as the effects of conditioning upon an increasing number of species, varied widely among species.

Implementation of Naïve Bayes Method Diagnosing Diseases Nile Tilapia

The Nile tilapia, also known as Oreochromis niloticus, was a freshwater fish species first produced in East Africa in 1969. It became a popular aquaculture fish in freshwater ponds across Indonesia. Besides its delicious taste, the Nile tilapia is rich in nutrients essential for human health. However, cultivating Nile tilapia was challenging due to frequent bacterial diseases. These diseases often led to mass fish deaths, causing financial losses, especially for new fish farmers. The rapid spread of diseases emphasized the need for prompt intervention to prevent further losses. Farmers needed adequate knowledge about Nile tilapia diseases, but often struggled to absorb information provided by the government. Hence, the presence of experts or veterinarians was crucial in assisting farmers to address these issues. Farmers of Nile tilapia sought assistance from experts or veterinarians, but this was not easy. It involved substantial costs and time, while quick intervention was necessary to mitigate losses. The solution proposed was the development of an expert system for diagnosing and treating Nile tilapia diseases. Thus, an expert system was built to assist fish farmers in identifying fish diseases and their treatments by implementing the naïve Bayes method. The expert system transferred human knowledge to computers, enabling them to solve problems like experts, thereby making expert knowledge accessible to non-experts. Naïve Bayes was implemented to determine the highest probability based on input symptoms. This research used five test data samples to apply the naïve Bayes method to diagnose Nile tilapia diseases, resulting in an accuracy rate of 80%. Therefore, the implementation of naïve Bayes in diagnosing Nile tilapia diseases is considered reasonably effective.

River hydrology mediates fish invasions in Addo Elephant National Park, South Africa

Invasive freshwater fish can often have severe negative effects on native fishes in river systems. The interactions between hydrology and habitat variability can mediate the speed and success of individual invasions and the consequent impact on biodiversity. The rivers within Addo Elephant National Park (AENP) in the Eastern Cape, South Africa experience cyclical droughts and wet periods and as a result are naturally episodic. These rivers were recently invaded by three non-native species, the invasive largemouth bass (Micropterus salmoides) as well as the extralimital sharptooth catfish (Clarias gariepinus) and Mozambique tilapia (Oreochromis mossambicus). Monitoring of key sampling sites along two rivers over a 12-year period that included two major droughts revealed unexpected patterns in the spread of these species and their interactions with native fishes. On the Coerney River, C. gariepinus repeatedly invaded and was extirpated from a seasonal reach of the river, wherein O. mossambicus was only occasionally captured. On the Wit River, two apparently independent introductions of M. salmoides in the lower and upper reaches of the river resulted in patchy habitat occupancy over the course of 12 years. While C. gariepinus regularly co-occurred with native species, M. salmoides appeared to locally extirpate the endangered Eastern Cape redfin (Pseudobarbus afer). During drought, both species persisted in close but disconnected pools, suggesting that the episodic hydrology and geomorphology of these rivers may offer temporary predation refugia for native species during drought.Conservation implications: Drought in episodic rivers can mitigate against the impact and spread of freshwater invasions within protected areas. Effects of drying on invasion corridors and spatial interactions with native species should be taken into consideration when managing such invasions. Severe droughts also offer an opportunity to actively control invasive species when they are confined to accessible drought refugia within the protected area.

Hair Mercury Levels in Pregnant Women: Fish Consumption as a Determinant of Exposure

The consumption of fish in food may contain mercury, a harmful element and dangerous chemical detrimental to human health. The purpose of this study was to determine the mercury level in the hair of pregnant women with different fish intakes in their diets. The concentration of total mercury in hair was determined using an atomic absorption spectrometer. In this study, 98 pregnant women were invited to participate (aged from 18 to 48 years). The mean content of mercury in the hair of pregnant women in Northwestern Russia was 0.428 mg/kg (ranging from 0.018 to 3.1 mg/kg). As a result, 22% of women had mercury values above 0.58 mg/kg, which is considered dangerous for the fetus. The hair mercury concentration in a village area was higher than that in a city area (i.e., 0.548 mg/kg and 0.326 mg/kg). Moreover, the maximum level of mercury was noted for a group of pregnant women who consumed more than 5 kg/month of fish and fish products. Furthermore, the consumption of freshwater fish in the diet leads to a higher mercury content in the hair of pregnant women than the consumption of marine fish.

Genomic analysis and phylogenetic characterization of Himalayan snow trout, Schizothorax esocinus based on mitochondrial protein-coding genes.

