Farming freshwater prawns

8ANNEXSize managementAS MENTIONED IN SEVERAL SECTIONS of this manual, freshwater prawns do not growat an even rate (Annex 8, Figure 1). This makes the management of size an essential componentof the efficient husbandry that is needed to ensure their successful farming. A considerablevolume of knowledge about the different (male) morphotypes which play a partin the phenomenon of uneven growth has been gained since the previous FAO manual onfreshwater prawn farming was written. The topic has been reviewed in depth by Karplus,Malecha and Sagi (2000), from which the material in this annex has been derived. Themain purpose of Sections 1-3 in this annex is to provide an introduction to the scientificbackground; it is necessary to study this to understand the phenomenon of size distributionand management. Practical advice on management contained in the main text of themanual has taken these factors into account. Section 4 of this annex provides a check-listof the various techniques which it is essential that farmers apply to get the maximum outputof marketable prawns.1. Major male morphological characteristicsFirstly, it is necessary to understand what is meant by the various morphotypes. Threemajor morphotypes have been described for sexually mature male M. rosenbergii (Annex 8,Figure 2). The most immediately distinctive feature is the size and colour of the claws, andthe robustness of their spines:Blue claw males (BC) have extremely long blue claws (second pereiopods) withlonger and stronger spines than OC males;Orange claw males (OC) have golden coloured claws that are generally shorter andhave shorter and less strong spines than those of BC males; andSmall males (SM) have small, slim, almost translucent claws.There are also a number of intermediary forms between these major morphotypes.The transition from the small male (SM) to the orange claw (OC) morphotype is gradual.The OC is therefore sometimes referred to as the strong orange claw (SOC), and an intermediatestage between these two forms, the weak orange claw male (WOC), has been recognizedin research work. Another intermediate form, this time between the orange claw(OC) and the blue claw (BC) is known as the transforming orange claw (TOC); this is thelast stage of the SOC male before it transforms into the BC male, as described later in thisannex.Karplus, Malecha and Sagi (2000) also describe some other external features whichcan be used to delineate the various morphotypes, such as the length and orientation of thespines on the claws, but these are less immediately obvious than claw colour and size.There are also a number of internal morphological and physiological differences, as well asANNEX 8177