Tetracycline was used as a chemical tag in a markrecapture study to examine the pattern
of increment formation in the otoliths of Tropheus moorii, a rockdwelling cichlid
from Lake Tanganyika. A total of 256 fish were captured by divers and injected with
tetracycline. Of these, nine were recaptured after either 1 or 2 years at liberty and eight
retained tags within their otoliths. Comparison of the number of growth increments formed
after the tag and the time at liberty demonstrated that increments were deposited on an
annual basis in the otoliths of this species. Furthermore, there was a strong relationship
between otolith mass and age suggesting that otoliths grew at a predictable rate throughout
the life of the fish. Validation of an annual pattern of increment deposition allowed age
and growth information to be derived from otoliths. This showed that T. moorii grew
rapidly to attain adult size by 3 years of age. Males grew faster than females and also
attained a larger size than females (8·74 v. 7·91 cm LS
respectively). The longevity of some of these small freshwater fish was surprising; the
oldest individual had an age of 10 years, while the average age of adults was 4 years.