Ion fluxes and hematological parameters of two teleosts from the Rio Negro, Amazon, exposed to hypoxia / Fluxos iônicos e parâmetros hematológicos em duas espécies de teleósteos do Rio Negro, Amazônia, expostos à hipoxia

The aim of this study was to describe the effect of hypoxia on whole body ion fluxes and hematological parameters in two Amazonian teleosts: Serrasalmus eigenmanni and Metynnis hypsauchen. The increase of Na+ and Cl- effluxes on M. hypsauchen exposed to hypoxia may be related to an increase of gill ventilation and effective respiratory surface area, to avoid a reduction in the oxygen uptake, and/or with the decrease of pHe, that could inhibit Na+ and Cl- transporters and, therefore, reduce influx of these ions. Effluxes of Na+ and Cl- were lower in hypoxia than in normoxia for S. eigenmanni, possibly because in hypoxia this species would reduce gill ventilation and oxygen uptake, which would lead to a decrease of gill ion efflux and, consequently, reducing ion loss. The increase on hematocrit (Ht) during hypoxia in M. hypsauchen probably was caused by an increase of the red blood cell volume (MCV). For S. eigenmanni the increase on glucose possibly results from the usage of glucose reserve mobilization. Metynnis hypsauchen showed to be more sensitive to hypoxia than Serrasalmus eigenmanni, since the first presented more significant alterations on these osmoregulatory and hematological parameters. Nevertheless, the alterations observed for both species are strategies adopted by fishes to preserve oxygen supply to metabolizing tissues during exposure to hypoxia.

O objetivo deste trabalho foi descrever o efeito da hipoxia no fluxo iônico corporal e nos parâmetros hematológicos em duas espécies de teleósteos da Amazônia: Serrasalmus eigenmanni e Metynnis hypsauchen. O aumento dos efluxos de Na+ e Cl- em M. hypsauchen expostos à hipoxia pode estar relacionado ao aumento da ventilação branquial e da eficiência da área da superfície respiratória, a fim de evitar redução na captação de oxigênio; e/ou com a diminuição do pHe, que pode inibir os transportadores de Na+ e Cl- e, então, reduzir o influxo destes íons. Os efluxos de Na+ e Cl- foram menores em hipoxia do que em normoxia para a espécie S. eigenmanni, possivelmente porque esta espécie em hipoxia poderia reduzir a ventilação branquial e a captação de oxigênio, a qual levaria a uma diminuição do efluxo branquial de íons e, conseqüentemente, à redução da perda de íons. O aumento do hematócrito (Ht) durante hipoxia em M. hypsauchen provavelmente foi causado pelo aumento do volume das células vermelhas do sangue (MCV). Para a espécie S. eigenmanni, o aumento da glicose possivelmente foi resultado do uso da mobilização da reserva de glicose. A espécie Metynnis hypsauchen mostrou ser mais sensível à hipoxia do que a espécie Serrasalmus eigenmanni, uma vez que a primeira espécie apresentou mais alterações significativas em seus parâmetros osmorregulatórios e hematológicos. Contudo, as alterações observadas em ambas as espécies são estratégias adotadas pelos peixes a fim de preservar o suprimento de oxigênio para metabolização nos tecidos durante exposição à hipoxia.

Dietary tissue cadmium accumulation in an amazonian teleost (Tambaqui, Colossoma macropomum Cuvier, 1818)

Understanding the effects of metal contamination in the Amazon basin is important because of the potential impact on this region of high biodiversity. In addition, the significance of fish as the primary source of protein for the local human population (living either alongside the Amazon River or in the city of Manaus) highlights the need for information on the metal transfer through the food chain. Bioaccumulation of metals in fish can occur at significant rates through the dietary route, without necessarily resulting in death of the organism. The goal of this work was to expose an economic relevant species from the Amazon basin (tambaqui, Colossoma macropomum) to dietary cadmium (Cd) at concentrations of 0, 50, 100, 200, and 400 µg.g-1 dry food. Fish were sampled on days 15, 30, and 45 of the feeding trials. Tissues were collected for analysis of Cd concentration using graphite furnace atomic absorption spectrophotometry. Cd accumulation in the tissues occurred in the following order: kidney > liver > gills > muscle. Relative to other freshwater fish (e.g., rainbow trout, tilapia), tambaqui accumulated remarkably high levels of Cd in their tissues. Although Cd is known to affect Ca2+ homeostasis, no mortality or growth impairment occurred during feeding trials.

