Otolith features and growth of juvenile Opsaridium microcephalum (Pisces: Cyprinidae) from the southwestern shoreline of Lake Malawi

Abstract

Sanjika, Opsaridium microcephalum, were collected from two sites (Nkhotakota and Chia) along the southwestern shoreline of Lake Malawi. The sagitta of the otolith was arrow headshaped with an obvious nucleus. Increments in the sagittae were  observable until the bases of the rostra but invisible in the rostra. The asteriscus was oval-shaped with an ambiguous nucleus, leading to difficulty in identifying the first increment. The lapillus was ‘a’-shaped with an obvious nucleus and increments were observable from the nucleus to the margin. The lapillus was therefore considered the most suitable structure for interpreting daily growth increments in this species. The estimated hatching months of fish based on lapilli increment counts were from November to July, suggesting that this species has a long breeding period of at least eight months per year. The growth rate of fish born in the rainy season (0.74mmTL per day) was higher than those in the dry season (0.56mmTL per day). This growth difference was considered to be due to the difference in water temperature in the lake.

Key words: Sanjika, otolith increment analysis, growth.