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Temperature regulates the life cycle of aquatic organisms. However, in the current climate change scenario, the warming of the planet is putting the resilience of many species at risk, resulting in organic disturbances. In the Amazon, the effects of warming demonstrate the low thermal tolerance of species that are already living near their upper temperature limits. In this study, we evaluated the physiological and biochemical responses of specimens of forty-eight (N = 48) pirarucu juveniles (Arapaima gigas) exposed to increasing levels of water temperature (normal environmental temperature of the period — Tenv), 31 °C, 34 °C, and 37 °C) for a period of 96 h, in triplicates (n = 12 fish per temperature). Our main findings show an increase in hematological parameters with a temperature elevation up to 34 °C, followed by suppression at 37 °C. Increases in glucose and lactate levels and reduced triglyceride levels were observed with the elevation in water temperature. Cholesterol levels remained unchanged throughout the experimental period. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes increased at 34 and 37 °C. Oxidative stress levels were elevated at Tenv and were higher at 37 °C when compared to animals at 31 °C. In the liver, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzymes increased with the increase in temperature, while the catalase (CAT) enzyme showed reduced activity at 37 °C. Thus, the data from the present study show that the pirarucu is a species that responds to increasing levels of water temperature. However, a temperature of 37 °C seems to offer a greater risk to the species' ability to cope with the effects of higher temperatures, as it requires greater energy expenditure and induces oxidative stress. Thus, the pirarucu seems to cope better with temperatures that do not exceed 34 °C. [ABSTRACT FROM AUTHOR]

The pirarucu, Arapaima gigas, is an emblematic endangered Amazon osteoglossid with high potential for aquaculture development. In this study, we report the in vivo collection of semen from pirarucu for the first-time and a complete description of the spermatozoa ultrastructure using scanning and transmission electron microscopy (SEM and TEM). The spermatozoon of pirarucu is biflagellate with no acrosomal cell, comprising a spherical head (8.26 ± 2.19 µm2), a short intermediate piece region and two long flagella (68.34 ± 5.69 µm). The nucleus is spherical and electron-dense, and at its base, there are two nuclear fossae where the centrioles are found. The anterior part of the flagellum is positioned at the lateral base of the nucleus, forming an intermediate piece. Lateral to the intermediate piece, an abundant number of mitochondria are present and occupy most of the cytoplasmic volume. The two flagella were found with a 9 + 2 axonemal structure (nine peripheral doublets and two central microtubules). The central microtubules are aligned with two side fins formed laterally by the axoneme plasma membrane. Side fins were observed from the anterior region to the posterior end. The results show that the spermatozoa of A. gigas are biflagellate, mitochondria-rich and robust, corroborating the external fertilization characteristic of the species. The novel description of sperm morphology presented herein will contribute to advancing the knowledge of and aiding future research on the reproductive biology of this species. [ABSTRACT FROM AUTHOR]

Abstract Arapaima gigas, an emblematic species of the Amazon region and a longstanding primary fishing resource, currently holds a “Data Deficient” status on the International Union for Conservation of Nature Red List, and is listed as an endangered species in Brazil. The Tocantins River is the most extensively modified large tributary of the Amazon Basin, and thus can affect the dynamics of ichthyofaunal populations. Over a period of 1 year, representatives of the fishing communities and fishermen from 25 fishing communities from four municipalities in the lower Tocantins River region were interviewed, and the obtained information was evaluated based on the literature to survey the population abundance status of A. gigas in the region and its impact on local communities. Among the fishermen interviewed, only one reported still encountering and fishing A. gigas on Jaracuera Island. The disappearance of A. gigas in the region are viewed as having economically disastrous consequences for the residents. Additionally, other endemic fish species are no longer observed in this locality either. If fishery management officials do not work together with local communities, A. gigas could disappear from the northern region of Brazil, where information on the dynamics of A. gigas fishing is lacking.

The pirarucu (Arapaima gigas) is a fast-growing Amazonian species of high commercial value. The present study aimed to determine the dietary crude protein (CP) level to promote maximum zootechnical performance for pirarucu fingerlings and as their resistance to Aeromonas hydrophila, as well as evaluate their hematological parameters. Pirarucu fingerlings (2.4 ± 0.08 g, 6.8 ± 0.52 cm) were distributed in 18 tanks (140 L, 40 fish per tank, n = 3) and fed six experimental diets consisting of increasing levels of CP: 300, 400, 450, 500, 550 and 650 g kg−1 in a completely randomized design. Data were submitted to one-way ANOVA (p < 0.05) and the ideal CP level for weight gain was determined using polynomial regression analysis. The dietary CP levels were evaluated using a quadratic polynomial regression and the level of 595 g kg−1 was determined for the best weight gain. The hematocrit of fish fed 300 g kg−1 was higher than in the other groups. No mortalities were observed after the 15-day bacterial challenge; however, number of pirarucu with bacterial damage on the pirarucu caudal fin was higher in the group that was fed the diet with 300 g kg−1. A dietary protein level of 618 g kg−1 is therefore recommended for providing maximum weight gain and immunological resistance in pirarucu fingerlings weighing 2.4–112.5 g. [ABSTRACT FROM AUTHOR]

Simple Summary: The world has been changing, and these changes have affected fish in the wild and in captivity. The Intergovernmental Panel on Climate Change (IPCC), which is an international body, predicts climate scenarios for the future that are based mainly on rising temperatures and carbon dioxide levels. Many species are sensitive to scenarios that are considered drastic, which suggests future losses in the rearing of aquatic organisms. In our study, we evaluate how these drastic climate scenarios and exposure to a sublethal concentration of ammonia, a product resulting from the consumption of dietary protein that can be toxic, affect the pirarucu Arapaima gigas, a carnivorous Amazonian fish species that can reach up to 12 kg in one year of farming, but needs to consume a large amount of protein in its feed to do so. Our results show that the pirarucu is sensitive to ammonia and climate change, and that this can impair the animal's growth and some vital body functions, implying economic losses for those who produce it and higher prices for those who consume it. Ammonia is toxic to fish, and when associated with global warming, it can cause losses in aquaculture. In this study, we investigated the physiological and zootechnical responses of Arapaima gigas to the current scenarios and to RCP8.5, a scenario predicted by the IPCC for the year 2100 which is associated with high concentrations of environmental ammonia (HEA). Forty-eight chipped juvenile A. gigas were distributed in two experimental rooms (current scenario and RCP8.5) in aquariums with and without the addition of ammonia (0.0 mM and 2.44 mM) for a period of 30 days. The HEA, the RCP8.5 scenario, and the association of these factors affects the zootechnical performance, the ionic regulation pattern, and the levels of ammonia, glucose, triglycerides, sodium, and potassium in pirarucu plasma. The branchial activity of H+-ATPase was reduced and AChE activity increased, indicating that the species uses available biological resources to prevent ammonia intoxication. Thus, measures such as monitoring water quality in regard to production, densities, and the feed supplied need to be more rigorous and frequent in daily management in order to avoid the accumulation of ammonia in water, which, in itself, proved harmful and more stressful to the animals subjected to a climate change scenario. [ABSTRACT FROM AUTHOR]

