3. RESULTS AND DISCUSSION

Results in terms of final average weight, percentage of survival and net production by ponds are presented in Table 3. The stocking and production data are converted to 1000 m² unit area to facilitate the comparison. Most important findings of the modified demonstration techniques are as follows:

3.1 Stocking

As against the traditional stocking rates of 40,000–140,000/1000 m² prenursed fry the modified system used only 7,750 – 18,900 fry/1000 m² and produced much higher biomass of larger fingerling of substantially higher sale value (Table 3 and 5). Appropriate application of improved system may therefore reduce unnecessary wastage of valuable carp fry resources.

3.2 Length of season

The modified system of nursery rearing was carried out also during low temperature period in September-mid December (in 1990) and from middle of January onward (in 1991), when carp nursery practices usually remain suspended in Bangladesh. The 5–7 week growth data have demonstrated that nursery rearing of various local, Chinese and mirror/common carp can be successfully carried out even during the season traditionally regarded as unsuitable for nursery activities. The results are of great significance in view of future need for year-around multispecies culture of fingerlings applying continuous stocking and harvesting techniques, and also to ensure full utilization of the nursery facilities.

3.3 Productivity of modified system

In the modified system as demonstrated, the average gross production was 120 kg/1000 m² (1200 kg/ha) within a range of 106–229 kg/1000 m² (1060–2290 kg/ha) fingerlings in 35–50 days approximately (Table 3). This rate of production in one cycle (considering the length of a cycle about 35 days) is about 4 times higher than the production under the traditional management system (90 days cycle) of large size fingerling rearing (Table 5). Productivity of this modified system (in term of gross weight) is about 10–40 % higher than productivity of management system applied for small size fingerling production in the best private farms in the country. This production is however highly dependent on daily dose of organic manure applied.

At the farmers level at least 3 crops of large size fingerling could easily be raised using this modified system. With increased management skills, raising of 4–5 crops of large size fingerling is also technically feasible. This means that the improved system has the potential for producing 5300–5500 kg of large size fingerling/ha/season (530,000–550,000 fingerling of 10 cm in average length and at least 10 g average weight). By further improvement of fertilization/feeding, production can be increased up to 9000–10500 kg/ha/season as observed in Pond no 5.2.

3.4 Growth and survival

Average individual growth of fingerling with the final individual weight is shown in Table 6. Growth of fish in modified semi-intensive fish ponds depended mainly on stocking density. To get 10 g weight fingerling, stocking of about 14/m² prenursed fry is necessary.

Average survival was 83% within the range of 60–96% in demonstration ponds (Table 3). Best survival rate of 92% was observed in silver carp (with the range of 85– 100%). Survival of grass carp was 81 % (range 41–96%), mirror/common carp 76 % (range 59–91%), mrigal 73% (range 53–94%), catla 73% (59–86%) and the shorputi 81%.

3.5 Economics of fingerling production

The economics of fingerling production has been summarized in Table 7. In working out the economics all costs have been included. The labour cost includes pond preparation, daily fertilization, feeding, watch and ward. In all the operations, seed, feed, pumping, labour and cost of money constituted the major cost elements. Seed cost alone represented 44 percent, while feed cost 22 percent of the total production cost. Taking into account of the average production of 120 kg/1000 m²/cycle (Table 3), the expenditures incurred for production of 1 kg of fingerling were about Tk.42 in modified technology (Table 7). Sale price of fingerling was Tk.67/kg, the profit over investment being Tk.25/kg (60%).

Different from management method applied by the Project, the private farmers produce prenursed fry for stocking fingerling rearing ponds in their farm, instead of purchasing stocking material. Accordingly, their expenditure for stocking material is less, only 1/3 (Tk.700 instead of Tk.2225 as seen in tables 5 & 7) of expenditure incurred in demonstration pond. Calculating the cost benefit of our fingerling production with this price of stocking material, production cost of 1 kg fingerling is Tk.27, profit over investment on production of 1 kg fingerling then being Tk.40 (148%).

TABLE 6
AVERAGE INDIVIDUAL GROWTH OF FINGERLINGS

TABLE 7
ECONOMICS OF LARGE SIZE FINGERLING PRODUCTION IN THE DEMONSTRATION PONDS*

c.   Average profit/kg = Tk.67 - Tk.42 = Tk.25 (60%)

* Data calculated in Taka/1000m2

Profit over investment of the Jessore suppliers which is about Tk.19/kg (18%) significantly lower than in the modified system developed for large size fingerling production.

3.6 Traditional contra modified system

Effect of feed and fertilization could be more meaningfully compared between ponds 3.1 and 4.1 in which all conditions (stocking dates, density, size and pond preparation) were the same except feed quality and post-stocking fertilization practice. Pond 3.1 received Type II feed with fish meal, and daily maintenance dose of manure and fertilizer. Pond 4.1 received Type I feed containing only traditional feed ingredients (i.e. mustard oil cake and rice bran) and no daily application of manure and fertilizer.

Although the fish survival rates in both ponds were quite comparable the extrapolated net biomass production in pond 3.1 was 945 kg/ha (net), nearly 43 percent higher than in pond 4.1 in which the extrapolated production was 537 kg/ha/crop. The higher production in pond 3.1 was obviously due to much higher average growth of fish and this in turn could be attributed to the effect of better feeding and fertilization.