S. Jasmine
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh
M. Molina
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh
M.Y. Hossain
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh
M.A.S. Jewel
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh
F. Ahamed
The United Graduate School of Agricultural sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan
B. Fulanda
The United Graduate School of Agricultural sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan
Prawn, Growth, Macrobrachium rosenbergii, Production, Carp polyculture
Rajshahi district.
Socio-economic and Policy
Study site and experimental setup: The study was conducted over a culture period of six months during September, 2007 to February, 2008 using six 100 m2 earthen ponds located at the Merherchandi of Boalia Upazilla in Rajshahi district of northwestern Bangladesh. The preparation of the ponds was conducted as follows. The ponds were initially drained and sun dried for a fallow period of one month. The ponds were limed using calcium oxide at the rate of 250 kg ha-1, and filled up to 1.5 m depth using canal water filtered through a finemesh net at the inlet. The ponds were then left for seven days to mature, and then fertilized to enhance pond productivity, using animal manure, Urea, and Triple super phosphate (TSP) at the rate of 2500 kg ha-1, 50 kg ha-1 and 50 kg ha-1, respectively. A deep tube well was fixed to supply water using a PVC pipe to retain the water depth up to 1.5 m level. A fine synthetic net (1.0 mm mesh size) was used to fence around the ponds to prevent prawn escape. Shelters were made using dried branches of bamboo and the leaf of palm at each pond. Fingerlings of C. catla, L. rohita, C. mrigala, H. molitrix of mean weight of 28.2 g, 24.7 g, 22.3 g, 22.2 g, respectively and 5.5 g post larvae of the freshwater prawn M. rosenbergii were stocked at the beginning of September, 2006 after completion of the initial pond preparations. The experiment employed a 3×2 treatment-replicate setup as follows. Treatment (T1) was an all-carp treatment, stocked with catla, rohu, mrigal and silver at the rate of 3000 fingerlings ha-1 for catla and mrigal and 2000 fingerlings ha-1 for rohu and silver, respectively. In treatments T2 and T3, a polyculture setup was designed with varied stocking density for the catla and silver carp, at 3000 fingerlings ha-1 in treatment T2 and 2000 fingerlings ha-1, in T3. The stocking density for the freshwater prawn M. rosenbergii post larvae in treatments T2 and T3 was 15000 and 20000 ha-1, respectively. Feed preparation and feeding: The cultured species were fed on pelleted feed prepared using rice bran (50%), fish meal (20%) and mustard oil cake (30%) obtained from the Rajshahi local market. Proximate analyses of the composition of the pelleted feed confirmed the protein content as 30%. Feeding was conducted twice a day based satiation feeding, and the amount of feed consumed was checked after each feeding using feed sampling trays., and thereafter, the feeding rates adjusted accordingly. The initial feeding rate was set as 12% of body weight and gradually adjusted to 5% of body weight after several samplings as the culture period progressed. Water quality parameters: Water quality was monitored throughout the study period to ensure optimal conditions for the cultured species my routine measurements of water temperature, dissolved oxygen (DO) and pH. Dissolved oxygen was measured using a DO (DO- 5510, Lutron electronic, USA) while temperature and pH were measured using a portable meter (EC10-50050, Hach, USA) between 10:00 and 11:00 h. Prawn and fish harvesting: The total culture period was 173 days. All the ponds were harvested separately by repeated netting and complete draining, and the harvests of Catla, rohu, mrigal, silver carp and prawn from each pond were counted and weighed to get the total numbers and biomass for each pond, and the data later pooled by treatment. The sizes at harvest were assessed by measuring the total length (TL) of each individual to the nearest 0.01 cm using digital slide calipers, and whole body weight (BW) was taken on a digital balance with 0.01 g accuracy. The survival rate (%) was calculated. Economic analyses: A simple economic analysis was performed to estimate the net profit (total returns from harvest - total cost of production) and cost benefit- ratio (CBR = total benefit - total cost) from polyculture of prawn with Indian major carps and silver carp for different treatments, separately. The cost of production was based on the whole sale market prices of the inputs used during the 2006-2007 period. The cost of feed ingredients, post larvae and fingerlings of the fish species and the sale price of harvest of fish and prawn as well as the rent costs for the earthen ponds used in the study. Statistical analysis: Statistical analyses were performed using Microsoft® Excel-add-in-DDXL and GraphPad Prism 5 software. All data was checked for homogeneity of variance. Tests for normality of each group were conducted by visual assessment of histograms and box plots and confirmed with the Kolmogorov- Smirnov test. Where test for normality assumption was not met, then the nonparametric Kruskal-Wallis test was used to compare the mean value among treatments, and if it indicated significant differences, then followed by a post hoc Dunns Multiple comparison test. But in case of two treatments, Mann-Whitney U test was applied to compare the mean value. In addition, Chi-square test was used to compare the survival rate of fish and/or prawn among treatments. All statistical analyses were considered significant at 5% (P<0.05).
Our Nature (2011) 9: 61-72
Journal