Simple Summary: Environmental enrichments are essential tools for providing appropriate welfare conditions for animals under human care by stimulating mental and physical activity. Enrichment programmes in zoos and aquariums have developed rapidly over the past two decades, especially for charismatic mammal and bird species. However, when it comes to lesser-known species such as the arapaima (Arapaima gigas), there is still room for improvement. The arapaima is one of the largest freshwater fish species. It is fished and farmed for its meat but also kept on display in Asian aquariums. Despite its agricultural and ecological importance, there is limited information on the behaviour of the species. Its conservation status on the IUCN Red List continues to be "Data Deficient". In this study, we investigate the use of a green laser pointer as a potential visual enrichment for arapaimas. Without displaying any aggression or territorial behaviour, the fish were more active and utilized more of their habitat in the presence of the novel stimulus. We believe that our findings support the use of the laser pointer as environmental enrichment for arapaimas and provide a basis for further behavioural and welfare research with the species. The arapaima (Arapaima gigas) is one of the largest freshwater fish species, known to exceed 3 m in total length. It is listed as Data Deficient by the IUCN. A. gigas is native to the Amazon River basin where they are an important food source. Arapaimas are also farmed for meat and for live specimens in various South American and Asian countries. Despite decades of keeping the species in public aquariums, little is known of its behaviour and cognitive abilities. This pilot study provides baseline data on using a green laser pointer as environmental enrichment for this species under human care. The data collection included 18 observations before the use of the laser pointer (baseline) and 18 observations during the use of the laser pointer (test). Ten behaviours were monitored, investigating physical contact, activity pattern and habitat use by the fish. During the test, the fish significantly increased their presence in the tank, their level of activity and their use of the habitat. This pilot study provides valuable baseline data for further investigations demonstrating the value of a laser pointer as environmental enrichment for A. gigas under human care. [ABSTRACT FROM AUTHOR]

We propose and describe Alobophora sandrae Cajiao-Mora & Bullard n. gen., n. sp. (Digenea: Caballerotrematidae) for specimens we collected from arapaima, Arapaima gigas sensu lato (Osteoglossiformes: Arapaimidae) in the Amazon River near Leticia, Colombia. Alobophora differs from Caballerotrema Prudhoe, 1960 by lacking head collar projections and by having clustered corner spines and a narrow head collar (4–5× wider than pharynx), whereas Caballerotrema has head collar projections, lacks clustered corner spines, and has a broad head collar (7–8× wider than pharynx). We reassign Caballerotrema annulatum (Diesing, 1850) Ostrowski de Núñez & Sattmann, 2002 to the new genus, as Alobophora annulata (Diesing, 1850) Cajiao-Mora and Bullard n. comb., and provide a supplemental description of Caballerotrema brasiliense Prudhoe, 1960 based on specimens we collected from arapaima. We also examined the holotype and a paratype of Caballerotrema piscicola (Stunkard, 1960) Kostadinova & Gibson, 2001 and concluded that C. piscicola is a junior subjective synonym of C. brasiliense. Our 28S phylogeny recovered A. sandrae sister to A. annulata, with that clade sister to a clade comprising C. brasiliense and an innominate species of Caballerotrema. Caballerotrematidae was recovered sister to Echinostomatidae. We also provide a dichotomous key to caballerotrematids based on head collar projections, corner spine arrangement, proportional pharynx and head collar breadth, testes shape and arrangement, body surface spine shape and distribution, vitellarium distribution, and abundance of prostatic cells.

The pirarucu, Arapaima gigas, is an emblematic endangered Amazon osteoglossid with high potential for aquaculture development. In this study, we report the in vivo collection of semen from pirarucu for the first-time and a complete description of the spermatozoa ultrastructure using scanning and transmission electron microscopy (SEM and TEM). The spermatozoon of pirarucu is biflagellate with no acrosomal cell, comprising a spherical head (8.26 ± 2.19 µm2), a short intermediate piece region and two long flagella (68.34 ± 5.69 µm). The nucleus is spherical and electron-dense, and at its base, there are two nuclear fossae where the centrioles are found. The anterior part of the flagellum is positioned at the lateral base of the nucleus, forming an intermediate piece. Lateral to the intermediate piece, an abundant number of mitochondria are present and occupy most of the cytoplasmic volume. The two flagella were found with a 9 + 2 axonemal structure (nine peripheral doublets and two central microtubules). The central microtubules are aligned with two side fins formed laterally by the axoneme plasma membrane. Side fins were observed from the anterior region to the posterior end. The results show that the spermatozoa of A. gigas are biflagellate, mitochondria-rich and robust, corroborating the external fertilization characteristic of the species. The novel description of sperm morphology presented herein will contribute to advancing the knowledge of and aiding future research on the reproductive biology of this species.

The aim of the present study was to assess the use of sodium chloride (NaCl) against monogenoid trematodes infestations in pirarucu (Arapaima gigas). Two assays were conducted with pirarucu juveniles, the first comprising an in vitro exposure to 8, 9, 10, and 11 g·L−1 NaCl and the second, in vivo exposure test to NaCl at the same concentrations. The best in vitro results were observed for 1-h exposures at 9, 10, and 11 g·L−1 NaCl, resulting in 60% and 100% parasite mortality, respectively. In vivo exposures to 8 and 10 g·L−1 NaCl were 36 and 22% efficient, respectively, following 2 h of exposure, with no mortality. Some dose-dependent changes were observed in exposed fish, such as decreased hemoglobin and MCHC values at the highest NaCl concentration compared to the other NaCl concentrations and the control group. Most frequent gill tissue alterations observed were capillary dilatation and mucus secretions compared to the control group at the highest NaCl concentrations (10 and 11 g·L−1). Decreased mean (p < 0.05) water pH values and increased mean electrical conductivity were noted compared to the control group. In conclusion, our findings suggest that NaCl exhibits low toxicity toward pirarucu without physiological alterations and anthelmintic activity to the monogenoid directly influenced by exposure time and concentration. Moreover, 100% of the monogenoids present in the gills of the fish were identified as Dawestrema cycloancistrium. [ABSTRACT FROM AUTHOR]

