4. DISCUSSION AND CONCLUSION

African magur grew well under various culture systems. The culture period varied from 2 to 4.3 months (Table VII and Fig.2). The fish attained marketable size of 200–300 g within 3 months. At this size range, the fish appeared most acceptable to the consumers, apparently because of its close resemblance to big size local magur (Clarias batrachus).

Production rates of African magur in all culture systems were found good and the production figures varied from 7.3 tons to 15 tons per hectare per year (Table VI, Fig. 1).

In polyculture of magur and carps in 5 ponds, magur contributed higher percentage (55.2% – 89.3%) in weight in production except in pond no.4 at Natore (Table XI). While in stocking, magur constituted the lower percentage (4%–35.7%) in weight in all ponds except at pond no.1 (50.6%) at Faridpur FTEC.

The reasons for lower survival of magur at pond no.3 (51%) and 7 (38%) (Table-VI) are difficult to identify. However, incidents of predation by birds and snakes were frequently encountered at these ponds. At pond no. 3 a water snake was found to prey on magur as large as 150 g size. Higher stocking density, smaller size of fry at stocking and the cannabalistic nature of the fingerling when hungry might have attributed to low survival rate of magur at pond 5 and 7 (Table II and VI).

TABLE-IX: TOTAL OPERATING COSTS INCURRED IN VARIOUS MAGUR PRODUCTION SYSTEMS

* Average pond rental cost estimated @Tk.2.5/m2 (Tk.3.338/bigha/year).

TABLE-X: COST-BENEFIT ANALYSIS OF MAGUR CULTURE SYSTEMS

* Two successive batches of broiler chicken reared in the same house

Wholesale price of harvested fish (Tk/kg)

TABLE XI: RELATIVE CONTRIBUTION OF MAGUR AND SURFACE FEEDING CARPS (BY WEIGHT) IN STOCKING AND HARVESTING

The concept of magur dominated polyculture, mainly using surface feeding carps like catla and silver carp, worked well. No sign of competition for food between the surface feeding carps and African magur was observed. Due to the presence of heavy organic load, dense population of phyto-and zoo-plankton developed in ponds. The surface feeders apparently transformed this “magur culture by-product” to fish protein very successfully (Table XII and Figs. 3a & b).

Even in polyculture trial with bottom feeding Mrigal, surface feeding Silver carp and Magur, showed good growth rate at Faridpur FTEC pond no.1 (Table XIII).

TABLE-XII: GROWTH RATE OF AFRICAN MAGUR AND SURFACE FEEDING CARPS

Fig.3 Growth Rate of African Magur and Surface Feeding Carps

TABLE XIII: COMPARATIVE GROWTH OF MAGUR, SILVER CARP AND MRIGAL IN THE SAME POND AT FARIDPUR FTEC

It can therefore be concluded that under the local conditions, semi-intensive African magur dominated polyculture (2–5 fish/m²) is technically feasible, and with improved management further increase in production per unit area may be possible. The suggested combinations in magur dominated polyculture system should be:
Magur : Silver carp : Catla = 90 : 7 : 3

With polyculture, chicken may also be integrated for further enhancement of fish production. In this regard, fish-cum-chicken integrated farming gives additional benefits, provided the broiler and layer operations are profitable by themselves. In such situations, parts of the chicken droppings and waste-feed are consumed directly by the African magur and the rest fertilize the pond, generating dense growth of plankton for silver carp and catla.

It was found that the waste from poultry sub-system was not enough to maintain proper growth rate of magur under semi-intensive conditions. Without supplementary feeding the size variations in the population becomes too wide, and the percentage of smaller fish increases considerably.

In monoculture, both growth rate (3.16 g – 3.76 g/day) and production (14 t/ha/yr) of magur were found better over other systems (Table VI and VII). Chief source of available protein based feed, good pond environment and better marketing outlet are the prerequisite of viable magur monoculture practice in Bangladesh. However, success of monoculture would largely depend on availability of cheap feed with high percentage of animal protein content.

In addition to 3 months of culture period, 4 more weeks are needed for harvesting, selling of fish, pond preparation and restocking. Therefore, 3 crops could easily be harvested in a year, which suggest that 8–12 tons of fish/ha/year could be produced. During peak winter months (January to mid-February) when water temperature goes down, growth rate of magur decreases considerably.

For the preparation of feed, each farm used a different composition by varying the ratios of almost similar ingredients (Table III.)

Depending on the composition of the feed, price of 1 kg of home mixed moist feed ranged from 3–8 Taka. Price variation depends on the quantity of fish meal and mustard oil cake, the two most expensive ingredients used. However, higher fish meal content did not necessarily result in better feed conversion ratio.

The idea of using slaughter house wastes/by-products has been found to be very good. These products could be collected regularly and economically. Slaughter house wastes/by-products from a village/ small town can satisfy the protein requirements of several tons of African magur production. Other agricultural by-products viz. mustard oil cake, rice polish, wheat bran, kitchen wastes etc. could easily be collected from the community.

The cost-benefit of these culture systems have been shown in terms of net profit as percentage return on operating cost (Table X). Operating cost included labour, dewatering or fish toxicant, lime, manure and fertilizer, feed, pond rental, interest on working capital etc.

The highest percentage (90.12%) of return on operating costs was achieved in African magur dominated polyculture system in Faridpur (Table X).

The poultry sub-system was profitable by itself only at Tongi FSMF with broiler raising. Egg production, both at Gachihata A.F. Ltd and Natore FSMF were not profitable.

African magur dominated polyculture showed better economic performance, 49–90% return over operating cost. Although highest production rate of 4740 kg/ha/103 days was obtained in magur monoculture in pond at Natore FSMF, the return on operating cost (8.49%) found to be lowest. This was mainly due to higher feed cost incurred by using higher quantity of fish meal in the diet. Similarly, in Jessore, feed cost was very high because high quantities of trash fish was used in the preparation of fish-feed (Table VIII and X).

The relatively high profit at Biman Poultry Complex (88.67%) was due to availability of unlimited, cheap chicken wastes as feed from their processing facilities. Such a situation could be found only in a few places in Bangladesh.

From the results of the trails described above, it could be concluded that --

1. a production rate of 8–12 t/ha/yr. could be easily achieved by rural fish farmers through 3 harvests a year, using semi-intensive magur monoculture, magur dominated polyculture or magur dominated polyculture integrated with poultry rearing;

2. magur dominated polculture with surface feeders like catla, silver carp etc. is more profitable, and a return of over 50% on operating cost could easily be achieved;

3. to ensure good growth rate, the magur feed must contain at least 30% animal protein in the form of slaughter house wastes, fish meal, etc.

4. magur culture should be carried out in areas where cheap slaughter house wastes/by-products (blood, viscera, etc.) or fish meal/trash fish are available throughout the year; and

5. magur-chicken integrated culture should be carried out only when the chicken sub-system can demonstrate its own profitability or at least its ability to break-even.