Biosecurity Practices: Part 2

Essential Considerations for the Pet Fish Industry:
Pathogen Exclusion

Words of a Wet Vet - Dr Tim Miller-Morgan

This post is really aimed at the retailer but the basic principles can be applied in all segments of the industry. Again, the specific approaches to biosecurity  must be tailored to the actual risks, needs and capability of each facility. TMM

The goal of pathogen exclusion is to prevent the entrance of an infectious agent into a facility, thereby preventing infection and possibly disease in a group of fish.  To accomplish this,

you must recognize and understand the various routes by which an infectious agent can enter a pristine fish tank or pond. This allows you to plan defensive measures that will block that entry.

Fish-associated entry:

An obvious route of entry of pathogens into a facility is via the incoming fish. These animals may be asympotmatic carriers of a pathogen, or may have frank disease. It can be very difficult to determine if one is receiving healthy fish, and rarely can a manager be totally confident that the fish he has received are in fact healthy. To help minimize opportunities for diseased fish to enter a facility, owners/managers must scrutinize potential suppliers before fish are purchased or shipped.

Water-associated entry:

The presence and persistence of pathogens in water makes this medium a potential source of pathogen entry into a fish facility.  Water supply is a major consideration when designing a biosecurity program based upon pathogen exclusion.

Food-associated entry:

Fish food can not only serve as a source of pathogens, but poor, contaminated or spoiled diets can compromise the fish and make them more susceptible to infection by pathogens.  In most cases, good quality commercial diets will satisfy the basic nutritional requirements of ornamental fish, and are unlikely to host infectious agents.  As with fish suppliers, one should consider reputation and history of service when selecting food suppliers.  The food should be carefully inspected to ensure that there is no spoilage.  Live foods deserve special consideration as there is a higher potential for harboring pathogens, and caution is warranted.  Pre-treatment or quarantine of the live food animals may be considered.

Person-associated entry:

The people that enter a facility, whether staff or customers, should be considered in a biosecurity plan as they can be a source of pathogen introduction as well as pathogen persistence.  Obviously, these people cannot be excluded from the facility, but the risks they pose can be managed.

Quarantine to prevent pathogen entry

Quarantine is critical to preventing introduction of pathogens into a facility. Quarantine also provides for the important process of acclimation of fish to new water conditions, new husbandry protocols, and new feeds.  Furthermore, the quarantine system and quarantine period allows time for the fish immune system to recuperate from the stresses of transport and handling.

All new fish that arrive at a facility should be quarantined.  Fish from separate sources should be quarantined separately. Additionally, any fish that have had contact with fish or water from other facilities, that are wild-caught or farm-raised, or have been returned to the facility by customers should also be quarantined before they are mixed with holding or display stock. Finally, many plants and invertebrates are capable of carrying potential fish disease agents including intermediate stages of many common fish parasites. Therefore it is wise to quarantine all plants and invertebrates in separate quarantine systems.

Quarantine Facilities and Systems

A quarantine facility should be distinct from the retail, wholesale, or import facility.  It can be located in a separate building or within a room adjacent to the main fish holding area, physically separated by a closed door and footbath.  Quarantine facilities should have designated equipment that is not used outside the quarantine area. Access to this facility is restricted to those employees assigned to this work area.  The restricted access to the quarantine area should be clearly emphasized by appropriate and well-placed signage, limiting access to those properly trained and authorized to be in that area.

Figure 1. illustrates the features of a quarantine system as well as the recommended movement of fish through the ornamental fish facility.



Figure 1. Recommended flow of fish through a quarantine facility at an ornamental fish retail establishment. The figure reiterates some of the important questions and issues a facility manager must consider in order to prevent disease introduction and propagation within a facility. These same considerations would be generally applicable within any ornamental fish enterprise.

The duration of quarantine is generally based upon the life-cycle of the most common disease organisms found in the fish species of interest. A quarantine period of 2-4 weeks at the optimal temperature is often recommended. The authors generally recommend a 4-week quarantine as a minimum for most species of fish, although many veterinarians would recommend 60-90 days of quarantine for many cool-water pond fish. However, this duration may not be practical for many businesses.  If a retailer is unable to complete recommended quarantine periods, they should strongly urge their customers to establish their own quarantine in the above fashion for the recommended period of time.

As the fish progress through the quarantine period, diseases may emerge, and treatment rather than culling of the affected fish may be considered. During quarantine fish must be examined daily. Dead or sick fish should be promptly culled and examined by trained staff or veterinarians to identify the cause of death or illness so that corrective and preventative measures and/or treatments can be started. When possible routine health monitoring of apparently healthy fish may be considered to identify emerging disease issues within a facility before they become a serious problem. Such monitoring may include: physical examination, skin scrapes, gill biopsies, fecal examinations, bacteriology, serology, molecular diagnostics and/or necropsy depending on the species and potential disease risks.

Your comments are always welcome. I’d be particularly interested in comments/experiences about implementing pathogen exclusion approaches at large import and/or production facilities.  In the next post I’ll discuss the principles of pathogen containment. TMM