In a previous work, the common gonadotrophic hormone α-subunit (ag-GTHα), the ag-FSH β- and ag-LH β-subunit cDNAs, were isolated and characterized by our research group from A. gigas pituitaries, while a preliminary synthesis of ag-FSH was also carried out in human embryonic kidney 293 (HEK293) cells. In the present work, the cDNA sequence encoding the ag-growth hormone (ag-GH) has also been isolated from the same giant Arapaimidae Amazonian fish. The ag-GH consists of 208 amino acids with a putative 23 amino acid signal peptide and a 185 amino acid mature peptide. The highest identity, based on the amino acid sequences, was found with the Elopiformes (82.0%), followed by Anguilliformes (79.7%) and Acipenseriformes (74.5%). The identity with the corresponding human GH (hGH) amino acid sequence is remarkable (44.8%), and the two disulfide bonds present in both sequences were perfectly conserved. Three-dimensional (3D) models of ag-GH, in comparison with hGH, were generated using the threading modeling method followed by molecular dynamics. Our simulations suggest that the two proteins have similar structural properties without major conformational changes under the simulated conditions, even though they are separated from each other by a >100 Myr evolutionary period (1 Myr = 1 million years). The sequence found will be used for the biotechnological synthesis of ag-GH while the ag-GH cDNA obtained will be utilized for preliminary Gene Therapy studies. [ABSTRACT FROM AUTHOR]

The introduction of non-native fish poses a major threat to aquatic fauna in freshwater ecosystems around the world, often as a consequence of increased predation pressure, which results in adverse environmental and socioeconomic effects. In this study, we present a survey of publicly available information on the occurrence of pirarucu (Arapaima spp.) throughout Brazil, with an emphasis on the status of native and non-native populations, and discuss the implications for the conservation of aquatic biodiversity and the urgent need for strict control and monitoring of pirarucu breeding programs, especially in regions where it is non-native. We believe that researchers and public policy makers/managers should collaborate in managing introductions of non-native fish, and develop regulations, scientific research, risk assessments, and environmental education with this end in mind. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study was to investigate the parasites occurrences and to determine the rates of infestation/parasitic infection in juvenile Arapaima gigas from seven fish farms in the state of Amazonas, relating to the characteristics of these fish farms. Of the 70 A. gigas evaluated, 43 were infested/infected, with a total of 133 parasites collected. Three fish farms (2, 4, 6) showed the highest levels of prevalence of parasites (100%, 70%, 70%), mean intensity (4.1±2.6, 8.1±9.2, and 2.1±1.3), and mean abundance (4.1±2.6, 5.7±8.1, and 1.5±1.5), respectively. Prevalence ranged from 30% to 100%, mean intensity from 1.0 to 8.1 and mean abundance from 0.3 to 5.7. Monogenea, Digenea, Nematoda (Hysterothylacium sp. and Spirocamallanus sp.) and Acanthocephala (Neoechinorhynchus sp. and Polyacanthorhynchus sp.) were identified. The parasites Hysterothylacium sp. and Neoechinorhynchus sp. were the most prevalent parasites with 31.43% and 15.71%, respectively. The fish presented negative allometry in growth and constant condition factor. Measures to prevent and control the parasitic diseases diagnosed are discussed as well prophylactic practices that contribute to the biosecurity of the farms.

Copyright of Acta Veterinaria Brasilica is the property of Acta Veterinaria Brasilica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Trichlorfon is a widely used drug to control ectoparasites in fish farming and is effective in treating protozoa, helminths, and crustaceans. However, prior to a concentration recommendation made for therapeutic purposes in aquaculture, it is necessary to establish its toxicity, behavioural and histological effects, and determine a safe use dose for each target species. Here we investigated the acute toxicity (LC50-12 h) of trichlorfon and its behavioural and histological effects on arapaima (Arapaima gigas) larvae and juveniles. For the acute toxicity tests (LC50), arapaima larvae and juveniles were exposed at 0, 50, 250, 500, 750, 1.000 and 1.250 mg L−1 of trichlorfon for 12 h. During this period, behavioural changes, mortality, and the water physico-chemical parameters were recorded. Immediately after a toxicity test, gills were collected for the histological analysis. The LC50–12 h for the arapaima larvae and juveniles were 411.8 mg L−1 and 587.3 mg L−1, respectively. The fish exposed for different times to the 250, 500, 750, 1.000 and 1.250 mg L−1 concentrations showed a dose-dependent effect with behavioural changes, such as erratic swimming, loss of balance, lethargy, gasping at the water surface and muscle spasms. Histological changes, such as lamellar hyperplasia and cell hypertrophy, total lamellar fusion, dilation, and vascular congestion in the central filament vessel, interlamellar hyperplasia, capillary congestion, proliferation of mucous cells, dilation of the venous sinus and capillaries, leukocyte infiltrate and haemorrhage, were observed and ranged from mild to diffuse lesions. However, branchial necrosis was presented only in the fish exposed to ≥ 500 mg L−1 of trichlorfon. In conclusion, sublethal trichlorfon concentrations (≤ 250 mg L−1) and short exposure times (up to 180 min) can be safely used in arapaima larvae and juveniles because they do not alter their normal behaviour nor induce mortalities and/or irreversible injuries to their gills.

Ammonia is toxic to fish, and when associated with global warming, it can cause losses in aquaculture. In this study, we investigated the physiological and zootechnical responses of Arapaima gigas to the current scenarios and to RCP8.5, a scenario predicted by the IPCC for the year 2100 which is associated with high concentrations of environmental ammonia (HEA). Forty-eight chipped juvenile A. gigas were distributed in two experimental rooms (current scenario and RCP8.5) in aquariums with and without the addition of ammonia (0.0 mM and 2.44 mM) for a period of 30 days. The HEA, the RCP8.5 scenario, and the association of these factors affects the zootechnical performance, the ionic regulation pattern, and the levels of ammonia, glucose, triglycerides, sodium, and potassium in pirarucu plasma. The branchial activity of H+-ATPase was reduced and AChE activity increased, indicating that the species uses available biological resources to prevent ammonia intoxication. Thus, measures such as monitoring water quality in regard to production, densities, and the feed supplied need to be more rigorous and frequent in daily management in order to avoid the accumulation of ammonia in water, which, in itself, proved harmful and more stressful to the animals subjected to a climate change scenario.

The arapaima (Arapaima gigas) is one of the largest freshwater fish species, known to exceed 3 m in total length. It is listed as Data Deficient by the IUCN. A. gigas is native to the Amazon River basin where they are an important food source. Arapaimas are also farmed for meat and for live specimens in various South American and Asian countries. Despite decades of keeping the species in public aquariums, little is known of its behaviour and cognitive abilities. This pilot study provides baseline data on using a green laser pointer as environmental enrichment for this species under human care. The data collection included 18 observations before the use of the laser pointer (baseline) and 18 observations during the use of the laser pointer (test). Ten behaviours were monitored, investigating physical contact, activity pattern and habitat use by the fish. During the test, the fish significantly increased their presence in the tank, their level of activity and their use of the habitat. This pilot study provides valuable baseline data for further investigations demonstrating the value of a laser pointer as environmental enrichment for A. gigas under human care.

