Fungi of the genus Branchiomyces cause the gill rot which is characteristic or branchiomycosis. The disease occurs in many species, including cyprinids and channel catfish, in the summer. Two species of Branchiomyces, namely B.sanguinis and B. demigrans, may be involved.In the beginning of the infection, the pale gills of the fish show deep red patches (figs. 9.14 and 9.15). As it progresses, necrosis of the gills sets in and the colour turns yellow-brown. Secondary infection of Saprolegnia often occurs at this time.
To prevent the infection, dense stocking of rearing facilities should be avoided, particularly during warm weather. High concentrations of organic matter in the water supply should be avoided, and clean fresh water should be provided as often as possible. Recommended curative treatment in ponds is 200 kg finely ground quicklime per hectare of pond area, maintaining pH below 9. Copper sulphate may be used at the rate of 8 kg per hectare of ponds of about 1 m depth. This may be applied in four monthly instalments of 2 or 3 kg each. Benza-lkonium chloride also can be used in one-hour baths at a concentration of 1–4 ppm. It is reported that baths of copper sulphate (1 g in 10 litres water) for 10–30 minutes will kill all the pathogens.
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