A fishery pond in Kohima district. (Morung file Photo)
Jyotish Barman and H Kalita
Rearing fish in winter months (November – January) is a difficult task. During these months the water level declines and the temperature comes down. As temperature of the surface water is colder than the bottom layers, the fish prefers to live in the bottom zone. It is advisable to keep the water depth up to 6 feet, so that the fish gets enough space for hibernating in the warmer bottom zone. In shallow waters, the whole water column becomes cold, which affects the fish and can prove fatal. With the decrease in pond water temperature, the fish become susceptible to diseases as disease affecting organisms like bacteria, virus, fungus etc. become active. Ponds in which the water quality parameters are not in the optimum range, these germs become active and attacks the fish. Affected fish will show the following symptoms.
• Fish becomes restless
• Would come to the surface to gulp air
• Erratic swimming behaviour
• Scratching the body on hard surface
• Slow movement
• Loss of appetite
• Appearance of red lesion on the body which later develops into ulcer
Due to poor water quality, the fish are highly affected by germs during winter months and may leads to huge mortality. This adversely affects the income of the fish farm. It is therefore necessary to give more importance on maintaining the productivity of the pond. Instead of waiting for the disease to occur and treating them, we should concentrate on preventing the occurrence of such diseases. For this the following management measures must be taken.
• Maintain the water quality parameters such as dissolved oxygen, pH, temperature, alkalinity, hardness etc. In optimum range. This shall provide a favourable environment for the fish to grow.
• Check the soil and water pH and apply lime accordingly
• Try to remove the bottom debris at least before the onset of winter months.
• The pond should be free from aquatic plants. If there are aquatic plants in the pond, it should be removed, so that the pond receives enough sunlight.
• Discourage the entry or bathing of animals in the pond.
• Washing of utensils and clothes in the pond should be avoided.
• The pond should not be overstocked. Maintain the recommended stocking density. If the density is high, partial harvesting should be done to reduce the density.
• Provide supplementary feed to the fish on daily basis. Do not overfeed.
• Periodically check the health status of the fish. Disease or injured fish should be dipped in 1 mg/litre potassium permanganate solution for one minute before releasing into the pond
• The fishing net should be germ free. Before operating, the net should be dipped in 1 mg/litre potash solution and after the operation it should be dipped in potash solution again and dried under sun.
• If there is occurrence of algal scam or bloom on the pond water surface, feeding and manuring should be immediately stopped till the bloom disappears.
• In winter months, the length of day and and intensity of light decreases, as a result of which oxygen levels decline in ponds due to reduced photosynthetic activity. The farmers are advised to aerate their ponds either by adding fresh water or by using aerators, especially during early hours of the day
• Since the water level declines in winter months, it is advisable to partially harvest some of the fish (weighing 700 g and above) to reduce the density. If silver carp and Grass carp are removed, Rohu and catla can grow better.
Month wise management measures to be followed during winter months
Always check the water quality. Catch some fish to check their growth status as well as health status. Before releasing into the pond, the fish should be dipped in potash solution for 1 minute. Potassium permanganate solution act as prophylactic agent and prevents the germs form affecting the injured part of the fish.
Check the pH of the water and accordingly apply lime as per the recommended dose. For one bigha pond area (120 x 120 sq ft), 10 kg Agricultural lime mixed with 1 kg turmeric powder should be applied into the pond. It acts as prophylactic agents.
If the pond water does not smell or if there is no algal bloom and there is sufficient water level (above five feet) then apply raw cow dung @ 135 kg /bigha and after seven days apply Urea @ 3.5 kg/bigha and single super phosphate @ 2.5 kg/bigha. If the water level is low, application of manure and fertilizers may be stopped.
Feed the fish daily and observe swimming behavior of the fish during morning hours. Discourage entry of birds into the pond.
In winter months, fish are under stress and may show symptoms like erratic swimming behaviour, not eating, gasping at the surface, and others, including mortalities. If such symptoms are observed, immediately stop feeding, liming and manuring. Consult an expert for remedial measures.
Occurrence of Epizootic Ulcerative Syndrome (EUS) disease is very common during winter months. To prevent occurrence of EUS, care should be taken to restrict entry of cattle, goat and birds into the pond as they may carry the germs, maintain water pH at around 8.0 steadily throughout the winter season, avoid netting as far as possible, scoop out the dead and moribund fishes and bury them at a distant place mixing with quick lime. Do not share fish harvesting net and other gears of others as they may carry the germs. Treat the pond with CIFAX @ 150 ml/bigha just before the onset of winters. Also treat the pond with potassium permanganate @ 350 - 600 g/bigha. Always consult a fishery expert for proper guidance.
While netting, some fish may get injured. Such injured fish or fish which are showing sign of disease should be dipped in 1 ppm potassium permanganate solution for 1 minute and then release into the pond.
As far as possible, try to get an idea of total amount of fish available in the pond. It is advisable to harvest the entire lot so that the pond can be drained and prepared for fish farming in the next season. However, if a farmer wish to continue stocking the fish, then try to harvest the bigger size fish for sale. This will enable the smaller one to grow fast. Also management measures as taken in December should be followed.
If we take appropriate measures as suggested above, then we can assure a good harvest at the end. Improper management may lead to outbreak of disease resulting in poor production. This adversely affects the farm profitability. Therefore, one should take utmost care to keep their farm properly managed and disease free.