Types of Crab Farms
|IRRIGATION DITCH/POND SYSTEMS
Irrigation ditch/pond systems are the oldest and most basic type of fish farming. These systems essentially duplicate a fish’s native habitat on an inland site. The pond contains a full predator/prey ecosystem, and is carefully balanced in terms of the flora and fauna present at any given time. The pond system must be quite large because it is designed to support a higher density of livestock than would be common in a naturally occurring biosystem. As global real estate goes up in value, and water resources are constrained, it is likely that the ditch/pond systems will over time give way to more intense forms of aquacultural production.
FRY FARMING SYSTEMS
Fry farming is a practice that has been used since the early 17th century. It essentially consists of culverts that channel water and fish from a nearby stream or body of water and allow these fish to grow up in a closed system supplied with an abundant artificial food source. These fish frys are typically concrete raceways, and can be cleaned by sluicing clean water into the system once the fish have grown to maturity and have been harvested. The great density of fish in these systems has proven a sticking point in the past. Disease and parasites are common, and entire crops can be lost without any warning.
Cage farming is the most toxic of the three types of intensive fish farming. It consists of large cage or net system in which fish are kept in super high densities. The cage is located in open waters such that the system is guaranteed a constant supply of freshwater (fig. 26). Organic debris are allowed to exit the system along with the flow of the open water. While there has been much recent interest in cage fish farming, there is, as yet, no means for purifying the debris from the water before the effluent is sluiced into the open water (fig 27).
Figure 26 - Winning Entry—South Street Seaport by N.E.E.D. Architects, 2008.
Figure 27 - Environmental Risks of Marine Aquaculture. Image Courtesy of: http://www.motherjones.com/environment/2006/03/aquaculture-environmental-impact
INTEGRATED RECYCLING SYSTEMS
Within the aquaculture industry, integrated recycling systems are thought to offer the best way of minimizing the use of natural water resources while at the same time limiting the production of effluent. Integrated recycling systems consist of large plastic, metal, or concrete tanks in greenhouses. The marine livestock are supplied with nutrients and a food source (typically algae); the waste in the system is slowly circulated to hydroponic beds near the tanks, where carefully cultivated microorganisms convert (“fix”) the ammonia to nitrates which fertilize the plants along with the phosphates from the tanks. Other wastes are strained out by the hydroponic media, which can double as aerated pebble-bed biofilters (fig. 28).
|BLUE CRAB FARMING 21||BLUE CRAB FARMING 22|
| McLarney, William. Freshwater Aquaculture: A Handbook for Small Scale Fish Culture in North America.
 Freshwater Aquaculture: A Handbook for Small Scale Fish Culture in North America, by William McLarney