H. Le Louarn, D.J. Webb-1998
Bulletin Francais de la Peche et de la Pisciculture (350-51) : 325-336 (from Current Contents)
Abstract:
The survival of fish embryos and larvae depends on many environmental factors and pH is of particular importance. The present study was investigated following the observation that, during the same period in spring, the pH was extremely basic in some ponds or very acid in forest ones, and the mortality of young pike very high. Experiments were carried out in aquariums with a range of pH from 4.5 to 10.5. Incubation at a particular value was either continuous or of short duration (1 h). Two developmental stages were studied: fertilized eggs up to hatching; alevins followed until absorption of the yolk sac. The parameters analysed were the following: survival, development, abnormalities, swimming performance and heart rate. The following results were obtained: The lethal pH values were 6 and 10 for alevins, 4.5 and 10.5 for unhatched embryos. The unhatched embryos were less sensitive, although a high mortality (46.7%) and weak swimming performance at pH below 6 would reduce the success of recruitment. The few survivors at pH 10.5 showed abnormal development. For alevins, even a short exposure of 1 hour reduced survival considerably at pH 5 (42.6%) and pH 10 (29.3%). There was a noticeable effect on heart rate into the tolerated pH range. These results allow a reconsideration of the conditions for recruitment of a widely distributed species according to the pH. In particular the sharp increases in pH in spring of the soft water ponds make the stocking with early stage pike much more hazardous.
(INRA, Aquat Ecol Lab, 65 Rue St Brieuc, F-35042 Rennes, France)