Observations on the embryonic development of the oriental river prawn macrobrachium nipponense (de haan, 1849) (decapoda: Caridea: Palaemonidae)

Abstract

The embryonic development of the oriental freshwater prawn Macrobrachium nipponense (De Haan, 1849) is described from observations on whole-mount embryos with nuclei stained using Sytox> Green. The prawn eggs are centrolecithal, non-polar, and oval-shaped, with a diameter of 300-500 μm. The early cleavage pattern shows mixed cleavage modes. Notably, cells could shift to the interior of the embryo to form a visual blastopore, which is characteristic during the gastrulation stage. The putative intracellular body (ICB) could be discriminated at fertilized-egg, four-cell, eight-cell, and 16-cell stages, with volume gradually decreasing along with cell division. It is noted that the embryonic development takes a long period of approximately twenty-one days before hatching, which is quite different to what is known from penaeid shrimps. The various modes and profiles of early cleavage existing in crustaceans could imply a transition in their evolution.