Sobrevivência e crescimento de juvenis de jundiá Rhamdia quelen expostos a diferentes níveis de amônia, oxigênio e Ca2+ na dieta e na água

• Autor(a) principal: Ferreira, Francesca Werner
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Manancial - Repositório Digital da UFSM
• Texto Completo: http://repositorio.ufsm.br/handle/1/4308
• topic: Cálcio na dieta; Dureza; Oxigênio dissolvido; Amônia; Rhamdia quelen; Dietary calcium; Water hardness; Oxygen; Un-ionized ammonia; Fish; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA

The present study examined the effect of experimentally elevating dietary Ca2+ and water hardness on survival and growth of silver catfish, Rhamdia quelen, exposed to different waterborne NH3 and O2 levels. In the dietary Ca2+ experiment of determination of NH3 lethal concentration in 96 h (LC50-96h) juveniles (4.06±0.27g and 7.82±1.2cm) were exposed to five different NH3 levels (in mg.L-1): 0.107±0.007 (control), 0.36±0.021, 0.773±0.074, 1.170±0.071 and 1.63±0.315 and four dietary Ca2+ levels (in % Ca2+): 0.45, 0.95, 1.45, and 2.45. In the waterborne Ca2+ experiment of LC50-96h juveniles (1.85±0.6g and 6.0±0.54cm) were maintained at five different NH3 levels (mg.L-1): 0.097±0.017 (control), 0.356±0.037, 0.779±0.141, 1.459±0.185 and 1.770±0.070 and four water hardness levels (in mg CaCO3.L-1): 34.5±4.4, 62.0±5.7, 116.0±9.3, and 174.0±22.42. In the dietary Ca2+ experiment of determination of O2 lethal concentration in 96 h (LC50-96h) juveniles (4.75 + 0.65 g e 7.56 + 0.61 cm) were exposed to five different O2 levels (in mg.L-1): (0.41±0.13, 0.71±0.15, 0.97±0.13, 1.44±0.35 e 6.41±0.60 mg/L) and four dietary Ca2+ levels (in % Ca2+): 0.45, 0.95, 1.45, and 2.45. In the waterborne Ca2+ experiment of LC50-96h juveniles (3.66 ± 0.75 g e 7.32± 0.5 cm) were maintained at five different O2 levels (mg.L-1): (0.27±0.10, 0.74±0.26, 1.33±0.14, 1.74±0.32 e 6.55±0.02 mg.L-1) and four water hardness levels (in mg CaCO3.L-1): (28, 116, 116 e 180). In the growth experiment juveniles (2.27±0.14g and 6.9±0.13cm) were exposed to two NH3 levels (mg.L-1), 0.021±0.001 and 0.623±0.039, and four water hardness levels (mg CaCO3.L-1): 32.1±4.6, 63.1±5.9, 119.9±10.0, and 177.3±8.1 for 40 days. In the growth experiment juveniles (3.66±0.75g and 7.32±0.5cm) were exposed to two O2 levels (1.47±0.04 and 6.46±0.06 mg.L-1), and four water hardness levels (mg CaCO3.L-1): 30±2.0, 61±2.5, 121±3.0 e 180±3.0 for 15 days. The NH3 LC50-96h was 0.73 mg.L-1 (0.63 - 0.84) in the dietary Ca2+ experiment, and LC50-96h was significantly higher in juveniles fed 0.45 and 0.95% dietary Ca2+. Water hardness did not change significantly NH3 LC50-96h, which was1.20 mg.L-1 (1.10 - 1.24). Weight gain, biomass and specific growth rate at end of the growth experiment were significantly higher in juveniles exposed to 0.021 mg.L-1 NH3 than those exposed to 0.623 mg.L- NH3. The increase of water hardness impaired all measured parameters in juveniles exposed to the lowest NH3 level, but increased them in those exposed to the highest NH3 level. The O2 LC50-96h was 0.89 mg/L (CI 0.64 1.34 mg/L) in the dietary Ca2+ experiment, and LC50-96h was significantly higher in juveniles fed 2.45 e 0.45% dietary Ca2+. Weight gain, biomass, length and specific growth rate at end of the growth experiment were significantly higher in juveniles exposed to 6.46±0.06 than those exposed to 1.47±0.04 mg.L-1O2 . The increase of water hardness increased all measured parameters in juveniles exposed to the lowest O2 level, but them impaired in those exposed to the highest O2 level. This study indicates that low dietary Ca2+ enhanced survival of silver catfish exposed to high NH3 and low O2 levels, and that the increase of water hardness is recommended only when this species is raised in waters with high growth NH3 and low O2 levels.