Effect of aqueous extract of Azadirachta indica A. Juss (neem) leaf on oocyte maturation, oviposition, reproductive potentials and embryonic development of a freshwater fish ectoparasite Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura)

In present study, a microcosm experiment is carried out to investigate the efficacy of 120 and 250-ppm crude aqueous extract of Azadirachta leaf on oocyte maturation, oviposition, embryonic development and hatching of the eggs of a fish ectoparasite Argulus bengalensis. Relative abundance of different maturing oocyte stages in the ovary of the parasite from different age groups was enumerated, and marked variations were obtained. Significant depletion in the abundance of pre-vitollogenic, vitellogenic and post-vitellogenic oocytes was recorded, which indicates impairment in maturation. Chromatin condensation of the oocytes of treated parasite indicates apoptosis of oogenic cells. Strong oviposition deterrence was evident by the elevated oviposition deterrence index of 0.18 and 0.52 at respective toxin levels. The treated parasites invested less number of eggs per oviposition, and hatching percentage of the eggs reduced markedly. In vitro treatment of eggs within 70 min of incubation exhibited coagulation of yolk material and subsequent reduction in hatching percentage. However, treatment applied after this critical period, hatching was not significantly altered. In vitro treatment of eggs at 80 min of incubation resulted in normal development. It signifies that azadirachtin affects the early developmental events but not the later. Presumably, azadirachtin either affects early gene expression of the embryo or antagonizes any of the substances of the zygote required for sustaining early developmental process. The result of the present experiment suggests that azadirachtin could be a promising agent to control argulosis through inhibition of the reproductive maturity of the parasite as well as through interference of its embryonic development.