Growing fish using recirculating aquaculture systems (RAS) has been well-established. Economics of such systems still remains a challenge with systems often being characterized as too capital intensive, too high costs of operation, too labor intensive, and too complicated. The basic engineering principles of employing RAS is well established: round tank diameter-depth ratios, biofilter design, and water quality unit processes for oxygen and carbon dioxide control. The mixed cell raceway (MCR) was first introduced in 2000 and is basically a rectangular fish tank but hydraulically functions as a series of round tanks each with its own center drain. There are numerous MCR’s around the world but just as RAS has not seen wide scale adaptation due economic viability, neither has the MCR design.
We have developed a completely different design that we refer to as the iMCR (provisional patent has been filed) where all processes are in the same tank structure with interior walls defining unit processes. The iMCR has several new features making the MCR simpler, less costly, reduced operating costs, and reduced risk for operational failure. The iMCR design results in the same water quality for the entire length of the raceway, whereas current MCR designs see a linear decrease in water quality from one end to the other end of the raceway. The iMCR design allows multiple stages of fish growth to be conducted in the ‘same’ tank by placing divider gates between stages (perpendicular to the long axis of the rectangular tank). In essence, fingerlings are never touched from placement till harvest at market size. Purging can be performed in the same iMCR.
These features all contribute to reduced fish stress, which is the key to fish performing near their genetic potential. The whole system operates on very low hydraulic head (less than 3 ft) and oxygen and CO2 control result from the design of the biological filter providing gas control at no additional cost (pure oxygen is made available as a backup only or for very high biomass loading). Since the fish are only ‘touched’ by humans at the beginning and end of the production cycle, labor costs are also reduced significantly.