Swamp eel

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.

Abstract: SUMMARY The swamp eel, Monopterus albus , is an air-breathing teleost which typically lives in freshwater but can also be found in estuaries, where it has to deal with ambient salinity fluctuations. Unlike other teleosts, its gills are highly degenerate. Hence, it may have uncommon osmoregulatory adaptations, but no information is available on its osmoregulatory capacity and mechanisms at present. In this study M. albus was exposed to a 5 day progressive increase in salinity from freshwater (1‰) to brackish water (25‰) and subsequently kept in 25‰ water for a total of 4 days. The results indicate that M. albus switched from hyperosmotic hyperionic regulation in freshwater to a combination of osmoconforming and hypoosmotic hypoionic regulation in 25‰ water. Exposure to 25‰ water resulted in relatively large increases in plasma osmolality, [Na + ] and [Cl – ]. Consequently, fish exposed to 25‰ water had to undergo cell volume regulation through accumulation of organic osmolytes and inorganic ions. Increases in tissue free amino acid content were apparently the result of increased protein degradation, decreased amino acid catabolism, and increased synthesis of certain non-essential amino acids. Here we report for the first time that glutamine is the major organic osmolyte in M. albus . Glutamine content increased to a phenomenal level of >12 μmol g –1 and >30 μmol g –1 in the muscle and liver, respectively, of fish exposed to 25‰ water. There were significant increases in glutamine synthetase (GS) activity in muscle and liver of these fish. In addition, exposure to 25‰ water for 4 days led to significant increases in GS protein abundance in both muscle and liver, indicating that increases in the expression of GS mRNA could have occurred.

Abstract: Synbranchus marmoratus, the ‘ swamp eel ’, is a protogynous diandric fish. The primary and secondary males can be distinguished from each other easily by diVerences in gonadal morphology. Primary males have lobular, unrestricted testes with central eVerent ducts. The secondary male has a ‘ lamellar ’ testis, eVerent 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. ? 1996 The Fisheries Society of the British Isles

Abstract: The Asian swamp eel (Monopterus albus) is an air-breathing, sex-reversing, eel-like exotic fish that was first reported from Florida waters in 1997. This illegally introduced fish is now abundant in four major southeastern Florida canal systems, and it continues to slowly spread into nearby areas, including the Everglades. Swamp eel feed on a wide variety of organisms, the most common of which are small fishes, crustaceans (mostly crayfish), and insects. In a laboratory study, swamp eel died at temperatures ≤8°C. No deleterious ecological effects associated with the swamp eel's presence were detected during the 11 years we studied this species, nor was there any evidence that it makes overland movements. Based on these data and observations, the swamp eel in Florida is best described as an illegally introduced, opportunistic and successful predator that feeds on a variety of small prey; fortunately, however, it is unlikely to perpetrate major ecological or economic disturbances.