Swamp Eel Research Articles

Nitrogen Metabolism and Excretion in the Swamp Eel,Monopterus albus, during 6 or 40 Days of Estivation in Mud

Monopterus albus inhabits muddy ponds, swamps, canals, and rice fields, where it can burrow into the moist earth, and it survives for long periods during the dry summer season. However, it had been reported previously that mortality increased when M. albus was exposed to air for 8 d or more. Thus, the objective of this study was to elucidate the strategies adopted by M. albus to defend against ammonia toxicity during 6 or 40 d of estivation in mud and to evaluate whether these strategies were different from those adopted by fish to survive 6 d of aerial exposure. Ammonia and glutamine accumulations occurred in the muscle and liver of fish exposed to air (normoxia) for 6 d, indicating that ammonia was detoxified to glutamine under such conditions. In contrast, ammonia accumulation occurred only in the muscle, with no increases in glutamine or glutamate contents in all tissues, of fish estivated in mud for 6 d. Similar results were obtained from fish estivated in mud for 40 d. While estivating in mud prevented excessive water loss through evaporation, M. albus was exposed to hypoxia, as indicated by significant decreases in blood P(O(2)), muscle energy charge, and ATP content in fish estivated in mud for 6 d. Glutamine synthesis is energy intensive, and that could be the reason why M. albus did not depend on glutamine synthesis to defend against ammonia toxicity when a decrease in ATP supply occurred. Instead, suppression of endogenous ammonia production was adopted as the major strategy to ameliorate ammonia toxicity when M. albus estivated in mud. Our results suggest that a decrease in O(2) level in the mud could be a more effective signal than an increase in internal ammonia level during aerial exposure to induce a suppression of ammonia production in M. albus. This might explain why M. albus is able to estivate in mud for long periods (40 d) but can survive in air for only <10 d.

Metabolic adjustments during semi-aestivation of the marble swamp eel (Synbranchus marmoratus, Bloch 1795) - a facultative air breathing fish

Metabolic changes, principally in intermediary metabolism and nitrogen excretion, were investigated in the marble swamp eel (Synbranchus marmoratus) after 15 and 45 days of artificially induced semi-aestivation. Glucose, glycogen, lactate, pyruvate, free amino acids, triglycerides, ammonia, urea, and urate contents were determined in liver, kidney, white muscle, heart, brain, and plasma. Lactate dehydrogenase, glutamate dehydrogenase, malate dehydrogenase, aspartate amino transferase, alanine amino transferase, glutamine synthase, ornithine carbamoyl transferase, and arginase enzymes were assayed. The teleost S. marmoratus maintained initial energetic demands by lipid oxidation. The course of normal oxidative processes was observed through tissue enzyme profiles. After the lipid stores were exhausted, the fish consumed body proteins. Constant values of hematocrit during induced semi-aestivation suggested that the water balance remained normal. Therefore, the surrounding water was probably did not trigger the semi-aestivation in this teleost. Decrease of ammonia and increase of renal urea synthesis after 45 days of semi-aestivation led to the assumption that an alternative form of eliminating ammonia exists. Metabolic changes entailed by starvation were proposed to explain the biosynthesis of small molecules involved in the semi-aestivation of S. marmoratus.

A fish prey found in the coral snake Micrurus alleni (Serpentes: Elapidae) in Costa Rica

A fish prey found in the coral snake Micrurus alleni (Serpentes: Elapidae) in Costa Rica. The presence of a small specimen of the swamp eel Synbranchus marmoratus (84 mm total length) in the stomach contents of an adult coral snake Micrurus alleni with 692 mm total length from the Caribbean versant of Costa Rica is reported. This eel was swallowed headfirst.

Analysis of sequence variation in Gnathostoma spinigerum mitochondrial DNA by single-strand conformation polymorphism analysis and DNA sequence

Morphological variations were observed in the advance third stage larvae of Gnathostoma spinigerum collected from swamp eel ( Fluta alba), the second intermediate host. Larvae with typical and three atypical types were chosen for partial cytochrome c oxidase subunit I (COI) gene sequence analysis. A 450 bp polymerase chain reaction product of the COI gene was amplified from mitochondrial DNA. The variations were analyzed by single-strand conformation polymorphism and DNA sequencing. The nucleotide variations of the COI gene in the four types of larvae indicated the presence of an intra-specific variation of mitochondrial DNA in the G. spinigerum population.

Defences against ammonia toxicity in tropical air-breathing fishes exposed to high concentrations of environmental ammonia: a review.