This study evaluated the mortality rate, histopathology and haematological parameters of Arapaima gigas against Aeromonas hydrophila after 68 days of dietary probiotic supplementation with autochthonous bacterium Enterococcus faecium. Three experiments were carried out: the first assay evaluated the lethality of A. hydrophila, the second and the third assay evaluated the fish supplemented subjected to A. hydrophila lethal dose 30% (106 CFU ml-1) and lethal dose 100% (108CFU ml-1) respectively. The clinical signs, blood changes, histopathological alterations and mortalities were evaluated. At the first experiment, the concentrations of 106 and 108CFU.mL-1 with A. hydrophila caused 33% and 100% of mortality. The A. hydrophila infection provoked clinical signs such as dark skin, ulceration, haemorrhage, pale gills and liver, hepatic alterations, hyperaemia, hepatic cord breakdown, cellular deforming, lipid degeneration and necrosis. In the second experiment, no mortality occurred onto fish fed with probiotic. Furthermore, in the third experiment, fish submitted to probiotic supplementation showed reduction in mortality of 75% compared with the control and fish fed with probiotic diets at 108CFU g-1 not presented any clinical signs. For these reasons, Arapaima gigas juveniles previously submitted to probiotic supplementation with E. faecium (108CFU g-1) shows better physiological and immunological response, improving resistance against A. hydrophila infection. [ABSTRACT FROM AUTHOR]

The increasing prevalence of multi-drug resistant (MDR) Escherichia coli in distinct ecological niches, comprising water sources and food-producing animals, such as fish species, has been widely reported. In the present study, quinolone-resistant E. coli isolates from Arapirama gigas, a major fish species in the Brazilian Amazon rivers and fish farms, were characterized regarding their antimicrobial susceptibility, virulence, and genetic diversity. A total of forty (40) specimens of A. gigas, including 20 farmed and 20 wild fish, were included. Thirty-four quinolone-resistant E. coli isolates were phenotypically tested by broth microdilution, while resistance and virulence genes were detected by PCR. Molecular epidemiology and genetic relatedness were analyzed by MLST and PFGE typing. The majority of isolates were classified as MDR and detected harboring blaCTX-M, qnrA and qnrB genes. Enterotoxigenic E. coli pathotype (ETEC) isolates were presented in low prevalence among farmed animals. MLST and PFGE genotyping revealed a wide genetic background, including the detection of internationally spread clones. The obtained data point out A. gigas as a reservoir in Brazilian Amazon aquatic ecosystems and warns of the interference of AMR strains in wildlife and environmental matrices. [ABSTRACT FROM AUTHOR]

The rapid coagulation of fish blood makes the use of anticoagulants in hematological analysis necessary and means that choosing the most appropriate product is important. The aim of the present study was to evaluate the effect of two different anticoagulants (heparin sodium and K2EDTA), storage time, and temperature on the hematological values of Arapaima gigas juveniles. Twelve juveniles (905.79 ± 111.2 g and 49 ± 1.74 cm) kept in captivity were used for the tests. Blood was collected from the caudal vein and divided for the analysis of the effects of K2EDTA 10% and heparin sodium 5000 IU, storage time (0, 5, 10, and 24 h), and temperature (4 and 28 °C). The hematocrit, erythrocyte count, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH), and differential leukocyte count were evaluated. The results revealed significant differences in the hematocrit, lymphocytes, and neutrophils when the anticoagulants were compared at 0 h of storage. In the hematocrit, heparin sodium produced variations, while K2EDTA maintained the values constant at 5 h, the erythrocyte count constant for up to 24 h, with the exception of at 4 °C, while hemoglobin produced variations in all the groups at 5 h. The blood indices MCV, MCHC, and MCH were best preserved, without variations, using K2EDTA at 28 °C for up to 5 h. In conclusion, K2EDTA 10% at 28 °C maintained constant hematological values of Arapaima gigas for 5 h, with the exception of hemoglobin, which should be analyzed as soon as possible. [ABSTRACT FROM AUTHOR]

This study investigated the in vitro and in vivo efficacy of trichlorfon against Dawestrema cycloancistrium, as well as its physiological effects on arapaima. Naturally parasitized arapaima gill arches were exposed in vitro to 100, 250, 500 and 750 mg/L of trichlorfon and a control group (only distilled water), in triplicate. Parasites were monitored, and mortality was used to determine the median effective concentration (EC50). The 750 mg/L concentration demonstrated 100% in vitro efficacy against D. cycloancistrium after 60 min, while the intermediate (500 mg/L) and the lowest (100 and 250 mg/L) tested concentrations were completely efficient after 90 and 130 min, respectively. The EC50‐1h of trichlorfon for D. cycloancistrium was determined at 171.73 mg/L. Parasitized arapaima juveniles were exposed to a control group and 150 mg/L of trichlorfon in triplicate. Fish were exposed to two therapeutic baths for 60 min with 24‐h intervals between treatments. Therapeutic baths with 150 mg/L of trichlorfon were 92.99% effective against D. cycloancistrium and did not bring about haematological alterations (erythrogram, white blood cell count, thrombogram, plasma glucose and total proteins). Therefore, 150 mg/L of trichlorfon can be used in therapeutic baths to control and treat D. cycloancistrium infestations with no physiological impairments for arapaima. [ABSTRACT FROM AUTHOR]

In a previous work, the common gonadotrophic hormone α-subunit (ag-GTHα), the ag-FSH β- and ag-LH β-subunit cDNAs, were isolated and characterized by our research group from A. gigas pituitaries, while a preliminary synthesis of ag-FSH was also carried out in human embryonic kidney 293 (HEK293) cells. In the present work, the cDNA sequence encoding the ag-growth hormone (ag-GH) has also been isolated from the same giant Arapaimidae Amazonian fish. The ag-GH consists of 208 amino acids with a putative 23 amino acid signal peptide and a 185 amino acid mature peptide. The highest identity, based on the amino acid sequences, was found with the Elopiformes (82.0%), followed by Anguilliformes (79.7%) and Acipenseriformes (74.5%). The identity with the corresponding human GH (hGH) amino acid sequence is remarkable (44.8%), and the two disulfide bonds present in both sequences were perfectly conserved. Three-dimensional (3D) models of ag-GH, in comparison with hGH, were generated using the threading modeling method followed by molecular dynamics. Our simulations suggest that the two proteins have similar structural properties without major conformational changes under the simulated conditions, even though they are separated from each other by a >100 Myr evolutionary period (1 Myr = 1 million years). The sequence found will be used for the biotechnological synthesis of ag-GH while the ag-GH cDNA obtained will be utilized for preliminary Gene Therapy studies.

