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3. ROLE OF AFRICAN MAGUR IN POND FISH CULTURE

Water quality requirement of African catfish is similar to that of other catfish species in egg and larvae stage (Table 2). In first phase of nursing it requires environment similar to that of carp fry (Viveen et. al., 1986; Janssen, 1987). After development of accessory repitatory organ, it can survive in extremely poor conditions from fingerling stage. Upper limits of water quality tolerance of carps is shown in Table 3 and the data on water quality in an intensive and pond culture system of African magur is compared with that. It shows that, water suitable for rearing catfish is quite different from that for carp species.

Table 2 Water quality requirement of catfish hatcheries (After Tucker, 1988 in Boyd, 1990)

Chemical and physical featureDesired level
Salinity100–8000 mg/liter
Total dissolved gases105 %
Dissolved oxygenmin. 6 mg/liter
Carbon dioxidemax. 10 mg/liter
Calcium hardnessmin. 20 mg/liter as CaCO3
Ammonia (Un-ionized)max.0.05 mg/liter
Ironmax. 0.5 mg/liter
Hydrogen sulfide0.0

Table 3 The upper limit of the water quality tolerance of carps and the prevailing water quality in a recirculated system and in a pond during African catfish rearing (After Haylor, 1989; Peteri et al. 1989)

ParametersUnitTolerance of carpsWater quality tolerated by magur
   Recirc*Pond
Salinitymg/l9–12000no data4300
pH 8.57.28.9
H2Smg/l0.00.20.4
NH4mg/l2.515.01.8
NH3mg/l0.10.20.5
NO2mg/l0.31.90.0
COD(Pot. permanganate)mg/l151848
O2mg/l4.01.7no data
Chlorophyll-amg/m380no data1942

* Recirculated system

This high tolerance of African magur makes it possible to stock it in significantly higher stocking density than any other fish species. High environmental tolerance and wide food spectrum are the main reasons why African catfish is excellent for tropical and subtropical pond fish culture (Haylor, 1989).

Though the fecundity of magur is less than that of carp broodfish, induced seed production of magur is easier. Incubation and larval rearing needs no sophisticated facilities. The simple non-sophisticated method of seed production (fingerling production in pond) is highly effective for this species.

As it develops the air breathing organ, transportation of the fish of any age group over 2 weeks is not difficult. No special equipment is necessary to keep the fish alive in the market.

Main disadvantage of the species is its high protein requirement in intensive culture. In the absence of adequate source of animal protein, only extensive culture of the species is suggested.

Important technical data relating to African magur, Tilapia and carp production are summarized for comparison in Table 4. Data are given from Woynarovich and Horvath (1980), Haylor (1989), Rana(1989).

Table 4 Relevant data on reproductive biology and rearing techniques of magur, tilapia and carps (After Haylor, 1989; Rana, 1989 and Woynarovich and Horvath, 1980)

SpeciesMagurTilapiaCarps
Maturity in nature1–3 years1–2 years1–3 years
in pond
7–10 months5–6 months1–3 years
Fecundity10–200 000200–1100300 000–1 000000
Embryonic development in 27–28°C30–35 hours90–100 hours20–45 hours
Firs food35–45 hours35–45 hours60–80 hours
Yolk absorption150–160 hours350 hours60–80 hours
Survival in pond nursing40–60 %70–90 %40–70 %
Protein requirement   
Fry50 %50 %50 %
Fingerling40 %35 %40 %
Adult25–35 %25–30 %35 %
Food conv. ratio (FCR)   
in tank0.7–1.21.4–2.20.9–1.2
in pond1.5–4.01.8–2.64.0–7.0
Growth (6 months)400–1000 g50–150 g300–1000 g
Pond production with manuring and feeding22,000
kg/ha/year
6000
kg/ha/year
4000–5000
kg/ha/year

Attempts on semi-natural and artificial seed production of African magur were first made in the middle of seventies. Micha (1975) stimulated the spawning changing the environment. He stocked 6 females and 4 males in shallow ponds with water surface area of 400m2 and increased the water depth upto 0.5 m. This was the triggering factor of spawning for broodfish collected from natural water bodies in natural breeding season.

Hogendoorn (1979) released the broodfish in pond after injection with DOCA (Desoxi-Corticosterone Acetate ) at the rate of 50 mg/kg. This work was carried out in 1975–1976. In the same year he injected females with carp pituitary glands and stripped the eggs. The males were sacrificed for removing testis. The fertilized eggs were pasted on plastic sheet and sank in pond water. Later eggs were incubated and hatched in trays and fry were reared in tanks (Hogendoorn, 1980).

Sometimes 15–17 fingerling/ m2 were produced following above mentioned methods, but usually the survival was very poor due to damage caused by aquatic insects and tadpoles.

Main limiting factor for survival of African magur fry in tank culture was the lack of quality fish food. Survival and growth was always better after feeding Artemia and zooplankton. Feeding with other feed than natural one always decreased the growth and survival in initial attempts (Hogendoorn, 1980). With a well balanced feed containing high ratio of protein (55%) Uys and Hetch (1985) got better growth compared to that of zooplankton feeding. Nowdays, for artificial reproduction of African magur, pituitary glands of market-size catfish (Viveen et al., 1986) or carp PG (Janssen, 1987) or HCG are used. The results of Chinese fish culturists showed that LHRH is not a good agent for induced breeding (Wembiao et al., 1988) of this species.

Stripping of magur females is similar to stripping of other fish species. The milt is usually collected after removing testes, though there are methods available for stripping of male fish also (Van der Waal, 1985).

Special troughs (Viveen et al. 1986, 1985; Janssen, 1987) or Zoug jars(Peteri et. al., 1989) are used for incubation. The same troughs are used for larval rearing in hatcheries.

Most accepted method of fingerling production in Africa, China and Thailand is the pond production method. Fingerlings are produced in warm water recirculation systems or in raceways supplied with warm water of power stations, in cooler areas.


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