In the tropics, air-breathing fishes can be exposed to environmental ammonia when stranded in puddles of water during the dry season, during a stay inside a burrow, or after agricultural fertilization. At low concentrations of environmental ammonia, NH(3) excretion is impeded, as in aerial exposure, leading to the accumulation of endogenous ammonia. At high concentrations of environmental ammonia, which results in a reversed NH(3) partial pressure gradient (DeltaP(NH3)), there is retention of endogenous ammonia and uptake of exogenous ammonia. In this review, several tropical air-breathing fishes (giant mudskipper, African catfish, oriental weatherloach, swamp eel, four-eyed sleeper, abehaze and slender African lungfish), which can tolerate high environmental ammonia exposure, are used as examples to demonstrate how eight different adaptations can be involved in defence against ammonia toxicity. Four of these adaptations deal with ammonia toxicity at branchial and/or epithelial surfaces: (1) active excretion of NH(4)(+); (2) lowering of environmental pH; (3) low NH(3) permeability of epithelial surfaces; and (4) volatilization of NH(3), while another four adaptations ameliorate ammonia toxicity at the cellular and subcellular levels: (5) high tolerance of ammonia at the cellular and subcellular levels; (6) reduction in ammonia production; (7) glutamine synthesis; and (8) urea synthesis. The responses of tropical air-breathing fishes to high environmental ammonia are determined apparently by behavioural adaptations and the nature of their natural environments.

Testicular interstitial cells, and steroidogenic detection in the protogynous fish, Synbranchus marmoratus (Teleostei, Synbranchidae)

The swamp eel, Synbranchus marmoratus, is a freshwater protogynic diandric species. Primary males develop directly as males while secondary males arise from the sex reversal of females. Fishes from Argentine and Brazil inland waters were collected, examined and compared for this study. In order to characterize the interstitial testicular compartment, light and electron microscopy techniques and an enzyme histochemical examination for steroidogenic cells detection were used. The interstitial compartment of S. marmoratus is composed of Leydig and myoid cells, collagen fibers, blood cells, macrophages,and amyelinic nerves. At the ultrastructural level, no differences were observed in the interstitial tissue, either between specimens from the different sampling sites or between primary and secondary males. Leydig cells are present in all testes examined throughout the year. A cytoplasmatic reaction of 3β-HSD was detected only in Leydig cells during sex reversal and in both type of males, mainly during the regressed and early maturation classes (autumn and winter). Leydig cells possess the typical fine structural characteristics associated with steroidogenesis. Furthermore, in both type of males, during sex reversal and after the spawning period, the number of granulocytes and macrophages present in the testes increased, suggesting that they could be involved in phagocytosis and resorption of damaged cells.

Involvement of the gonadal germinal epithelium during sex reversal and seasonal testicular cycling in the protogynous swamp eel, Synbranchus marmoratus Bloch 1795 (Teleostei, Synbranchidae).

The swamp eel, Synbranchus marmoratus, is a protogynous, diandric species. During sex reversal, the ovarian germinal epithelium, which forms follicles containing an oocyte and encompassing follicle cells during the female portion of the life cycle, produces numerous invaginations, or acini, into the ovarian stroma. Within the acini, the gonia that formerly produced oocytes become spermatogonia, enter meiosis, and produce sperm. The acini are bounded by the basement membrane of the germinal epithelium. Epithelial cells of the female germinal epithelium, which formerly became follicle (granulosa) cells, now become Sertoli cells in the developing testis. Subsequently, lobules and testicular ducts form. The swamp eel testis has a lobular germinal compartment in both primary and secondary males, although the germinal compartment in testes of secondary males resides within the former ovarian lamellae. The germinal compartment, supported by a basement membrane, is composed of Sertoli and germ cells that give rise to sperm. Histological and immunohistochemical techniques were used to describe the five reproductive classes that were observed to occur during the annual reproductive cycle: regressed, early maturation, mid-maturation, late maturation, and regression. These classes are differentiated by the presence of continuous or discontinuous germinal epithelia and by the types of germ cells present. Synbranchus marmoratus has a permanent germinal epithelium. Differences between the germinal compartment of the testes of primary and secondary males were not observed.

Expression of pejerrey gonadotropin-releasing hormone in three orders of fish.

Molecular variants of GnRH were characterized by reverse-phase, high-performance liquid chromatography from brain extracts of fish in three different orders: Synbranchiformes (swamp eel [Synbranchus marmoratus]), Cyprinidontiformes (platyfish [Xiphophorus maculatus] and green swordtail [X. helleri]), and Atheriniformes (Patagonia pejerrey [Odontesthes hatchery]). Also, pituitary gland extracts from the pejerrey O. bonariensis (Atheriniformes) were characterized. Eluted fractions were tested in radioimmunoassays with antisera specific to GnRH, including both antisera that detected only one form of GnRH and those that detected several forms. The results show that brain extracts obtained from all species contained the same three molecular forms of GnRH, which were immunologically and chromatographically undistinguishable from chicken GnRH-II, pejerrey GnRH (pjGnRH), and salmon GnRH. This study supports the hypothesis that expression of these three forms is common in different fish orders and that pjGnRH is the main regulator of pituitary function in these fish.