Mitochondrial DNA (mtDNA) has become a significant tool for exploring genetic diversity and delineating evolutionary links across diverse taxa. Within the group of cold-water fish species that are native to the Indian Himalayan region, Schizothorax esocinus holds particular importance due to its ecological significance and is potentially vulnerable to environmental changes. This research aims to clarify the phylogenetic relationships within the Schizothorax genus by utilizing mitochondrial protein-coding genes. Standard protocols were followed for the isolation of DNA from S. esocinus. For the amplification of mtDNA, overlapping primers were used, and then subsequent sequencing was performed. The genetic features were investigated by the application of bioinformatic approaches. These approaches covered the evaluation of nucleotide composition, codon usage, selective pressure using nonsynonymous substitution /synonymous substitution (Ka/Ks) ratios, and phylogenetic analysis. The study specifically examined the 13 protein-coding genes of Schizothorax species which belongs to the Schizothoracinae subfamily. Nucleotide composition analysis showed a bias towards A + T content, consistent with other cyprinid fish species, suggesting evolutionary conservation. Relative Synonymous Codon Usage highlighted leucine as the most frequent (5.18%) and cysteine as the least frequent (0.78%) codon. The positive AT-skew and the predominantly negative GC-skew indicated the abundance of A and C. Comparative analysis revealed significant conservation of amino acids in multiple genes. The majority of amino acids were hydrophobic rather than polar. The purifying selection was revealed by the genetic distance and Ka/Ks ratios. Phylogenetic study revealed a significant genetic divergence between S. esocinus and other Schizothorax species with interspecific K2P distances ranging from 0.00 to 8.87%, with an average of 5.76%. The present study provides significant contributions to the understanding of mitochondrial genome diversity and genetic evolution mechanisms in Schizothoracinae, hence offering vital insights for the development of conservation initiatives aimed at protecting freshwater fish species.

Winter mortality of freshwater fish associated with parasitic infection

This study reports an episode of fish mortality occurred in the Garupá and Pindapoy Grande streams, near the confluence with the Paraná River (Garupá, Argentina). Dead and moribund fish of various species were observed floating on the water surface. Environmental parameters measured were temperature 5 °C, water temperature 15.1 (±0.6) °C, dissolved oxygen 8.7 (±1.2) ppm, pH 7.5 (±0.2), electrical conductivity 67.6 (± 8.8) mS cm-1 and mean depth of 1.7 (±1.0) m. Macroscopic examination of moribund fish revealed corneal opacity, whitish tegument, increased gill mucus, and whitish areas on gill filaments. Microscopic analysis of gills revealed severe generalized epithelial hyperplasia, lamellar fusion, congestion, and inflammatory infiltrate, particularly lymphocytes and eosinophilic granular cells. In addition, microscopic examination allowed the identification of the following ectoparasites found in gills and tegument: Chilodonella, Ichthyophthirius, Dactylogyridae and Trichodinidae, representing 98%, 1.2%, 0.6% and 0.2%, respectively. This study constitutes a novel record of wild fish mortality associated with extreme environmental conditions and parasitosis. Furthermore, our findings are significant as there are no prior reports in Argentina of epizootic cases linked to Chilodonella sp. infection in wild or farmed fish populations, being the first report of chilodonelliasis for this region.

Temperature rise and its influence on the toxic effects caused by cyanotoxins in a neotropical catfish

Potentially toxic cyanobacterial blooms (cyanoHABs) have become a problem in public water supply reservoirs. Temperature rise caused by climate change can increase the frequency and intensity of blooms, which may influence the cyanotoxins concentration in the environment. This study aimed to evaluate the effect of the temperature on the responses of a Neotropical catfish exposed to a neurotoxin-rich cyanobacterial crude extract (Raphidiopsis raciborskii T3). Juveniles of Rhamdia quelen were exposed to four treatments, based on study data: control at 25 °C (C25), control at 30 °C (C30), crude extract equivalent to 105 cells.mL-l of R. raciborskii at 25 °C (CE25) and 30 °C (CE30). After 96 h of exposure, the fish were anesthetized and blood was taken. After euthanasia, the gill, posterior kidney, brain, muscle, liver and gonad were sampled for hematological, biochemical, genotoxic and histopathological biomarker analysis. Liver was sampled for proteomic analysis for identification of proteins related to energy production. Water samples were collected at the beginning and the end of the experiment for neurotoxins quantification. Different parameters in both males and females were altered at CE25, evidencing the effects of neurotoxins in freshwater fish. At CE30, a water warming scenario, more effects were observed in females than at 25 °C, such as activation of saxitoxin metabolism pathway and genotoxicity. More damage to macromolecules was observed in females at the higher temperature, demonstrating that the increase in temperature can aggravate the toxicity of neurotoxins produced by R. raciborskii T3.