O. niloticus fingerlings were exposed to graded Gramoxoneor detergent concentrations (range 1.0 - 5.1m1/1 and 0.40-0.250, respectively) each treatment
having a control. High dissolved oxygen level was maintained by continous aeration and the tests
were conducted under static toxicity testing conditions (FAO, 1977). Observations of the effects of
Grarnoxone or detergent on fish behaviour were made every six hours. The range of
concentrations used in the tests was predicted to give a mortality range of 0-100% (no mortality -
total fish kills), and the lethal concentration that will kill half of the test population (LC50) was
determined graphically. The data obtained were subjected to the student t-test to determine the
significant differences among means.