Otoliths versus scales: evaluating the most suitable structure for ageing largemouth bass, Micropterus salmoides, in South Africa

  • Taylor G
  • Weyl O
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Abstract

The suitability of scales for ageing Micropterus salmoides was
determined by comparing the precision of growth zone counts on scales
with those obtained from sectioned sagittal otoliths from a sample of
496 fish collected from Wriggleswade and Mankazana Impoundments in the
Eastern Cape, South Africa. Otoliths (1.4% rejected) were more readable
than scales (41.7% and 7.5% rejected) for Wriggleswade and Mankazana
Impoundments respectively. Otolith readings were more precise (average
percentage error (APE) = 13.6%; coefficient of variation (CV) = 15.8%)
than scales (APE = 18.0%; CV = 21.9%) for the total sample. Growth
zone counts between structures were not symmetrically distributed around
the agreed ages (otolith age = scale age) of the fish from Wriggleswade
Impoundment (Bowker's test H-2 : X-2 = 136, d.f. = 27, P < 0.05) and
graphical comparison showed that scales tended to underestimate age,
particularly for fish older than five years. Scales are therefore not
suitable structures for ageing South African M. salmoides which may
attain ages of up to 13 years.

Author-supplied keywords

  • Micropterus salmoides; sagittal; otoliths; precisi

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Authors

  • G C Taylor

  • O L F Weyl

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