The predatory behaviour of nymphs of dragonfly ( Africocypha varicolor ) on fry of African mud catfish ( Clarias gariepinus ) and control by skunk weed ( Petivera alliacea ) root-extract in aquaculture

The use of natural organic extract instead of synthetic chemicals in harvesting wild fish and eliminating unwanted aquatic biota is popular in Nigeria. This research, therefore, investigated the possibility of using the root extract of a common weed in southwestern Nigeria, named P. alliacea, in checkmating the predatory influence of nymphs of dragonfly which frequently attack fry of African mud catfish. Activity of extract was first assessed through a brine shrimp test in a 24 hr investigation before concentrations of 0.0 g/l, 0.22 g/l, 0.48 g/l, and 1.06 g/l were applied under laboratory conditions in plastic aquaria against the naiads. The 96 hr Lc50 was 0.47 g/l obtained using probit analysis. The regression equation for the probit curve was y=3.173+3.5 (y=probit value, x=actual concentration and r=0.7=coefficient of correlation). An average of six fry and one fry were consumed by one dragonfly nymph every 96 hr at two weeks and three weeks old, respectively.