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Aquatic health management in aquaculture has always faced a fundamental tension: how to maintain the well-being of organisms living in systems that are simultaneously production units and dynamic, living ecosystems. The history of inquiry into this subfield is a story of successive expansions of scale—from the individual animal to the facility, then to the surrounding ecosystem, and finally to the intersection of human, animal, and environmental health. Each expansion did not simply discard earlier approaches but narrowed, absorbed, or coexisted with them, creating a layered intellectual landscape.
The earliest formal framework for aquatic health was the Clinical Veterinary Paradigm, which imported the methods and assumptions of terrestrial veterinary medicine into the aquatic realm. Its central commitment was pathogen-centric: disease was understood as a clinical event caused by a specific infectious agent in an individual animal. Diagnosis relied on necropsy, microscopy, and culture of pathogens; treatment meant therapeutic intervention—antibiotics, antiparasitics, or disinfectants—applied directly to affected stock. This paradigm professionalized aquatic animal health by establishing diagnostic laboratories, veterinary training programs, and treatment protocols for species such as salmon, trout, and channel catfish.
Yet the Clinical Paradigm was built for a world of relatively low-density, extensive production. As aquaculture intensified in the 1970s and 1980s—larger facilities, higher stocking densities, continuous production cycles—the limitations of the individual-treatment model became acute. Diseases spread too quickly for case-by-case intervention; subclinical infections went undetected until outbreaks were underway; and therapeutic chemicals accumulated in the environment and in harvested products. The paradigm's narrow focus on the pathogen-host dyad left no conceptual room for the facility-level conditions that made outbreaks possible.
The Biosecurity and Risk Management School emerged in response to the Clinical Paradigm's inability to prevent large-scale disease losses. Rather than treating disease after it appeared, this framework reframed disease as a facility-level risk to be managed through prevention. Its core methods included quarantine protocols, disinfection of incoming water and equipment, movement controls on live animals, and risk analysis based on epidemiological surveillance. The school's most important institutional anchor was the World Organisation for Animal Health (OIE) Aquatic Animal Health Code, first developed in the 1990s, which established international standards for disease notification, import risk analysis, and compartmentalization.
The Biosecurity School did not fully replace the Clinical Paradigm; it narrowed its scope. Clinical diagnosis and treatment remained necessary for managing outbreaks that breached biosecurity barriers, but they were subordinated to a preventive logic. The two frameworks coexisted in a division of labor: biosecurity for routine prevention, clinical intervention for emergency response. However, the Biosecurity School's unit of analysis was still the facility or the production zone. It had little to say about the ecological conditions beyond the farm boundary that could drive disease emergence, nor about the human health dimensions of aquatic animal disease.
The Ecosystem Health Approach expanded the causal model of disease from a pathogen-host dyad to a host-pathogen-environment triad. Disease, in this view, was not simply the presence of a virulent agent but a symptom of ecosystem dysfunction—poor water quality, degraded habitat, nutritional stress, or disrupted microbial communities. The framework drew on ecological theory and systems thinking, emphasizing indicators of ecosystem resilience such as biodiversity, nutrient cycling, and self-purification capacity. It was particularly relevant to open-water and extensive systems—cage culture in lakes and coastal waters, pond polyculture, and integrated agriculture-aquaculture systems—where farm boundaries are porous and environmental conditions directly shape health outcomes.
The Ecosystem Health Approach coexists with the Biosecurity School rather than replacing it. Where biosecurity focuses on preventing pathogen entry, ecosystem health focuses on maintaining conditions that suppress pathogen virulence and host susceptibility. The two frameworks can be complementary: a well-managed ecosystem reduces the need for strict biosecurity, and biosecurity measures protect ecosystem health from pathogen introductions. However, they also generate tension. Ecosystem health advocates argue that excessive biosecurity—chemical disinfection, complete water exchange—can degrade the very ecological processes that support long-term health. Biosecurity proponents counter that ecosystem-level management is too diffuse and slow to prevent acute outbreaks in high-value intensive systems.
It is important to distinguish the Ecosystem Health Approach in aquatic health from the broader Ecosystem Approach to Aquaculture (EAA) at the discipline level. The EAA is a planning and governance framework for siting, scaling, and regulating aquaculture within ecosystem limits. The Ecosystem Health Approach, by contrast, is a methodological school within aquatic health that uses ecological indicators and system-level diagnosis to guide health management. The two share intellectual roots in systems ecology but operate at different scales: the EAA at the level of policy and spatial planning, the Ecosystem Health Approach at the level of farm and water-body management.
The One Health in Aquaculture framework extends the unit of analysis beyond the farm ecosystem to the human-animal-environment interface. It emerged from the recognition that aquatic animal health cannot be managed in isolation from human health and environmental health. Three cross-sectoral challenges drove this expansion. First, antimicrobial resistance (AMR): the use of antibiotics in aquaculture selects for resistant bacteria that can transfer resistance genes to human pathogens via water, food, or direct contact. Second, zoonotic pathogens: organisms such as Streptococcus iniae and Mycobacterium marinum can cause disease in both fish and humans, especially among aquaculture workers. Third, environmental contamination: therapeutic chemicals and waste from aquaculture facilities can affect wild aquatic populations and ecosystem services on which human communities depend.
One Health synthesizes elements from all three predecessor frameworks. From the Clinical Veterinary Paradigm, it retains the need for accurate diagnosis and targeted treatment, but insists that treatment decisions account for AMR risks to human medicine. From the Biosecurity School, it adopts risk analysis and surveillance, but extends them across species boundaries—monitoring not just pathogen introduction into farms but also pathogen spillover into human populations. From the Ecosystem Health Approach, it takes the host-pathogen-environment triad and adds a fourth dimension: the human social and institutional environment, including food safety regulations, occupational health standards, and global trade rules.
Today, the Ecosystem Health Approach and One Health in Aquaculture are the leading frameworks in the subfield, but they are not in full agreement. They share a commitment to multi-factorial causation, preventive management, and cross-scale thinking. Both reject the reduction of disease to a pathogen-centric clinical event. Their disagreement centers on the primary locus of intervention. Ecosystem Health advocates argue that the most effective and sustainable interventions target the ecological conditions that drive disease—improving water quality, restoring habitat complexity, and managing nutrient loads. One Health advocates, while sympathetic to ecological management, argue that the most urgent interventions target the human behaviors and institutional structures that create AMR and zoonotic risk—regulating antibiotic use, improving worker health surveillance, and strengthening food safety systems.
This disagreement becomes concrete in debates over antimicrobial use policy. Ecosystem Health proponents tend to favor a precautionary approach that minimizes all chemical inputs, including antibiotics, as a way to preserve ecosystem function. One Health proponents, while also seeking to reduce antibiotic use, are more willing to accept targeted therapeutic use when the alternative is uncontrolled disease outbreaks that could generate even greater AMR risk through prolonged environmental contamination. The two frameworks thus offer competing prescriptions for the same problem, and the choice between them depends on how one weighs ecological resilience against human health security.
The Clinical Veterinary Paradigm and the Biosecurity School remain operational in specific niches. Clinical diagnosis and treatment are still essential for managing acute outbreaks in high-value broodstock and for certifying disease-free status in international trade. Biosecurity protocols remain the standard for intensive recirculating aquaculture systems (RAS) and hatcheries, where pathogen exclusion is feasible and economically rational. Neither framework has been abandoned; both have been absorbed into the larger toolkit that the Ecosystem Health and One Health perspectives now organize. The subfield's history is not a linear replacement of old by new but a progressive layering of frameworks, each adding a new scale of analysis while preserving the practical utility of its predecessors.