Predisposing Factors
There is no dormant stage in the lifecycle. Ich does not lie in wait for a weakened fish to infect. However, any factor that reduces immunity like changes in water temperature and quality may, in a subclinically infected fish, accelerate an outbreak of Ich. The presence of ammonia, nitrite and high levels of nitrate in water does not in itself cause clinical cases of Ich. However, poor water quality will stress fish, allow an outbreak to spread rapidly and increase mortality rates in infected fish.
It has also been shown that other abiotic factors can increase both fish and tadpole susceptibility to ich. These factors include, decreased temperature, predatory cues and increased levels of UV-B radiation.
Read more about this topic: Ichthyophthirius Multifiliis
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