Oogenesis in the swamp eel Synbranchus marmoratus (Bloch, 1795) (Teleostei; synbranchidae). Ovarian anatomy, stages of oocyte development and micropyle structure

Synbranchus marmoratus (Synbranchidae), commonly known as the swamp eel, is a protogynous diandric teleost fish widely distributed throughout South America. The purpose of this work was to study the ovarian anatomy and to describe oocyte developmental stages in the swamp eel, Synbranchus marmoratus. S. marmoratus has a unique sacular ovary. It is covered by a conspicuous muscular wall, probably involved in an egg-releasing system acting as a peristaltic-like mechanism. The internal ovarian anatomy shows a U-shaped ovarian lamella delimiting a dorsal ovarian lumen. The microscopic study shows evidence of the existence of a germinal epithelium in the inner surface of the lamella, which contains germinal cells, pre-follicular cells and epithelial cells. The complete oogenesis process is divided into four stages: oogonia, primary growth, cortical alveoli and vitellogenesis. Besides, the ovulated oocytes, and atretic structures were described. The structure of the micropyle was studied by scanning electron microscopy (MEB). Near the animal pole the vitelline envelope forms crests that fuse together becoming furrow-like structures with a slightly spiraled direction that converge into the micropyle pit where is located the micropylar canal. Although the sex reversal process of Synbranchids has been subject of many studies, this is the first complete description of the ovarian anatomy and oogenesis.

Characterization of molecular variants of GnRH, induction of spermiation and sex reversal using salmon GnRH-A and domperidone in the protogynous diandric fish, Synbranchus marmoratus Bloch, (Teleostei, Synbranchidae)

This paper studies the molecular variants of gonadotropin-releasing hormone (GnRH) present in the brain of the protogynous swamp eel, Synbranchus marmoratus, and the effects of the administration of salmon GnRH analogue (sGnRH-A) and the dopamine receptor antagonist, domperidone (DOM) on final maturation and gamete release in this species. Evidence for the presence of two GnRH variants, sGnRH and cIIGnRH were obtained by reverse phase high-pressure liquid chromatography (RP-HPLC) and radioimmunoassay with different antisera. The effects of treatment with sGnRH-A+DOM were checked by three ways: oocyte and milt release by stripping, histological analysis of the gonadal tissue, and androgen serum levels at different times throughout the experiment. In males, spermiation was induced after three weeks of treatment. In the female group, sGnRH-A+DOM did not induce ovulation at the end of the experiment. Histological analysis of the gonads from the female group showed evidence of sex reversal. All the treated fish had elevated androgen serum levels from the third week, with respect to control fish. In all cases, serum estradiol levels were undetectable. These results suggest that treatment with sGnRH analog and DOM induce sex reversal in female and spermiation in males.

Presence of primary and secondary males in a population of the protogynous Synbranchus marmoratus

Synbranchus marmoratus, the ‘swamp eel’, is a protogynous diandric fish. The primary and secondary males can be distinguished from each other easily by differences in gonadal morphology. Primary males have lobular, unrestricted testes with central efferent ducts. The secondary male has a ‘lamellar’ testis, efferent ducts are present in the ventral region (new formation), lateral supports and it is covered by the former ovarian capsule. The length of primary male varies from 13 to 88 cm while secondary males range from 56 to 91 cm. Transitional individuals vary between 45 and 60 cm in length. The swamp eel population studied is composed of 80% primary males and 20% secondary males. Although gonadosomatic indices are always higher in primary males, they increase in secondary ones as the newly acquired stage progresses. The lamellar organization of the gonad of secondary males, the absence of this kind of testis in individuals smaller than 56 cm, and the presence of hermaphroditic fish, is evidence for protogyny in this species.

Caribbean Marine Occurrence in Mangroves of a Typically Fresh-water Synbranchiform Fish

The capture of the swamp eel Ophisternon aenigmaticum in the hypersaline waters of a mangrove island 15 km off the coast of Belize, Central America, is the first marine record for any of the New World species of Synbranchiformes, with dispersal from the mainland through sea water sometime in the past 7,000 years the likely explanation for its island occurrence.

