Efficacy of treatment with some plant parts containing ingredients viz. rotenone, azadirachtin, and nicotine for
control of a piscine ectoparasite Argulus bengalensis has been tested in laboratory experiments. Among those
plant preparations, tobacco leaf dust (TLD) containing nicotine is found potentially active against the adult
parasitic morphs at a lethal concentration of 8 ppm which is sublethal and tolerable to the host fish. However,
nicotine is not effective on the embryonic life stages of the parasite and thus the gene pool is retained in the
form of egg investment. Embryonic development and subsequent hatching of the eggs occurs normally in the
post treatment period which results in recurrence of parasitaemia (F1 generation) within 12 to 16 days in summer
and 15 to 18 days in winter in a temperature dependant manner. Considering maturation of F1 generation
and subsequent investment of their first clutch of eggs at the age of 21 days onwards, one vulnerable time
window of 17 to 19 days for summer experiment and another of 19 to 21 days for winter experiment have
been identified. Since the time windows are brief and exist only for three days and those windows overlap at
day 19, the day 19 has been targeted for application of a second phase of treatment in both seasons. The study
recommends a new approach of biphasic treatment for complete eradication of A. bengalensis infestation.