Low pH, dissolved oxygen and high temperature induces Thelohanellus rohita (myxozoan) infestation in tropical fish, Labeo rohita (Hamilton)

In Labeo rohita, myxozoan infection is very common and here occurrence and distribution of myxozoan gill parasites were studied with an objective to evaluate the relationship between myxozoan infections with different abiotic factors. All ponds were infected with myxozoan infection. Sampling of water and fish was done fortnightly and soil sample on monthly basis for about 6 months. L. rohita is infected with the one myxozoan species Thelohanellus rohita. The first, second and third gill arches showed higher distribution of myxozoans than the fourth one. Posterior hemibranch of second gill arch was the most preferred site for parasite attachment. The mean intensity of parasite was significantly higher (p < 0.05) in the size class of 8–9 cm in comparison to the other size classes. There were profound variability in the prevalence, abundance and mean intensity of gill myxosoporeans from three ponds. During the start of the sampling, myxozoans were present in all the ponds but their intensity varied in different ponds. These may be due to the variability in the abiotic factors of individual ponds. Most importantly acidic pH, lower DO and higher temperature promote myxozoan infestation and their propagation. Low soil pH is also seen to enhance their propagation. Our data clearly highlighted that prevalence, intensity and abundance of T. rohita strongly influenced by the above environmental parameters and suggested that its life cycle is probably effected by their change; our hypothesis must be regarded as speculative as long as further detail study is not carried out.