Avnimelech, Y. (Commercial Fish and Shellfish Technologies Program, Virginia Tech, 2005-06-01)
Intensive aquaculture systems are being used to efficiently produce fish and shrimp. However, an intrinsic problem of these systems is the rapid accumulation of feed residues, organic matter and toxic inorganic nitrogen species. This cannot be avoided, since fish assimilate only 20-30% of feed nutrients. The rest is excreted and typically accumulates in the water. Often, the culture water is recycled through a series of special devices (mostly biofilters of different types), investing energy and maintenance to degrade the residues. The result is that in addition to the expense of purchasing feed, significant additional expenses are devoted to degrade and remove two thirds of it. There is a vital need to change this cycle. One example of an alternative approach is active suspension pond (ASP) systems, where the water treatment is based upon developing and controlling heterotrophic bacteria within the culture component. Feed nutrients are recycled, doubling the utilization of protein and raising feed utilization. Other alternatives, mostly based upon the operation of a water treatment / feed recycling component besides the culture unit are also relevant. Active suspension ponds are being practiced and their numbers have increased dramatically during the last 10 years, most notably with shrimp culture. The purpose of this paper is to raise discussion on alternative routes to the classical recycling approach.