Water (Rearing) Environments and Water Use

Each aquatic species has specific environmental requirements. The various salmonids (salmon and trout) for example require cold (50-60° F), highly oxygenated waters (oxygen greater than 6 mg/L), but the water can be fresh or salt water. Catfish are grown in fresh water but can tolerate a wide variety of water temperatures growing best at water temperatures above 75°F with oxygen concentrations above 4 mg/L. Marine mollusks, such as oysters, and crustaceans, such as shrimp, must be grown in water where salt (NaCl) levels are higher and where the water is saturated with oxygen.

In all cases, waters used in aquaculture production must be free of compounds that could contaminate or taint the flesh. These waters must obviously be free of anything that could cause aquatic animal mortality. Aquaculturists strive to protect their rearing waters from contaminates. As part of industry-developed HACCP programs, rearing areas and influent waters are tested for pesticides or other contaminants. Because the environment of many aquacultured animals is controlled and protected from contaminants, animals raised under these conditions are typically free of contaminants. FDA records as well as university research surveys of aquacultured animals demonstrates farm raised aquatic animals are generally free of harmful chemicals. Aquaculture is a water dependent industry. Aquaculturists must be good stewards of water use, our success depends on it.

The FDA instituted a mandatory seafood processors safety program to ensure that the US consumer continues to receive safe wholesome seafood. This program relies upon a HACCP plan and is enforced by seafood processors but inspected by FDA. The National Aquaculture Association (NAA) endorses this program and has been instrumental in developing various aquaculture producer quality assurance programs. Environmental quality is identified in these plans as an important factor needed to ensure wholesome aquatic animals.

Water Use

Another reason for aquaculture’s environmental sustainability is its minimal use or consumption of water. Globally and within the US, water is a precious resource. Minimal consumption is important because conflicts over availability are expected to increase dramatically over the next several decades. Contrary to common perception, aquaculture has minimal water consumption.

Water used by aquaculture operations is generally returned back to the environment after some brief period of use. For example, in Idaho, where most US trout production occurs, gravity fed, naturally flowing spring water is diverted into cement raceways holding trout. The water flows through the raceways after which it is treated to remove solid wastes and then discharged into the Snake River. The water is not consumed or used up in the production process nor does it deplete the aquifer.

In the western part of the US, use of water (whether for irrigation purposes, home use or for aquaculture) is contingent upon having a valid water right. Western states rely upon the prior appropriation doctrine that stipulates that the individual claiming use of water first in time will be able to use the water before a more junior water right holder can use the same water. These water rights are called usufructuary rights indicating that while the water belongs to the state, the water can be rightfully used for beneficial purposes by a private individual. The state determines validity of water rights and otherwise manages use of this resource. The water must be put to beneficial use for the usufructuary right to be maintained. Similarly, net pens commonly used for salmon production in the northeast or northwest US do not consume water. Oysters and clams simply filter the water that passes over them. In many states, aquaculture has been legally classified as a beneficial, nonconsumptive, use of water.

In some aquaculture situations water is indeed consumed but this is usually minimal and is due to evaporation. Catfish ponds can lose water during the summer due to evaporation. This water is replaced by precipitation throughout the year so that in any one year, a net gain or loss of water might occur depending upon prevailing climatic conditions. Appropriate pond water level management can minimize the need for adding water. Some aquaculturists discharge their effluent onto fields for irrigation or nutrient control, thus integrating well with existing agriculture. This practice is minimal in most areas because there is insufficient land for such discharge or the cost of pumping the water is prohibitive.

Aquaculturists using semi-closed or closed recirculating systems often need to add new fresh water to ensure appropriate rearing environments and to replace water lost to evaporation. These intensive production systems are generally more expensive to operate and more technically demanding than raceway, pond or net pen culture systems.

Water use on US shrimp farms has changed in recent years. Research suggests the frequent exchange of pond water with marine waters for supplemental aeration is unnecessary. The only additional waters needed are those to replace pond water lost to evaporation so that pond salinities do not become excessive.