The Arapaima gigas is an endemic fish to the Amazon basin and with great potential for aquaculture, although its reproduction in captivity is limited by the absence of sexual dimorphism. The demand increase for pirarucu in the Northern region of Brazil, has led to new studies on the reproduction of the species. Thus, we aimed to investigate patterns of sex‐biased genes in brain and gonad tissues of A. gigas. A total of of 451,490,808 short sequencing reads were produced using the SOLiD v4 plus sequencing platform. An average of ~30% of sequencing reads were mapped to Asian arowana reference cDNAs, species that belong to the same group of bony‐tongue fishes. Gene expression analysis identified 305 sex‐biased genes for the brain, with 297 genes up‐regulated in females and only eight genes up‐regulated in males. The analysis of the gonads identified 120 sex‐biased genes, with 110 genes up‐regulated in females and only ten genes up‐regulated in males. Gene ontology analysis found more than 50 terms enriched for the sex‐biased genes in a wide range of pathways suggesting that multiple functions and processes differ between the sexes. Thus, the following areas of interest were approached: sex steroids/hormones, organism development process and macromolecule biosynthetic process, which exhibited sex‐biased gene expression; these areas are known to influence sexual development in other species. Lastly, the information obtained in this study concerning the sex‐biased genes in the A. gigas species is a contribution to further studies approaching the processes of gonadal development, and downstream molecular mechanisms in species. [ABSTRACT FROM AUTHOR]

The obligate air‐breathing Amazonian fish, Arapaima gigas, hatch as water‐breathing larvae but with development, they modify their swim bladder to an air‐breathing organ (ABO) while reducing their gill filaments to avoid oxygen loss. Here, we show that significant changes already take place between 4 weeks (1.6 g) and 11 weeks (5 g) post hatch, with a reduction in gill lamellar surface area, increase in gill diffusion distance, and proliferation of the parenchyma in the ABO. By using a variety of methods, we quantified the surface area and diffusion distances of the gills and skin, and the swim bladder volume and anatomical complexity from hatch to 11‐week‐old juveniles. In addition, we identified the presence of two ionocyte types in the gills and show how these change with development. Until 1.6 g, A. gigas possess only the H+‐excreting/Na+‐absorbing type, while 5‐g fish and adults have an additional ionocyte which likely absorbs H+ and Cl− and excretes HCO3−. The ionocyte density on the gill filaments increased with age and is likely a compensatory mechanism for maintaining ion transport while reducing gill surface area. In the transition from water‐ to air‐breathing, A. gigas likely employs a trimodal respiration utilizing gills, skin, and ABO and thus avoid a respiratory–ion regulatory compromise at the gills. Highlights: Significant transformations in gill, skin, and ABO between 1.6 and 5.5 g body mass of A. gigas with the transition from water‐ to air breathing Larval A. gigas gills have one ionocyte type for Na+ and H+ regulation, while older juveniles and adults have an additional ionocyte type for Cl− and HCO3− [ABSTRACT FROM AUTHOR]

Abstract The use of biopesticides based on Bacillus thuringiensis (Berliner 1915) in agriculture has been considered harmless for non-target organisms such as fish. The present study aimed to investigate the effects of a biopesticide based on B. thuringiensis on the physiology and histology of the liver, kidney and intestine of Arapaima gigas (Schinz, 1822), via exposure to water (0.13 g/L) and in the diet (0.13 g), after 24 and 48 h. Fish subjected to B. thuringiensis in the water of their breeding and feeding tanks exhibited mortality due to changes in erythrogram (hematocrit, hemoglobin, erythrocytes), thrombogram and leucogram blood parameters, and plasma (sodium, chloride, potassium, cholesterol, glucose, triglycerides, cortisol and total proteins) and enzymatic (Aspartate Amino Transferase and Alanine Amino Transferase) biochemistry. Histopathological alterations in the liver and kidney ranged from mild to severe and were characterized by the presence of cytoplasmic vacuolization, nuclear hypertrophy and atrophy, melanomacrophage centers and necrosis, and in the intestine by changes to the number of villi and goblet cells. Therefore, these physiological and histopathological alterations indicate that care should be taken with the dispersion of biopesticides based on agricultural B. thuringiensis in fish farming.

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Abstract Background Arapaima gigas (Schinz, 1822) is the largest freshwater scaled fish in the world, and an emerging species for tropical aquaculture development. Conservation of the species, and the expansion of aquaculture requires the development of genetic tools to study polymorphism, differentiation, and stock structure. This study aimed to investigate genomic polymorphism through ddRAD sequencing, in order to identify a panel of single nucleotide polymorphisms (SNPs) and to simultaneously assess genetic diversity and structure in wild (from rivers Amazon, Solimões, Tocantins and Araguaia) and captive populations. Results Compared to many other teleosts, the degree of polymorphism in A. gigas was low with only 2.3% of identified RAD-tags (135 bases long) containing SNPs. A panel of 393 informative SNPs was identified and screened across the five populations. Higher genetic diversity indices (number of polymorphic loci and private alleles, Shannon’s Index and HO) were found in populations from the Amazon and Solimões, intermediate levels in Tocantins and Captive, and very low levels in the Araguaia population. These results likely reflect larger population sizes from less urbanized environments in the Amazon basin compared to Araguaia. Populations were significantly differentiated with pairwise F ST values ranging from 0.086 (Amazon × Solimões) to 0.556 (Amazon × Araguaia). Mean pairwise relatedness among individuals was significant in all populations (P

In fish, bacteriosis has been widely linked with Aeromonas species, but co‐infection by these bacteria has been little addressed. The aims of this study were to report on an outbreak of disease in pirarucu Arapaima gigas caused by Aeromonas and to investigate experimental co‐infection and characterize resistance profile, virulence factors and phenotypic and molecular differentiation. Fish samples with clinical signs of bacteriosis were collected and used to study experimental co‐infection. The bacterial isolates were characterized phenotypically as Aeromonas hydrophila and Aeromonas jandaei. Virulence genes aerA, gcat, lip, dnase and hlyA were detected using the polymerase chain reaction, while the alt, act and ser genes were not found. Resistance to imipenem and ceftriaxone was observed; however, all isolates were susceptible to most of the antibiotics assayed. Phenotypic tests to determine the presence of metallo‐β‐lactamases showed positivity only for A. jandaei strains. Assays for the resistance genes kpc, ndm, imp, oxa‐48 and vim showed negative results. The co‐infection and pathogenicity of A. hydrophila in association with A. jandaei in A. gigas, established in accordance with Koch's postulate, provided experimental support for the existence of synergism between these bacteria. This has several implications relating to occurrences of this co‐infection and determinants of virulence. [ABSTRACT FROM AUTHOR]

