Validation of annulus formation in otoliths of largemouth bass Micropterus salmoides outside their native range

The periodicity of growth zone formation was validated for largemouth bass Micropterus salmoides using edge analysis (EA) and mark recapture of chemically-tagged wild fish (MRCT) to test the hypothesis that one opaque and hyaline zone was deposited annually in sagittal otoliths sampled from temperate South African M.salmoides populations. For 35 fish recaptured in the MRCT experiment, the relationship between the number of growth zones posterior to the chemical mark and the time at liberty (0.041.38years) did not differ significantly from a 1:1 relationship (t-test, t=0.76, d.f.=2,33, P=0.45). This result was supported by EA, where periodic logistic regression and a binomial model linked with a von Mises distribution for circular data demonstrated that the frequency of otoliths with opaque margins followed a unimodal distribution (maximum OctoberJanuary). Both the timing of growth zone deposition (spring) and the annual rate were consistent with results from validation studies conducted globally in localities ranging from 45 degrees N to 33 degrees S, and indicate that the growth zone deposition rate is annual throughout the native and introduced range of this species.