Tilapia Diseases an introduction

Tilapia tolerate adverse water quality and other stressors better than most other commercial aquaculture species. Because stress and environmental quality play such important roles in the disease process, tilapia are labeled as being very "disease-resistant." This basically means that in the presence of pathogens, tilapia are the last to break with disease.

As a result, tilapia growers worldwide did not historically practice clean culture methods. Moreover, they did not generally implement the biosecurity measures that had become standard in industries that grew less disease-resistant fish such as trout and salmon. In other words, there was no apparent penalty for being careless - or so it seemed.

Ten years ago, it was generally believed that there were very few commercially significant diseases in aquaculture. This is no longer true. There are now several significant diseases in tilapia. Some are very new, while others are old foes that have come on with a new vengeance. This resurgence of disease in tilapia is most likely related to the intensification of fish culture methods globally. Tilapia are being reared at higher densities than ever before and more tilapia are being reared in recirculating systems every year. Although tilapia perform exceptionally well in recirculation systems, so do pathogens.

Once a pathogen is introduced into a recirculating system, it is nearly impossible to eradicate. Eradication of a pathogen generally involves depopulating, sterilizing, and repopulating the facility. Of course, the farmers lose all the money they had invested in the fish themselves, and even after the "sterilization," they never quite knows if they destroyed all the pathogens. And, if by some miracle the farmers survive the next seven months without revenues, while pouring money into new fish, they've lost their faithful customers. Bleak picture? - just ask any tilapia grower that suffers from Streptococcus, Trichodina, systemic Columnaris, or Aeromonas.

In order to avoid disease, one needs to consider how the pathogens reach a facility, and once there, how they overwhelm the disease resistance of tilapia. The most common means of introducing disease to a clean facility is by introducing contaminated fish. Pathogens would generally come into a facility with the fingerlings purchased from hatcheries. Once a pathogen reached the facility, it was able to multiply at a very fast rate. The recirculating systems provided an ideal environment for the pathogens to multiply - warmth, nutrient-rich water, lots of places to hide, and PLENTY OF HOSTS!

Other growers were infected when water from infected facilities came onto their premises. Dripping live-haul trucks that travel from one farm to another provide a wide variety of pathogens that are just waiting to get into a farmer's facility. The pathogens can enter a facility on the soles of employees shoes, on a live-hauler's dipnet that was used at another facility, or on the hands of a driver that is allowed to feel the temperature of a farmer's tank water. People can’t afford to live in a bubble, but by addressing the obvious routes of pathogen transfer (fish, water, employees' hands and shoes), a farmer can dramatically reduce the risk of becoming infected.

The best way to avoid disease is to buy clean fish in the first place. A farmer can further reduce his or her risk of disease by implementing the following simple methods:

    maintain good fish nutrition
    avoid over-crowding
    maintain good personal hygiene
    hand-washing with antibacterial soaps
    disinfectant foot baths
    live-haul truck disinfection
    limit visitors