On the hatching mechanism of a fresh water prawn Macrobrachium idae

Abstract

1) Depending on the body size, the fresh water prawn Macrobrachium idae carries 40 to 160 eggs; at the termination of an incubation period of 14 to 16 days the eggs are usually hatched at nights; 63% of the eggs are hatched as first batch on the first hatching day; another 33% and 2% eggs are hatched on the second or third day respectively. 2) Differences observed in water and salt contents between the eggs waiting to hatch on the subsequent days and the larvae hatched on the previous day are not statistically significant. 3) Apparently ripe eggs exposed to distilled water, tap water or pond water hatched successfully, while those exposed to osmotically concentrated solutions of 0.01 to 0.04 M sucrose failed to hatch. The need for osmotic inflow of water for successful hatching is thus demonstrated. 4) On exposure even to distilled water carrying females exhibited batching effects in hatching which lasted for 2 days. The immediate causative factor for egg hatching seems therefore not an osmotic one. 5) Swimmerets beating (more than 138 times per minute) seems to stimulate the embryo inside the egg to accelerate its movement which eventually causes the hatching. 6) The eggs held in the distal end of the appendages are subjected to a greater mechanical agitation when the mothers sway the swimmerets during the hatching period and hence hatch on the first day; those situated in the proximal end seem to experience sufficient mechanical agitation only on the second night and hence hatch as the second batch.