Rearing Spawn to Fry

• The first step of the seed raising activity begins with the rearing of 3-4 days old spawn (5-6 mm in length) of cultivable carps in nursery pond. At this stage yolk absorption process of the hatchlings is completed and they start feeding independently from extraneous sources.
• The spawns are stocked in pre-prepared nursery ponds.
• Nursery ponds are usually smaller in size, 100-500 m2 (0.01-0.05 ha) in area with water depth 1-1.5 m.
• Seasonal earthen ponds which retain water during the monsoon season only may also be used for this purpose.

Nursery Pond Management:

The perennial nursery ponds should be subjected to specific management practices which encompasses the following steps-

Pre-stocking management

For pre-stocking management practice, the perennial ponds should be dewatered completely and the bottom should be sun dried so that the pond can be cleared off the undesirable weeds, predatory and weed fishes as well as insects and crustaceans. When complete draining is not possible, following steps need to be taken.

• Clearance of weeds
• Eradication of predatory and weed fishes

Lime should be applied according pH range.

Fertilization of pond:

• Cow dung should be applied @ 5000-6000 kg ha-1, after 7-8 days of application of lime and 15 days prior to the anticipated date of stocking by mixing with water and broadcasting all over the pond which increases the plankton production in due course for the stocked spawn.
• In nursery ponds use of inorganic fertilizers is not recommended. In lieu of only cowdung following combination may be applied @ MOC 75% + cowdung 20% + SSP 5%.
• This mixture is applied @ 1000 kg ha-1. 50% of this requirement is applied before 2-3 days of stocking of spawn and rest 50% is applied at 5-7 days interval during the rearing period depending on the level of plankton production.

Insect control in nursery pond:

• Soap oil emulsion is most commonly used for control of harmful insects like notonecta, ranatra, nepa etc. Soap-oil emulsion is a mixture of oil and soap (vegetable oil @ 56 kg ha-1 with soap @ 18 kg ha-1) used to kill primarily the air breathing insects. The mixture is prepared by slight heating and after mixing the ingredients and sprayed over the surface of the water to create an oil film covering the entire pond water surface.
• The mixture should be applied before 20-24 hours of stocking of spawn in the pond. For this a comparatively calm weather with no rain or wind is selected so that the oil film is retained for sufficient period of time to kill the air breathing insects through suffocation.
• After killing, the dead insects may be removed through netting.
• Liquid detergent may also be used in place of soap and in lieu of vegetable oil, diesel, kerosene oil or turpentine may be used. Emulsion of kerosene @ 100-200 litre ha-1 or diesel @ 75 litre ha-1 and liquid soap @ 560 ml ha-1 or detergent powder @ 2-3 kg ha-1 water area can be applied as an effective substitute.

Stocking of spawn:

• The 3-4 days old spawns are transferred from the hatchery to the nursery tanks preferably in cool morning hours.
• The stocking should be done at the rate of 30-50 lakh ha-1. However, higher densities of 10-20 million ha-1can be followed for nursery rearing in cement tanks with provision for water circulation as well as water quality maintenance.
• Though mono species rearing is basically recommended, in case of lack of sufficient number of ponds, multi-species rearing is also practised.
• For short distance transport, open container filled with sufficient water may be used, while for long distance transport polythene bags filled with water and oxygen is the most suitable option.
• At the time of stocking of seeds transported in open container, preliminary acclimatization is done by adding and mixing pond water with the water of the container for temperature adjustment.
• While in case of spawn transported in closed polythene bags, the bags before opening may be kept floated for some time in the pond water and then the spawn are released by opening the bag and allowing the seeds to swim out of the bag on their own.
• Touching or catching by hand during stocking should be avoided to minimize handling stress.

Post stocking management:

• Liming and manuring should be done during this period at scheduled rate. For supplementary feeding a mixture of finely powdered groundnut/mustard oil cake and rice bran polish, in equal proportion by weight is supplied to the spawn. In addition to this mixture of micronutrients like cobalt chloride may be added for better result.
• 'Sushama' the balanced fish feed produced by Fisheries Research Centre, Assam Agricultural University, Jorhat is one of the efficient feeds available for this purpose.
• Generally at this stage, finely grind feed is supplied through broadcasting over the pond surface commencing from the day of stocking during the morning hours and it should be stopped one day earlier to the harvesting programme.

In adverse ecological conditions, feeding should be suspended temporarily. In grass carp spawn raising programme, chopped and minced vegetations like wolffia and hydrilla may be provided as feed after 10-12 days of stocking.

Feeding schedule for raising spawn to fry stage

Harvesting of fry:

• The fry in about 15 days generally grows up to 25-30 mm in size. They are harvested with fine meshed (1.5 mm) dragnet/nursery net in the cool morning hours avoiding heavy shower or too hot days.
• Under the agro-climatic condition of Assam, a low rate of growth is observed particularly during the month of April-May, when the ambient temperature is not within the optimum range. For this reason a longer duration of around 20-25 days is needed to attain the fry stage.
• The fry produced in nursery ponds are harvested after attaining the desired length and are transferred to rearing pond to raise them up to fingerling stage, which is considered as the suitable stage for stocking in culture or grow out ponds.
• In a seed raising farm, a nursery pond can be utilized for raising of 5-6 batches of spawn to fry stage considering average culture period of 20-25days per batch. The fry stage of cultivable carps can be identified by their specific distinguishing characteristics.
• During harvesting, better to avoid creation of turbidity in pond.

Economics (For 40 lakh spawn ha-1 area per operation)

A. Capital Cost

B. Recurring Cost

Production = 20 lakh fry assuming 50% survival rate.

Revenue earned by selling fry @ Rs. 400/1000 = Rs. 8,00,000.00

Total operational cost = Rs. 2,89,250.00

Profit: Rs. 8,00,000.00 – Rs. 2,89,250.00 = Rs. 5,10,750.00

% profit over operational cost = 177% approx