On hikui and the importance of fresh food?

Once the “freshness” of koi food falls under suspicion it may no longer offer the nutritional guarantee that is imperative for koi health. Lourens de Wet and Hannes Uys highlight the importance of antioxidants in koi food in preventing the occurrence of disease conditions such as hikui in koi.

Hikui (“red eating disease” or “red cancer”) refers to the thickening of hi or red pigment in koi, primarily occurring in the gosanke varieties. It causes thick, light orange patches on the hi (red colour) patterns, mostly on the koi’s back. These appear as a result of a thickening of the overlying epidermal layer of the fish after weakening or inflammation of the skin caused, for instance by overexposure to sunlight (sunburn) where koi are kept in shallow ponds, in full sunlight or due to handling damage, such as netting abrasions. Furthermore, these thickenings are complicated with infection of opportunistic anaerobic bacteria that attracts minute particles of dirt floating in the water and cause them to decompose. These bacteria proliferate in ponds with low oxygen levels and attach themselves to the weakened parts of the koi’s body. Although there is a lot of controversy on whether it is actually a form of skin cancer or UV light sensitivity, fact is, it is very frustrating to see these spots appear on the best, and often the most expensive of fish, due to the fact that koi with weak hi is less prone to the disease. Besides from being a cosmetic problem, hikui may be detrimental to the health and longevity of koi.

Although a three-week topical hikui treatment may offer some relief once the condition has reached a visible stage, the only real solution lies in the prevention thereof through a combination of a fully functioning supportive immune system of the koi and optimum pond-hygiene and -DO levels. From these, especially the immune-force of the koi plays an imperative role in protecting its body from microorganism intrusion and carcinogenic (cancer forming) oxidation. Just as oxidation can cause rust and deterioration in metals, a similar type of oxidation occurs in koi, resulting in a destruction of essential body protecting components. It is ironic that the cellular activities that keep the koi’s body alive actually generate reactive oxygen molecules (free radicals) as highly destructive byproducts. These free radicals, which are produced following exposure to a number of external hazards (including UV light, pathogen invasion and pond pollutants), can cause extensive damage to the koi’s body cells and are therefore believed to contribute to some of the degenerative diseases of ageing, such as immune system decline and certain cancers. The use of synthetic antioxidants in companion animal foods has, for many years, proved to be an effective and economical method for inhibiting oxidative damage. Etoxyquin, BHA and BHT are among the widely used synthetic antioxidants with documented efficacy and safety. Nonetheless, they have fallen in disfavor with certain owners of companion animals that prefer “all natural” ingredients. This has resulted in growing use of combinations of the natural antioxidants such as sources of vitamins (i.e. ascorbic acid and alpha tocopherols), carotenoids (i.e. ß-carotene) and bioflavonoids. The latter is sourced from a variety of plants of which probably the best-known source in households is Rooibos, a leguminous shrub indigenous to the Ceder mountains of the northwestern Cape in South Africa. Its leaves and stems are used for the manufacture of rooibos tea, a popular health beverage for humans. Bioflavonoids are scavengers of active oxygen species that may adversely affect fish health. In this way bioflavonoids partly take over the function of the antioxidant vitamins and make them more available for other important body functions.

This Kohaku was valued at R25000-00 in 1998, but due to Hikui she has no more value. Note the melanin (black) pigment on the shoulder as natural healing is taking place.

Although the colour of our koi may be an indication of its nutritional and immune status, a more proactive approach towards koi keeping would be combining optimum pond conditions with the supply of a reliable immune supporting koi food. It cannot be stressed enough that it is imperative that a good quality koi food with a guaranteed supplementation of effective antioxidants should be fed daily. Moreover, that the activity of the antioxidant should not be under any suspicion and the koi owner should make sure that the food is still fresh when purchased since it might have just as well been part of a long chain of distribution, especially if it is imported. Feeding fresh food with good nutritional value will not only prevent diseases such as hikui, but also enhance the luster of our koi.

Lourens de Wet