1.1 Names, natural range, and characteristics of freshwater prawns

NAMING FRESHWATER PRAWNS (NOMENCLATURE)

All the freshwater prawns that have been cultured so far belong to the genus Macrobrachium, Bate 1868, the largest genus of the family Palaemonidae. About 200 species have been described, almost all of which live in freshwater at least for part of their life.

The giant river prawn, Macrobrachium rosenbergii, was one of the first species to become scientifically known, the first recognisable illustration appearing in 1705. The nomenclature of freshwater prawns, both on a generic and a species level has had quite a muddled history. In the past, generic names have included Cancer (Astacus) and Palaemon.
Previous names of M. rosenbergii have included Palaemon carcinus, P. dacqueti, and P. rosenbergii and it was not until 1959 that its present scientific name, Macrobrachium rosenbergii (De Man 1879) became universally accepted.
Some taxonomists recognize a western sub-species (found in the waters of the east coast of India, Bay of Bengal, Gulf of Thailand, Malaysia, and the Indonesian regions of Sumatra, Java and Kalimantan) and an eastern sub-species (inhabiting the Philippines, the Indonesian regions of Sulawesi and Irian Jaya, Papua New Guinea and northern Australia). These are referred to as Macrobrachium rosenbergii dacqueti (Sunier 1925) for the western form and Macrobrachium rosenbergii rosenbergii (De Man 1879) for the eastern form.

However, from the perspective of freshwater prawn farmers, exact nomenclature has little relevance, especially because the species M. rosenbergii has been transferred within its natural geographical range and been introduced into many other zones where it may become established.

THE NATURAL HOME OF FRESHWATER PRAWNS (DISTRIBUTION)

Species of the freshwater prawn genus Macrobrachium are distributed throughout the tropical and subtropical zones of the world. Holthuis (1980) provides useful information on the distribution, local names, habitats and maximum sizes of commercial (fished and farmed) species of Macrobrachium.
They are found in most inland freshwater areas including lakes, rivers, swamps, irrigation ditches, canals and ponds, as well as in estuarine areas. Most species require brackishwater in the initial stages of their life cycle (and therefore they are found in water that is directly or indirectly connected with the sea) although some complete their cycle in inland saline and freshwater lakes. Some species prefer rivers containing clear water, while others are found in extremely turbid conditions. M. rosenbergii is an example of the latter.
There is a wide interspecific variation in maximum size and growth rate, M. rosenbergii, M. americanum, M. carcinus, M. malcolmsonii, M. choprai, M. vollenhovenii and M. lar being the largest species known. M. americanum (Cauque river prawn) is found naturally in western watersheds of the Americas while M. carcinus (painted river prawn) is found in those connected with the Atlantic. M. choprai (Ganges river prawn) is found in the Ganges and Brahmaputra river systems. M. lar (Monkey river prawn) is native from East Africa to the Marquesas Islands of the Pacific (and was introduced into Hawaii). M. malcolmsonii (monsoon river prawn) is found in the waters of Bangladesh, India and Pakistan.
M. rosenbergii (giant river prawn) is indigenous in the whole of the South and Southeast Asian area as well as in northern Oceania and in the western Pacific islands. M. vollenhovenii (African river prawn) is naturally distributed in West Africa, from Senegal to Angola.
Many Macrobrachium species have been transferred from their natural location to other parts of the world, initially for research purposes. M. rosenbergii remains the species most used for commercial farming and consequently is the one which has been introduced to more countries. Following its import into Hawaii from Malaysia in 1965, where the pioneer work of Ling (1969) was translated into a method for the mass production of postlarvae (PL) by Fujimura and Okamoto (1972), it has been introduced into almost every continent for farming purposes. M. rosenbergii is now farmed in many countries; the major producers (>200 mt) are Bangladesh, Brazil, China, Ecuador, India, Malaysia, Taiwan Province of China, and Thailand (FAO 2002). More than thirty other countries reported production of this species in the year 2000. Viet Nam is also a major producer, according to New (2000b). In addition, there are also valuable capture fisheries for M. rosenbergii, for example in Bangladesh, India, and several countries in Southeast Asia.

 

IDENTIFYING MACROBRACHIUM ROSENBERGII FROM OTHER FRESHWATER PRAWN SPECIES

Macrobrachium rosenbergii (Figure 1) can be distinguished from other species in the genus by the following characteristics (the morphological terms used below are explained in the glossary – Annex 11):

it has a very long rostrum, with 11-14 dorsal teeth and 8-10 ventral teeth (the ventral characteristics are especially important);

the tip of its telson reaches distinctly beyond the posterior spines of the telson;

FIGURE1
The external features of Macrobrachium rosenbergii

SOURCE: EMANUELA D’ANTONI

the adult male has very long second chelipeds in which all segments are elongate and have blunt spines;

the movable finger of the second chelipeds of the adult male is covered by a dense velvetlike fur (except the extreme tip) but this fur is absent from the fixed finger and the rest of the cheliped; and

it is the largest known of all Macrobrachium species, adult males having been reported with a total body length of up to 33 cm, and adult females of up to 29 cm.