Integrated multitrophic aquaculture as a means of improving resilience
Integrated aquaculture systems share the management of resources, such as water and feeds, with other farming systems. Typically, a new aquaculture species is integrated into an agricultural or agro-industrial system. Outputs from one subsystem, which otherwise may have been wasted, become an input to another subsystem. This leads to greater efficiency in the use of outputs produced from the land and water resources that are under a farmer’s control. Integrated aquaculture is widely practiced by small households, mainly in Asia, as a low-cost and efficient food production system in freshwater environments. In recent years, the idea of integrated aquaculture has been often considered as a mitigation approach to curb the excessive quantities of nutrients and organic matter generated by intensive aquaculture activities. This has led to the emergence of integrated multitrophic aquaculture (IMTA). Multitrophic refers to the explicit incorporation of species from different trophic positions or nutritional levels in the same system (Chopin and Robinson, 2004).
Two-season farming system of integrated shrimp culture with Manila clam and rabbit fish in Southeast China
This farming system, which produces two seasons or cycles annually, is mainly used by shrimp farmers in Fujian and eastern Guangdong provinces of China. Shrimp (Penaeus monodon in Spring, Marsupenaeus japonicas in Autumn), Manila clams (Ruditapes philippinarum) and rabbit fish (Siganus fuscescens) are farmed together in the same pond. The pond size typically ranges from 0.5 to 3 ha, with muddy-sandy sediment and marine water depth of 1.0-1.5 metres. Two aerators (1.5 kilowatt) are equipped per ha. Only the shrimp are artificially fed with commercial shrimp feed or trash fish. The Manila clam and rabbit fish eat the by-products inside the pond (Shao, 2007; Weng, 2006; Feng et al., 2009).
Inputs and yield of the system (according to Shao, 2007; Weng, 2006; and personal survey in 2011)
Table 1.
Seasonal seeding of the farming model
Season | Species | Seeding amount (/ha) | Size |
|---|---|---|---|
Autumn (August) | Ruditapes philippinarum | 2.6 tonne | 1180-1290 ind/Kg |
Marsupenaeus japonicus | 0.3×106 individuals | 0.8~1.0 cm | |
Siganus fuscescens | 15×103 individuals | 400 ind/Kg | |
Spring (March) | Ruditapes philippinarum | 1.9 tonne | 400-460 ind/Kg |
Penaeus monodon | 0.4×106 individuals | 0.7-0.9 cm | |
Siganus fuscescens | 15×103 individuals | 400 ind/Kg |
Table 2.
Annual production* and potential for increasing yield
Species | Average annual yield (t/ha) in monoculture | Estimated yield in the integrated farming system (t/ha) |
|---|---|---|
Marsupenaeus japonicus | 1.8 | 2.4 - 3.0 by intensive feeding and disease control |
Penaeus monodon | 2.2 | 2.8 - 3.5 by intensive feeding and disease control |
Ruditapes philippinarum | 14.2 | 14.6 - 16.0 |
Siganus fuscescens | 1.1 | 1.4 - 1.8 |
Penaeus monodon | 0.4×106 individuals | 0.7-0.9 cm |
Siganus fuscescens | 15×103 individuals | 400 ind/Kg |
* The shrimp production in Table 2 represents the average yield in monoculture model for these two species in Southeast China. This figure could be lower because the possibility for disease outbreaks is much higher than it is for IMTA. However, the production level of L. vannamei is much higher (average 6-8 tonne/ha) but not included in the current IMTA model.
Carbon footprint and energy use Carbon input (ton/ha) | Carbon output / harvest (tonne/ha) | Carbon balance (tonne/ha) | Energy use (KW*H) |
|---|---|---|---|
Seeding 0.18 Feeds 0.70 | Shrimp & fish 0.35 Manila Clam 0.57 | -0.04 | 900 - 1200 |
Carbon content of fresh Manila clam: 4 percent (Lu et al., 2005); carbon content in shrimp feed: 10 percent; carbon content in shrimp and fish: 6.8 percent. Energy use according to Shao, 2007. 2005.dile lowing.3.
Ecosystem services
Manila clam filter feeds on phytoplankton and organic detritus. Rabbit fish feed on macroalgae. Because of these feeding habits, the system acts as a carbon sink, absorbing 0.04 tonnes per ha. The average electricity use of the farm is about 1 200 kilowatt hours (kWh), which is the equivalent of about 0.2 tonnes of carbon. Electricity use is much lower than in normal semi-intensive shrimp monoculture. There are nearly no organic pollutants and nutrients discharged. To make this IMTA system carbon neutral, the shrimp stocking intensity could be reduced in favour of increased stocks of bivalve shellfish and integrated with macroalgae culture. However, current levels of shrimp stocking are driven by potential profits, which is the strongest factor in determining the composition of farming systems.
The system employed 0.5 -1 person per ha during routine farm management. But more than 20 persons per ha are employed during the clam harvest. These figures only take into account direct employment. Indirect employment can be an order of magnitude higher.
Value of the production (mainly for domestic market)
Species | Yield (t/ha) | Price(US$/kg) | Annual value (103US$/ha) |
|---|---|---|---|
Marsupenaeus japonicus | 1.8 | 12.7 - 16 | 26 |
Penaeus monodon | 2.2 | 4.4 - 8.0 | 14 |
Ruditapes philippinarum | 14.2 | 1.0 - 1.2 | 13.5 |
Siganus fuscescens | 1.1 | 2.5 - 4.0 | 3.5 |
Sum | 19.3 | - | ≈57 |