| dc.description.abstract | Oreochromis niger fry were exposed to various
concentrations of DOT, Carbofuran, Trifenmorph and
Niclosamide to determine the toxicity of these
chemicals to the fish. The concentration lethal to
50% of the fish population in a given time range
24 hrs - 96 hrs, for each of the chemicals, was
determined. The growth and swimming patterns of
these fish in sub - lethal concentrations of the
biocides were also studied.
DOT was found tobe the most poisonous to fish
with a 24 hr LC 50 of 0.042mg/litre. Carbofuran was
the least toxic with an LC 50 of 0.225 mg/litre. The
toxicity of all the four chemicals increased with
concentration and time.
The swimming. activity of the fish decreased with
time in all the experiments except in Niclosamide.
There was a negative linear relationship between fish
activity and time.
The fish increased weight very slowly from the
first to the fifth week. Growth or increase in fish
weight had a positive linear relationship with time
in all the experiments. Increase in weight was however
slower in the treatments than in the control except
in sub - lethal levels of Carbofuran. The experiment
shows that fish cannot be grown in water containing
sub - lethal amounts of DOT, Trifenmorph and
Niclosamide as they are highly toxic. The fish safe
levels would be too low for the control of snails. | en |
