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.

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