Trichodina
the Details
(Posted on the NI web board, 6/19/2002, 11:06 pm)

Trichodina gets the most unfair rap of all the protozoa. All trichodina are actually commensals, meaning they benefit from the relationship with the host and (under normal circumstances) the host is not harmed. The koi is nothing more than the handy surface for hovering over and sometimes resting on. Their natural food is detritus derived from the surrounding water and the surface of the fish. It also does a good job of consuming bacteria in the water column and on the koi's slime coat. In a normal situation, trichodina never harms the fish and only occasionally attaches to the surface.

BUT if the water quality is able to support masses of these guys (DOCs again, bioreactor and BB users!) and the koi's natural resistance (endobiotics and chemicals within the slime coat) breaks down, trichodina will quickly explode in numbers. The new, non-fortified secreted slime coat that responses to their increasing numbers, seems to actually attract and encourage even larger trichodina numbers. This is their ectoparasite phase. As they feed on the layer of bacteria present they soon disrupt the living cells below. As they wear down the slime coat, the mucous cells work overtime. This dying slime coat and the unhealthy remaining and new coat, may appear gray or white in color. Frayed and worn fins appear in later stages and bacterial infections, pseudomonas and aeromonas infections, are not far behind. In fact, this part-time ectoparasite is second only to flukes in introducing opportunistic pathogenic bacteria to our koi.The exact reasons for the high degree of bacterial infection associated with an infestation are not well understood, but studies have shown that in the infestation stage, trichodina will frequently parasite even flukes in it's search for food (epithial cells and bacteria). What ever the case, this association of pathogenic bacteria with flukes and trichodina is undeniable. Whether this is the result of a general weakening and damaging of epithial cells and therefore an opening for opportunistic secondary invaders, or a more active, direct roll (such as vector,) is unknown. These dynamics can lead to stunted growth for the entire season. One study showed that young koi infested with trichodina had a 26% weight loss over a twelve month period.

Trichodina have no eggs or cysts. They simply split via binary fission, one becomes two, two becomes four, four becomes eight, etc. Trichodina have a wheel of conical projections that are known as denticles. The individual projections are called blades or thorns. As the terms imply, these "thorns" are sharp and can bite into the surface they hover over, as they are vaulted. But it is actually the entire adhesive disc that causes most of the damage to the skin.

There are MANY subspecies of trichodina that will infest a weak or very young koi. They are not limited to the gills and skin. Many species will live within the intestines, anus, urinary tract, kidney tubules, oviducts and nasal passages of carp. It is only when a koi is weakened by poor water quality and cooler water temperatures that these protozoa seem to show their dark side and gain an upper hand. As a result, trichodina are often thought of as a seasonal opportunist, seen most frequently in spring and fall.

JR

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