Ecological Diversity With Reference To Aesthetascs in Freshwater Prawns

Abstract

AbstractThe aesthetascs of the prawns are chemo- and mechano-receptors which exhibit diversity in number and shape depending on habitat and environment. In marine forms (both adults and larvae) they arc more numerous, longer, slender and uniformely thin wallcd. In adults of freshwater prawns they are fewer, shorter, divided into a thick walled stalk and a thin distal cob-like portion. However, they arc structurally different and positioned differently in the atyid genus Caridina and palaemonid genus Macrobrachium. Further, Caridina exhibits sexual dimorphism with males possessing a greater number of aesthctascs-bearing segments than females, unlike Macrobrachium which does not show such dimorphism. As far as larvae are concerned, in the 'inland species' of both genera, which complete their metamorphosis purely in freshwater, the 'freshwater- type aesthetases' appear in the first and second zoeal stages in totally or partially abbreviated type of development respectively. On the other hand, the early zoeal stages of 'coastal species' possess 'marine-type aesthetascs' indicating salinity dependence for their successful metamorphosis. These aesthetascs get shortened in late larval stages and subsequently get transformed into typically 'freshwater type' from postlarva onwards. A unique kind of 'branched larval aesthetascs' has been observed in two species of Macrobrachium. Thus, despite their common sensory function, the aesthetascs exhibit structural variations depending on environment and also play an important role as salinity indicators in the culture of freshwater prawns.