The arapaima is the largest of the extant air-breathing freshwater fishes. Their respiratory gas bladder is arguably the most striking of all the adaptations to living in the hypoxic waters of the Amazon basin, in which dissolved oxygen can reach 0 ppm (0 mg/l) at night. As obligatory air-breathers, arapaima have undergone extensive anatomical and physiological adaptations in almost every organ system. These changes were evaluated using magnetic resonance and computed tomography imaging, gross necropsy, and histology to create a comprehensive morphological assessment of this unique fish. Segmentation of advanced imaging data allowed for creation of anatomically accurate and quantitative 3D models of organs and their spatial relationships. The deflated gas bladder [1.96% body volume (BV)] runs the length of the coelomic cavity, and encompasses the kidneys (0.35% BV). It is compartmentalized by a highly vascularized webbing comprising of ediculae and inter-edicular septa lined with epithelium acting as a gas exchange surface analogous to a lung. Gills have reduced surface area, with severe blunting and broadening of the lamellae. The kidneys are not divided into separate regions, and have hematopoietic and excretory tissue interspersed throughout. The heart (0.21% BV) is encased in a thick layer of lipid rich tissue. Arapaima have an unusually large telencephalon (28.3% brain volume) for teleosts. The characteristics that allow arapaima to perfectly exploit their native environment also make them easy targets for overfishing. In addition, their habitat is at high risk from climate change and anthropogenic activities which are likely to result is fewer specimens living in the wild, or achieving their growth potential of up to 4.5 m in length.

The arapaima is the largest of the extant air-breathing freshwater fishes. Their respiratory gas bladder is arguably the most striking of all the adaptations to living in the hypoxic waters of the Amazon basin, in which dissolved oxygen can reach 0 ppm (0 mg/l) at night. As obligatory air-breathers, arapaima have undergone extensive anatomical and physiological adaptations in almost every organ system. These changes were evaluated using magnetic resonance and computed tomography imaging, gross necropsy, and histology to create a comprehensive morphological assessment of this unique fish. Segmentation of advanced imaging data allowed for creation of anatomically accurate and quantitative 3D models of organs and their spatial relationships. The deflated gas bladder [1.96% body volume (BV)] runs the length of the coelomic cavity, and encompasses the kidneys (0.35% BV). It is compartmentalized by a highly vascularized webbing comprising of ediculae and inter-edicular septa lined with epithelium acting as a gas exchange surface analogous to a lung. Gills have reduced surface area, with severe blunting and broadening of the lamellae. The kidneys are not divided into separate regions, and have hematopoietic and excretory tissue interspersed throughout. The heart (0.21% BV) is encased in a thick layer of lipid rich tissue. Arapaima have an unusually large telencephalon (28.3% brain volume) for teleosts. The characteristics that allow arapaima to perfectly exploit their native environment also make them easy targets for overfishing. In addition, their habitat is at high risk from climate change and anthropogenic activities which are likely to result is fewer specimens living in the wild, or achieving their growth potential of up to 4.5 m in length. [ABSTRACT FROM AUTHOR]

Dawestrema cycloancistrium is the main ectoparasite causing mortality in fingerlings of pirarucu (Arapaima gigas) in Amazonian aquaculture. Very little is known about the D. cycloancistrium reproductive index and appropriate methods of collecting eggs for investigation. This study aimed to determine the oviposition rate of D. cycloancistrium. To achieve this aim, two egg quantification methods were tested: the estimative method (ME) and the total counting method (MT). Compared with the MT, the ME overestimated the number of eggs counted, which were 2943.5 ± 2840.6 and 1041.5 ± 533 eggs, and the oviposition rate, which was 80.1 ± 58.7 and 31.4 ± 16.4 eggs/parasite/day, for ME and MT, respectively. These results show that for studies quantifying D. cycloancistrium eggs, the total eggs in the sample must be counted, as the estimates made using subsamples are not representative. Using the MT, the oviposition rate for D. cycloancistrium was determined to be 31.4 ± 16.4 eggs per adult parasite per day. The present study demonstrates the egg production capacity of a monogenean species parasite of A. gigas , providing basic biological data for D. cycloancistrium. [ABSTRACT FROM AUTHOR]

Abstract The nutritional quality and lipid stability of Arapaima gigas fillets were investigated. A total of 27.32 kg of A. gigas fillets were obtained and the proximate composition and fatty acid profile immediately determined. In addition, the lipid oxidation parameters were analyzed during 15 and 90 days at 4 °C and –20 °C, respectively. The A. gigas fillets presented high protein (> 15%) and low lipid (< 2%) contents with elevated polyunsaturated fatty acid (PUFAs) contents (43.97%). The nutritional quality indices were the atherogenicity index (0.35), thrombogenicity index (0.28) and the hypocholesterolemic acid/ hypercholesterolemic acid ratio (2.37). Overall, an increase followed by a decrease was observed in the peroxide index (PI) and malondialdehyde content (MDA) results at both storage temperatures ( p < 0.05). The lipid profile exhibited great nutritional quality, however new conservation methods should be investigated for this matrix due to increased lipid oxidation during refrigerated and frozen storage.

Intensive fish farming has resulted in an increased concern for disease outbreaks. Probiotic use is one of the strategies being developed to improve fish health and productivity. Measures of probiotic colonization, growth performance, haematological characteristics and parasite load were used to evaluate the effect of diets supplemented with Enterococcus faecium on growth and health of Arapaima gigas juveniles. A completely randomized design with four treatments (diet with E. faecium at 1 × 106 CFU/g and 1 × 108 CFU/g, control diet and diet with the culture medium MRS) and three replicates was used. Ninety‐six Arapaima juveniles were distributed in 12 cages fed with the specified diet for 68 days. Colonization of the intestinal tract by lactic acid bacteria reduced the total number of heterotrophic bacteria in fish fed with probiotics compared to controls. Fish fed a supplemented diet containing 1 × 108 CFU/g presented higher values of weight gain, survival and fish growth uniformity, and lower values of feed conversion ratio. The prevalence of Trichodina sp. could have affected the survival of fish in the control group. Reduction in parasite load and an increase in haematocrit, the number of erythrocytes, thrombocytes, neutrophils and monocytes were also observed in fish fed the diet containing 1 × 108 CFU/g. Enterococcus faecium presented a probiotic effect in A. gigas juveniles and can be recommended for use at a concentration of 1 × 108 CFU/g to modify the gut microbiota, improve growth performance and haematology and reduce parasitic load. [ABSTRACT FROM AUTHOR]

