Influence of color background and shelter availability on jundia (Rhamdia quelen) stress response

Jundia (Rhamdia quelen) is a Heptapteridae fish native of South America, commonly found in rivers, and intensively cultured in artificial ponds. A feasible sequence for jundia culture consists of hatchery, nursery, and termination. Before dispatch to fish farms. fingerlings are transferred from nursery tanks to indoor tanks for a waiting period of approximately 10 days. This "dispatch period" can be highly stressful because of dietary changes, maintenance at high densities, daily handling, and a noisy and disturbing environment. Four experiments were performed to determine whether color background and shelter availability influences the cortisol response to stress in Rhamdia quelen fingerlings. The first and second experiments tested the influence of color background on the acute cortisol response with or without shelter. In the third and fourth experiments, the time course of cortisol levels after stress was measured in fingerlings kept in tanks with white or blue backgrounds, with or without shelter. The results clearly demonstrated that the adaptation period of 10 days in white and blue tanks had no effect on the cortisol response to an acute stressor. However, the tank color combined with the presence of an appropriate shelter both reduce the magnitude and duration of the stress response evaluated in terms of cortisol concentrations. Taken together, the results suggest that, because a totally dark environment is not feasible in jundia hatcheries, the best alternative to maintain R. quelen fingerlings are tanks with blue walls provided with shelter. These results may have strong applications in fish welfare and health during the transfer period of jundia fingerlings and on its survival rate in the early periods in fish farms. (C) 2008 Elsevier B.V. All rights reserved.