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Concept: Anabas testudineus

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

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

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Nitric oxide (NO), a short-lived freely diffusible radical gas that acts as an important biological signal, regulates an impressive spectrum of physiological functions in vertebrates including fishes. The action of NO, however, on thyroid hormone status and its role in the integration of acid-base, osmotic and metabolic balances during stress are not yet delineated in fish. Sodium nitroprusside (SNP), a NO donor, was employed in the present study to investigate the role of NO in the stressed air-breathing fish Anabas testudineus. Short-term SNP treatment (1mM; 30min) interacted negatively with thyroid axis, as evident in the fall of plasma thyroxine in both stressed and non-stressed fish. In contrast, the cortisol responsiveness to NO was negligible. SNP challenge produced systemic alkalosis, hypocapnia and hyperglycemia in non-stressed fish. Remarkable acid-base compensation was found in fish kept for 60 min net confinement where a rise in blood pH and HCO(3) content occurred with a reduction in PCO(2) content. SNP challenge in these fish, on the contrary, produced a rise in oxygen load together with hypocapnia but without an effect on HCO(3) content, indicating a modulator role of NO in respiratory gas transport during stress response. SNP treatment reduced Na(+), K(+) ATPase activity in the gill, intestine and liver of both stressed and non-stressed fish, and this suggests that stress state has little effect on the NO-driven osmotic competence of these organs. On the other hand, a modulatory effect of NO was found in the kidney which showed a differential response to SNP, emphasizing a key role of NO in kidney ion transport and its sensitivity to stressful condition. H(+)-ATPase activity, an index of H(+) secretion, downregulated in all the organs of both non-stressed and stressed fish except in the gill of non-stressed fish and this supports a role for NO in promoting alkalosis. The data indicate that, (1) NO interacts antagonistically with T(4) (2) modifies respiratory gas transport and (3) integrates acid-base and osmotic actions during stress response in air-breathing fish. Collectively, this first evidence in fish indicate that NO promotes compensatory physiologic modification and that can reduce the magnitude of stress-induced acid-base and osmotic disturbance.

Concepts: Kidney, Physiology, Fish, Hormone, Thyroid, Thyroid hormone, Anabas testudineus, Thyroglobulin

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A survey was performed to investigate the infection status of zoonotic trematode (ZT) metacercariae in fish from a local market in Yangon City, Myanmar. A total of 264 fish (12 species) were collected through 4 times from December 2013 to June 2015. All collected fish were transferred to our laboratory on ice and examined by the artificial digestion method. More than 7 species of ZT metacercariae, i.e., Haplorchis taichui, H. pumilio, H. yokogawai, Centrocestus spp., Stellantchasmus falcatus, Pygidiopsis cambodiensis, and Procerovum sp. were detected. Metacercariae of H. taichui were collected in 58 (42.3%) out of 137 fish (5 species), and their average density was 42.9 per fish infected. Metacercariae of H. pumilio were detected in 96 (49.0%) out of 196 fish (9 species), and their average density was 23.6 per fish infected. H. yokogawai metacercariae were found in 40 (50.0%) out of 80 fish (5 species), and Centrocestus spp. metacercariae in 91 (50.8%) out of 179 fish (8 species), and their densities were 306 and 25.8 per fish infected, respectively. Metacercariae of S. falcatus and P. cambodiensis were detected only in mullets, Chelon macrolepis. A total of 280 Procerovum sp. metacercariae were found in 6 out of 12 climbing perch, Anabas testudineus. Morphological characteristics of adult flukes recovered from experimental animals were described. It has been first confirmed that fish from Yangon, Myanmar are commonly infected with various species of ZT metacercariae.