O entendimento dos efeitos da contaminação por metais na Bacia Amazônica é importante devido ao potencial impacto sobre esta região de elevada biodiversidade. Além disso, a relevância dos peixes como fonte primária de proteína para a população humana local (tanto nas comunidades ribeirinhas ao longo do rio Amazonas, quanto na cidade de Manaus), ressalta a necessidade de informação sobre a transferência de metais através da cadeia alimentar. Bioacumulação de metais em peixes pode ocorrer em taxas significativas através da dieta, sem necessariamente resultar na morte do indivíduo. O objetivo deste estudo foi expor cronicamente uma espécie de importância comercial nativa da Amazônia (tambaqui, Colossoma macropomum) a dietas enriquecidas com cádmio (Cd) em concentrações de 0, 50, 100, 200, and 400 µg.g-1 alimento seco. Os peixes foram amostrados nos dias 15, 30 e 45 do tratamento experimental. Os tecidos foram coletados para análise quanto a concentração de Cd por meio de espectrofotometria de absorção atômica acoplado a forno de grafite. O acúmulo de Cd nos tecidos ocorreu na seguinte ordem: rim > fígado > brânquias > músculo. Comparando-se com outras espécies de peixes de água doce (por exemplo, truta arco-íris, tilápia), o tambaqui acumulou níveis de Cd extremamente mais elevados em seus tecidos. Apesar do Cd ser conhecido por afetar a homeostase do Ca2+, não houve mortalidade ou retardo no crescimento durante os testes dietários.

Ion fluxes of Metynnis hypsauchen, a teleost from the Rio Negro, Amazon, exposed to an increase of temperature

The aim of this study was to investigate the effect on an increase of temperature on the net ion fluxes on Metynnis hypsauchen, a teleost species from the Rio Negro. Fish were collected in the Anavilhanas archipelago, Rio Negro, Amazon. After 24 h adaptation fish were placed in individual chambers served with a steady flow of recirculated water. Na+ and Cl- fluxes were determined at 26 and 33ºC. After 18 h in the chambers, fish presented an influx of Na+ and Cl-, and the temperature raise to 33ºC led to an efflux of both ions, which remained even after 6 h in this temperature. Six hours were not enough to promote a significant reduction of net ion effluxes, but certainly the fluxes would be in net balance after a longer period of time, since this species can be exposed to this temperature in its natural environment

Low pH and calcium effects on net Na+ and K+ fluxes in two catfish species from the Amazon River (Corydoras: Callichthyidae)

The present study analyzes Na + and K + disturbances caused by low pH in two catfish species from the Amazon River. Corydoras adolfoi inhabits ion-poor, black-stained, low pH (3.5-4.0) waters, while C. schwartzi is native to ion-rich waters at circumneutral pH. Fish were exposed to pH 3.5 Ca2 + - free, and Ca2 + - enriched (approximately 500 mu mol/l) water to determine the protective effects of calcium. Net Na+ and K+ fluxes were measured in the water collected from the fish experimental chambers. C. adolfoi was unable to control the Na+ efflux at low pH, exhibiting Na+ loss up to -594 ± 84 nmol g-1 h-1 during the first hour. After 3 and 6 h, net Na+ flux increased by 7- and 23-fold, respectively. In C. schwartzi, at pH 3.5, the initial high Na+ loss (-1,063 ± 73 nmol g-1 h-1) was gradually attenuated. A K+ loss occurred in both species, but remained relatively constant throughout exposure. High [Ca2+] affected ion losses in both species. C. adolfoi had 70 percent loss attenuation, indicating incapacity to control Na+ efflux. In C. schwartzi, elevated [Ca2+] completely prevented the Na+ losses caused by exposure to low pH. Rather different patterns were seen for K+ fluxes, with C. adolfoi showing no K+ disruption when exposed to low pH/high [Ca2+]. Thus, C. adolfoi loses Na+ during acid exposure, but has the ability to control K+ loss, while C. schwartzi controls diffusive Na+ loss but exhibits a slightly higher K+ loss. Ion balance was influenced by [Ca2+] at low pH in C. schwartzi but not in C. adolfoi

Karyological, biochemical, and physiological aspects of Callophysus macropterus (Siluriformes, Pimelodidae) from the Solimöes and Negro Rivers (Central Amazon)

