Question

Gill rot disease in fishes is caused by which of the following organisms?
A. Aeromonas sp.
B. Paenibacillus polymyxa
C. Branchiomyces sanguinis
D. Bacillus subtilis

Answer 1

Hint:- Gill rot disease is known as Branchiomycosis and is an acute infection caused in the gills of fishes. It is also known as bad management disease because of its occurrence in poor quality of water.

Complete Answer:- Fishes suffer from several diseases may it be marine fishes, freshwater fishes or ornamental fishes. In gill rot disease gills get attacked by fungus which enter into them through the branchial vessels and cause vast damage to the respiratory surfaces. Major causative agents of this disease is Branchiomyces sanguinis, it grows in the blood vessels of gills arches, lamellae and filaments and Branchiomyces demigrans, it grows in the parenchymal tissues of gills. When the gills are affected by this fungus then the operculum starts to show rapid movement, gills undergo refractive necrosis, marbling appearance on the gills and anorexia.
Several factors like low oxygen levels in water, overcrowded conditions, increase in the temperature of water, overgrowth of phytoplankton and eutrophication aid in the development of this disease. After being transferred from water to the gills of fishes the fungus produces spores which stick to the gills and germinate producing hyphae. These hyphae penetrate the epithelium of gills thereby degrading/rotting them. When the temperature is suitable for the fungi it takes 2-4 days to spread and show its effects.
Signs shown by fishes infected with this disease include :
- Fishes are not active and can be easily caught by hand.
- They gather together at the place where the water moves out and after they move out with water they die.
- Gills appear red in colour.
Thus, the right option is C.

Additional Information :-
- Diagnosis of the disease can be done by observing clinical signs, microscopic observation of the gills.
- The causative agents of this disease belong to the species of non-septate and branched hyphae, which grow at 14-35°C temperature.
- These fungi are cultured on Sabouraud’s dextrose agar medium.
- Ponds having fishes with this disease are dried and treated with calcium oxide/ quicklime.

Note:- This disease is also observed in fishes that are kept in aquariums so proper sanitation and sterilisation of the aquarium should be done from time to time. Fishes with this disease should be treated with malachite green and if dead should be removed as soon as possible.