Mercury distribution in different tissues and trophic levels of fish from a tropical reservoir, Brazil

Concentrations of organic (OrgHg) and inorganic mercury (InorgHg) were assessed in different fish tissues (liver, muscle, kidney, gut and gonads) and trophic levels collected in an impacted tropical reservoir in southeastern Brazil. Organic mercury concentrations in muscle were remarkably higher in the carnivorous species Hoplias malabaricus and Oligosarcus hepsetus. The ratios of OrgHg in relation to total mercury (%OrgHg) in muscle also varied according to the species trophic level: 93% for carnivores, 84% for omnivores, 73% for algivores/planktivores and 58% for detritivores. The %OrgHg in the gut tissue of carnivores (78%) was much higher than that found in omnivores (30%), possibly reflecting a process of trophic biomagnification in the reservoir. On the other hand, the InorgHg concentrations in muscle decreased with the trophic level increase, suggesting that this form of mercury did not biomagnify through the food web. Gonads contained the least total mercury, and approximately all of this mercury was represented by the organic form (83 to 98%). The kidney and the liver of all fish species contained less than 50% OrgHg. We suggest that the low %OrgHg in the liver is related to different capacities or strategies of OrgHg detoxification by the fish. © 2009 Sociedade Brasileira de Ictiologia

Estudo da dieta natural de peixes no reservatório de Ribeirão das Lajes, Rio de Janeiro, Brasil - DOI: 10.4025/actascibiolsci.v27i4.1270

The aim of this study was to know the natural diet of species from Ribeirão das Lajes reservoir, from the stomach content analysis of fishes captured in two different seasons by using gillnets. Characterizing the natural diet, the methods of frequency of occurrence and abundance percentage of items from the diet were applied. Eleven species were registered, representing approximately 62% of the listed species for that reservoir, being Trachelyopterus striatulus and Metynnis maculates the most abundant. These two species, as well as Geophagus brasiliensis and Tilapia rendalli showed an omnivorous microphageous habit and also showed a great diversity in choosing food items, due to the consumption of items from the water column and also from the forest-water ecotone. Astyanax bimaculatus also presented an omnivorous habit, although with a tendency to insectivore while Oligosarcus hepsetus and Cichla monoculus showed a piscivorous habitO presente estudo objetivou conhecer a dieta natural de espécies residentes no reservatório de Ribeirão das Lajes (RJ), sendo realizada a análise do conteúdo estomacal de peixes capturados por meio de redes de espera, em duas épocas distintas. Na caracterização da dieta alimentar, foram calculados a freqüência de ocorrência de itens e o percentual de abundância de cada item na dieta. Foram registradas 11 espécies, representando cerca de 62% delas inventariadas para o reservatório, sendo as espécies encontradas com maior abundância Trachelyopterus striatulus e Metynnis maculatus. Essas duas espécies, bem como Geophagus brasiliensis e Tilapia rendalli, apresentaram hábito onívoro micrófago, sendo observada uma plasticidade alimentar principalmente devido à utilização de itens alimentares tanto originários da coluna d’água como do ecótono água-floresta. Astyanax bimaculatus apresentou hábito também onívoro, mas com tendência à insetivoria, enquanto Oligosarcus hepsetus e Cichla monoculus mostraram um hábito alimentar piscívor