Lethal temperatures for Rhamdia quelen larvae (Pimelodidae)

ABSTRACT

The lower and upper lethal temperatures (LT50) of R. quelen larvae were determined. The larvae were obtained from two spawning periods with hatching temperatures of 21 and 26ºC respectively. Larvae were placed in tanks at which the temperatures were either increased 1ºC every 15min, or reduced 1ºC every 20min until larval movement ceased. This temperature was then maintained for 96h. Minimum mortality (29.0 ± 1.5%) was observed in the larvae held at hatching temperatures. The lower LT50 were 15.01 and 16.72ºC, and the upper LT50 were 29.25 and 27.83ºC for the larvae hatching at 21 and 26ºC, respectively. Thus, apparently there is no difference with relation to temperature change tolerance between larvae hatched in both temperatures.

RESUMO

Foram determinadas as temperaturas letais (TL50) inferiores e superiores de larvas de R. quelen. As larvas foram obtidas em dois períodos de desova com temperatura de incubação de 21 e 26ºC, respectivamente. Larvas foram colocadas em aquários onde a temperatura foi elevada em 1ºC, a cada 15min, ou reduzida 1º C, a cada 20min, até as larvas cessarem seus movimentos. Esta temperatura foi então fixada e mantida por 96h. O mínimo de mortalidade foi de 29 ± 1,5% obtido nas temperaturas de incubação. As TL50 inferiores foram 15,01 e 16,72ºC e as TL50 superiores foram 29,25 e 27,83ºC para as larvas incubadas a 21 e 26ºC, respectivamente. Portanto, aparentemente, não há diferença com relação à tolerância a variações de temperatura nas larvas incubadas nas duas temperaturas.