Ureotelism is inducible in the neotropical freshwater Hoplias malabaricus (Teleostei, Erythrinidae)

Abstract

Increased environmental pH decreases ammonia transport through the gills, impairing nitrogenous waste. The consequent toxicity is usually drastic to most fishes. A few species are able to synthesize urea as a way to detoxify plasma ammonia. We studied three teleosts of the family Erythrinidae living in distinct environments, and assumed the biochemical behaviors would be different in spite of their being closely related species. Adult fish collected in the wild were submitted to alkaline water and the urea excretion rate was determined. The specific activity of urea cycle enzymes was determined in liver samples of fish from neutral waters. The studied species Hoplias lacerdae, Hoplerithrynus unitaeniatus, and Hoplias malabaricus are ureogenic. Urea synthesis is not a metabolic way to detoxify ammonia in H. lacerdae and Hoplerithrynus unitaeniatus exposed to an alkaline environment. The plasma ammonia profile of both species showed two distinct biochemical responses. Urea excretion of H. malabaricus was high in alkaline water, and the transition to ureotelism is proposed. The nitrogen excretion rate of H. malabaricus was among the highest values reported and the high urea excretion leads us to include this species as ureotelic in alkaline water.Key words: ureotelism, ammonia, toxicity, urea cycle, Hoplias malabaricus. RESUMO Ureotelismo é indutível em Hoplias malabaricus (Teleostei, Erythrinidae)

The Distribution of the Enzyme Arginase in the Tissues of Selected Cichlidae Species: <i>Tilapia zillii, Sarotherodon galilaeus</i> and <i>Oreochromis niloticus</i>

“…However, the high arginase activity observed in the tissues of these organisms could be an indication of ureotelism in alkaline water, as observed by other workers (Mommsen & Walsh, 1992;Wood, 1993;Wright, 1995;Moraes & Polez, 2003).…”

“…Also Ozan et al (1999), working on Rainbow trout (Oncorhynchus mykiss), found that arginase level in the liver was highest followed by kidney, skin, gills, muscle and eyes. The high level of arginase in the liver of these Tilapia species has been found to be caused by increase in the environmental pH which decreases ammonia transport through the gills, and then impairing nitrogenous waste (Campbell & Anderson, 1991;Moraes & Polez, 2003). The consequent toxicity is usually drastic to most fishes.…”

“…A few species are able to synthesize urea as a way to detoxify plasma ammonia. Moraes & Polez (2003) in their study of three teleost family of Erythrinidae (Hoplias lacerdae, Hoplerithrynus unitaeniatus and Hoplias malabaricus), living in distinct environments with distinct biochemical behaviours, were subjected to alkaline water and the urea excretion rate was determined. The studied species showed ureogenicity.…”

“…The studied species showed ureogenicity. Urea excretion of H. malabaricus was high in alkaline water, and the transition to ureotelism was proposed (Moraes & Polez, 2003). Hartenstein (1971) reported the distribution of crayfish arginase which occurs in soluble and particulate fractions of the hepatopancreas, abdominal muscle and thoracic wall of the crayfish.…”

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

“…A set of ornithine-urea cycle enzymes has been reported for some teleost species. Moreover, specific environmental conditions such as those created by ammonia increase (Saha & Ratha, 1994;Saha et al, 1999;Moraes & Polez, 2004b), alkaline waters (Randall et al, 1989;Moraes & Polez, 2004a), and confinement and/or crowding (Walsh et al, 1990;Walsh & Milligan, 1995) augment the presence of these enzymes. The Neotropical facultative airbreather Synbranchus marmoratus (marble swamp eel) is able to survive up to three months embedded in mud (Bicudo & Johansen, 1979), carrying out the gas-exchange process in the buccopharyngeal epithelium and in the branchial chamber.…”