LIMITS FOR THE DETECTION OF DAILY OTOLITH INCREMENTS IN WHITEFISH (COREGONUS-LAVARETUS L) LARVAE

The formation of daily otolith increments in European lake white-fish was evaluated in the laboratory during 40 days at 4, 6, and 8-degrees-C under limited and ad libitum food supply. Daily increments were easily identified in larvae reared at 8-degrees-C. At 6-degrees-C and, more, at 4-degrees-C, an unstructured perinuclear zone was formed, and daily increments could only be recognized in the light microscope starting from 10 to 35 days after hatching. In some larvae from the 4-degrees-C groups, no increments at all were found. Scanning electron microscopy (SEM) could not improve increment resolution. Only those increments could be viewed by SEM which were visible in the light microscope as well. We conclude that whitefish larvae which experience low (4-6-degrees-C) temperatures during their first weeks of life, hence those which hatch in the lake, cannot be aged by the currently employed preparation techniques.