Concepts: Density, Water, Anabas testudineus, Relative density, Perciformes, Yangon

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Antimicrobial potentials of bacteria isolated from Anabas testudineus have been evaluated through in vitro antagonistic activity against potent fish pathogens. The cellular components and filtered culture medium were effective against six fish pathogens. Altogether 110 strains were isolated from the fish gut, out of which 10 strains were selected through well diffusion method. From them, a strain HGA8B having cumulative maximum score was selected as candidate probiotic. The whole-cell product, heat-killed whole-cell product, Ethyl acetate extract, and the filtered broth were exhibited bactericidal activity against the tested pathogens. In addition, the isolated bacterium was capable of producing extracellular enzymes important for the digestion of food materials and was capable of growth in fish mucus from Oreochromis niloticus. The strain tolerated bile juice secreted by the host and effectively produced biofilm. Analysis of 16S rRNA sequence revealed that isolated strain HGA8B was Bacillus sp. (MF351637). Furthermore, intraperitoneal injection of the bacterium did not induce any pathological signs, symptoms or mortalities in Oreochromis niloticus and revealed the safety of this bacterium as a candidate probiotic in aquaculture.

Concepts: Immune system, Archaea, Bacteria, Gut flora, Microbiology, Cichlid, 16S ribosomal RNA, Anabas testudineus

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The climbing perch, Anabas testudineus, is an air-breathing fish having great consumer preference as a food fish and is considered a prime candidate species for aquaculture. Spawning success is an important issue while using hormones for captive induced breeding. In the first experiment, a trial was conducted to assess the efficacy of a synthetic Gonadotropin Releasing Hormone analog (sGnRHa) on the spawning success of climbing perch. Female fish were administered six different doses each with a single intramuscular injection of sGnRHa hormone at 0.002 (TOD1), 0.005 (TOD2), 0.01 (TOD3), 0.015 (TOD4), 0.02 (TOD5), 0.03 (TOD6) μg/g body weight. Similarly, males were administered half of the hormone dose of females in all the respective treatment groups. The greatest (P<0.05) relative fecundity (715.13±15.0 eggs/g female body weight) and fertilization percentage rates (93.1±8.0%) occurred when female fish were treated at the 0.015μg/g body weight dose. There was a reduction in relative fecundity and hatching rate in female fish injected with the largest dose (1.5μL/g body weight) of sGnRHa. A second experiment was conducted to assess the effect of a different male-female ratio on optimum spawning success in climbing perch. For this study a different female to male ratio (1:1, 1:2, 1:3 and 1:4) and male to female ratio (1:1, 1:2 and 1:3) were used. There were a greater (P<0.05) relative fecundity (886.62±17.9 eggs/g female body weight), fertilization (98±6.7%) and hatching (99±5.4%) rates with the female to male ratio of 1:2. This indicated that the hormone dose of 0.015μg/g body weight and a female-male ratio of 1:2 are optimal for enhanced spawning success in the climbing perch.

Concepts: Male, Reproduction, Female, Fish, Gender, Sex, Anabas testudineus, Sex ratio

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Organophosphates (e.g. chlorpyrifos ethyl) and carbamates (e.g. fenobucarb) are commonly used to control a wide range of pests in rice fields of the Mekong Delta in Vietnam. This study assesses the combined effect of chlorpyrifos ethyl (CPF) and fenobucarb (F), applied at concentrations used by rice farmers, on the brain acetylcholinesterase (AChE) activity in climbing perch fingerlings from rice fields in the Mekong Delta. It also investigates if Pyridine-2-aldoxime methiodide (2-PAM) can be used to reactivate cholinesterase that has been blocked by CPF. Three days after spraying, the water concentrations of both insecticides decreased quickly below the detection levels. However, the brain AChE activity in fish was inhibited for more than 7 days. The results indicate a quicker but less prolonged inhibition of the brain AChE activity by the mixture than by only CPF. The inhibition levels were above 70 % only during the first 48 h, which could explain why all fish survived. 2-PAM resulted in a significant reactivation of the cholinesterase blocked by a combination of CPF and F, and it is proposed that the reactivation by 2-PAM could provide a way to assess the AChE inhibition levels in organisms, when no unexposed individuals are available as controls. The results indicate that the current use of CPF and F in rice farming in the Mekong Delta is likely to cause negative effects on non-target organisms. Many of these effects may be sub-lethal, and there is a need to develop biomarkers that are relevant, inexpensive and easy to apply. The results show that brain AChE in climbing perch fingerling is a relevant biomarker for monitoring of exposure to, and sub-lethal impacts from organophosphates and carbamates under tropical conditions in developing countries.

