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Pythium: The causative agent for root rot in plants, Pythium sp. are found naturally in the culture environment and impact a wide variety of plants. Symptoms include brown, rotting roots that slough off easily when disturbed (Figure 22e). Plants may appear stunted or nutrient-deficient. Different species of Pythium are prevalent at specific temperatures; however, in aquaponics they commonly appear at water temperatures above 78circF and conditions with high organic solids. Controlling temperature and implementing effective solids removal will limit Pythium sp. in an aquaponics system.

FIGURE 22e Pythium on lettuce roots.

Steps to Prevent Plant Disease

in Aquaponic Systems:

• Control temperature and humidity of the growing environment. High temperature and humidity often are the ideal environment for growth and spread of fungal and bacterial disease in plants. Particularly in a greenhouse or indoor facility, forced air ventilation and prevention of evaporation will reduce these parameters. It is also important to control these in and around the plant structure. This is accomplished through appropriate plant spacing and pruning fruiting crops with dense foliage.
• Sanitation. Implementing sanitation standard operating procedures (SSOPs) will help prevent disease outbreak in vegetable production units. Sanitizing propagation and harvesting tools and growing equipment such as rafts and NFT channels will also help prevent disease outbreak.
• Remove dead or diseased plants. Prompt removal and disposal of affected plants can help the spread of disease in the facility.
• Choose appropriate plant species. If external environmental conditions cannot be controlled, choosing resistant or appropriate varieties will save practitioners time and money.
• Seed quality and storage. Buy quality seeds and store them under refrigeration to prevent the seeds from molding and to increase germination.

Food Safety and Sanitation

Sanitation and cleanliness of an operation is critical to ensure Good Agricultural Practices (GAP) regarding food safety (Hollyer et al. 2012). This is important because as of 2018, the CDC estimated that each year, 48 million people get sick from a foodborne illness, 128,000 are hospitalized, and about 3,000 people die. If the aquaponics industry wants to become a larger part of global food production and the fresh-cut sector, it is critical to maintain a good reputation and positive public perception of food safety for both fish and plants cultured within the same system.

The largest food safety concern within aquaponics is the spread of zoonotic pathogens (E. coli, salmonella, etc.), which can be present in harmful quantities within the water. The contamination can happen from people contacting the water or from consuming plant leaves that have been in contact with the aquaponic water (Hollyer et al. 2012). Analyzing water and plant samples annually will help producers build a strong understanding of potential sources of contamination.

Prevention is the best tactic for biosecurity and food safety, which is why every aquaponics operation should have SSOPs (Sanitation Standard Operating Procedures) and follow the seven principles of HACCP (Hazard Analysis and Critical Control Point). SSOPs are written rules for food processing that