Abstract:The exposure of fish to air is normally expected to interfere with the nitrogen excretion process. Hoplias malabaricus and Hoplerythrinus unitaeniatus, two teleost species, display distinct behaviors in response to decreases in natural reservoir water levels, although they may employ similar biochemical strategies. To investigate this point, plasma levels of ammonia, urea, uric acid, and the two urea cycle enzymes, ornithine carbamoyl transferase (OCT) and arginase (ARG), as well as glutamine synthetase (GS) w… Show more
“…malabaricus is a voracious piscivore feeding on numerous fish species and even birds (Ringuelet et al, 1967) and small mammals (Teixeira-de Mello unpublished data), which may enhance its carrying capacity. It exhibits parental care of hatchings (Ringuelet et al, 1967) and tolerates very turbid and hypoxic conditions (Rantin & Johansen, 1984;Polez et al, 2003), which are common features of eutrophic systems. These characteristics, considered as the key factors for its successful colonization of almost all water ecosystems in the region, may also be useful in the biomanipulation of eutrophic ecosystems.…”
While the cascading effect of piscivorous fish on the pelagic food-web has been well studied in north temperate lakes, little is known about the role of native piscivores in warm lakes. Here, the fish communities are typically characterized by high abundances of small, omnivorous fish exerting a high predation pressure on the zooplankton. We conducted a 1-month replicated mesocosm experiment at subtropical conditions to test the effects of piscivorous (Hoplias malabaricus) fish on phytoplankton biomass and water transparency. Our experimental design comprised two (phytoplankton ? zooplankton), three (phytoplankton ? zooplankton ? planktivores) and four (phytoplankton ? zooplankton ? planktivores ? piscivores) trophic levels. We designed two different four trophic level treatments, one with juveniles of H. malabaricus (\15 cm) and the other with adults ([30 cm), to evaluate the strength of the effects of juveniles and adults. A major trophic cascade response was observed. In the planktivores treatment, chlorophyll a (Chl a) and turbidity significantly increased, while total zooplankton abundance (especially Daphnia obtusa) and water transparency decreased. In both H. malabaricus treatments and in the two trophic levels control, the opposite pattern was observed; thus, Chl a and turbidity decreased, while zooplankton abundance and water transparency increased. The differences observed reflected the strong control on the planktivore Jenynsia multidentata by both sizes of H. malabaricus, propagating down through the trophic web. Hoplias malabaricus is widely distributed in South America and may, therefore, be a good candidate for restoration by biomanipulation in eutrophic lakes of subtropical and tropical regions. However, detailed investigations at whole-lake scale are needed to determine its potential.
“…malabaricus is a voracious piscivore feeding on numerous fish species and even birds (Ringuelet et al, 1967) and small mammals (Teixeira-de Mello unpublished data), which may enhance its carrying capacity. It exhibits parental care of hatchings (Ringuelet et al, 1967) and tolerates very turbid and hypoxic conditions (Rantin & Johansen, 1984;Polez et al, 2003), which are common features of eutrophic systems. These characteristics, considered as the key factors for its successful colonization of almost all water ecosystems in the region, may also be useful in the biomanipulation of eutrophic ecosystems.…”
While the cascading effect of piscivorous fish on the pelagic food-web has been well studied in north temperate lakes, little is known about the role of native piscivores in warm lakes. Here, the fish communities are typically characterized by high abundances of small, omnivorous fish exerting a high predation pressure on the zooplankton. We conducted a 1-month replicated mesocosm experiment at subtropical conditions to test the effects of piscivorous (Hoplias malabaricus) fish on phytoplankton biomass and water transparency. Our experimental design comprised two (phytoplankton ? zooplankton), three (phytoplankton ? zooplankton ? planktivores) and four (phytoplankton ? zooplankton ? planktivores ? piscivores) trophic levels. We designed two different four trophic level treatments, one with juveniles of H. malabaricus (\15 cm) and the other with adults ([30 cm), to evaluate the strength of the effects of juveniles and adults. A major trophic cascade response was observed. In the planktivores treatment, chlorophyll a (Chl a) and turbidity significantly increased, while total zooplankton abundance (especially Daphnia obtusa) and water transparency decreased. In both H. malabaricus treatments and in the two trophic levels control, the opposite pattern was observed; thus, Chl a and turbidity decreased, while zooplankton abundance and water transparency increased. The differences observed reflected the strong control on the planktivore Jenynsia multidentata by both sizes of H. malabaricus, propagating down through the trophic web. Hoplias malabaricus is widely distributed in South America and may, therefore, be a good candidate for restoration by biomanipulation in eutrophic lakes of subtropical and tropical regions. However, detailed investigations at whole-lake scale are needed to determine its potential.
