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Abstract
INTRODUCTION
Giant freshwater prawn Macrobrachium rosenbergii is an important species and has become an important part of the rice-fish and small scale carp-tilapia polyculture ecosystem in developing countries due to large size attainment, tolerance to water quality changes, ability to cope with handling stress and ability to feed on un-conventional feeds (El- Sayed, 1997; Giap et al., (2005) and Hossain & Islam 2006). The global annual production of freshwater prawn (excluding crayfish and crabs) has significantly increased from 50,000 metric tons (Mt) in 1995 to > 280,000 Mt in 2003 (New, 2005 and FAO, 2005).
Tilapia is the most representative variety of freshwater aquaculture crops. It belongs to the Cichlidae family, which encompasses more than 100 species widely distributed in tropical areas of Africa, America and Asia. Tilapias are euryhaline fish, able to live in both freshwater and salt (brackish) water. Tilapia is often considered filter feeders because they can efficiently harvest plankton from the water. Tilapia is one of the most widely cultured species in Egypt. The total aquaculture production of tilapia increased from 24 916 Mt in 1990 to 460 000, metric tons / year and accounted for 53% of total production (830 000 Mt / year) (GAFRD, 2007).
Nowadays, the methods applied in tilapia culture are diverse; it can be all male culture monosex, a mixed sex culture or polyculture with predators such as catfish. The success of the rearing method applied depends on local consumer preferences economics, availability, and costs of inputs. However, the potential for economically successful monoculture of the freshwater prawn M. rosenbergii in temperature climates has been a subject of investigation for approximately last 30 years. Results suggest that prospects for success would be greatly enhanced by stocking juveniles rather than newly metamorphosed post larvae Uddin et al., (2007). All methods of management are principally directed toward realizing an increase in the total production per surface area. Another major management concern for the intensive pond culture of M. rosenbergii in temperature climates is the initial stocking density D´Abramo, (2002). The absence of a year-round growing season and the fact that average harvest weight decreases as density increases demand that particular attention by placed on the proper stocking density to attain a harvest size (weight) and yield that will optimize revenue.
In Egypt, the relatively long larval period (18-35 days) and low larval survival are disadvantages to commercial monoculture culture of this species (Goda, 2008). The cost of producing nursed juveniles has emerged as a major factor influencing the profitability of the nursery operators and prawn framers in Egypt. However, the polyculture system of Giant freshwater prawn, M. rosenbergii with Nile tilapia, Oreochromuis niloticus provide an addition high-valued to tilapia culture Keysami et al., (2007).
Recently, polyculture of Giant freshwater prawn, M. rosenbergii with Nile tilapia, O. niloticus may provide an opportunity to develop a sustainable aquaculture system Fitzsimmons, (2001). In polyculture setting, tilapia and prawn can utilize different niches in the culture niches in the culture setting. In an extensive fa