Do hydroelectric dams affect the abundance and population structure of freshwater shrimps?

Freshwater shrimps play an important role in many ecological processes since they are epibenthic detritivores but also prey on other invertebrates and are predated by fishes. The knowledge about their biology allow the development of management strategies to improve the use of natural resources by avoiding overfishing and enhancing productivity. Here we evaluated the population structure of the shrimp Macrobrachium amazonicum in the river Rio Grande, upstream of the Água Vermelha hydroelectric dam. They were captured monthly from October 2017 until March 2018, in six sites along the river. The first site was ∿1000 m distant from the dam and the sixth was ∿4000 m distant. A sac-like sieve and traps were used to capture the shrimps. The sieve was dragged three times for 180o. The traps were left by the river margins for six hours. In the laboratory, the shrimps were sexed and measured (carapace length; CL). In total, 6455 individuals were captured: 4499 females (294 breeding), 1445 males, and 217 juveniles. Female mean size was 7.50 ± 3.47 mm, male mean size was 7.44 ± 2.40 mm, and juvenile mean size was 3.24 ± 1.10 mm. The smallest individual was found in site III and it was a juvenile of 1.08 mm. The largest had 20 mm and was found in site II. The smallest breeding female had 3.8 mm CL. The largest individuals were more abundant in the sites near the dam, whereas the smallest were more abundant in the farthest sites. The highest abundance was seen in sites III and IV, and the lowest, in site VI. Unlike males and juveniles, females (both breeding and non-breeding) were more abundant (Anova, p < 0.01) near the dam. By knowing the population structure of M. amazonicum it is possible to understand how they are being affected by the environmental changes caused by the hydroelectric dam

Survival and behavior of silver catfish, Rhamdia quelen, submitted to antibiotics and sodium chloride treatments

In order to evaluate the use of antibiotics and NaCl on the behavior and survival of silver catfish, Rhamdia quelen, infested by Ichthyophthirius multifiliis and infected with Aeromonas hydrophila, juveniles were treated with chloramphenicol, chloramphenicol + salt, oxytetracycline, oxytetracycline + salt and water alone (control). Fish survival in the treatments with chloramphenicol + salt and oxytetracycline + salt was significantly higher than in the other treatments. The treatment with chloramphenicol presented higher survival than the treatment with oxytetracycline and both showed significantly higher survival than control. Swimming activity was higher in the fish treated with antibiotics and salt compared to control fish. A combination of the studied antibiotics plus salt is more effective to treat both A. hydrophila infection and I. multifiliis infestation in silver catfish, but since the use of chloramphenicol is not allowed in Brazil, oxytetracycline plus salt seems to be the best treatment option.

Com a finalidade de avaliar o efeito de antibióticos e NaCl sobre o comportamento e a sobrevivência de jundiá, Rhamdia quelen, infestados por Ichthyophthirius multifiliis e infectados com Aeromonas hydrophila, juvenis foram tratados com cloranfenicol, cloranfenicol + sal, oxitetraciclina, oxitetraciclina + sal e apenas água (controle). A sobrevivência dos peixes dos tratamentos com cloranfenicol + sal e oxitetraciclina + sal foi significativamente mais elevada que nos demais tratamentos. O tratamento com cloranfenicol apresentou sobrevivência mais elevada que a do tratamento com oxitetraciclina e ambos tiveram sobrevivência significativamente maior que o controle. A atividade natatória foi maior nos peixes tratados com antibióticos e sal do que nos do controle. A combinação dos antibióticos com sal se mostrou mais eficaz no tratamento de jundiás infectados com A. hydrophila e infestados com I. multifiliis, mas, como o uso de cloranfenicol é proibido no Brasil, a oxitetraciclina com sal parece ser a melhor opção de tratamento.

Refúgios artificiais coloridos e o desempenho e sobrevivência de alevinos de Leporinus macrocephalus (Garavello & Britsky, 1988) / Artificial colour haven evaluation, aveting and survival of Leporinus macrocephalus (Garavello & Britsky, 1988) fryes

O presente experimento foi realizado no Laboratório de Aqüicultura da Universidade Estadual de Maringá com o objetivo de avaliar o desempenho e a sobrevivência de alevinos de Leporinus macrocephalus alojados em aquários de vidro com capacidade para 12L, com ou sem refúgios artificiais de diferentes coloracões. Foram utilizados 240 alevinos com peso inicial de 0,20 n 0,06g por um período de 28 dias. Os animais foram distribuídos em um delineamento inteiramente casualizado com seis tratamentos (sem refúgio e com refúgios de cor verde, vermelha, azul, marrom e branca) e quatro repeticões. As variáveis analisadas foram peso, comprimento total, sobrevivência, fator de condicão e uniformidade do lote. Ao fim do experimento, verificou-se que as variáveis peso, comprimento e fator de condicão não diferiram entre os tratamentos com e sem refúgio. Houve maior índice de sobrevivência com a não utilizacão de refúgio e com refúgios de cor vermelha e verde (P < 0,05) do que quando utilizado o de cor azul. O emprego de refúgios de cor branca proporcionou lotes mais uniformes (P < 0,05) do que os refúgios de cor marrom e verde. Portanto, ao se utilizarem refúgios coloridos no cultivo de piavucu, recomenda-se preferencialmente as cores brancas e vermelhas, cujos resultados foram satisfatórios e semelhantes ao tratamento sem refúgio.