First records of introduced carps (Teleostei, Cyprinidae) in the natural habitats of Mirim and Patos Lagoon estuary, Rio Grande do Sul, Brazil

This is the first record in the wild of occurrence of four carp species (bighead Aristichthys nobilis (Richardson, 1845), common Cyprinus carpio carpio Linnaeus, 1758, silver Hypophthalmichthys molitrix (Valenciennes, 1844), and grass carp Ctenopharyngodon idellus (Valenciennes, 1844)) in the Mirim Lagoon and Patos Lagoon estuary. Our findings reinforce the hypothesis that during periods of elevated rainfall and freshwater discharge, exotic species could be easily transported from overflowed ponds and lakes into the Mirim-Patos Lagoon and then estuarine area.<br>Este trabalho registra a ocorrência de quatro espécies de carpas (cabeça-grande Aristichthys nobilis (Richardson, 1845), comum Cyprinus carpio carpio Linnaeus, 1758, prateada Hypophthalmichthys molitrix (Valenciennes, 1844), e capim Ctenopharyngodon idellus (Valenciennes, 1844)) em ambientes naturais da Lagoa Mirim e do estuário da Lagoa dos Patos. Os resultados reforçam a hipótese de que durante períodos de excesso de chuvas e elevada descarga continental, espécies exóticas poderiam ser facilmente transportadas de tanques de cultivos e lagos transbordados para a Lagoa Mirim e a região estuarina da Lagoa dos Patos

Preliminary examination of food web structure of Nicola Lake (Taim Hydrological System, south Brazil) using dual C and N stable isotope analyses : scientific note

Taim Ecological Reserve is located within the Taim Hydrological System and was created to protect a heterogeneous and productive landscape harboring exceptional biological diversity in southern Brazil. Using stable isotope ratio analyses of carbon (δ13C) and nitrogen (δ15N), we provide a preliminary description of the food web structure, including estimates of production sources supporting fish populations and vertical trophic structure, within a representative lake of this system. A total of 21 organisms (5 macrophytes, 3 mollusks and 13 adult fishes) representing 16 species were collected for isotope analysis. Fishes had δ13C values ranging from -24.30 ‰ to -28.31 ‰, showing concordance with the range of values observed for macrophytes (-25.49 to -27.10 ‰), and suggesting that these plants could be a major carbon source supporting these fishes. δ13C signatures of Corbicula (-30.81‰) and Pomacea (-24.26‰) indirectly suggest that phytoplankton and benthic algae could be alternative carbon sources for some consumers. Nitrogen isotope ratios indicated approximately three consumer trophic levels. The pearl cichlid Geophagus brasiliensis was a primary consumer. Two catfishes (Trachelyopterus lucenai and Loricariichthys anus) were secondary consumers. Two congeneric pike cichclids (Crenicichla lepidota and C. punctata), a catfish (Pimelodus maculatus) and the characids Astyanax fasciatus and Oligosarcus robustus were tertiary consumers. Further studies including additional primary producers and consumers and greater sample numbers should be conducted to provide a more complete and detailed description of food web structure and dynamics within the reserve.A Estação Ecológica do Taim está inserida dentro do Sistema Hidrológico do Taim e foi criada para proteger uma região heterogênea e produtiva no sul do Brasil, abrigando uma diversidade biológica excepcional. A partir da análise de isótopos estáveis do carbono (δ13C) e nitrogênio (δ15N), esse trabalho fornece uma descrição preliminar da estrutura da teia alimentar numa lagoa representativa desse sistema, incluindo estimativas dos produtores primários que sustentam suas populações de peixes e a estrutura trófica vertical. Um total de 21 organismos (5 macrófitas, 3 moluscos e 13 peixes adultos), representando 16 espécies, foram coletados para a análise da composição isotópica. Os peixes tiveram valores de δ13C variando entre -24.30 ‰ e -28.31 ‰, com uma amplitude de variação concordante com as macrófitas (-25.49 e -27.10 ‰), sugerindo indiretamente que essas plantas poderiam ser uma fonte de carbono importante para os peixes. As assinaturas δ13C de Corbicula (-30.81‰) e Pomacea (-24.26‰) sugerem que fitoplâncton e algas bentônicas podem ser outra fonte de carbono para alguns consumidores. As razões isotópicas do nitrogênio indicaram aproximadamente três níveis tróficos de consumidores. O cará Geophagus brasiliensis foi um consumidor primário, enquanto o penharol Trachelyopterus lucenai e o cascudo-viola Loricariichthys anus foram consumidores secundários. Duas espécies congenéricas de joaninha (Crenicichla lepidota e C. punctata), o pintado Pimelodus maculatus, o lambari Astyanax fasciatus e o dentudo Oligosarcus robustus foram consumidores terciários. Novas investigações, incluindo outros produtores primários e consumidores e um maior número de amostras, deveriam ser conduzidas para propiciar uma descrição mais completa e detalhada da estrutura e dinâmica da teia alimentar no Taim

Evidence of habitat fragmentation affecting fish movement between the Patos and Mirim coastal lagoons in southern Brazil

The communication between the Patos and Mirim lagoon systems occurs via a natural channel called São Gonçalo. In 1977, a dam was built in this channel to prevent entrance of saline waters from Patos Lagoon estuary into the Mirim Lagoon. Our results showed an abrupt discontinuity in salinity and fish species distribution along the study sites. Sites below the dam showed salinity values higher than zero, whereas sites above had zero salinity values across all sampling periods. Marine and estuarine fishes (e.g., mullets Mugil platanus, M. curema, silversides Odontesthes argentinensis, Atherinella brasiliensis, sardine Brevoortia pectinata, and white croaker Micropogonias furnieri) were not captured above the dam. If these juvenile fishes could enter the Mirim lagoon in greater numbers, they probably would enhance catches in the artisanal fishery. We hypothesized that the São Gonçalo dam acts as a barrier hindering the entrance of salinity water and fishes inside the Mirim Lagoon