netpens

Netpens are floating mesh enclosures used in aquaculture to culture fish in coastal, offshore, or freshwater environments. They confine individuals within a defined volume of water while allowing the exchange of water, oxygen, and waste through the netting. Netpens are typically anchored to the seabed or supported by moorings and floats, and they consist of a netting shell attached to a rigid frame, with lines for feeding and monitoring.

Design and operation commonly involve a circular or rectangular netted chamber suspended below the surface. The size and stocking density vary by species and site conditions, but pens are generally placed in areas with adequate water flow to dilute waste and maintain oxygen levels. Feeding is usually done manually or with automated systems, and monitoring includes water quality, fish health, and equipment integrity. Harvesting typically involves draining or netting fish from the enclosure.

Species farmed in netpens are primarily finfish such as salmon, trout, and other carnivorous or omnivorous species, though some operations may culture certain shellfish or tilapia in related cage structures. Advantages of netpens include scalable production, controlled feeding, and the ability to use existing coastal infrastructure. Disadvantages include the potential for localized pollution, disease and parasite transmission to wild populations, and the risk of stock escapes or predator interactions.

Environmental and regulatory considerations emphasize responsible siting, waste management, biosecurity, and monitoring. Practices such as fallowing, multi-trophic approaches, strict containment, and incident reporting aim to minimize ecological impacts and ensure sustainable production. Netpens remain a common method in open-water aquaculture, particularly where local conditions support open-water culture and regulatory frameworks permit it.