Concepts: Acetylcholine, Anabas testudineus, Acetylcholinesterase, Insecticide, Vietnam, Carbamate, Perciformes, Mekong Delta

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This study assesses the effects of sequential applications of the insecticides Bassa 50EC (fenobucarb-F) and Vitashield 40EC (chlorpyrifos ethyl-CPF), sprayed at concentrations used by rice farmers in the Mekong Delta, on the brain acetylcholinesterase (AChE) in climbing perch fingerlings. After spraying the pesticides on the rice fields, the water concentrations of both insecticides decreased below the detection levels within 3 days. The sequential applications caused significant inhibition on the brain AChE activity in the exposed fish. The inhibition by F was quicker, but less prolonged, than for CPF. The inhibition levels caused by the sequential applications were lower than those caused by only CPF and by a mixture of CPF and F. The results indicate that sequential applications of pesticides could have a negative impact on aquatic organisms and fish yields, with implication for the aquatic biodiversity, local people’s livelihood and the aquaculture industry in the Mekong Delta.

Concepts: Fish, Acetylcholine, Anabas testudineus, Insecticide, Pesticide application, Vietnam, Gourami, Perciformes

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In this study we showed that a freshwater fish, the climbing perch (Anabas testudineus) is incapable of using chemical communication but employs visual cues to acquire familiarity and distinguish a familiar group of conspecifics from an unfamiliar one. Moreover, the isolation of olfactory signals from visual cues did not affect the recognition and preference for a familiar shoal in this species.

Concepts: Fish, Anabas testudineus, Freshwater fish, Gourami, Perciformes, Ichthyology, Dangerous Visions

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The high use of pesticides in intensive rice farming in the Mekong Delta constitutes a potential hazard to the environment and to people’s health. Chlorpyrifos ethyl (CPF) is a commonly used organophosphate (OP) insecticide, but information about its potential negative impacts on the aquatic environment in the Mekong Delta is scarce. Both acute and subacute toxicity tests were performed in a static nonrenewable system to investigate the effects of CPF on brain acetylcholinesterase (AChE) activity in native climbing perch fingerlings (Anabas testudineus, Bloch, 1972). Environmental parameters, such as dissolved oxygen, water temperature, and pH, were similar to field conditions in the Mekong Delta. In a 96-h lethal concentration (LC50) test, fingerlings of climbing perch were randomly exposed to five levels of CPF ranging from 0.8 to 4.5 ppm. Five sublethal levels of CPF (1, 5, 10, 15, and 20 % of the 96-h LC50 value) were tested to assess the sensitivity and recovery of the brain AChE activity in climbing perch fingerlings exposed to CPF. The results showed that CPF were moderately toxic to climbing perch with a 96-h median LC50 of 1.73 ppm. CPF also caused long-term AChE inhibition with 70 % inhibition remaining after 96 h for the four highest test concentrations. The recovery of brain AChE activity in fish placed in CPF-free water was very slow, and after 7 days the brain AChE activity was still significant lower in fish from the four highest concentrations compared with the control. The results from this study indicate that OP insecticides, such as CPF, can have long-lasting sublethal effects on aquatic species in the Mekong Delta.

Concepts: Medicine, Environment, Natural environment, Acetylcholine, Anabas testudineus, Insecticide, DDT, Perciformes

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In the present study, the complete mitochondrial genome sequence of Anabas testudineusis reported using PGM sequencer (Ion Torrent, Life Technologies, La Jolla, CA). The complete mitogenome of climbing perch, A. testudineusis obtained by the de novo sequences assembly of genomic reads using the Torrent Mapping Alignment Program (TMAP), which is 16 603 bp in length. The mitogenome of A. testudineus composed of 13 protein- coding genes, two rRNA, and 22 tRNAs. Here, 20 tRNAs genes showed typical clover leaf model, and D-Loop as the control region along with gene order and organization, being closely similar to Osphronemidae and most of other Perciformes fish mitogenomes of NCBI databases. The mitogenome in the present study has 99% similarity to the complete mitogenome sequence of earlier reported A. testudineus. The phylogenetic analysis of Anabantidae depicted that their mitogenomes are closely related to each other. The complete mitogenome sequence of A. testudineus would be helpful in understanding the population genetics, phylogenetics, and evolution of Anabantidae.

Concepts: DNA, Gene, Genetics, Biology, Organism, Genome, Anabas testudineus, Perciformes