Otolith features and utility of lapillus for daily increment analysis in Opsaridium microcephalum (Cyprinidae) juveniles collected from Lake Malawi

Abstract

Features of otoliths in Opsaridium microcephalum juveniles were observed, and the increment formation pattern was validated using Alizarin Complexone (ALC). The sagitta was arrowhead shaped with an obvious core and rostra, the latter being fragile and easily destroyed by extracting and grinding processes. Increments around the core were readable but not in the rostra. The asteriscus was oval shaped with an ambiguous core leading to difficulty in discerning the first increment. The lapillus was round and fan shaped with an obvious core. Increments in the lapillus were clearly deposited from the core to the margin. These features made the lapillus the most appropriate for reading otolith increments. Increments counts in the lapillus formed after ALC treatment agreed with days elapsed, showing the daily formation of increments. Consequently, the lapillus is only appropriate for daily increment analysis in Opsaridium microcephalum.