TILAPIA IN HIGH-RATE AQUACULTURE PROCESSES

Globally, aquaculture continues to grow in importance. Equally important is the need to intensify all forms of modern agriculture, in particular, aquaculture.  Internationally, aquaculture poses a potential threat to fresh and saline water resources.  Aquaculture systems and practices are needed that offer potential to reduce or completely eliminate water and waste discharge to the environment. Tilapia co-culture offers potential as a technique to intensify and improve aquaculture production practices, while recovering, recycling and reusing aquaculture nitrogen and phosphorus discharges as valuable by-product foods, feeds, and fuels.

The Partitioned Aquaculture System (PAS) combines the water treatment capability of high-rate algal production with pond aquaculture. The primary advantage is to increase algal production, thereby accelerating ammonia assimilation and oxygen production.  Of particular importance is the use of tilapia co-culture, allowing operator control of pond algal genera dominance, algal density, and zooplankton grazing. Maintaining 10-25% of fed fish biomass as tilapia biomass was seen to reduce average algal cell age from 6-10 days to 2-3 days  Use of tilapia co-culture significantly increased catfish production in 0.13 ha PAS units at Clemson University to as much as 19,575 kg/ha at an average feed application of 295 kg/ha/day.  

Marine shrimp production has a proven track record of enhancing rural economies in developed and developing countries. However, wastewater discharge from shrimp aquaculture poses a potential threat to freshwater and coastal aquatic environments. In SE Asia and China water discharge from shrimp culture ponds is of growing concern as impacts become evident. As aquaculture expands, widespread adoption of more sustainable practices is likely to gain increasing attention.  At Clemson University tilapia co-culture equal to 20% of marine shrimp biomass was used to control microbial solids level.  Hybrid (O. mossambicus x O. aureus) and monosex tilapia (O. niloticus) played a key in role providing low-cost control over microbial and fecal solids enabling zero-discharge high-rate shrimp production.

In Hawaii, batch cultures of marine microalgae (Chaetoceros sp. and Nannochloropsis sp.) were grown as a source of feed for copepod and rotifer culture supporting larval marine fish fingerling production. These cultures were observed to be subject to frequent algal population crashes. Preliminary results suggest that microalgal culture combined with tilapia co-culture offers potential to provide stable algal production by dramatically reducing opportunistic ciliate invasions.

Over a 20 year period investigators at Clemson University developed and demonstrated the application of modified PAS units to concentrate and remove nutrients from wastewater and agriculture irrigation discharge. The technique, named the Controlled Eutrophication Process (CEP), relies on populations of single-celled algae cultivated in high-rate algal ponds and harvested using tilapia-driven biosedimentation. The bulk of the algal biomass passes through the fish and is excreted in rapidly settling fecal chains.  Field trials showed that 90-95% of the algal production could be harvested using this method and sun dried to moisture content as low as 15%.

Tilapia co-culture is likely to continue to play an integral role in on-going development of The Partitioned Aquaculture System, The Controlled Eutrophication Process, and offers potential to enable improved zero-discharge marine shrimp production and aquaculture live food production.