Diel Patterns of Nitrogen Excretion, Plasma Constituents, and Behavior in the Gulf Toadfish (Opsanus beta) in Laboratory versus Outdoor Mesocosm Settings

In order to elucidate the cues for, and the biochemical mechanisms of, the transition to ureogenesis in the gulf toadfish Opsanus beta, experiments on the effects of confinement/crowding were carried out. Confinement of toadfish to small volumes of water initiated a switch to nearly complete reliance on ureogenesis for nitrogen excretion within 2448 h. Further experiments suggested that this switch was probably due to the physical confinement per se, rather than to a measurable build-up of ammonia in the water. However, the possibility of the response being triggered by a very low concentration of a pheromone-like substance was not excluded by our experimental design. The activities of several enzymes of ureogenesis, ornithinecitrulline transcarbamoylase, aspartate amino transferase and glutamine synthetase, increased in the liver of toadfish during confinement. Notably, glutamine synthetase activity increased almost fourfold within 24 h, and this increase preceded increases in urea excretion. A number of plasma and liver amino acid concentrations changed during confinement: there were declines in plasma asparagine, glutamate and glycine levels and an increase in plasma valine, as well as a decline in liver alanine and an increase in liver arginine concentrations. Liver glutamine was not detectable. When the amino acid data are taken together with the enzyme activity changes, it appears that the switch to ureogenesis occurs primarily upstream of the ornithineurea cycle, at the level of supply of nitrogen to the pathway. The results are discussed in the context of the habitat of toadfish.

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Effects of feeding and confinement on nitrogen metabolism and excretion in the gulf toadfish Opsanus beta

Journal of Experimental Biology ◽

10.1242/jeb.198.7.1559 ◽

1995 ◽

Vol 198 (7) ◽

pp. 1559-1566 ◽

Cited By ~ 7

Author(s):

P Walsh ◽

C Milligan

Keyword(s):

Total Nitrogen ◽

Ammonia Excretion ◽

Nitrogen Loading ◽

Nitrogen Excretion ◽

Turnover Rates ◽

Opsanus Beta ◽

Urea Excretion ◽

Dietary Nitrogen ◽

Excretion Rates ◽

Gulf Toadfish

In order to elucidate further the cues for, and the biochemical mechanisms of, the transition to ureogenesis in the gulf toadfish Opsanus beta, experiments on the effects of feeding (i.e. nitrogen loading) were carried out. Baseline nitrogen excretion rates were first measured on solitary toadfish in large water volumes (i.e. unconfined conditions). These nitrogen excretion rates were higher, and had a higher proportion as ammonia (61 %), than previously published 'control' measurements. Feeding of unconfined toadfish elevated total nitrogen excretion approximately threefold, with little change in the proportion of urea versus ammonia. During the first 24 h of confinement of unfed toadfish, absolute levels of urea excretion remained constant while ammonia excretion rates fell to near zero, so that toadfish became 90 % ureotelic. When fed prior to confinement, urea excretion rates remained constant for the first 24 h, and the bulk of the nitrogen was excreted as ammonia (80 %); excretion of the excess dietary nitrogen took up to 48 h to complete. If pre-adapted to confinement and then fed, toadfish excreted only about 55 % of their nitrogenous waste as ammonia, and excretion of excess dietary nitrogen was completed by 24 h. Elevations of hepatic glutamine synthetase (GNS) activities accompanied confinement and were shown to be almost exclusively in the cytosolic compartment and to be correlated with a decrease in the ratio of hepatic levels of glutamate:glutamine. These GNS activity increases also appear to account in part for the decrease in the percentage of ammoniotely in toadfish under conditions of nitrogen loading after confinement. However, additional means of regulating total nitrogen excretion (e.g. changes in protein turnover rates) and the degree of ureogenesis versus ammoniogenesis (e.g. N-acetylglutamate stimulation of carbamoylphosphate synthetase) must be postulated to account fully for changes in nitrogen excretion rates and activation of ureogenesis under some circumstances.

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The role of uptake and degradation in the regulation of peripheral serotonin dynamics in Gulf toadfish, Opsanus beta

Comparative Biochemistry and Physiology Part A Molecular & Integrative Physiology ◽

10.1016/j.cbpa.2021.110980 ◽

2021 ◽

pp. 110980

Author(s):

John Sebastiani ◽

M. Danielle McDonald

Keyword(s):

Opsanus Beta ◽

Gulf Toadfish

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The effects of acute and chronic ammonia exposure during early life stages of the gulf toadfish, Opsanus beta

Aquatic Toxicology ◽

10.1016/j.aquatox.2005.08.005 ◽

2005 ◽

Vol 75 (3) ◽

pp. 225-237 ◽

Cited By ~ 17

Author(s):

John F. Barimo ◽

Patrick J. Walsh

Keyword(s):

Early Life ◽

Life Stages ◽

Early Life Stages ◽

Opsanus Beta ◽

Ammonia Exposure ◽

Gulf Toadfish

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Subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis in the batrachoidid fishes Opsanus beta, Opsanus tau and Porichthys notatus

Journal of Experimental Biology ◽

10.1242/jeb.198.3.755 ◽

1995 ◽

Vol 198 (3) ◽

pp. 755-766 ◽

Cited By ~ 3

Author(s):

P Walsh

Keyword(s):

Glutamine Synthetase ◽

Subcellular Localization ◽

Biochemical Properties ◽

Nitrogen Excretion ◽

Urea Synthesis ◽

Carbamoyl Phosphate ◽

Opsanus Beta ◽

Opsanus Tau ◽

Porichthys Notatus ◽

The Family

The subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis were examined in three representatives of fishes of the family Batrachoididae, the gulf toadfish (Opsanus beta), the oyster toadfish (Opsanus tau) and the plainfin midshipman (Porichthys notatus). The primary objective of the study was to compare the biochemical characteristics of these fishes, which represent a range between ammoniotelism and ureotelism (O. beta being facultatively ureotelic), with previous patterns observed for an ammoniotelic teleost (Micropterus salmoides, the largemouth bass) and an obligate ureogenic elasmobranch (Squalus acanthias, the dogfish shark). The present study documents the expression of mitochondrial carbamoyl phosphate synthetase (CPSase) III and cytosolic CPSase II (and its associated enzymes of pyrimidine synthesis, dihydro-orotase and aspartate carbamoyltransferase) in the livers of all three batrachoidid species. Both mitochondrial and cytosolic activities of arginase were present in the livers of all three species, as were cytosolic glutamine synthetase and argininosuccinate synthetase and lyase. However, O. beta also showed mitochondrial glutamine synthetase activity and higher total hepatic levels of glutamine synthetase than either O. tau or P. notatus. Taken together, these observations confirm that the arrangement of these enzymes in the batrachoidid fishes has greater similarity to that of M. salmoides than to that of S. acanthias. However, differences within the family appear to coincide with the different nitrogen excretion strategies. O. tau and P. notatus are primarily ammoniotelic and most closely resemble the ammoniotelic M. salmoides, whereas ureotelism in O. beta is correlated with the presence of a mitochondrial glutamine synthetase and the ability to induce higher total glutamine synthetase activities than O. tau or P. notatus. Additionally, isolated mitochondria from O. beta were able to generate citrulline from glutamine, whereas those from O. tau were not. Also in contrast to S. acanthias, glutamine synthetase activities in the mitochondria of O. beta are consistently lower than those of CPSase III. This and other kinetic observations lend support to the hypothesis that glutamine synthetase may be an important regulatory control point in determining rates of ureogenesis in O. beta.

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