Monday, November 10, 2008

Brood Fish Maintenance

Culture of brood fish or care of brood fish which is called brood fish management is the essential factor or key factor for successful artificial induced breeding. The benefits of brood stock management are the availability of brooders in proper condition during the breeding season. For this the healthy stock of brood fish is specially taken care in well managed ponds for proper sexual development.

Selection of Brood fish Pond:

The size of brood fish ponds may vary from 0.5-1.0ha and with depth of 1.5m-2.0m preferably rectangular shaped ponds with uniform slope. The bottom of the pond should be compact and flat with clay-loam soil with bottom silt not exceeding 10-15cm. The pond should be with controlled pipe system for complete drainage system with proper inlet and outlet facilities. Flashing system of pond is required to provide riverine condition. The pond should be well protected with flood and draught and its should be in such condition to get sufficient wind and exposure of bright day lights for at least 6-8 hrs a day for at least 2-3 months (January-February onwards) (Nataranjan, 1984). The temperature should be moderate with 27°C - 32°C, to optimise the gonad development.

Selection of Brood Fish:

Healthy disease free breeders of Catla catla, Labeo rohita, Cirrhinus mrigala with some exotic carps of 2-4yrs of age with 1-5kg of weight are normally selected.

Sources of Brood Fish:

The brood fish are selected from different river systems, to avoid inbred species. Brooders can also be selected from selective breeding process. The better brood fish can also be selected from different farms or different lakes or reservoirs. To prevent inbreeding in a hatchery, it is necessary that fresh fish germplasm from natural sources are introduced regularly with timed periodicities. If it is not done, inbreeding depression may set in, which is apprehended to have occurred in some existing aquaculture system in India.

Stocking of Brood fish

Stocking of fish is done @ 1000-3000kg/ha with species composition of 4:3:3. That is surface feeders catla – 30 to 20 and silver carp 10 to 20, depending upon the concentration of phytoplankton. The column feeder i.e. rohu 20 and grass carp 10 with bottom feeder i.e. mrigal 20 & common carp 10. The species ratio appears to be quite proportionate in Indian tropical environment since the different niches of water bodies are fully exploited. Brood fish can be stocked in following ways also,

· Sex-wise segregation of all six species individually or sex wise stocking in individual brood fish ponds; this system will require 12 brood fish ponds.
· Segregation in following way i.e. common carps in 2 ponds, catla in 2 ponds, and others in 2 ponds needs 6 ponds.
· Segregation of catla in 2 ponds and others in 2 ponds can be done also, if the numbers of ponds are not sufficient.
The reason why catla is especially sought to be separated from rest of the species, if sufficient numbers of brood fish ponds are available, is that relatively the species shows considerable frigidity to hormonal injection due to ill understood reasons and it is believed that catla spawners need special diet such that deposition of mesenteries fat in the maturation phase dose not hinder gonad development of the species.

Fertilisation of Pond:

Initial manuring of brood fish pond is done by 3 weeks prior to stocking with cattle dung @ 20,000kg/ha or compost manure prepared from land/aquatic weeds and farm animal droppings at the ratio of 1:1 with 5% quick lime @10,000kg/ha. A prophylactic quicklime treatment @ 200kg/ha given in the pond 7 days before of manuring. Monthly dose with raw cow dung @ 2000kg/ha are given also.

Constant manuring and using heavy supplementary feed may cause repressive factor (Swingle, 1956) and this might inhibit the maturation to the point of ovulation and spawning of fishes in the captivity. Frequent changes of water (monthly, fortnightly or weekly) can reduce the chances of accumulation of metabolic wastes. Fresh ground water/canal water/rain water at the volume of 1/4th or 1/8th of the total volume of water in each operation. Sudden lowering of temperature are beneficial for maintain good health of breeders and development of this gonads.

Others Management:

Regular netting should be done to increase the D.O level in the pond water. Regular netting is helpful to exercising the fish in the pond water also. It removes the harmful gases from the pond bottom also.

Supplementary Feeding:

Supplementary food is given to the breeders with well balanced food at a fixed schedule until the water blooms appeared, when the feeding is stopped. The feeding is resumed after disappearance of the bloom.

Composition of Feeds:

· The semi-composite mixture – prepared from half-cooked rice and pulses (1:1, 50%)
· Oil cakes – 20%
· Cattle dung – 20%
· Fish Meal or Silk worm pupae
· Cooked slaughter house refuses – 10%

The food should be given in sunny days, and stopped in cloudy days. Supplementary foods with vegetative matter such as Hydrilla, Vallisneria, Najas, Utricularia, and soft young leaves of other plants are given some times as food for better results. The grass carps are always fed with vegetative matter. Thick planktons – Spirulina, Oscillatoria and Chlorella are cultured and given to the pond for silver carp. The feeding rates should be lowered with the maturity of gonads. Feeding should be stopped before a week of breeding.

Inducement:

To accelerate the gonado-somatic development, HCG (activity 30 IU/mg powder; dilution of the prepared solution 10mg/ml distilled water is administered to catla and grass carp spawners at 5mg/kg body weight at one month intervals during last week of December, January & February. Rohu & Mrigal are dealt with two doses of HCG at 4mg/kg of body weight in the last week of December and first week of February. Silver carps do not any maturation dose. The HCG administered fishes are found to attain maturity relatively faster than the non injected fishes. A fairly good percentage of brood stock achieved full maturity between last week of February & middle of March, when their first breeding can start.

Some Important Steps:

1. If the fishes appear to surface, due to depletion of oxygen, application of manure and supplementary feed should be stopped.
2. To add fresh water to the pond
3. To agitate the pond water
4. Small pieces of banana plants to scattered in the pond
5. To carry out repeated netting in the pond
6. To apply common salt @ 30-40kg/ha
7. If the snails are coming out of the pond during day time signifies that their would be severe oxygen depletion at night.

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