Environmental effects on primary increment formation in the otoliths of newlyhatched Arctic charr

Otolith microincrements were investigated in Arctic charr Salvelinus alpinus , reared from hatching under various temperatures (1, 3, 5, 7° C) and feeding conditions (starved, fed every third day, fed daily). Larval charr otoliths were marked with oxytetracycline and alizarin complexone. Alizarin complexone was found to be 100 per cent successful in marking otoliths while oxytetracycline marks could be seen in <10 per cent of the otoliths viewed. Otolith microincrements were viewed by light and scanning electron microscopy to investigate the daily nature of increment deposition. Low temperatures (1 and 3° C) and starvation depressed daily increment formation. Increment deposition was found to be daily among the larvae reared at warmer temperatures (5 and 7° C) and fed at least every third day. Scanning electron microscopic analysis allowed us to confirm the results of light microscope increment counts from all temperatures except 1 ° C, where the number of increments enumerated were higher than the number obtained during light microscopy analyses. Increased feeding and warmer temperatures also resulted in increased increment width. The difference in increment number and width seems to be dependent upon fish growth rate which we have found to be affected by both temperature and feeding conditions.