ABSTRACT An experiment was conducted during 60 days with forty pacu males fed diets supplemented with increasing concentrations of ractopamine (0.00, 11.25, 22.50, 33.75, and 45.00 mg kg−1). Eight fish were evaluated for each experimental diet. Performance and survival rate of the fish were measured. At the end of the experiment, blood was collected to determine the levels of cortisol, triacylglycerol, and protein. Moreover, the liver was collected to determine the activities of glucose-6-phosphate dehydrogenase and malic enzymes. The fillets were collected to determine chemical composition, and histologic cuts were analyzed to verify muscle growth and deposition of adipose tissue between muscle fibers. Increasing concentrations of dietary ractopamine did not change feed intake, fillet yield, fillet content of protein and ash, and frequency of relative distribution of muscle fibers. By increasing the dietary ractopamine concentration, the serum cortisol level was elevated. Ractopamine supplementation (45.00 mg kg−1) increased serum levels of triacylglycerol and protein and reduced the activity of hepatic lipogenic enzymes and the survival rate of the fish, probably in response to the high concentration of circulating cortisol. In addition, the higher level of ractopamine supplementation evaluated in this research impaired the weight gain and feed conversion. However, 11.25 mg kg−1 ractopamine reduced the ether extract level determined in the fillet and the fat deposition between muscle fibers, improving the nutritional quality of meat.

A piracanjuba (Brycon orbignyanus Valenciennes, 1849) é uma espécie de peixe migratória, ameaçada de extinção. O objetivo do presente estudo foi determinar a dose inseminante na fertilização artificial de ovócitos de piracanjuba. Para isso, utilizou-se delineamento em blocos casualizados, com quatro tratamentos e três repetições. Três casais de piracanjuba, selecionados dos tanques de reprodutores da Estação Ambiental de Itutinga (EAI - CEMIG), no período de piracema 2006/2007, receberam aplicação de hormônio extrato bruto de hipófise de carpa (EBHC) para obtenção dos gametas. Adotaram-se quatro tratamentos diferentes para a fertilização de 0,1 grama de ovócitos: 10µL, 20µL, 30µL e 40µL de sêmen. As amostras foram ativadas com 5 mL de água do próprio tanque e, em seguida, levadas para incubadoras, dotadas de renovação constante de água, à temperatura de 28ºC. Após 8 e 16 horas, analisaram-se as taxas de fertilização (ovos viáveis) e de eclosão dos ovos, respectivamente. Os resultados obtidos foram comparados pelo teste de Tukey a 5%. As relações sêmen-ovócitos testadas não alteraram as taxas de fertilização e eclosão (P>0,05). O número de espermatozoides-ovócitos, variando de 10,4 x10(5) a 41,6 x10(5), foi eficiente para obtenção de boas taxas de fertilidade.

Piracanjuba (Brycon orbignyanus Valenciennes, 1849) is an migratory fish listed as an endangered species. The aim of this study was to determine the insemination dose for in vitro fertilization of piracanjuba oocytes. The experiments were arranged in a randomized block design with four treatments and three replications. Three piracanjuba couples selected from the breeding tanks at the Itutinga Environmental Station (IES-CEMIG), Minas Gerais State, Brazil, in the spawning period of 2006-2007, were applied crude extract of carp pituitary hormone for the production of gametes. Four different treatments were used for fertilization of 0.1 gram of oocytes: 10 µL, 20 µL, 30 µL and 40 µL of sperm. The samples were activated with 5 mL of water from the tank and then taken to a hatchery with constant water flow and temperature at 28 ºC. After 8 and 16 hours, the rates of fertilization (viable eggs) and hatching eggs were analyzed, respectively. The results were compared by Tukey test at 5% probability level. Tested sperm/oocyte ratios did not alter the rates of fertilization and hatching (P>0.05). The sperm/oocyte ratio ranging from 10.4 x10(5) to 41.6 x10(5) was efficient to achieve good fertility rates.