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Production of Murrels

The murrels are common air-breathing fishes available naturally in all types of freshwater bodies including marshy fields. They are commonly known as snakehead fish due to the elongated and cylindrical body, flattened head and anteriorly placed eyes on head. Murrels with aquaculture potential available in India are Channa striatus and Channa marulius which attain 1 kg by 6-8 months and grow in high density even in a tank of 40 m2. They feed on insects, worms and small fishes. The flesh is whitish, hard with fewer spines and good flavour, which contains more protein and less fat. Murrels are known for their nutritional and medicinal value; especially for asthma and for convalescing patients and are believed to have wound healing property due to high content of arachidonic acid, glycine and polyunsaturated fatty acids in the flesh. Murrels have immense culture potential due to its fast growth rate, hardy nature, high consumer preference, lucrative market value and their ability to withstand adverse conditions.

Channa striatus

Channa marulius

Murrels survive in drought by aestivating for months in moist mud. They can live out of water for a long period, if covered with a wet cloth. They can tolerate salinity up to 12 ppt and annual temperature variation from l50C to 350C. Though sensitive to a sudden change in pH, they can survive in both acidic (down to pH 4) and alkaline waters (up to pH 9).

Murrels attain sexual maturity within 1-2 years and breed naturally throughout the year with a peak during monsoon season. They build a trough-like nest using vegetation in shallow marginal waters. The eggs float at the surface and are kept within the circle by the parents who guard them fiercely. They are highly predatory and exhibit cannibalism during early stages. As it hooks easily, it has excellent scope in sport fishing or angling tourism. In fry stage, the murrels are treated as ornamental fish owing to its beauty.

Seed Production

Broodstock management

Pond design is same as that explained for pond farming of carp. The pond is prepared by de-siltation, bund strengthening, draining, drying, tilling, eradication of aquatic weeds, liming and manuring as explained for the major carps. Before breeding season, adult fish are procured during November-January period from farm or wild and disinfected by dip in 200 ppm formalin for 40 seconds and stocked in a pond at a density of 1-2 no/m2. It is fed thrice daily at 5% of the body weight with a mixed diet containing animal and vegetable protein sources in the ratio 4:1. The animal protein sources comprise of forage fish, prawn waste, tadpole, beef liver and silkworm pupae.

Selection of brooder

Male and female fish are identified easily by external visual examination. Male has an oval head and dark body colour, rough pectoral fin, pale vent and prominent reddish genital papillae with a pointed tip, while the female is characterized by rounded head and light body colour with a soft swollen belly, round and reddish vent and broad and blunt anal papilla with reddish dots. When it attains sexual maturity, on applying gentle pressure on the belly, the male oozes milt and the female releases eggs. Physical condition and maturity stage of fishes are checked periodically to select them for spawning.

Spawning

A pair of conditioned male and female are selected and transferred to each breeding pond. The breeding pond can be a circular (4 m diameter) or square (4x4 m) earthen pond with 1.5 m depth or circular cement cistern of 2 m diameter provided with 15 cm thick layer of soil. No need of water circulation in breeding pond as it spawns successfully in stagnant freshwater. The breeding pond is covered with grass or floating aquatic weeds like water hyacinth to one-fifth of the water surface area to stimulate spawning by providing natural environment. The fish usually prefers to lay eggs in a nest made of aquatic vegetation. There should be at least two feet of free board in breeding pond with a net covering, to avoid jumping out of fish during spawning.

Usually, the pair spawns naturally in breeding pond or can also be induced to spawn by intramuscular injection at the base of pectoral fin of female and male fish with synthetic hormone like Wova-FH @ 0.6 ml/kg and 0.4 ml/kg body weight, respectively. Before spawning, they move in pair and chase each other. Spawning begins within 16-18 hours after injection. The spawning process extends for 15-25 minutes, and the eggs laid by the female in the nest are fertilised with the milt oozed by the male. The fertilised eggs are transparent spherical, non-adhesive, golden-yellow and freely float at the centre of the nest as a thin film while the unfertilised eggs are opaque/white. The egg mass is 6-14 cm in diameter. The size of the fertilised eggs range between 1.1-1.4 mm. Fecundity is 5000-15,000/kg bodyweight. The fertilization rate is 80%.

Incubation

Usually, the egg mass is allowed to be in the breeding pond for incubation and it hatches out within 16-20 hours. The parents, especially the male, guard the hatchlings. Hatching rate is 70-95%. In certain cases, the eggs are collected with the help of plankton net and kept in FRP tanks for hatching.

Rearing of hatchling

Three days are required for the complete absorption of yolk sac and formation of mouth. By this time, the hatchling attains a size of 3.5 mm and starts to swim freely and feeds on zooplankton. As the fish exhibits intensive parental care, the hatchling is allowed to stay with the parents and fed with live zooplankton dominated by Moina up to 10 dph and later with Moina and minced trash fish for a period of 10-20 dph. The young one attains 25 mm size in 20 dph with a survival rate of 50%.

