According to the new State of Fisheries and Aquaculture in the World report published by the UN FAO, the amount of fish obtained through aquaculture is about 20% of catches in the 1990s, but now half by 2020. If we think about fish farming, we see aquaculture as a good tool to reduce and recover the pressures on declining populations in the wild, while other industry stakeholders have other ideas. But one of the most promising aspects of the job is that fish farms located far from the coast, supported by artificial intelligence, and highly automated are not far from today. With the "smarting" of fish farms, some unpleasant problems that are closely related to the coastal ecosystem and coastal stakeholders seem to be resolved.

Industrial marine fish farming is relatively new to other fish farming business', but has become a major industry globally, producing around 6.6 million tons of fish per year in many parts of the world. Standard production units, defined as marine cages, are variations of a common idea. The birth of this technology comes from the first Atlantic salmon farms in Norway and Scotland in the 1960s and 1970s, where nylon trawling nets were hung on wooden or polyethylene pipe structures. The development of this technology used in fishing has evolved from steel platforms and round plastic rings, from nets hanging into the water to highly engineered products.

Despite the widespread use of “traditional” cages in the marine fishing business around the world, cages come with a host of problems, including escapes, parasites and disease, conditions caused by high temperatures or low oxygen levels, algae and jellyfish explosions, and mesh breakage and deformations from storms. In addition, the behavior of fish with high commercial value such as sea bream and cod to move between deeper or shallower parts of the water in their daily lives puts cages kept at fixed depths in a disadvantageous position.

Aquaculture in cages with the ability to be positioned in different locations within the water column, whether temporary or permanent, can circumvent many of the problems that come with rigid cages. Deep waters typically have more stable temperatures and salinity, are better protected from storms than surface cages, and reduce the possibility of parasite contamination. The widespread use of submersible fish cages in aquaculture and the adoption of these cages in the sector will play a key role in the development of new production areas.

The history of submersible cages is based on experiments on Rainbow trout (Oncorhynchus mykiss) in the 1970s and extensive trials on Atlantic Salmon in the 1980s. The main purpose of these experiments in fish farming was to ensure that they are affected as little as possible by the negative conditions that occur on the surface for a temporary period of time. Since then, the number of studies in submersible cages has increased, and to date, breeding trials have been conducted with at least 11 species of finfish of various sizes, at different depths, at different immersion times. Many species, including Rachycentron canadum and Seriola rivoliana, appear to do well in submersible cages, but few species have yet been produced on a commercial scale.

While growing up fish in the open sea has been criticized by some environmental groups, it is seen as a sustainable and environmentally sensitive future way within the industry. This aquaculture method is turning into a new and remarkable trend in aquaculture. Forever Oceans, a subsidiary of Lockheed Martin and ambitious in breeding Seriola dumeri, has developed a cage system for offshore fisheries. The cage system developed by Forever Oceans can be positioned approximately 16 km offshore and at a depth of approximately 2 km. The most striking feature of this new cage model is that the cages will allow natural movements caused by ocean currents with a patented single point mooring mechanism.

The technology Forever Oceans uses to manage its offshore operations and control the water and the behavior of the fish at the facility is directly linked to sensors, receptors, cameras and management software called AI-driven. With this software, feeding work and timing can be adjusted precisely, and necessary controls can be made to avoid the effects of algal blooms that may occur near the facility. Images captured by the system's cameras are analyzed by biomass software to determine when fish can be harvested. It only takes one professional to have a PC, tablet or mobile phone to manage the facility, which is promising in terms of reducing human activity in places that are not suitable for physical work, such as the open sea.

It is obvious that locating fish farming facilities in the open seas and deeper provides stability to the fish within the facility in water conditions such as more natural environment temperature and salinity. In addition, large water flows in the deep seas are expected to have a positive effect on aquaculture operations by removing the negative factors that cause diseases. Another example presented that cages positioned in the deep sea are relatively better than other systems is that offshore facilities use ocean tides as a natural filter. This increases the consumption of less energy and the utilization of natural nutrients to operate the facility.

To explain with a few examples, the cages can be moved in the water column in order to eliminate the oxygen solubility that decreases due to the increasing surface temperature in the hot seasons, or to protect the fish in the cages from the effects of cold air and extremely cold water in extremely cold weather. Lepeophtheirus salmonis which is seen as one of the biggest problems in salmon farming, is mostly seen in the upper layers of the water. To protect the fish from this influx of parasites, immersing them deeper seems to be an antibiotic-free and economical solution to combat sea lice. Harmful algae, which are directly related to the illuminated area of the water and usually increase in number and "explode" due to nutritional and physical changes in this column, are less abundant due to less light in the deep waters, thus reducing their potential to adversely affect fisheries due to their large presence.

Although marine fisheries make up the vast majority of fish farming operations in the world today, deep-sea fish farming is still in its growth stage. Since the first deep-sea aquaculture project launched on the Norwegian coast in 2018, a number of initiatives including Forever Oceans, Mowi, Innovasea and Blue Ocean Mariculture have been working on systems that will enable open ocean fish farming.

It is true that offshore fishing seems more advantageous than near-shore fishing, which has the potential to directly affect coastal ecosystems. Fishing in the sea is easier than in the past, thanks to geographic information systems and comprehensive maritime information. We will witness a new transformation of fishing with the rational solution of unique problems such as logistics and ensuring that the facility is constantly connected to the internet. Despite considerable interest in fishing in submersible cages, there has been limited success in Trout. While small-scale trials in freshwater have shown that such cages can be used to overwinter fish under surface ice, a number of industry-scale studies show mixed results of submersion as a viable production method. For example, Salmonids do not thrive when kept in cages that have been submerged in seawater for more than a month, and the growth rate remains lower than in surface cages, although continuous lighting eliminates some downsides.

Aquaculture in submersible cages can offer the right answers to some of the problems encountered in today's traditional aquaculture methods. However, this does not mean that this type of cage is suitable for the cultivation of all fish species, it brings its own problems. Finding optimal aquaculture sites based on the biology of the species, focusing on streamlining operational techniques, and documenting the behavioral responses of cages to long-term inundation on a commercial scale will base the benefit predictions of submesible cage aquaculture. At this stage, the species with or without a closed swim bladder stand out more than the others. Those with open swim bladders, such as salmonids, have to fill their bladders from the air. Submerged cages for extended periods of time without contact with sea surface air can adversely affect the health and growth of open swim bladder fish, but new technological advances such as underwater air domes in underwater cages may be a solution to this challenge.

If aquaculture in submersible cages matures and fulfills its promises, research to experimentally document production and environmental benefits and issues including the living conditions of fish in the facility throughout the production cycle will need to be spearheaded. New production technologies are difficult but possible to test solidly on an industry scale, and achieving them requires joint investment from all fisheries-related stakeholders, including government and industry.

The more researches on sink cages are made, the more these systems will be used in aquaculture.

Read more at for extended information about submersible cages in aquaculture.