A New Model of Intensive Recirculating Aquaculture
1.Introduction:
The modern model of recirculating aquaculture systems (RAS) is characterized by the purification and reuse of aquaculture wastewater through water treatment equipment. It is a multidisciplinary system that integrates principles from zoology, mechanical engineering, environmental engineering, computer control technology, and civil engineering. This innovative form of intensive aquaculture represents the convergence of advanced technology and sustainable practices.
2.Development Overview:
The Rise of RAS in Foreign Countries
The concept of factory-based recirculating aquaculture originated in the 1960s in developed European countries. Its foundational technologies stemmed from inland marine aquariums, intelligent aquarium systems, and high-density flow-through fish farming models.
The development of RAS has progressed through three major phases: pre-industrial, factory-based, and industrialized aquaculture. Today, many systems have achieved mechanization, automation, informatization, and intelligent management, marking a transition toward modern scientific fishery management.
Driven by the implementation of the EU Water Framework Directive, RAS has become a national policy priority in several European and American countries, as well as a key focus in the sustainable development of their aquaculture industries.
Technical Features and Species Diversity in Europe
Early RAS development in Europe was pioneered by the Netherlands and Denmark, focusing primarily on freshwater species such as African catfish, trout, and eel:
♢Dutch RAS systems: Typically indoor and closed-loop, optimized for African catfish and eel production.
♢Danish RAS systems: Semi-closed outdoor systems, mainly used for trout farming.
With the evolution of RAS technologies and increasing attention from industry and government, the diversity of farmed species has expanded significantly. Currently, common species cultivated in RAS include:
Atlantic salmon, tilapia, eel, trout, turbot, African catfish, halibut, and shrimp - totaling over a dozen varieties.
Deployment Scale and Industrial Integration
As of 2014, more than 360 RAS-based aquaculture facilities had been established across the United States and Europe. Among these, Norway and Canada are recognized as global leaders in RAS for salmon farming.
From 1985 to 2000, a typical European farm's production capacity for salmon fry (in terms of biomass) increased by approximately 20 times. In Scotland, salmon fry production doubled from 1996 to 2006, reaching an annual output of over 150,000 juvenile salmon.
Large multinational aquaculture corporations in Northwest Europe, Canada, and Chile have continuously acquired smaller enterprises, forming specialized and vertically integrated groups. For instance, companies in Scotland, Norway, and the Netherlands now account for over 85% of the global salmon output.
Industrial Maturity and Representative Enterprises
In Europe, more companies are embracing closed RAS technology for seedling production and full-cycle farming. Representative enterprises include:
♢Bluewater Flatfish Farm (UK)
♢France Turbot SAS (France)
♢Ecomares Marifarm GmbH (Germany)
These companies are moving toward specialization and large-scale development, gradually forming a comprehensive industrial chain that covers:
Equipment manufacturing → System integration → Commercial deployment.
This industrial evolution has laid a solid foundation for globalizing recirculating aquaculture as a sustainable, high-tech, and efficient fish farming model.
Current Status of Recirculating Aquaculture System (RAS) Equipment Development Abroad
1.Strong Industrial Foundation Enabling Advanced RAS Equipment
Relying on their highly developed industrial infrastructures, foreign countries have made significant progress in the research and development of key equipment for recirculating aquaculture systems (RAS). The performance and reliability of core farming facilities in these countries are among the best globally, supporting full-process automation and efficient system integration.
2.Leading International RAS Equipment Manufacturers
Several global companies are at the forefront of RAS facility manufacturing, each focusing on different components within the aquaculture production chain:
♢AKVA Group (Norway):
Specializes in the development and production of complete aquaculture equipment for the entire lifecycle - including fish breeding, grow-out, harvesting, and processing, as well as large-scale offshore farming vessels.
♢VAKI Aquaculture Systems (Iceland):
Focuses on supporting equipment for farm operations, such as fish pumps, grading machines, and automatic feeders.
♢HYDROTECH (Sweden):
Renowned for producing high-quality micro-screen drum filters, critical in water purification and solid waste removal within RAS setups.
3. Intelligent Feeding Systems at the Global Forefront
In the field of automated feeding technology, several companies have developed internationally leading systems that improve feed efficiency and reduce waste:
♢Fishtalk-Control by AKVA Group (Norway):
A smart feeding management platform integrating data monitoring, feeding strategy optimization, and environmental sensing.
