Being a cold-blooded aquatic animal, fish needs special care during winters. Dr Meera D Ansal, scientist (fisheries), College of Fisheries, GADVASU, said this in an advisory issued on protecting fish in winter. She said, “Temperature of surface water is colder than the bottom layers, so fish prefers to live in the bottom zone.
Farmers shall keep the water depth up to six 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.
Varsity experts said, “As the day length and light intensity decreases during winters, the oxygen levels declines due to poor photosynthetic activity in the pond and the situation 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 required during continuous cloudy days in winters. In case there are trees (especially deciduous trees) around the pond, trim them during winters, so that direct sunlight falls 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 the 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.
Presence of algal blooms (rapid accumulation of algae population) is another serious problem, as they blocks the penetration of sunlight in to the water. Algal blooms appear due to the presence of excess nutrients in the water.