Validation of growth zone formation in Oreochromis mossambicus otoliths collected from an irrigation pond in the Sundays River Valley, Eastern Cape, South Africa

Abstract

In fisheries science, life-history trait information is widely used to estimate fish population recruitment, growth, and mortality. The aging and growth of Oreochromis mossambicus from the Sundays River Valley irrigation pond in the Eastern Cape province of South Africa were determined using otoliths. Mark recapture of chemically-tagged wild fish was used to confirm the periodicity of growth zone creation. A total of 150 specimens of O. mossambicus were obtained using a combination of seine and fyke nets. Female total lengths (L_t) ranged from 20 to 340 mm, while male L_t ranged from 82 to 374 mm. Growth zone deposition rates of wild O. mossambicus otoliths fluorochrome-marked with oxytetracycline hydrochloride (OTC) and recaptured after one year was consistent with the deposition of one growth increment annually. According to the three-parameter von Bertalanffy model, growth was described using different coefficients for females and males, respectively. The maximum age estimate for both females and males was 12 years. Oreochromis mossambicus in this warm temperate pond had relatively long life spans compared to subtropical populations, which suggest likely long-term population persistence within cooler, novel environments.

Keywords:

• impoundment
• oxytetracycline
• chemical tagging
• ring formation
• von Bertalanffy model