Some observations on the food of the gwyniad Coregonus clupeoides pennantii Valenciennes of Llyn Tegid (Lake Bala), North Wales

The seasonal variations in the diet of adult gwyniad Coregonus clupeoides pennantii=C. lavaretus from Llyn Tegid, North Wales were studied. Stomachs were examined to determine fullness, volume and identity of contents.
A clear seasonal cycle in food intake was found. Feeding rates were low from January to April but increased during the summer (May-June) and remained at a high level until December. The period of low feeding intensity coincided with the time of spawning and the time of annulus formation of both scales and otoliths. The diet showed seasonal changes and two main periods were distinguished : December to July, when the fish fed mainly on bottom fauna, and August to November, when the diet included both bottom fauna and midwater and surface foods.
The gwyniad were shown to be opportunistic in feeding, the composition of the diet reflecting availability of food items rather than selective feeding on the part of the fish.