Does water calcium content influence the distinctness of daily growth increments in the otoliths of larval whitefish (Coregonus lavaretus L.)?

In larval and juvenile whitefish (Coregonus /avaretlls L.) from Lake Constance, Germany, the otolith increments are deposited daily, whereas daily deposition could not be confirmed in larval whitefish from Lake Pyhaselka, Finland. The calcium concentration in Lake Constance is high (around 1.3 mM), while calcium deficiency is typical for Finnish lakes (around 0.15 mM). Therefore, the hypothesis that the distinctness of daily otolith increments in whitefish is related to water calcium content was tested by rearing three groups of Lake Constance whitefish in water of 0.2, 1.3 and 4.7 mM Ca. The eggs were incubated in lake water (1.3 mM Ca), and the larvae were acclimated to the experimental calcium concentrations on the day of hatching. After 39 days of ad libitum-feeding with Artemia nauplii, the three groups did not differ significantly in total length, wet and dry weight, and otolith length and width. The daily increments were easily recognizable, and contrast between dark (D)and light (L)-zones was the same in the fish of all test groups. For the experimental set-up of this study, and particularly the range of calcium concentrations tested, the hypothesis that water calcium content influences the distinctness of daily 'otolith increments was rejected.