Red tilapia in tanks at IMA's Re-circulating
Aquaculture System production facility.

Re-circulating Aquaculture Systems - RAS

Innovative technologies in tilapia farming

Jul 26, 2012

A previous article by the Institute of Marine Affairs (IMA) gave an overview of aquaculture in Trinidad and Tobago and the challenges faced by this industry.  Today we feature new technologies used at the IMA for more sustainable and profitable aquaculture ventures

Aquaculture as a vibrant and profitable industry is still in the developmental stage locally. Food fish culture is constrained and its full economic potential still unrealised, partly due to adherence to traditional pond-based systems with its myriad of environmental and security concerns.

Local and international demand for fish and fish products, coupled with declining stocks, as well as the need to diversify the local economy, demand a more innovative approach to aquaculture to achieve profitability as a business venture.

The IMA conducted research in culture technologies for freshwater food fish, like tilapia and cascadura and is now planning for mariculture species as a means of fast-tracking the development of the local aquaculture industry.

Re-Circulating Aquaculture Systems (RAS) is a fast growing field, both in terms of research and for commercial activities.  The advantages of a RAS over pond-based systems are that this system can be used where land is limited, water scarce or when ambient environmental conditions are not suitable for the cultured species. However, given its more intense approach high stocking densities and very controlled environmental conditions, risks are higher and there are costs associated with appropriate back-up systems.

The RAS is essentially a closed production system that re-uses more than 85 per cent of its water for continuous production and which can be incorporated into other agriculture production systems, such as aquaponics.

In 2009, the Institute teamed up with the Seafood Industry Development Company (SIDC) to implement a pilot project of the RAS for intensive fresh water tilapia production adapted to local conditions. Imported YY or super male tilapia from Swansea, UK were crossed with Swansea red, silver and IMA-bred red hybrid females to produce the offspring used in the production system.  The genetically male tilapia, Oreochromis niloticus, and red hybrid tilapias were used to demonstrate the technical and economic feasibility of commercial production, with a view to encouraging entrepreneurs and investors. A handbook, technical reports and a demonstration facility for industry users were other outputs anticipated from the pilot project. 

All treatment processes involved in a RAS, as well as its management, are not unique to aquaculture but are closely related to wastewater treatment systems used for a range of domestic as well as industrial applications. The general design of this system allows for flexibility and ease of management and requires minimum inputs of manual labour except at times of sampling and harvesting. 

The basic components of a RAS are the culture tanks, mechanical filters for solids removal, biological filters for breakdown and removal of excretory wastes, aeration and re-circulation of the water. In addition, gas removal of carbon dioxide and ammonia, pumping and disinfection devices such as ultra-violet filters, ozone generators and foam fractionation for bacteria and other solids removal are considered. 

The tilapia RAS, located at the IMA's facilities in Chaguaramas, consists of a covered shade-house of approximately 740 m2 with ten 30,000-litre circular production tanks and other tanks which serve as sumps for water treatment and recirculation. In addition, there are two mechanical filters for solids removal as well as eight 3,000-litre moving bed bio-filters for nitrification. A secured control room to house pumps, blowers, feed timer, alarm system and data logger was constructed from a 6.09 m (20-ft) shipping container while another was retro-fitted for feed storage.

In the pilot stage of the project, fish were fed a complete ration of 42-35 per cent imported crude protein over a 180-day production cycle. Market size fish were purged with clean well-water for a minimum of 24 hours before final harvest. Approximately 5,564 kg (12,255 lbs) of harvested fish were distributed by the SIDC to wholesalers, retailers, processors and other end-users in 2010 and 4,967 kg (10,941 lbs) in 2011. Up to May of this year, production was approximately 16,782 kg (36,694 lbs).

Re-circulating aquaculture facilities are fully contained and can be located in rural or urban areas and in most warehouses. Site selection is not dictated by proximity to a natural source of water but rather by the business opportunity. The RAS can be modified to accommodate the species for target markets and environmental conditions can be monitored and controlled to fit the requirements of the species of interest.                                    

RAS have strong 'green credentials'. Products are promoted as sustainable because, as closed systems, they abstract little water from natural water bodies and produce minimal effluent discharges, thereby reducing the potential impacts from pathogens and fish release into natural water courses.  There is also improved bio-security which reduces the risk of disease outbreaks and eliminates losses to predators. Research continues at the IMA into Re-circulating aquaculture systems for the production of commercial marine fish such as cobias, snappers and groupers.

Paul Gabbadon, Senior Research Officer, Fisheries and Aquaculture Research Programme.

The IMA is an agency of the Ministry of Housing, Land and Marine Affairs.