Abstract
- The experimental results prove the existence of a two-days' rhythm of sclerite formation in
juvenile Matrinchâ (Brycon sp.).
- Identical scale patterns of wild-fish and pond-fish permit the application of a formula for age determination derived from pond experiments, also to fish from natural environments.
- The exactness of the formula for age determination can only be met by the otolith method. since the latter requires considerably more technical effort, and includes the risk of dealing with unreadable otoliths, the scale method presents itself as quite feasable, also for field work.
- All back-calculated spawning events coincide with increasing water-level, and high precipitations, thus confirming the fishermens' knowledge about interactions between these two ecological factors and their importance for the onset of spawning.
- The back-calculated spawning events let assume, that no spawning takes place before a certain level of the river (ca. 20 m above sea-level) has been surpassed, which seems to be an ecological necessity.
Large numbers of fry can only survive when sufficiently large areas of land have become inundated.
Further research is necessary to confirm whether the method for age determination is applyable to other populations and age groups, too.
