Analysis of production and environmental effects of Nile tilapia and white shrimp culture in Thailand

Two case studies from Southeast Asia are used to analyse production, environmental effects, and economic optimisation of Nile tilapia (Oreochromis niloticus) and white shrimp (Penaeus vannamei) pond culture. A projection of these data is made for the whole of Thailand. The results are analysed on a regional scale based on site selection using multi-criteria evaluation (MCE).  Farm-scale culture was simulated for (i) tilapia monoculture in Chiang Rai; (ii) shrimp monoculture in Chanthaburi; and (iii) Integrated Multi-Trophic Aquaculture (IMTA) of tilapia and shrimp in Chon Buri. Together, these provinces produced 17,500 tonnes of tilapia in 2012, with a significant proportion exported to North America and Europe.  Growth models for both species were developed, calibrated, and validated, and used to simulate population dynamics of cultivated animals, and sediment diagenesis and eutrophication in ponds. Co-cultivation stimulates nitrogen dissolution (134 kg N cycle−1), which is greater than in tilapia (96 kg N) or shrimp (52 kg N) monoculture, and doubles the NH4+ discharge to the environment (10.7 kg in tilapia monoculture, 20.5 kg in co-cultivation). However, eutrophication as a result of shrimp monoculture decreases sharply chlorophyll emissions fall from 0.17 kg to 0.02 kg. A modelled IMTA scenario including the green seaweed Ulva reduced NH4+ outflow to 0.32 kg cycle−1.  Scaling to the national level, for a 2010 production of 158,293 t y−1 (tilapia), and 553,899 t y−1 (shrimp), gives calculated emissions of 2,105,118 and 34,904 Population Equivalents (PEQ) respectively. Only part is a negative externality, because rural agro-aqua systems in Thailand reuse discharges in holding ponds, rice culture, etc.  Commercial tilapia and shrimp aquaculture have a value added share of total GDP of 0.38, and value added of 96.24, resulting in indirect impacts of the industry on the Thai economy of $35 million, and the creation of 16,000 additional jobs.  The MCE scenario analysis suggests sustainable expansion is possible for both species. The highly suitable class for tilapia would triple in the dry season, but halve in the rainy season. For shrimp the corresponding areas would decrease in both seasons. However, the suitable class is two orders of magnitude greater than the current level of tilapia farming, and shrimp could increase tenfold (limited by the rainy season due to low salinity). These projections which are constrained by competing land claims, will be further influenced by socio-economic factors, and would depend upon national or regional policy decisions.  These models, together with economic indicators developed for the aquaculture industry in Thailand, provide an overview of this important contributor to world aquaculture, which has a volume production greater than both the US and EU, and explore some of the lessons that may be learnt worldwide at both the local and national scales.