by Diogo Thomaz, Director, Oraseas LP, Greece
Cage aquaculture has evolved enormously over the past four decades. Feed formulations, genetics, feeding systems, monitoring technologies and production scale have all advanced rapidly. Yet, in many regions, particularly in the Mediterranean sea bass and sea bream farming, one critical aspect of production has remained surprisingly unchanged: net management.
Biofouling — the accumulation of algae, hydroids, mussels, tunicates and other marine organisms on cage nets — remains one of the most underestimated operational and biological challenges in marine aquaculture. While often treated as a routine maintenance issue, biofouling directly affects water exchange, oxygen availability, fish welfare, feeding efficiency, labour requirements, operational logistics and even disease pressure within fish cages.
As fish farming becomes more industrialised and sustainability expectations increase, net management systems are beginning to shift from a reactive maintenance activity toward a continuous environmental management strategy. Increasingly, technologies such as autonomous and semi-autonomous in-water net cleaning systems are changing how producers think about cage operations.
Biofouling: More than a maintenance problem
The primary function of a cage net is simple: allow unrestricted water exchange while safely containing fish. Biofouling progressively compromises this function.
As fouling accumulates, the open area of the net decreases, restricting water flow through the cage. Reduced water exchange leads to lower oxygen renewal rates and poorer removal of metabolic waste products. In many farming environments, particularly warm-water regions with high biomass densities, oxygen availability becomes one of the key limiting factors for fish performance.
This issue is especially important in Mediterranean aquaculture, where water temperatures are relatively high for half the duration of the production cycle. Elevated temperatures reduce oxygen solubility at precisely the same time that fish metabolic demand increases. Any reduction in water exchange caused by fouling can therefore have disproportionate biological consequences.
The impact extends beyond oxygen levels. Fouled nets also create highly complex biological surfaces that can harbour parasites, bacteria and pathogens. Biofouling communities may act as reservoirs for disease organisms and increase the persistence of pathogens within cages. Hydroids and other fouling organisms may additionally contribute to gill irritation and chronic stress.
In practical terms, heavily fouled nets often create a more stagnant and biologically unstable microenvironment around the fish. Farmers frequently observe reduced feeding activity, slower growth and less consistent fish behaviour as fouling intensifies.
Interestingly, many Mediterranean farms have historically accepted levels of fouling that salmon farmers in Northern Europe would consider severe. In Norway, Scotland and other salmon-producing regions, continuous in-water net cleaning has become standard practice across much of the industry. In contrast, Mediterranean operations have traditionally relied heavily on net changes and antifouling coatings, often allowing nets to become substantially fouled between exchanges.
This difference in operational philosophy may partially explain why feeding performance and feed conversion ratios in Mediterranean marine fish farming have not improved as dramatically over the past 40 years as many other areas of aquaculture technology.
The hidden cost structure of traditional net management
One reason net management is often undervalued is that its true costs are dispersed throughout farm operations rather than tracked as a single production category.
Traditional cage farming systems relying on periodic net changes involve a wide network of associated costs, including:
- Large inventories of spare nets
- Net removal and installation operations
- Boats and specialised vessels
- Cranes and lifting equipment
- Labour for handling and logistics
- Transport of dirty and clean nets
- Onshore net washing facilities
- Net inspection and repair
- Antifouling coating application
- Storage infrastructure
- Fuel and energy consumption
- Production interruptions during net exchanges
These costs can become substantial, even in relatively small farms and especially in large farming groups operating across multiple sites.
Antifouling coatings alone represent a significant operational expense. Although coatings delay fouling accumulation, they rarely prevent it entirely. Even treated nets in Mediterranean conditions frequently develop significant fouling after a few months at sea, especially during warmer periods with intense biological activity.
The logistical burden is also considerable. Many farms maintain extensive net inventories to support regular exchange cycles. Dirty nets must be transported ashore, cleaned, repaired, dried, repainted and stored before reuse. This creates an industrial support system around the farming operation that consumes labour, capital and energy.
Importantly, the biological cost of operating with partially fouled nets between exchanges is rarely quantified accurately. Reduced oxygen availability, suboptimal feeding behaviour, lower growth performance and stress-related impacts may collectively represent one of the largest hidden costs in marine fish farming.
The shift toward continuous in-water net management
An alternative operational philosophy has emerged over the past two decades: instead of allowing nets to foul heavily and periodically replacing them, the objective becomes maintaining nets continuously clean in the water.
Under this approach, nets may remain installed for one or even multiple production cycles while undergoing regular in-water cleaning, often every one to two weeks depending on local fouling pressure.
