ubmitted by naipagropediaraichur]
The main objective of rearing fish seeds in nursery pond is to ensure maximum survival and production of spawn to fry. At this stage, they are extremely delicate and are easily susceptible for predators. Utmost care should be taken to ensure maximum survival rate. Any small change in the physico-chemical and biological characteristics of water affects their survival and growth. A good nursery management ensures rising of a good crop of fry from hatchlings / spawn.
The occurrence of large scale mortality of spawns stocked in unprepared nurseries is a common experience. Some times there will be 90 –95 % mortality of spawns. This mortality of spawns is due to a number of factors such as wide fluctuation in the physico-chemical condition of water in the nursery pond (Depth is 1.0-1.5 m to control) Lack of adequate quality of required kind of fish food in the water.Accidental introduction of predatory fish along with carp fry.Predatory propensity of aquatic insectsPredatory nature of weed fishes, exhibits cannibalism.Over growth of phytoplankton might cause depletion of oxygen.
Management of Nursery Ponds
Popularly called as transplantation ponds.Mostly seasonal ponds constructed near spawning and rearing ponds.Should be small (0.02-0.06 ha in size) and shallow (1-1.5 m in depth)Here the hatchlings / spawn (5-6 mm) are reared to fry stage (25-30 mm) for about 15 days.Sometimes the spawn are cultured for 30 days also.Usually pond is in rectangular shape.Bottom should have gentle slope towards outlet to facilitate easy netting operations.Approximately 10 million spawn / ha are stocked in nursery ponds.
Pre Stocking Managements
Drying Up of Pond Bottom
Drying up of nursery ponds usually begins in summer itself.It helps in Mineralization of soil.Removal of organic detritus.Destruction of predators and aquatic weeds.Destruction of pathogens. Often ponds have to be desilted. Desilted earth containing rich humus matrix could be used to fill up the sides or eroded bundhs inside the nursery ponds. This helps in the manurial value of the rich superficial layer of earth and adds to the productivity of the pond. This can be used to agricultural purpose.
Dried pond bottom
Green Manuring In Pond
The growth of plants in a pond bed is a necessary to enrich the soil. This process is known as green manuring.The short term crops of the leguminous family members like peas, beans, etc., helps in enrichment of the soil with nitrogen.After the growth of the plants, the pond bed is ploughed and levelled with the roots of the plants in the soils.The nodules of these plant roots enrich the soil with nitrogen and are beneficial for enhancing pond productivity, resulting in a high survival rate and fast growth of fry.