Abstract The practice of indoor larviculture can be an alternative to enhance the rearing of arapaima larvae, improving their survival and the supply of arapaima juveniles for the grow-out stage. We aimed to evaluate different live microcrustaceans as feed for arapaima larvae to verify groups that can be safely used in laboratory trials, as well as in commercial larviculture. Arapaima larvae (39.45 ± 7.04 mg and 2.09 ± 0.13 cm) were housed in 12-L circular tanks (n = 4 tanks; 30 larvae per tank) in a static water system. The tanks were cleaned twice a day, when 50% of the water was changed. Fish were fed three types of live feed 9 times/day: brine shrimp Artemia sp. nauplii (AR), Cladocera-rich zooplankton (CZ), and Ostracoda-rich zooplankton (OZ) for 15 days. Fish fed CZ and AR showed a similar fast growth rate with low mortality rates. The OZ fed Arapaima larvae presented intact Ostracoda in their rectums. This findins, demonstrates their poor digestibility, which resulted in poor growth and low survival. Ostracoda-rich zooplankton must be avoided in arapaima larviculture until 8 days after they begin swimming to the water surface or 17 days after hatching. Highligths • Cladocera-rich zooplankton and Artemia sp. nauplii were suitable live feed sources to arapaima larvae providing fast growth rates with low mortality; • Ostracoda-rich zooplankton were well consumed by arapaima larvae; • The presence of intact ostracoda in the arapaima rectum demonstrates its low digestibility; • Arapaima larvae fed ostracoda-rich zooplankton presented poor growth and low survival. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the survival and growth of Arapaima gigas larvae reared in slightly salinized water. Pirarucu larvae (183.1 ± 41.2 mg and 3.4 ± 0.3 cm) were stocked in PVC tanks (20 L; n = 4; 40 larvae per tank) in a static system. A. gigas larvae were reared in increasing levels of salinized water (0, 1, 2, 3 and 4‰) for a period of 15 days. Fish were fed six times a day with Artemia nauplii (2,900 nauplii per larvae per meal in the beginning). The salinized water increased by at least four times the Artemia nauplii lifespan, which prolonged the time of live food supply to Arapaima larvae. Pirarucu larvae kept in freshwater presented the lowest values in weight gain, final weight and survival. Larvae reared in water with 4‰ of salinized water showed the highest final weight. Slightly salinized water enhances the growth and survival of A. gigas larvae and it can be a simple practice with low cost that can be applied in the routine of pirarucu larviculture. [ABSTRACT FROM AUTHOR]

Early‐life survival of Arapaima gigas is one of the main challenges of its farming. In this study, we described the morphological and histochemical development of the gastrointestinal tract of arapaima larvae. Larvae were collected from a pond when they started to swim to the water surface (initial day) and were housed in indoor tanks. Daily samplings (n = 10) were performed from 0 to the 11th day after the collection (DAC) and then on the 14th, 17th, and 20th DAC. On the initial day, arapaima larvae (0.05 ± 0.01 g; 2.21 ± 0.06 cm) had opened mouth and anus and no yolk sac. In addition, larvae presented well‐developed digestive organs. Gastric glands were fully formed, with positive reactions to alcian blue (AB) pH 1.0 as well as to periodic acid‐Schiff (PAS) in the simple columnar epithelium. There were folds throughout the intestine and brush border, with an AB pH of 2.5 + PAS positive mucins. From 1 to 11 DAC, larvae presented increasing concentrations of gastric glands and thickness of the stomach muscular layer. From 14 to 20 DAC, the intestine presented high‐fold complexity. We suggest that arapaima larvae may be fed exogenous inert diets at a size of around 2 cm. [ABSTRACT FROM AUTHOR]

Background: Arapaima gigas (Schinz, 1822) is the largest freshwater scaled fish in the world, and an emerging species for tropical aquaculture development. Conservation of the species, and the expansion of aquaculture requires the development of genetic tools to study polymorphism, differentiation, and stock structure. This study aimed to investigate genomic polymorphism through ddRAD sequencing, in order to identify a panel of single nucleotide polymorphisms (SNPs) and to simultaneously assess genetic diversity and structure in wild (from rivers Amazon, Solimões, Tocantins and Araguaia) and captive populations. Results: Compared to many other teleosts, the degree of polymorphism in A. gigas was low with only 2.3% of identified RAD-tags (135 bases long) containing SNPs. A panel of 393 informative SNPs was identified and screened across the five populations. Higher genetic diversity indices (number of polymorphic loci and private alleles, Shannon's Index and HO) were found in populations from the Amazon and Solimões, intermediate levels in Tocantins and Captive, and very low levels in the Araguaia population. These results likely reflect larger population sizes from less urbanized environments in the Amazon basin compared to Araguaia. Populations were significantly differentiated with pairwise FST values ranging from 0.086 (Amazon × Solimões) to 0.556 (Amazon × Araguaia). Mean pairwise relatedness among individuals was significant in all populations (P < 0.01), reflecting a degree of inbreeding possibly due to severe depletion of natural stocks, the species sedentary behaviour and possible sampling biases. Although Mantel test was not significant (P = 0.104; R2 = 0.65), Bayesian analysis in STRUCTURE and discriminant analysis of principal components (DAPC) showed populations of Amazon and Solimões to be genetically differentiated from Araguaia, with Tocantins comprising individuals from both identified stocks. Conclusions: This relatively rapid genotyping by sequencing approach proved to be successful in delineating arapaima stocks. The approach and / or SNP panels identified should prove valuable for more detailed genetic studies of arapaima populations, including the elucidation of the genetic status of described discrete morphotypes and aid in delivery of conservation programs to maintain genetic diversity in reservoirs across the Amazon region. [ABSTRACT FROM AUTHOR]

The community‐based management of Arapaima gigas for sustainable commercial use allows that wild fish legally harvested in the Brazilian Amazon supply the demand for exotic leather in the US, supporting the conservation of the forest and providing income for fishers communities if based in fair‐trade. We provide a more optimistic view than Heinrich et al. (2019) on the effects of international trade of arapaima leather in the conservation of the species in Brazil. [ABSTRACT FROM AUTHOR]