Rearing of fry

The 20 dph fry is transferred to outdoor cement cistern of 2-4 m diameter and 75 cm depth at a stocking density of 25-75 no./m2. It is fed with aquatic insects, tubifex worm, minced trash fish, prawn, chopped earthworm and powdered artificial feed (42- 44% protein) for a period of 20-30 dph and after that restricted to pelleted feed till 60 dph @ 10% of the bodyweight. Heterogeneity and cannibalism can be reduced by grading and high feeding rate. After two months, the fry attains 5-6 cm with a survival rate of 30%. Water should be completely removed after every batch of operation. Fry of each species have different colours and retain its colour up to 3 months. Fry of giant murrel has dark grey body and a lateral orange-yellow band from eye to the caudal fin while that of striped murrel has a bright red body with a reddish golden band and a dark black band from eye to the caudal fin.

Production of forage fish

Two months before the stocking of murrel, forage fishes like barb (3- 5 cm size) and tilapia (5-7 cm size) are stocked at a density of 1000 each in a seperate earthen pond of 400 m2 and it is manured with cow dung @ 500-1000 kg/ha/week to enhance plankton production for forage fish. The young-ones produced by the forage fishes are used to feed murrel.

Production of zooplankton

Moina is cultured in the same pond used for broodstock development. The pond is manured with a mixture of 300 kg groundnut oil cake, 2000 kg cow dung and 75 kg single super phosphate per ha and inoculum of Moina is poured into the pond. It is estimated that 150 kg of Moina can be collected in a day for giving to the young-ones in the rearing pond.

Health

The fry and fingerling may be affected with fin rot in the nursery. This can be controlled by giving a bath in 0.3% formalin solution for 10 minutes or till the fry and fingerlings show sign of distress.

Packing and transportation

The seeds are harvested when they attain a size of 60-80 mm. One day prior to that, feeding shall be stopped. Harvesting is done with a fine-meshed (2 mm) dragnet in cool morning hours. If the distance is less, seeds are transported in a perforated container by leaving enough space for its habitual breathing. Small amount of aquatic plants may be provided in the container to avoid fish seed from jumping out during transportation. If the distance is more, it is better to transport them in oxygen packed polythene container.

Farming in Pond

Selection of pond

Rectangular earthen pond with 0.1 ha area and 1 m depth is ideal. The sides of the pond are fenced with pole and net up to a height of 90 cm to prevent the escape of fish by jumping and crawling through moist land. If the side bund of the earthen pond is weak, it should be lined with materials like polythene sheet. At the bottom of the pond, layer of mud should not be more than 15 cm.

Preparation of pond

The pond is prepared by desiltation, bund strengthening and installation of water inlet and outlet. Draining, drying, tilling, eradication of aquatic weeds and predators, liming, and manuring are done similar to that explained for the major carps.

Water quality parameters

  • Salinity  : 0-5 ppt
  • pH         : 7.5-8.2
  • Temp     : 28-310C

Stocking

As cannibalism is high in the earlier stages, uniform-sized fingerlings having the size of 8 cm are stocked into the pond after acclimatisation at a density of 2 no./m2.

Feeding

The weaned seed is fed twice daily at 2-10% of the body weight with a formulated feed (36-45% protein). It is also fed with trash fish, prawn waste, boiled slaughterhouse waste and silkworm pupae. The details of feed requirement, feed size and protein requirement are given in Table 3.1, but it can be modified according to the plankton production, health condition and growth rate of fish at frequent interval. The daily requirement of feed quantity is calculated by multiplying the number of fish seed stocked, survival rate, average body weight and feeding rate.

Feed requirement

ABW (g) Protein content (%) Feed size (mm) Daily feeding rate (% of ABW)
<5 45 0.8 10
5-20 40 1.2 8
20-100 40 1.8 5
100-500 36 2.5 4
500-1000 36 4.0 3
>1000 32 6.0 2

Care and maintenance

Murrels are generally hardy and tolerate organic pollution in derelict waters to some extent. However, the replacement of 10% of water fortnightly is ideal. Growth assessment is carried out monthly by cast netting. Intermittent application of agricultural lime, manure and other monitoring procedures are similar to that of the major carps. Incidence of the disease is not common, but there is a possibility of infestation by ectoparasites like Lernea and Argulus.

Harvesting

If the management practices are proper, murrels attain a growth of 1 -1.5 kg within a culture period of 8-10 months. Partial harvesting is done by seining after lowering the water to 60 cm. Final harvesting is done during summer season after complete dewatering of the pond and picking them manually as the fish shows burrowing habit in the bottom mud. The fish can be kept in live condition out of water for a long time. Hence, it is transported and marketed in live state to distant markets and fetches high demand and decent price. The fish gets high market value, especially during festival seasons.

Farming in Cage

HDPE floating cage (100 m3) and GI floating cage(30 m3) are generally used for murrel farming. Site selection and cage design are similar to that explained for the Nile tilapia. Advanced fingerlings of 8-10 cm size are stocked at a density of 80 no./m3 and fed with a floating pelletted feed (36-45% protein) twice daily at 10% of the body weight initially and 2% at the final stage. Other aspects of cage farming are same to that explained for the Nile tilapia. The anticipated production is 64-80 kg/m3/crop.

Source : Department of Fisheries, Government of Kerala



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