MASS-MARKING OF BONE TISSUE OF COREGONUS-LAVARETUS L AND ITS POTENTIAL APPLICATION TO MONITORING THE SPATIOTEMPORAL DISTRIBUTION OF LARVAE,FRY AND JUVENILES OF LACUSTRINE FISHES

Mass labelling techniques have great potential for the study of larval fish dynamics in closed habitats (lakes, ponds and flooded quarries). Different methods of mass labelling of bone tissue were tested: bathi ng in tetracycline solutions with or without osmotic shock, and modifi cation of otolith microstria by temperature, photoperiod or feeding ma nipulations using different batches of eggs, eleuteroembryos, larvae a nd prefed fry of Coregonus lavaretus L. from Lake Leman. A short perio d of immersion with osmotic shock produced better results than longer bathing (6 to 18 h) in low concentration (400 mg l(-1)) tetracycline s olutions. At the 'eyed' stage of eggs when otoliths appear, it is poss ible to use the immersion technique in a hyperosmotic solution (5 to 1 2% sodium chloride) with 1% tetracycline (as the Hydrochloride or Oxyt etracycline). Optimal immersion times (maximal labelling with minimal mortality) were determined as follows: 10 to 15 minutes for 'eyed' egg s, 3.5 min. for eggs just before hatching and eleuteroembryos, 1.5 min , for prefed larvae and less than 1 min. for fry of more than 20 mm to tal length. Microscopic examination of otoliths and caudal vertebrae f rom coregonid larvae and juveniles reared for two years has allowed us to determine the effectiveness and persistence of fluorescent tetracy cline makers.