Moulting and spawning cycles in Macrobrachium nobilii(Henderson and Mathai)

Abstract

Macrobrachium nobilii is a diecdysic decapod and moults every 18–22 days. A moult is usually followed by spawning and the female incubates the eggs for a fortnight; hatching lasts for 3 days. Following a moult, a few (39%) females skip spawning until the next moult. The ovaries of such individuals remain quiescent for up to 3 subsequent moults. Removal of eggs from females 3 days after berrying increases the percentage of females spawning, following the next moult, to 81 from 61%. Differences in the intermoult period, body growth/moult and number of eggs/brood between normal females and females from whom eggs were removed, was not statistically significant. Relieving the females from the task of incubation increases the egg production by 47% by increasing the spawning frequency. The realised total growth and reproductive output of a breeding female is over 47% of its own body. Treating this as 100 it was found that 61, 24 and 15% of the converted food energy is channeled for egg production, exuvium and body growth, respectively. There is a definite physiological tilt from somatic growth to reproduction in older individuals.