Title: The Ecology of Opsaridium microcephalum (Gunther)(Pisces: Cyprinidae) in the Lower Ruhuhu River Basin (Tanzania)

Authors: Francis M.M. Chale

Faculty of Science and Technology, Teofilo Kisanji University, P.O. Box 1104, Mbeya, United Republic of Tanzania.

*Correspondence: francischale@gmail.com

Abstract

Studies were made in the Ruhuhu River and mouth of Lake Nyasa on the ecology of Opsaridium microcephalum. The species is endemic to Lake Nyasa and makes spawning runs in the river throughout the year and in small tributaries to the river during the rainy season when the water level in the tributaries is high. O. microcephalum is economically important though currently its contribution to the fishery is very low. Turbidity of the Ruhuhu River which is a result of mining activities in the catchment has grossly affected the species. The main objective of the study was to try get baseline data on the ecology of the species which currently is listed as threatened. The species was found to make spawning runs in the river throughout the year. The river was found to act as a nursery ground for the species and the juveniles descended to the lake to lead a pelagic life when they are about 8.0 cm in standard length. Adults making spawning runs were found to have standard lengths ranging between 14.0 cm and 30.10 cm with a mean fecundity of 4603 eggs. The sex ratio was approximately 1:2 with the males dominating. The study showed that high turbidity of the Ruhuhu River which is a result of mining for coal, gold and gem stones may be the main factor affecting the species.

Keywords: Opsaridium microcephalum, Ruhuhu River, spawning runs, turbidity.