6.3 Management Points for Infectious Disease Prevention and Control

The diagram presented in Figure 6.5 encapsulates the interconnected factors that contribute to the emergence of disease. The depth of intertwining among the circles signifies the host’s strength; a stronger host has less interconnection. When the fish’s environment deteriorates, it can lead to unwanted combinations of microbial and host changes. Environmental shifts, such as temperature changes, can alter microbial populations and impact the host’s physiology and immune response. Being observant of changes in the host, environment, and microbial elements is necessary for fish owners and clinicians to manage disease effectively.

Microbial agents responsible for diseases encompass viruses, bacteria, fungi, and prions. However, René Dubos’ insights into the germ theory highlight that exposure to a disease agent does not guarantee infection; the susceptibility of the host is influenced by environmental or microbial changes. In the context of captive fish, identifying the source of disease often involves examining four broad categories where deficiencies give rise to infectious diseases outbreaks:

• Husbandry Practices
• Water Quality
• Nutrition
• Biosecurity

The listed categories are clear challenges for management and operations control. These fall squarely in the midst of daily activities of livestock care employees in livestock rearing facilities.

Husbandry Practices

Husbandry practices encompass various aspects of raising and keeping animals in captivity, including protection, feeding, shelter, breeding, and management. Irrespective of the type of fish facility, be it a farm, aquarium, hatchery, or research laboratory, the principles of disease and husbandry apply universally.

Water Quality

Water quality is a prime contributor to disease, particularly in overpopulated aquariums, koi ponds, research tanks, and large commercial tanks. Poor water quality often emerges from overpopulating tanks without corresponding filtration system updates. While seemingly healthy, long-standing aquariums can become hubs of disease if the biomass (fish growing bigger) outpaces  the tank’s filtration-system capacity. It’s important to differentiate this from commercial operations where healthy fish might be observed right before harvest; these scenarios usually involve fish biomass exceeding the system’s capacity for a short period. This topic is explored in more depth in the Water Quality chapter (coming soon).

Nutrition

Nutritional deficiencies can lead to disease even for experienced operators. Changes in life stages or the transition of fish from nursery to production tanks can create nutritional imbalances. Fingerlings might struggle to find food in larger spaces, and nutritional factors, such as elevated aflatoxins in feed ingredients, can drive infectious disease outbreaks. For instance, moldy feed ingredients can lead to undetected aflatoxin increases. Paying attention to feed quality and potential issues arising from weather disasters is crucial. This topic is explored in more depth in the Nutrition chapter.

Biosecurity

Biosecurity entails measures aimed at preventing pathogen intrusion into healthy livestock. Failures in biosecurity are a significant contributor to disease outbreaks and subsequent business failures. The chapter on Biosecurity elaborates on this concept, its components, and its significance.