Environmental Diseases in Fishes and their Management

      a) Acidosis and Alkalosis Disease:

• A great majority of fish live in pH 7-8
• If the pH of water goes down drastically owing to reduction of calcium salts or release of humic acids from the soil. This phenomenon known as “ACIDOSIS”.
• In acidosis condition, fish may show very rapid swimming movements and a tendency to jump out of water.
• Acidosis causes dark greyish deposits in the gills of carps, darkening of the edges and mucous secretion.
• In the event of mortalities in ponds due to acidosis. The pH must be normalized with powdered calcium carbonate and not with quicklime.
• Aquatic plants present in high densities liberate enormous quantities of oxygen during photosynthesis which is responsible for the formation of insoluble calcium carbonate from calcium bicarbonate followed by the formation of calcium oxide with the elimination of carbon dioxide. This phenomenon is known as “ALKALOSIS”.
• Excessive alkaline condition leads to the corrosion of branchial epithelium and fins. Alkalosis can be prevented by buffering the medium by means of suitable calcification.
•  Excessive plant growth in ponds should also be avoided. The lethal acid and alkaline ranges are <4.8 and >9.2 in trout, <5.0 and >10.8 in carps and <4.0 and >9.2 in perches respectively.

      b) Gas Bubble Disease:

•  When nitrogen of the water is higher than 125 percent saturation due to rapid temperature change, gas bubble disease may results and fish fry particularly, die in large numbers.
• Fish affected by this disease often swim at an angle of 45⁰ with their head pointing down.
• Presence of bubbles beneath the skin, on fins, around the eyes, in the stomach and intestine or in blood capillaries are the major symptom
• In such conditions, water should be well agitated to bring down the nitrogen saturation below 110 percent or affected fish should be transferred to other ponds.
•  Besides nitrogen, supersaturated levels of oxygen (>350 percent air saturation) have also been reported to cause gas bubble disease in fishes.

    Management  against Environmental Diseases:

• Proper sanitation by removing muck from pond bottom regularly and exposing the bottom soil to the sun.
•   During summer months, when water level in perennial pond remains at its lowest. Lime and potassium permanganate can be used in maintaining sanitation.
• Liming of ponds has become a must in maintaining sanitation in nursery, rearing and stock ponds.
• Through restricted use of manure, fertilizer and fish feed, both primary producer (algae) and primary consumer (zooplankton) need to be kept under control, or else the supersaturation or depletion of oxygen will create problems.