The concept fundamentally changes the role of net cleaning.
Rather than acting as a corrective intervention for heavily fouled nets, cleaning becomes a preventive environmental management tool designed to maintain optimal cage conditions continuously.
When nets are kept consistently clean:
- Water exchange remains near maximum levels
- Oxygen availability improves
- Waste removal becomes more efficient
- Pathogen reservoirs associated with fouling are reduced
- Fish experience more stable environmental conditions
- Feeding activity tends to remain stronger and more consistent
The operational model also changes significantly. Farms can reduce dependence on large net inventories, frequent net exchanges and extensive shore-based net servicing infrastructure.
This transition mirrors developments seen in other industrial sectors, where preventive maintenance strategies increasingly replace periodic corrective interventions.
Automation and the evolution of net cleaning technology
The shift toward continuous net management has been enabled largely by technological advances in in-water cleaning systems.
Early net cleaning operations often relied on diver-based cleaning or manually operated remotely operated vehicles (ROVs). While effective in some applications, these systems can be labour intensive, operationally complex and dependent on highly skilled operators.
More recently, the industry has seen increasing interest in semi-autonomous and autonomous cleaning technologies designed to reduce operational complexity while increasing cleaning frequency.
One example is the development of systems such as AutoBoss, distributed in Europe by Oraseas LP. The system was designed around the concept of continuous in-water net management rather than periodic heavy cleaning operations.
Unlike traditional vessel-dependent cleaning approaches, newer autonomous systems increasingly aim to operate directly from the cage structure itself, reducing the need for large support vessels and minimising labour requirements. Some systems are now capable of following programmed cleaning paths and operating with limited operator intervention.
This evolution is important because cleaning frequency is often more critical than cleaning intensity. A lightly fouled net cleaned every seven to fourteen days generally requires significantly less energy and mechanical force than a heavily fouled net cleaned after several months.
Lower-pressure, high-frequency cleaning strategies may also reduce long-term mechanical stress on nets compared with aggressive recovery cleaning of heavily fouled cages.
Automation additionally addresses one of the major constraints facing aquaculture globally: labour availability. Many fish farming regions face increasing difficulty recruiting and retaining specialised marine equipment operators. Technologies that simplify operations and reduce dependence on highly skilled personnel are therefore becoming increasingly attractive.
Lessons from different aquaculture markets
Experience across different farming regions demonstrates that net management strategies are strongly influenced by local environmental conditions, regulatory frameworks and industry traditions.
In Norway and Scotland, regular in-water cleaning has become deeply integrated into salmon farming operations. The combination of large farm sizes, strong currents and industrial-scale logistics favoured the early adoption of dedicated net cleaning services and ROV technologies.
Mediterranean aquaculture has historically followed a different path, relying heavily on antifouling coatings and net replacement cycles. However, this model is increasingly being questioned due to rising operational costs, environmental concerns surrounding antifouling products and greater focus on fish welfare and sustainability.
Across several Mediterranean markets, there is growing interest in transitioning toward cleaner nets maintained continuously in the water. Farmers increasingly recognise that net cleanliness is not simply a maintenance issue but a core biological parameter influencing oxygen dynamics, fish behaviour and feeding efficiency.
In emerging markets such as the Middle East, where high temperatures and oxygen limitations can become critical, continuous clean-net strategies may become even more important. In these environments, maintaining maximum water exchange throughout the production cycle can directly influence farm productivity and biological risk management.
At the same time, each farming region presents unique operational realities. Exposure levels, fouling species, net types and labour structures vary widely, meaning there is no single universal solution. The trend, however, is clear: net management is becoming more integrated with overall production strategy rather than remaining an isolated maintenance function.
A changing philosophy in aquaculture
The evolution of net cleaning systems reflects a broader transformation occurring across aquaculture.
Historically, cage nets were viewed primarily as passive infrastructure requiring periodic maintenance. Increasingly, they are being recognised as active environmental interfaces that directly influence fish welfare and farm performance.
This shift changes the question from ‘How do we clean dirty nets?’ to ‘How do we continuously maintain optimal cage conditions?’
As the industry faces pressure to improve sustainability, reduce operational costs and optimise biological performance, net management strategies are likely to continue evolving rapidly.
Technologies enabling more frequent, efficient and autonomous in-water cleaning are becoming part of a larger movement toward precision aquaculture — where environmental conditions inside cages are actively managed rather than passively accepted.
In that context, clean nets are no longer simply about appearance or maintenance efficiency. They are increasingly becoming a central component of fish health, production efficiency and sustainable marine farming.