Although biodiversity has value for the global community, biodiversity protection often imposes costs on local communities. Correcting this misalignment requires appropriate local incentives. Conservation agreements (i.e. negotiated transactions in which conservation investors finance social benefits in return for conservation actions by communities) are a form of direct incentive. The results of this approach depend on effective monitoring of ecological and socio-economic impacts to verify that environmental and development objectives are met. Monitoring is also needed to verify that parties to the agreements comply with their commitments. Ecological monitoring results for agreements between Conservation International and communities in the Colombian Amazon show positive conservation impacts. These agreements are designed to protect forest areas and two threatened fish species that are important to local livelihoods and have high commercial value. We show how effective monitoring is essential for identifying long-term sustainability options. Lessons learned from this project inform reflection on emerging frameworks for scaling up the approach to the national level. [ABSTRACT FROM AUTHOR]

The Pirarucu (Arapaima gigas) is one of the world's largest freshwater fishes and member of the superorder Osteoglossomorpha (bonytongues), one of the oldest lineages of ray-finned fishes. This species is an obligate air-breather found in the basin of the Amazon River with an attractive potential for aquaculture. Its phylogenetic position among bony fishes makes the Pirarucu a relevant subject for evolutionary studies of early teleost diversification. Here, we present, for the first time, a draft genome version of the A. gigas genome, providing useful information for further functional and evolutionary studies. The A. gigas genome was assembled with 103-Gb raw reads sequenced in an Illumina platform. The final draft genome assembly was ∼661 Mb, with a contig N50 equal to 51.23 kb and scaffold N50 of 668 kb. Repeat sequences accounted for 21.69% of the whole genome, and a total of 24,655 protein-coding genes were predicted from the genome assembly, with an average of nine exons per gene. Phylogenomic analysis based on 24 fish species supported the postulation that Osteoglossomorpha and Elopomorpha (eels, tarpons, and bonefishes) are sister groups, both forming a sister lineage with respect to Clupeocephala (remaining teleosts). Divergence time estimations suggested that Osteoglossomorpha and Elopomorpha lineages emerged independently in a period of ∼30 Myr in the Jurassic. The draft genome of A. gigas provides a valuable genetic resource for further investigations of evolutionary studies and may also offer a valuable data for economic applications. [ABSTRACT FROM AUTHOR]

Summary: The gill structure of the Amazonian fish Arapaima gigas (Cuvier 1829) shows ontogenetic changes during development, particularly due the transition from the aquatic to the obligatory air breathing mode of respiration. However, three main cell types can be found in the gills: mitochondrial rich cells, pavement cells and mucous cells (MCs). The MCs are involved in the secretory pathway. The functions of the secreted molecules include mechanical protection of epithelia, protection against parasites and bacterial infection, and role on ion regulation. In this study, we analysed mucous cell location and mucous cell type, based on pH, during the development of A. gigas. Using samples obtained from the environment, gills were collected and fixed in buffered solution. Histological techniques for the identification of MCs were performed Alcian Blue (AB) and periodic acid‐Schiff (PAS). The results showed the presence of PAS+ and AB+ cells in the whole filament in all examined fish. In animals less than 50 g, few MCs were present, and no differences were observed in AB+ and PAS+ cells. In animals weighing close to 500 g, more PAS+ cells than AB+ cells were observed, and in animals that weighed more than 1,000 g, more AB+ cells than PAS+ cells were observed. These observations may be a result of the ontogenetic changes in the gill epithelia, which can change the osmorespiratory compromise in ion regulation functions as well the glycosaminoglycans secreted by PAS cells, which in large animals can play a role in the protection against parasites and bacterial infection. [ABSTRACT FROM AUTHOR]

Copyright of Pesquisa Veterinaria Brasileira is the property of Colegio Brasileiro de Patologia Animal - CBPA and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: In carnivorous fish species, zooplankton is one of the main food items in the early life stages and some fish species continue feeding on such food items further along the life stages even in the farming environment. In this study, the intake of natural food items was assessed in juvenile pirarucu Arapaima gigas reared in earthen ponds. Juvenile pirarucu (12.2 ± 4.32 g and 12.1 ± 1.13 cm) were stocked in fertilized earthen ponds (240 m²). For the analysis of the fish stomach content and plankton in the pond water, the fish and pond water were sampled weekly for 75 days and biweekly until the fish reached a mean weight of 750 g. Although artificial feed was used, pirarucu also ingested the natural food available in the pond water. Among the zooplankton, pirarucu demonstrated feeding preference for cladocerans despite the abundance of rotifers and copepods. Cladocerans were present in more than 80% of the stomach contents of fish up to 300 g and in 65%, 45% and 17% of fish of 301–500 g, 501–700 g and 701–900 g respectively. Copepods were present only in fish up to 500 g at low abundance. High ingestion of insects and plant material was observed in the stomach content of fish of all size classes. The results demonstrate that juvenile pirarucu ingest natural food available in the farming pond and suggests that the adoption of pond fertilization practices may have positive effects on fish growth performance. [ABSTRACT FROM AUTHOR]

This study was carried out to evaluate morphometry and direct and indirect effects of measurements and morphometric relationships on the weight of pirarucu body components. A total of 96 fish were raised in captivity at the Federal University of Rondônia, Presidente Médici - RO, Brazil, with a mean body weight of 9.18 ± 0.1 kg and 104 ± 0.3 cm in length. After desensitizing, the fish were sacrificed, weighed and morphometric measurements of total (TL), standard (SL), head (HL), trunk (LA) and tail (CL) lengths and frontal perimeter (FP), larger perimeter (LP) and tail perimeter (CP) were determined. The fish were dissected and the following body components were measured: leather (with scales), head, viscera and carcass divided into meat layer and spines. The data were submitted to descriptive and multiple regression analyses and the correlation coefficients were separated into direct and indirect effects by a path analysis. Most of the measurements and morphometric ratios showed significant correlations with body weights and body components (carcass, head, meat layer, leather, viscera and spines). LP showed a greater direct and positive effect and was determinant for the variation of total weight and meat layer weight. [ABSTRACT FROM AUTHOR]

Isopods Cymothoidae are organisms that parasitize several fish species, both marine and freshwater, provoking important physiological alterations and secondary infections. The genus Braga was proposed to harbor three species of parasitic isopods in freshwater fish from South America: B. brasiliensis, B. cichlae and B. nasuta. Posteriorly, other four species were included: B. patagonica, B. amapaensis, B. fluviatilis and B. bachmanni. Regarding the geographical distribution of the genus, there are registers in Brazil, Argentina, Suriname and Paraguay. In this study, 3,625 fingerlings of pirarucu Arapaima gigas were examined from a commercial fish farm in the Amazon region, Pará State, to observe and identify possible parasites. A total of eleven ectoparasitic isopods were carefully removed from the body surface of the hosts and fixed in alcohol 70%. They were processed and identified as Braga nasuta. Parasitological indexes were prevalence of 0.303%, mean intensity of 1.000±0.000 and mean abundance of 0.003±0.055. This is the first report of B. nasuta in pirarucu fingerlings.