“…Clearly, both exposure methods cause stress, and this is associated with increases in blood cortisol, catecholamines, ammonia, and lactate levels (Arends et al, 1999;Maxime et al, 1995;Polez et al, 2003). We measured the blood cortisol levels, as described by Lankford et al (2003), from each of two air-and hypoxic water exposed sturgeons immediately, 6, and 30 h after the hypoxic insults.…”
Hypoxia is a frequent challenge to aquatic vertebrates as compared with that for their terrestrial counterparts. All vertebrates respond to hypoxia in a similar, but not identical manner, indicating that these responses appeared early in the evolution of vertebrates. The aim of this study is to find out the effects of hypoxia on apoptosis in the central nervous system (CNS) of sturgeon, an archaic fish. With the regional specialization of the CNS, we hypothesize that if cell death does occur, the response will vary between regions, i.e., some CNS areas will be more susceptible to hypoxia than the others would. Sturgeons (Acipenser shrenckii) were subjected to hypoxia by exposure to either air or hypoxic water. After 6- or 30-h recovery they were sacrificed and the following regions of the CNS: retina, olfactory lobe, optic tectum, pituitary, cerebellum, pons/medulla, and spinal cord were examined by the terminal transferase mediated dUTP nick end labeling technique and for the cleaved fragment of activated caspase-3 by Western blotting. In hypoxia-treated sturgeons, the retina, optic tectum, pituitary, and spinal cord were found to have significantly more apoptotic cells than did untreated sturgeons at both 6 and 30 h after the hypoxic insults, indicating prolonged damage. Apoptosis was confirmed by Western blotting of the cleaved fragment of activated caspase-3. Olfactory lobe, cerebellum, and pons/medulla had relatively few apoptotic cells. The CNS of sturgeon showed a differential pattern of apoptosis in response to hypoxia.
“…O gênero Hoplerythrinus possui como principal característica a capacidade de sobreviver a longos períodos de hipóxia pela habilidade de absorver oxigênio atmosférico (Polez et al 2003, Jucá-Chagas 2004, Oliveira et al 2004. A respiração aérea facultativa é resultante da grande vascularização e esponjosidade da bexiga natatória, conferindo-lhe a possibilidade de fazer incursões terrestres entre corpos de águas adjacentes (Val & Almeida-Val 1995, Graham 1997, Jucá-Chagas 2004.…”
Section: Leal Me Klein Gf Schulz Uh and Lehmann P Primeirounclassified
“…Segundo Sato et al (2003) a média de ovócitos para a espécie encontra-se na faixa de 1.064 a 1.370 ovócitos.g -1 gerando ovos do tipo adesivo, comum para espécies não-migradoras e com cuidado parental como o jeju. Encontrado em ambientes lênticos apresenta facilidade de adaptação às mudanças ambientais, físicas e químicas da água (Nelson 1984, Polez et al 2003.…”
Section: Leal Me Klein Gf Schulz Uh and Lehmann P Primeirounclassified
Hoplerythrinus unitaeniatus is popularly known as jeju or aimara. Widely distributed, occurs in many Central and South America basins, with the São Francisco River as type locality. In Brazil, the southernmost record of the species is the Uruguay River, Rio Grande do Sul State. This study reports the first record of H. unitaeniatus in the Patos Lagoon system, Guaiba hydrographic region, state of Rio Grande do Sul, Brazil. The capture occurred in a floodplain adjacent of the Sinos River near São Leopoldo city (29° 44' 14.04" S and 51° 05' 11.08" W). Two specimens were collected with drag net in May 2008. One specimen was anesthetized with 2-phenoxy-ethanol solution, fixed in formalin 10%, identified and included in the Museu de Ciências e Tecnologia da Pontífícia Universidade Católica do Rio Grande do Sul fish collection. The second specimen was kept alive in aquarium. After ten months it died of Lernaea cyprinacea (Crustacea, Copepoda) infestation. The presence of Lernaea and ease of captive breading of this species support the hypothesis that the collected fish escaped from regional fish farms. The accidental capture does not necessarily reflect a self-sustaining population, but shows the absence of supervision on breeding and marketing of non-native species, which may lead to a homogenized aquatic community.
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