Nursery rearing of jundia, Rhamdia quelen (Quoy & Gaimard) in cages:: cage type, stocking density and stress response to confinement

The use of net cages allows the exploration of some water bodies, without usual aquacultural techniques for earthen ponds. Several advantages are proposed for the use of cages, however some disadvantages, as the higher possibility of stress and diseases are known. Growth parameters, survival rate and stress response of hatchery-bred Jundia (Rhamdia quelen, Quoy & Gaimard) fry reared at different cage types and densities in net cages suspended in pond were evaluated. The first experiment compared fry reared at the circular and cubic-shaped cages at a density of 100 fry /m(3). Fish held in cubic cages were heavier than the fish held in circular cages, presented higher weight gain and daily weight gain and a better food conversion. The survival rates were similar between fish raised in both types of cages. In the second experiment, cubic cages were stocked with 100, 200 and 300 fry/m(3). Fish held in cages with lower density were heavier than the ones held at higher densities, presented higher weight gain and daily weight gain. Food conversion and survival rates were similar between different fish densities. According to the results presented in this study, the growth of jundia in cubic-shaped cages was density dependent. In terms of weight parameters, the most effective stocking density of jundia was 100 fry/m(3) that reaches 63.74 +/- 3.69 g of body weight. However, if the desirable weight was from 30 to 40 g, the density of 300 fry /m(3) is Most effective because the fingerling production increases three times. In experiment 3, in all sample days, the serum cortisol levels were higher than the pre-stock and basal levels. The 80 days of cage confinement were not enough for adaptation of fingerlings to cage environment. The maintenance of high cortisol concentrations after 80 days of experimental period suggests the presence of typical chronic stress response that might have some detrimental effects over fish growth. Taken together, the data presented herein suggests that the improvement of rearing conditions (e.g. water quality, food quality, cage design, culture management, etc.) capable to minimize the stress response, may affect positively the growth, performance in jundia during the nursery period. (C) 2004 Elsevier B.V. All rights reserved.