Melano‐macrophage centres in the gonads of the swamp eel, Synbranchus marmoratus Bloch, (Pisces, Synbranchidae): histological and histochemical characterization

Abstract. During a study of the gametogenesis of the swamp eel. Synbranchus marmoratus Bloch, conspicuous structures were found randomly distributed among the germinal cells and gonadal stroma. At low magnification, these structures appeared as yellowish to dark spherical bodies. Histological and histochemical examination showed clusters of cells with generally pyknotic nuclei and cytoplasm containing lipofusein‐like substances. A comparison of these structures with the melano‐macrophage centres (MMCs) present in the liver and spleen, showed the same structure and features. Their presence and function in the gonads of S. marmoratus might be related not only with the basic functions of the MMCs, but also with the degradation of atretic and/or non‐ovulated follicules, principally during the post‐spawning period.

Vasculature of the head and respiratory organs in an obligate air-breathing fish, the swamp eel Monopterus (=Amphipnous) cuchia.

Methyl methacrylate vascular corrosion replicas were used to examine the macrocirculation in the head region and the microcirculation of respiratory vessels in the air-breathing swamp eel Monopterus cuchia. Fixed respiratory tissue was also examined by SEM to verify capillary orientation. The respiratory and systemic circulations are only partially separated, presumably resulting in supply of mixed oxygenated and venous blood to the tissues. A long ventral aorta gives rise directly to the coronary and hypobranchial arteries. Two large shunt vessels connect the ventral aorta to the dorsal aorta, whereas the remaining ventral aortic flow goes to the respiratory islets and gills. Only two pairs of vestigial gill arches remain, equivalent to the second and third arches, yet five pairs of aortic arches were identified. Most aortic arches supply the respiratory islets. Respiratory islet capillaries are tightly coiled spirals with only a fraction of their total length in contact with the respiratory epithelium. Valve-like endothelial cells delimit the capillary spirals and are unlike endothelial cells in other vertebrates. The gills are highly modified in that the lamellae are reduced to a single-channel capillary with a characteristic three-dimensional zig-zag pathway. There are no arterio-arterial lamellar shunts, although the afferent branchial artery supplying the gill arches also supplies respiratory islets distally. A modified interlamellar filamental vasculature is present in gill tissue but absent or greatly reduced in the respiratory islets. The macro- and micro-circulatory systems of M. cuchia have been considerably modified presumably to accommodate aerial respiration. Some of these modifications involve retention of primitive vessel types, whereas others, especially in the microcirculation, incorporate new architectural designs some of whose functions are not readily apparent.

The Transition to Air Breathing in Fishes: IV. Impact of Branchial Specializations for Air Breathing on the Aquatic Respiratory Mechanisms and Ventilatory Costs of the Swamp Eel Synbranchus Marmoratus

ABSTRACT The gills, adjacent buccopharyngeal epithelium, and skin of the swamp eel Synbranchus marmoratus (Bloch) function for both aerial and aquatic respiration. Aquatic cutaneous O2 uptake occurs continuously at rates that, while dependent upon aquatic O2 tension , are in direct proportion to body surface area. Branchial aquatic O2 uptake takes place during intermittent ventilation which occurs in proportion to body mass. Because of reductions in the body surface area to volume ratio that occur with growth, cutaneous oxygen uptake comprises a larger percentage of the total oxygen uptake of small fish and, to compensate, large fish ventilate more. The mass exponent for total rate of oxygen uptake (0·894 ± 0·145) is within the range predicted from the contributions of cutaneous (mass exponent 0·651 ± 0·167) and the number of minutes each hour that branchial ventilation occurs (0·378 ± 0·105). Hyperoxia increases cutaneous and reduces branchial ventilation. Total was also reduced in hyperoxia and calculations relating this to the reduction in ventilation time yield ventilatory cost estimates that increase with body size and that are high compared to those of other fish when the large component of cutaneous respiration in this species is considered. Large ventilatory costs reflect gill and branchial apparatus specialization for aerial respiration. Accessory cutaneous respiration and intermittent aquatic ventilation reduce these costs, and intermittent gill use in aquatic breathing, which is the exact analogue of the pattern for branchial respiratory use during air breathing, seems to optimize aquatic O2 uptake with minimal ventilatory cost.

