ABSTRACT
The most intensive level of aquaculture is fish production in recirculating systems that recycle all, or nearly all, of the water through the fish rearing units. Recirculating systems are one of two general types depending upon the amount of water that is recycled. The so-called water reuse systems were developed by U.S. governmental agencies to accelerate the production of salmonid smolts by using heated water. Water was reused at a rate of 90% per flow cycle in order to conserve energy used in water heating. The flow through the system is therefore 90% used water and 10% new, heated water. This is equivalent to using the water 10 times in a serial raceway system with reaeration between each of the raceways. Water reuse hatcheries use biological filters to remove ammonia, but this level of treatment may not be necessary in low-pH waters (Figure 11.1).