♢Feedmaster by ETI Company (USA):
An advanced feeding control system tailored for precision aquaculture.
♢Feeding robots developed by ArvoTec (Finland):
These robots enable automated, programmable, and species-specific feeding, enhancing precision and labor efficiency.
Development of Diversified RAS Models for Fish, Shrimp, Algae, Shellfish, and Sea Cucumber
China has already established a mature and scalable RAS technology and equipment system for fish and shrimp aquaculture.
In addition, significant research and industrial practice have been carried out in the factory farming of microalgae, shellfish, and sea cucumbers:
- or unicellular algae cultivation, as well as shellfish and sea cucumber seedling production, a mature RAS technology system has been developed.
- The Institute of Oceanology, Chinese Academy of Sciences has developed closed-loop tubular photobioreactors for large-scale cultivation of Haematococcus pluvialis, and has established a complete process system for extracting astaxanthin from this algae.
- East China University of Science and Technology adopted a "heterotrophic-dilution-photoinduced continuous cultivation process" for the factory-scale high-density cultivation of Chlorella, addressing problems such as low cell density, poor growth rate, low productivity, high harvesting costs, and inconsistent product quality seen in traditional photoautotrophic methods.
For shellfish and sea cucumber seedling production:
- Technologies are relatively mature and have been applied at scale.
- However, the industry still primarily adopts flow-through factory farming models, with low levels of mechanization and automation.
- There remains considerable room for improvement in terms of facility modernization and farming model upgrades.
International Issues in the Recirculating Aquaculture System (RAS) Industry
1.High Construction Costs and Energy Consumption Are Major Challenges in RAS Models
According to related research, factory-based aquaculture systems consume more energy (electricity and fuel) and incur higher construction costs compared to traditional aquaculture models. These factors pose the greatest challenges to the sustainable development of RAS. Although RAS adopts intensive production systems that significantly reduce water and land use, the high energy consumption increases operational costs and contributes to the potential environmental and energy impacts associated with fossil fuel use.
To achieve both economic and environmental sustainability, it is essential to strike a balance between water use, waste discharge, energy consumption, and production efficiency.
Therefore, research on energy-saving and emission-reduction technologies in RAS facilities, along with the development of green and efficient new technologies and equipment, will be a key focus area for the future advancement of the RAS industry.
2.Disease Problems Hinder the Healthy Development of RAS
Disease outbreaks are one of the most critical factors affecting the healthy development of factory-based aquaculture. Infectious Salmon Anemia (ISA), caused by the ISA virus, is a severe viral disease. Its impact led to a sharp decline in Chile's Atlantic salmon production during 2009–2010. Another major disease in global salmon farming is Rainbow Trout Fry Syndrome (RTFS), caused by the cold-water bacterium Flavobacterium psychrophilum.
This Gram-negative bacterium causes necrosis in the spleen, liver, and kidneys of infected rainbow trout, leading to anorexia and abnormal swimming behavior. The disease has a high mortality rate in salmon fry and results in significant losses annually.
In shrimp aquaculture, disease issues are even more severe than those affecting fish. Common shrimp diseases include White Spot Disease (WSD), Yellow Head Disease (YHD), and many others. These diseases continue to trouble the RAS shrimp farming industry and have become major barriers to its healthy development.
Prospects: Towards Efficient, Intelligent, and Precision Aquaculture
Efficient, intelligent, and precision farming represents a key direction for the future green development of China's aquaculture industry. This evolution will involve breakthroughs in the research and development of aquaculture IoT, intelligent control systems, big data technologies, robotics, and smart equipment, integrated with recirculating aquaculture systems (RAS) designed according to the biological characteristics of cultured species.
Together, these advancements aim to build land-based, factory-style "unmanned" intelligent fish farms.
With the rapid progress of domestic water quality monitoring sensors, intelligent information processing, and IoT platforms, the application of intelligent technologies in factory-based aquaculture is becoming increasingly feasible. However, it must be emphasized that true intelligent aquaculture can only be realized by first thoroughly studying and understanding:
- the physiological conditions and behavioral characteristics of the cultured species;
- their growth patterns and energy budgets;
- the dynamics of water quality in the farming process;
- and the mechanisms for environmental regulation.
Only on this foundation can we effectively integrate IoT-based big data collection and analysis to build an aquaculture expert management system-one that combines health monitoring and evaluation of cultured organisms, farming process management, water quality control, and equipment operation. This will be essential for achieving the goals of smart aquaculture.