Reproductive potential of male calanoid copepod Sinodiaptomus (Rhinediaptomus) indicus Kiefer: A potential live prey for fish larvae

Copepods are a morphologically, physiologically, and ecologically highly diverse group with different reproductive characteristics and have evolved structural specialties of sperm form and spermatophore structure. These reproductive peculiarities are important for their implications in applied biology. Copepods are the preferred food for finfish and shellfish larvae due to their optimal size range and nutritive value. Although many copepod species are successfully mass-cultured, limited success is still reported in commercial-level production for use in aquaculture hatcheries. Unlike rotifers and Artemia, which reproduce by parthenogenesis and attain high-density production easily, copepods reproduce sexually, involving mate selection, a copulatory process, and leading to the transfer of spermatophores and fertilization of eggs. This necessitates an understanding of the reproductive biology of cultivable copepod species to establish effective culture protocols. The freshwater calanoid copepod Sinodiaptomus (Rhinediaptomus) indicus is a promising candidate for mass culture, and this article describes the reproductive biology of the male using histological and electron microscopic studies. The ultrastructure of the spermatozoon of this species is reported for the first time. Laboratory experiments showed long lifespan and high spermatophore production (34 in 25 days) in this animal, which is a key factor in deciding male-female ratio formulation in the inoculum for mass culture. It is suggested that the S. (R.) indicus could be an ideal species for mass culture and use as live feed in fish and prawn larval rearing.