Fish spawn rearing techniques – rearing ponds

Fish spawn rearing techniques – rearing ponds

• Spawn stocked in nursery ponds normally attain a length of 20-25mm in 15 days with artificial feeding, giving survival rates ranging from less than 10 % to as high as 95-100%.
• If the fry is to attain better growth and survival, it should be netted out and released in rearing ponds.
• The rearing ponds are pre-prepared more or less on the lines of the nursery ponds.
• The rearing ponds form the second phase of carp culture and are used for growing fry to fingerlings by providing more space and food so that they reach the latter size as early as possible.
• The rearing period may vary between 2 and 3 months.

5.2.1. The management of rearing ponds

The management of rearing ponds is aimed at culturing maximum number of IMC fry to fingerlings within the shortest period of time. The management includes:

(i) removal of weeds by manual/mechanical method 
(ii) eradication of predatory and weed fishes by netting and/or poisoning 
(iii) manuring with organic and inorganic fertilizers, 
(iv) stocking with carp fry in suitable combinations and ratios, 
(v) supplementary feeding and 
(vi) harvesting.

• The experiments conducted (during 1965-1967) at Pond Culture Division of CIFRI on rearing of carp fry to fingerling stage in various combinations of IMC and exotic carps, showed average survival of 76.6% (range 53.5 to 97.4%).
• The species combination consists of catla, rohu, mrigal and common carp; silver carp and grass carp; silver carp, grass carp and common carp.
• While the rate of stocking varied between 62,500 and 1,25,000 fry/ha, the number of fingerlings harvested ranges between 33,425 and 95,900/ha. 
  The production values were in the range of 1,505-3,486 kg/ha (av. 2,204 kg/ha) per 3 months.
• The CIFRI later conducted 6-month rearing experiments during 1967-1971 and obtained survival rates of 62.1- 98.0% (av. 78.2%) and gross production values 755-2,462 kg (av. 1,712 kg/ha/6 months).
• In these experiments, fry of grass carp, silver carp and common carp were stocked at 0.1-0.25 million/ha in the ratio of 4:3:3.
• The survival of silver carp was 99%, while that of grass carp was 80-98%. Zooplankton is the most preferred food of catla fry.
• The fry of rohu and mrigal accept other feeds, with silk worm pupae resulting in better growth and survival than other feeds such as mustard/groundnut oil cake/rice bran/wheat bran/soybean/prawn waste.
• A recirculatory system was developed at CIFRI, Barrackpore for carp fry rearing wherein ponds arranged in series were supplied with water passed through a biological filter by means of a pump.
• Advanced fry of catla (35mm/2.2g) and rohu (45mm/2.9g) recorded high survival of 84.4 and 96.6% and a growth of 90mm (7.0g) and 117mm (14.7g), respectively, in 32 days.

5.2.2. Rearing carp seed in pens/cages

• Carps are generally cultured up to adult size in ponds with little water exchange. The alternatives are cage and pen systems.
• These can be used for rearing larvae, fry and fingerlings.
• Cages and pens in flowing waters can enjoy an abundant supply of oxygen, flushing of metabolic wastes of the stocked fish, and nutrients from the catchment area.
• Grow out of fish in cages is well known in the Indo-Pacific region, but the rearing of fish seed in pens, located in running waters, has not been widespread.
• In India, rearing of major carp seed in pens located in the Bhavanisagar and the Tungabhadra reservoirs was carried out as early as 1978.
• Investigations on rearing of Indian major carp spawn up to fingerlings in the periphery of the Tungabhadra reservoir were carried out.

5.2.3. Rearing of carp seed in pens erected in the Tungabhadra reservoir

• Rearing of larvae in pens made from locally Tungabhadra Board which has one of the best managed and largest fish seed farms in south India. In the early 1980s, initial trials were made to establish pens in the periphery of the reservoir.
• The main objective was to nurse the delicate carp spawn in pens up to fingerling stage and then stock them in the same reservoir in order to improve the fish landings and boost the socio-economic status of fisher folk.
• Since then, the practice of raising carp spawn up to fingerlings has become well-established.
• The Tungabhadra reservoir has a maximum water area of 37,814 ha and offers vast scope for fish production. It produced 24 t in 1954-55 and 4,200 t in 1981-82 : mainly catfishes, minor carps, minnows, etc.
• With the release of pen-cultured carp fingerlings starting from 1982, the major carps, which were not formerly part of the catch, accounted for nearly 60% of the total catch in 1994.
• An ideal site for pen erection will generally have a gentle slope with red loamy soil where water remains for a period of 2-3 months between August and November. 
  The site should be will protected from wind and wave action by small hillocks surrounding the area.
• A pen is normally made up of casuarinas poles, 2 m high, fixed at intervals of about 1.2 m, enclosing an area of 2,000 to 5,000 m².
• Between the vertical poles, three horizontal rows of spilt bamboo stripes are tied to give support for the net materials.
• Close mesh (monofilament nylon fabric, 30 mesh) having a width of 1.5 m is used as the pen wall material.
• The bottom of the nylon fabric is inserted firmly into the mud and the vertical part securely tied to the poles and bamboo stripes.
• Pen preparation starts 15-20 days before the dam reaches its full level.
• After establishment of pen, the enclosure is limed, fertilized with cattle dung and treated with soap-oil emulsion.
• The water in the pen is about 1.0-1.2m deep.
• The pen is then stocked with three-day-old major carp larvae (4-5 million/ha), produced in the adjacent fish seed farm, fed thereafter with a mixture of groundnut oil cake and rice bran at a ratio of 1:1, from a boat.
• In addition, the pens are periodically manured with organic and inorganic fertilizers to sustain production of zooplankton.
• There is a basal application of 10,000 kg cow dung, 400kg urea and 100 kg superphosphate per ha, followed by repeated applications, at 10% of these rates, every two or four weeks.
• Survival to 70-80 mm fingerlings is as high as 60% after three to four months.
• Periodic sampling is done to monitor growth and adjust the feed quantity.
• The fingerlings thus grown are stocked in the same reservoirs to enhance major carp production.
• Fishing licenses are given to local residents to uplift their socio-economic status.
• Although the pen construction is simple, easy, easy, less expensive and efficient for the nursery rearing of carp fry, one drawback is the shortage of foreshore area for large-scale pen operation.

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