Infestation of isopode parasites on prawns of the genus Macrobrachium Bate (Palaemonidae) of Cochin region

Abstract

The major objective of the research work is to study the taxonomy, species diversity, host specificity, intensity of infestation, length - weight relationship and reproductive biology of bopyrid parasite infesting the genus Macrobrachium Bate, 1868 of the Cochin region. Collections were taken from 3 stations Perumbavoor (Periyar River) and Panangad (Vembanad lake) for a period of 13 months (July 2002 to July 2003) and Champakkara (Vembanad lake) for a period of one year (October 2003 to September 2004). The study revealed that of the five species of Macrobrachium inhabiting water bodies of Cochin region, only two species were found infested with bopyrids. Macrobrachium idella was infested with Palaegyge alcocki whereas M. scabriculum with a new variety, P. alcocki var. novo cochinensis. This shows that bopyrid infestation is species specific. Diagnostic characters of both the parasite species are given in the text. Regarding the intensity of infestation, prawns from the Perumbavoor region of Periyar River had maximum infestation in comparison with other regions (Panangad and Champakkara). The infestation during different months also revealed the same trend. It indicates that infestation is more at the freshwater region than at the estuarine region. Relationships between length and weight of infested M. idella, P. alcocki separated from the host, total length of host and parasite, total length of male and female parasite, carapace length of the host and total length of male as well as female parasite are all statistically significant. . The study has brought out the ways of association of male and female parasites as well as attachment of female parasite to the host. Mature female parasite has been distinguished from the immature. Fecundity studies revealed that the number of eggs produced by the parasite ranges from 8148 (1 cm total length, 0.9 cm total width, 0.12 g total weight) to 29,683 (1.2 cm total length, 1.0 cm total width, 0.168 g total weight). Number of ova per milligram body weight ranged from 67.9 to 185.518 (126.709 average). Relationships between fecundity and total length, total weight, total width and total weight of brood of the parasite are all significant. The chapter on reproductive biology reveals important observations on marsupial brooding, ovulation, embryonic development and incubation, hatching and epicaridea stage of P. alcocki. The last chapter is on the effect of parasitism on the host. Here the aggressive behaviour of infested host, parasitic castration, degeneration of gills and secondary infections are dealt with in some detail.