The Transition to Air Breathing in Fishes: III. Effects of Body Size and Aquatic Hypoxia on the Aerial Gas Exchange of the Swamp Eel Synbranchus Marmoratus

ABSTRACT Synbranchus marmoratus (Bloch) breathes air during terrestrial excursions and while dwelling in hypoxic water and utilizes its gills and adjacent buccopharyngeal epithelium as an air-breathing organ (ABO). This fish uses gills and skin for aquatic respiration in normoxic (air-saturated) water but when exposed to progressive aquatic hypoxia it becomes a metabolic O2 conformer until facultative air breathing is initiated. The threshold (aquatic O2 tension or partial pressure in mmHg) that elicits air breathing in S. marmoratus is higher in larger fish. However, neither air-breathing threshold nor the blood haemoglobin (Hb) concentration of this species were changed following hypoxia acclimation. In hypoxic water S. marmoratus supplies all of its metabolic O2 requirement through air breathing. ABO volume scales with body weight raised to the power of 0 ·737 and the amount of O2 that is removed from each air breath depends upon the length of time it is held in the ABO. Ambient directly affects the air-breath duration of this fish, but the effect is smaller than in other species. Also, average air-breath duration (15·7 min at mmHg) and the average inter-air-breath interval (15 1 min) of 5. marmoratus are both longer than those of other air-breathing fishes. Although the gills of 5. marmoratus are involved in aerial O2 uptake, expelled air-breath CO2 levels are not high and always closely correspond to ambient , indicating that virtually no respiratory CO2 is released to air by this fish. CO2 extrusion therefore must occur aquatically either continuously across another exchange surface or intermittently across the gills during intervals between air breaths. This study with S. marmoratus from Panama reveals physiological differences between this population and populations in South America. The greater Hb content of South American S. marmoratus may be the result of different environmental selection pressures.

The Effects of Dissolved O₂ and CO₂ on Metabolism and Gas-Exchange Partitioning in Aquatic Salamanders

Previous articleNext article No AccessThe Effects of Dissolved O₂ and CO₂ on Metabolism and Gas-Exchange Partitioning in Aquatic SalamandersJohn M. Wakeman and Gordon R. UltschJohn M. Wakeman Search for more articles by this author and Gordon R. Ultsch Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 48, Number 4Oct., 1975 Article DOIhttps://doi.org/10.1086/physzool.48.4.30155660 Views: 7Total views on this site Citations: 20Citations are reported from Crossref Journal History This article was published in Physiological Zoology (1928-1998), which is continued by Physiological and Biochemical Zoology (1999-present). PDF download Crossref reports the following articles citing this article:Do Thi Thanh Huong, Chau Huynh Thuy Tram, Nguyen Thi Kim Ha, Le Thi Hong Gam, Atsushi Ishimatsu, Nguyen Thanh Phuong Effects of carbon dioxide (CO2) at different temperatures on physiological parameters and growth in striped catfish (Pangasianodon hypophthalmus) juveniles, Aquaculture 534 (Mar 2021): 736279.https://doi.org/10.1016/j.aquaculture.2020.736279Phan Vinh Thinh, Do Thi Thanh Huong, Le Thi Hong Gam, Christian Damsgaard, Nguyen Thanh Phuong, Mark Bayley, Tobias Wang Renal acid excretion contributes to acid–base regulation during hypercapnia in air-exposed swamp eel ( Monopterus albus ), The Journal of Experimental Biology 222, no.99 (Apr 2019): jeb198259.https://doi.org/10.1242/jeb.198259Le Thi Hong Gam, Frank Bo Jensen, Do Thi Thanh Huong, Nguyen Thanh Phuong, Mark Bayley The effects of elevated environmental CO 2 on nitrite uptake in the air-breathing clown knifefish, Chitala ornata, Aquatic Toxicology 196 (Mar 2018): 124–131.https://doi.org/10.1016/j.aquatox.2018.01.011Gerhard Heldmaier, Gerhard Neuweiler, Wolfgang Rössler Atmung, (Oct 2012): 149–212.https://doi.org/10.1007/978-3-642-25155-9_4Gordon R. Ultsch Metabolism, gas exchange, and acid-base balance of giant salamanders, Biological Reviews 87, no.33 (Dec 2011): 583–601.https://doi.org/10.1111/j.1469-185X.2011.00211.xJohn N. Maina Functional Designs of the Gas Exchangers, (May 2011): 141–221.https://doi.org/10.1007/978-3-642-20395-4_5Gordon R. Ultsch, Elizabeth L. Brainerd, Donald C. Jackson Lung collapse among aquatic reptiles and amphibians during long-term diving, Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 139, no.11 (Sep 2004): 111–115.https://doi.org/10.1016/j.cbpb.2004.07.002Gordon R. 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Respiratory control of arterial pH as temperature changes in rainbow trout Salmo gairdneri.

Respiratory control of arterial pH as temperature changes in rainbow trout Salmo gairdneri.

Effect of temperature and hemoglobin concentration on solubility of O2 in blood.

Effect of temperature and hemoglobin concentration on solubility of O2 in blood.