STATUS OF FRESHWATER PRAWN - TILAPIA POLYCULTURE: A REVIEW  

The global production of farmed Macrobrachium spp. is approaching 0.5 billion mt/yr. Total production of all species of tilapia is approximately ten times greater but there is a marked differential in average farm-gate unit value (freshwater prawns = >3 times tilapia). As both are therefore important components of warmwater aquaculture, seeking some synergy in their farming systems could be beneficial. With this goal in mind, our paper provides a brief review of the status of the polyculture (and co-culture) of freshwater prawns (Macrobrachium spp.) with tilapia. Actual and potential prawn-tilapia interactions are discussed and four decades of research into prawn-tilapia polyculture are reviewed. Commercial prawn-tilapia polyculture practices are also appraised.

It is almost certain that prawns do not affect the performance of tilapia in earthen ponds and stocking them in such ponds may significantly enhance total revenues. Thus, polyculture is recommended for tilapia-pond culture farmers, who want to retain tilapia as the major species. On the other hand, the presence of tilapia in prawn ponds may reduce prawn yield, but is unlikely to reduce total revenue. The main constraint is the feeding of prawns when polycultured with tilapia (i.e. free-swimming within the ponds). Tilapia very rapidly consume pelleted feed and eat much more than they need for growth (superfluous feeding). Thus, prawns do not have the opportunity to ingest the supplied pellets.

The stocking size of both tilapia and prawns in pond polyculture seems to be irrelevant, since tilapia are stocked after the fry phase (generally at < 3 g). No injuries inflicted by prawns on tilapia have been described. Stocking density and the proportion of tilapia and prawns stocked appear to be important factors. It certainly depends on the site characteristics (such as water quality and natural productivity), the general management system utilized (such as the use of artificial substrates and aerators), and the choice of the major species (tilapia or prawns), which will be determined by the characteristics of the intended market. Most research work has been performed using 1-2 tilapia/m² and 2-4 prawns/m². However, it is the total biomass of both species rather than the individual numbers that should be considered; this has been neglected by investigators. The best situation would be to consider the amount of waste feed necessary for the prawns and to provide only the tilapia with floating pelleted feed.

We conclude that both polyculture and co-culture are technically feasible today and that they can maximize the use of natural resources, reduce the need for commercial diets, and increase profits. However, further research is required to provide science-based information to enhance the efficiency of these examples of polyculture and co-culture. This will enable farmers to take full advantage of their potential as a real multitrophic and multispatial equilibrated system (IMTA).