oa Journal of East African Natural History - An analysis of the features of Sardinella gibbosa (Bleeker) Scales, with special reference to the problem of age determination



Five species of Sardinella have been recorded in East African waters (Losse, 1968), S. gibbosa and S. albella (Valenciennes) being the most common in inshore waters of the Tanzanian coast. This investigation on the scales of S. gibbosa was a product of an attempt to find out whether there was any possibility of reading from the scale of the age of this species of sardine from its scales. In temperate waters where the seasons are well marked, many of the piscine structures, e.g. scales, otoliths, vertebrae, dorsal spines, pectoral spines and opercular bone, show well defined differences in their growth. The seasonal growth zones in scales and otoliths have provided a relatively easy and quick way of assessing the absolute ages of commercially important fishes such as herring, cod, plaice, and salmon with a satisfactory degree of accuracy. Beside these growth rings which are formed as a result of the accelerated and retarded growth processes during spring and winter respectively, ""the scales of many fishes show spawning rings and marks which are the result of the cessation of feeding and exhaustion during the spawning period"", (Nikolsky, 1963, page 194). Therefore if the fish spawns once a year and at the same time leaves a spawning ring on its scales, the number of these rings can be used to read the age of the fish since it first started spawning.


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