Ludhiana 02. Jan-2012: Being a cold blooded aquatic animal, fish needs special care during winters. With decrease in temperature, basic metabolic rate of fish declines and so does its activity, food intake and growth rate. Further, immune system of fish also becomes weak and it gets more vulnerable to attack of pathogens and serious disease outbreaks occur leading to sudden loss of stock. Dr. Meera D. Ansal, Scientist (Fisheries), College of Fisheries, GADVASU said that it is vital to take up few management practices during winters to protect your fish not only from diseases but also to keep it in good state of health for higher survival and production of fish.
During winters, temperature of surface water is colder than the bottom layers and the fish prefers to live in the bottom zone. So with the onset of winters, the farmers shall keep the water depth more than 6 feet, so that fish gets enough space for hibernating in the bottom zone. In shallow waters, the whole water column becomes cold which affects the fish and can prove fatal. 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 therefore advised to aerate their ponds either by adding fresh water regularly or by using aerators, especially during early hours of the day. Regular addition of tube well water also keeps the pond water warm. In case there are some trees (especially deciduous trees) around the pond, trim them during winters, so that direct sunlight could fall over the pond. Leaves from these trees should not be allowed to fall in the pond, as they will add to the organic load of the pond and deteriorate the water quality on decomposition. During winters, it has been observed that various fungal, bacterial and parasitic diseases like fin rot, gill rot and argulosis also appear in the fish. It shall be addressed well in time through prophylactic measures to disinfect the pond. Treat the pond with CIFAX @ 400 ml/acre. Also treat the pond with potassium permanganate @ 1-2 kg/acre or limestone @ 50-100 kg/acre.
As the feed intake of fish decreases with temperature, 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. On feeding the fish at the same rates, it remains unconsumed and accumulates at the pond bottom which deteriorates the water quality. Reducing the feeding rate will not only save on the feeding cost but also help in keeping the pond environment clean. Slowing down of fish growth during winters is a natural process and it cannot be compensated by adding more feed. Besides reducing feeding rates, it is also necessary to reduce/stop adding organic manures like cow dung, poultry droppings, pig dung etc. in the pond as during winters rate of decomposition of organic manures declines due to poor microbial activity and they keep on accumulating and can affect the water quality suddenly on the onset of summers. Production of algal blooms is another serious problem during winters as they blocks the penetration of sunlight in the water column and is a great threat to survival of fish as it may lead to extreme oxygen depletion leading to mass mortality. Algal blooms appear due to the presence of excess nutrients in the water. Hence it is also required to avoid using excessive 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 also 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.
By following the above management practices the farmers can not only save the expenditure on input costs and protect their stock from diseases, but also keep their fish in a good state of health and activity during winters leading to higher production and economic returns.