Karyological characteristics, i.e., diploid number, chromosome morphology and nucleolus organizer regions (NORs), biochemical characteristics, i.e., electrophoretic analysis of blood hemoglobin and the tissue enzymes lactate dehydrogenase (LDH), malate dehydrogenase (MDH), alcohol dehydrogenase (ADH), and phosphoglucose isomerase (PGI), and physiological characteristics, i.e., relative concentration of hemoglobin and intraerythrocytic concentrations of organic phosphates were analyzed for the species Callophysus macropterus collected from Marchantaria Island (white water system - Solimöes River) and Anavilhanas Archipelago (black water system - Negro River). Karyological and biochemical data did not reveal significant differences between specimens collected at the two sites. However, the relative distribution of hemoglobin bands I and III (I = 16.33 ñ 1.05 and III = 37.20 ñ 1.32 for Marchantaria specimens and I = 6.33 ñ 1.32 and III = 48.05 ñ 1.55 for Anavilhanas specimens) and levels of intraerythrocytic GTP (1.32 ñ 0.16 and 2.76 ñ 0.18 for Marchantaria and Anavilhanas specimens, respectively), but not ATP or total phosphate, were significantly different, indicating a physiological adaptation to the environmental conditions of these habitats. It is suggested that C. macropterus specimens from the two collecting sites belong to a single population, and that they adjusted some physiological characteristics to adapt to local environmental conditions.

Oxygen transfer in fish: morphological and molecular adjustments

A wide range of organismic, physiological and biochemical adjustments to improve oxygen transfer is observed in fish exposed to environmental hypoxia and during anemia. Many fish species of the Amazon obtain oxygen directly from air when water oxygen is low. The accessory air-breathing organs include modifications of the gills, mouth, stomach and intestine, and swimbladder vascularization. Other species extend the lower lip and skim to improve oxygen uptake from the oxygen-rich surface layer of the water. The amount of oxygen uptake from air wp estimated for Hoplosternum littorale and Lipossarcus pardalis. In addition, the oxygen uptake from the water surface was estimated for Colossoma macropomum. Blood oxygen content was reduced by 30 per cent in Hoplostemum littorale and Colossoma macropomum and 70 per cent in Lipossarcus pardalis if they were denied access to air. Adjustments of intraerythrocytic levels of ATP and GTP significantly improve oxygen transfer in fish during environmental hypoxia and anemia. In contrast to environmental hypoxia, intraerythrocytic levels of ATP and GTP increase during anemia in fish facilitating oxygen unloading to the tissues. It is suggested that the increase in ATP and GTP levels during anemia occurs because the conditions required to increase the activity of adenylate and guanylate phosphate synthetic pathways are similar.

Biochemical adjustments to hypoxia by Amazon cichlids

The isozyme distribution of cichlid lactate dehydrogenase (LDH) is related to species environmental preferences. Cichlasoma amazonarum. occurs in different environments and presents LDH tissue distribution patterns that correlate with oxygen tension at the capture location. Cichlasoma amazonarum was exposed to long term severe hypoxia (51 days at 36.4 +/- 5.9 mmHg), tissue LDH isozyme distribution was analyzed by electrophoresis and enzyme activities were measured by monitoring the oxidation of NADH as pyruvate was reduced to lactate. The exposure of Cichlasoma amazonarum to long-term severe hypoxia resulted in changes in the tissue distribution of LDH isozymes. The major changes in response to hypoxia occurred in heart, liver and brain: isozyme A4 was activated in heart and brain, whereas isozyme B4 was activated in liver. The most significant quantitative change occurred in brain LDH of hypoxia-exposed animals which adopted muscle type kinetics, reflecting a new LDH isozyme distribution. LDH activity was significantly reduced (P<0.05) in animals exposed to hypoxia (N = 8), suggesting an overall LDH suppression. Pyruvate inhibition decreased in all hypoxia-exposed tissues. Thus, the ability of Cichlasoma amazonarum to regulate LDH tissue expression according to oxygen availability allows the animal to survive chronic hypoxic environments. This phenotypic plasticity may occur in other hypoxia-tolerant fish species.

Effects of temperature on leucocytes of Colossoma macropomum and Hoplosternum littorale (Pisces)

1. The effects of different thermal regimens on qualitative and quantitative characteristics of leucocytes were evaluated in two fish species of the Amazon region. 2. The proportion of circulating types of leucocytes changed significantly in Colossoma macropomum (tambaqui) but not in Hoplosternum littorale (tamoatá) exposed for four-week terms to 20, 25, 30, 35, and 40 degrees C. 3. The proportion of circulating lymphocytes decreased significantly in tambaquis exposed to 30, 35, and 40 degrees C. No changes in lymphocyte proportions were observed in tamoatás. 4. Neutrophils were almost absent in tambaquis, except in animals exposed to 40 degrees C. No significant changes in circulating neutrophils were observed in tamoatás. 5. The circulating leucocytes of Colossoma macropomum and Hoplosternum littorale are affected in different ways by temperature changes, suggesting species-specific adjustments to this parameter.