Nutrition - a good gut feeling about disease prevention?

Nutrition-related diseases are more common than is generally recognized because the weak condition of the fish makes them susceptible to other contagious agents, causing confusion in diagnosis. Lourens de Wet explains.

Disease is a complex interaction between the koi, the environment, and the disease-causing pathogen. These pathogens may be categorized into bacteria, fungi, parasites and viruses. A pathogen can be present on the host, but will not cause disease if the balance among these factors is well maintained. A change in any factor may disrupt the balance of the relationship, resulting in the outbreak of disease (Figure 1).

Figure 1. Host-environment-pathogenic relation

Any form of stress increases the susceptibility of koi to disease. These sources may include transport, handling, crowding, low oxygen levels, sudden drastic variations in temperature over short periods of time, elevated ammonia or suspended solid levels, and domination of small koi by larger ones. In general, any rapid change in the “normal” environment of the koi will cause stress.

Koi subjected to nutritional deficiencies or imbalances of the diet may not show obvious symptoms and the condition may go undetected. Under these circumstances, if the host is infected by secondary infection by pathogens, the situation can be misinterpreted. Thus the nutritional condition could be camouflaged and diagnosed as a disease caused by a secondary pathogen.

If there is an outbreak of disease, check for all possible stress factors and take appropriate measures to overcome the problem. Introduction of medicine without prior removal of stress factors will further complicate the problem. Get immediate help from a disease specialist or fish veterinarian to subscribe a approved therapeutic antibiotic. The administration of medication through the food is often the only practical way to treat pathogenic infections. Several important recommendations should be kept in mind when antibiotic containing food is administered to the fish:

1. An accurate diagnosis of the specific disease must be obtained before effective treatment can be expected.
2. Administer antibiotics a separate quarantine pond as it may damage or your filter flora, causing insufficient future filtration capacity.
3. It is important to keep in mind that if any strain resistance develops against a specific antibiotic, this may mean that it could be impossible in future in to treat an outbreak of disease due to a shortage in legal antibiotics. It must be ensure that the correct dosage of antibiotic is administered and that the fish eat sufficient quantities of the feed – if not, resistance will readily develop. This is especially true for the use of antibiotics for preventative disease treatment.

Feeding of sick koi is very difficult because they often do not eat well, if at all. Therefore, a good practice to follow is the weekly administration of a probiotic paste food to healthy fish to assist in preventing the occurrence of disease. It is especially beneficial to feed probiotics prior to conditions of severe stress occurrence such as handling or transport. Probiotics are organisms that, rather than killing pathogenic bacteria like antibiotics, help stimulate proliferation of desirable organisms. A probiotic is a culture of one or more microorganisms, which benefit the host by stimulating the positive properties of its natural occurring microflora in the gut. The use of a probiotic affects the composition of the gut microflora in such a way that pathogenic microorganisms such as harmful bacteria cannot practice their harmful action. A well-balanced intestinal flora blocks the way to pathogens trying to enter the body.

Lourens de Wet