LUDHIANA: Fish needs special care during winters, being a cold-blooded animal. Dr. Meera D. Ansal, Dean, College of Fisheries, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana said that during winters farmers shall keep the pond water depth up to 6 feet to provide enough space to the fish 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 decreases during winters, oxygen levels decline due to poor photosynthetic activity in the pond. The situation further aggravates during continuous cloudy days. Hence, 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 subsequently accumulation of carbon dioxide. If the water pH falls below 7.0, add lime @ 100kg/acre in two installments.
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 also decreases with decrease in temperature in winters and hence, it is advised to reduce feeding rate gradually by 25-75% and stop feeding in the month of December. Excess feed remains unconsumed and accumulates at the pond bottom and deteriorates the water quality. Further, reduce/stop adding organic manures like cow dung, poultry droppings, pig dung etc. in the pond, which leads to accumulation of organic matter due to reduced microbial activity in winters. Protection against predatory birds also needs special care in this season.
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 use of inorganic fertilizers during winters. Algal bloom can be controlled by application of either lime @ 50-100 kg/acre or potassium permanganate (KMnO4) @ 2-3kg/acre. The farmers are advised to check the pH of water before lime application. In case it is above 8.5, they shall not use lime.
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, KMnO4 @ 1-2 kg/acre or limestone @ 50-100 kg/acre. Salt application @ 50-100 kg/acre also helps in protecting fish against disease outbreak in winters. Marketable size fish (>500g) shall be marketed during this season, so as to create enough space for next crop stocking in the month of March/April.