This fish was introduced into abandoned fishponds at an altitude of 1,880 m and the
effect measured over six months on the numbers of mosquito immatures. For comparison an
untreated control pond was used. During this time, all ponds were regularly cleared of emergent
vegetation and fish re-stocking was not needed. Significant autocorrelation was removed from the
time series data, and t-tests were used to investigate within a pond and within a mosquito type any
differences before and after the introduction of O. niloticus. Mulla's formula was also used on the
raw data to calculate the percentage reduction of the mosquito larvae.