DESIGN AND OPERATION OF OCEAN AQUACULTURE INSTALLATIONS

INTRODUCTION

All aquaculture market projections uncover a dramatic supply-demand imbalance in the next two to three decades. Focusing on fin fish supply specifically uncovers that output level is close to a saturation point for traditional areas with sheltered aquaculture. As a result of the current situation fish farming is growing out of sheltered, near-shore areas and moved to locations more exposed and further offshore. Several innovative solutions are being tried out in offshore fish farming in the process of industrialization.

MAIN APPROACH

The numerous concepts planned and implemented may be split into three main categories: Open trusswork with traditional net or grating, semi-closed units and at last closed aquaculture installation. All these concepts may be operated with permanent manning or a combination of remote operation and daily visits. A more specific description of the main solutions applied in the development of ocean farming:

• Open trusswork. Further development of the traditional sheltered net pen usually with rigid floating collar in steel or concrete. Additional structural arrangements for additional buoyancy, ballasting/de-ballasting and distention of net panels are common features. This category may be split in two sub-sets. One includes operating at the ocean surface only while an increasing number of designs have the option of submerged position to avoid splash-zone dynamics at rough sea states.
• Semi-closed units. These designs aim to separate fish environment from sea for the first few meters of the water column. This separation is established to protect fish from parasites living in the upper levels of the water column. Sufficient water circulation to maintain sufficient growing condition and fish welfare is often a change for these solutions.
• Closed fish farming units. A wide variety of solutions are currently being explored in this category. The ability to control quality of intake water to optimize fish environment combined with possibility to collect fish waste and feed surplus promote the applicability of this solution. Water may be cleaned and re-cycled or filtered before emitted to sea resulting in less environmental impact per unit biomass. Establishing full separation between fish environment and sea results less parasites and disease in addition to absolute fish control (no escape) and controlled aquaculture emissions to marine environment.

Concepts and solutions listed have several advantages and weaknesses that must be considered and evaluated. These various solution’s ability to perform depends on a long list of functional aspects. The essential parameters to be taken into consideration assessing performance are considered to be: Oxygen level in sea water, crowding and live transfer of fish, dead fish handling and ensilage processing, logistics of supplies and goods going both on and off the fish farming installation and personnel safety.