Being a cold blooded aquatic animal, fish needs special care during winters. Dr. Meera D. Ansal, College of Fisheries, GADVASU said that during winters, temperature of surface water is colder than the bottom layers and the fish prefers to live in the bottom zone. Farmers shall keep the water depth up to 6 feet, so that 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. Regular addition of tube well water at dusk helps in keeping the surface water warm.
As day length and light intensity also decreases during winters, oxygen levels declines due to poor photosynthetic activity in the pond. The situation further aggravates during continuous cloudy days. The farmers are advised to aerate their ponds either by adding fresh water or by using aerators, especially during early hours of the day. Regular monitoring of water pH is also needed during continuous cloudy days in winters, which may fall to harmful levels due to poor photosynthetic activity and hence higher carbon dioxide levels in the pond. In case there are trees (especially deciduous trees) around the pond, trim them during winters so that direct sunlight could fall over the pond and leaves do not fall in to it, as they will add to the organic load and deteriorate the water quality on decomposition. Shaded ponds are more susceptible to oxygen depletion during winters.
Feed intake of fish decreases with decrease in temperature as its digestive system becomes sluggish. Hence it is essential to reduce the feeding rate by 50-75% depending on the temperature. In case the temperature falls below 50C, it is advised to stop feeding. Excess feed remains unconsumed and accumulates at the pond bottom, which deteriorates the water quality. Farmers are further advised to use low protein diets. It is also recommended to feed your fish with high protein diets just before the onset of winters. It is also necessary to reduce/stop adding organic manures like cow dung, poultry droppings, pig dung etc. in the pond as rate of decomposition of organic manures declines due to poor microbial activity during winters. It is also advised to go for periodic raking of bottom soil (with the help of barbed wire) to prevent any suspected accumulation of toxic gases at the pond bottom.
Presence of algal blooms is another serious problem during winters as they block the penetration of sunlight in to the water. Algal blooms appear due to the presence of excess nutrients in the water. Hence it is also recommended to avoid excessive use of inorganic fertilizers during winters. Algal bloom can be controlled by application of either lime @ 50-100 kg/acre or copper sulphate @ 1-2 kg/acre. The farmers are advised to check the pH of water before lime application. In case it is above 8.5, they shall use copper sulphate to control the algal blooms.
During winters, various fungal, bacterial and parasitic diseases like fin rot, gill rot, EUS and argulosis may appear in the fish. Treat the pond with CIFAX @ 400 ml/acre just before the onset of winters. Also treat the pond with potassium permanganate @ 1-2 kg/acre or limestone @ 50-100 kg/acre. Salt application @ 100 kg/acre also helps in protecting fish against disease outbreak during winters.