Body segments (somites) in Macrobrachium rosenbergii and appendage function:
Female prawns are sometimes referred to as virgin females (V or VF), berried (egg carrying) females (BE or BF) and open brood chamber (spent) females (OP). Egg-carrying females are shown in Figure 4.
There are three major types of freshwater prawn males and a number of intermediate forms, which were not fully described in the original FAO manual.
All three major types of males are illustrated in Figure 5. The ability to distinguish between these forms is important in understanding the need for size management during the grow-out phase of culture (Annex 8).
The first type consists of blue claw males (BC), which have extremely long claws.
The second type of males, sometimes known as runts, have small claws and are now called small males (SM). Although this type is similar in size to younger juveniles, the prawns are much older.
The third type of males are known as orange claw males (OC). OC males have golden coloured claws, which are 30 to 70% shorter than the claws of BC males. The three major types of males can generally be distinguished by sight.
However, more reliable ways of determining which type males are can be found in Karplus, Malecha and Sagi (2000). As mentioned, a number of intermediate male forms have also been recognized, including weak orange claw (WOC), strong orange claw (SOC) and transforming orange claw (TOC) males.
The relationship and transformation of these various male types, and their importance in size management is covered later in this manual (Annex 8).
Many people find it hard to distinguish between Macrobrachium and penaeid (marine) shrimp, once they have been harvested and the heads have been removed. If the ‘tail’ still retains its shell there are, in fact, two easy ways of distinguishing them (Fincham and Wickins, 1976). Firstly, Macrobrachium spp., have a smooth rounded dorsal surface to the abdomen while penaeids have a simple or complex ridge at the dorsal apex of the abdomen (Figure 6).
Secondly, the second pleuron of the abdomen (or tail) of Macrobrachium (in common with all caridean prawns, including some marine shrimp such as Crangon spp., Pandalus spp., and Palaemon spp.) overlaps both the first and the third pleuron. In penaeids the second pleuron overlaps the third pleuron only and is itself overlapped by the first (Figure 7).
Author:
Michael B. New
