CHALLENGES AND DEVELOPMENTS IN OFFSHORE FISH PENS

Offshore fish farming has its challenges as listed in Table 1. Nevertheless, it is gaining traction for more sustainable and high-quality fish production due to larger water space, better water quality, stronger currents to dilute waste and avoid coastal ecosystem degradation often seen in nearshore fish farms.

Recently, many offshore fish pen design concepts have been proposed. Below are some key observations on offshore fish pen developments:

• Most offshore fish pen designs are at their conceptual stage.
• There are, however, some full scale proto-type pen designs been built (e.g., Ocean Farm 1 and Havfarm 1 in Norway, Shenlan 1 in China) in the last few years. So, operation of offshore fish farms is still in its infancy.
• Instead of an array of pens used in nearshore fish farms, offshore fish farms tend to have a single “mega” fish pen that can accommodate more than a million fish. These mega pens with their rigid steel frames and stiffer nets (e.g., polyethylene terephthalate) are better to withstand the more energetic environment.
• Submerged pens are also pursued as a solution for offshore fish farms as it avoids strong surface waves, algae bloom, parasites, warm surface waters during summer. Their structural strength and stiffness do not need to be overly designed as surface floating structures. Examples of submerged pens are the Atlantis in Norway and Innovasea pens in Hawaii. 
• Offshore fish pens have to be equipped with remote and autonomous devices for operation, maintenance, monitoring and surveillance of feeding, venturation, lighting, cleaning, and removal of wastes and dead fish.
• Offshore fish pens, sited at a considerable distance from the shoreline, will have to tap on offshore renewable energy sources such as wind, wave and solar energies for power supply to minimize OPEX and environmental impacts due to the dependency on fossil fuels
• Integration or co-location of fish farming with other synergetic marine activities (such as renewable energy production) are desirable from an economic viewpoint. The overall infrastructure and operational procedure will no doubt be more complex, and the increased functionalities will bring more risks and require more rigorous assessments for insurance coverage. More research and developments are needed in this space.