A study was conducted to compare the survival, production and economics of mud crab fattening in cage with fattening in encircled earthen brackishwater pond. Thirty cages of 1m (L) × 1m (W) × 0.3m (H) partitioned into 16 compartments (each 25 × 25 × 30 cm) were set in a 40 m 2 pond and another pond with same area was encircled with bamboo fence. Mud crab fattening in cage and in encircled earthen area were considered as Treatment-1 and Treatment-2, respectively with three replications each to compare the fattening system. Single adult non-gravid female crab (204.42 ± 2.58g) was stocked into each compartment of the cages and 80 crabs (204.42± 2.58g) were also stocked into earthen pond @ 2 indiv./ m 2 . The crabs were fed with chopped tilapia @ 8% of body weight twice daily. Survival rate of crab was found 93.75 ± 6.25% and 86.12 ± 2.16% respectively in cages and encircled earthen area. Significantly (P<0.05) higher total production of crab from cages (3.30±0.08 kg/m 2 ) was recorded than the encircled earthen area (0.37±0.01 kg/m 2 ). Comparative benefit-cost analysis showed that bamboo cage fattening attained higher net profit (Tk 91,630.00) than crab fattening in encircled earthen area (Tk 9,345.00) from 12 crops (12-16 days per crop) fattening period. The present study revealed that mud crab fattening using bamboo cage might be better than encircled earthen area with fencing in Bangladesh.
An experiment was conducted for a period of eight weeks under laboratory conditions to determine the effect of different salinity levels on the survival and growth of crablings of mud crab, Scylla serrata. The different salinity levels tested were: 5 ppt, 10 ppt, 15 ppt, 20 ppt and 25 ppt. The differences in growth increment in terms of body weight (BW) were significant (p<0.05) among different salinity treatments. The specific growth rate (SGR%/day) values of 2.67, 2.85, 4.07, 4.39 and 4.46 at 5 ppt, 10 ppt, 15 ppt, 20 ppt and 25 ppt, respectively were found significant (p<0.05). The survival rates of crablings were found to be the highest (47.67%) at 25 ppt and lowest (10%) at 5 ppt (p<0.05). The results indicated that increase of salinity from 5 to 25 ppt had significant effect on the survival and growth of mud crablings.
The study on socio-economic status and constraints of the fishermen engaged in Sundarbans fishing revealed that the age group of the fishermen varied between <12 to 60 years of which 31-40 year group was dominant (26.91%), Most were scheduled Muslim (73.07%) and scheduled Hindus (23.08%) where higher caste was totally absent. Main occupation was fishing by bom (88.46%) with 11-20 years of experience. Among them 61.54% were illiterate, 30.77% were primary educated. Most of the fishermen were married (75.00%), leading joint family status with large family members (5-6). Most of the fishermen had own Dingi type hand operated wooden boat, the size varied from 10.6-11.6 m. They also had nylon made, own set bag net. A section of them had no boats and nets. They caught fish 261-280 days/year (71.15%) and spent an average of 8 hours/day (65.08%). The average general catch during pick season was 111-130 kg/month provided the income of 801-900 Tk./month, but during off season the income decreased to 401-500 Tk./month. During off-season they were found to be engaged in net making, mending, repairing, boat making and repairing, daily labour, fish sale, crab and fry collection etc. Most of the poor fishermen had grown the habit of taking loan or borrowing: most often (59.62%), some often (21.15%), a bit regular (11.54%) and never (7.69%). The resourceful poor fishermen suffered from various problems like unavailability of fund, piracy and extortion, licensing complication, ownership right of boat and net, lack of organized market, ice, electricity and mechanization. They also suffered very often physically by intoxication, stomach disease and so.
Three standard microalgae species viz. Nannochloropsis oculata, Tetraselmis chui and Chaetoceros muelleri , commercially used in aquaculture in many countries, were cultured in small scale batch culture for 28 days to determine the effect of salinities (05 ppt to 30 ppt ) on the growth under laboratory conditions at Brackishwater Station of Bangladesh Fisheries Research Institute (BFRI). The BFRI microalgae culture nutrient medium, which is the modification of Guillard’s f/2 medium (Gillard & Ryther, 1962), was used as the culture medium. Nannochloropsis oculata showed maximum cell growth (345 X 104 cells /ml) at 20 ppt salinity. Tetraselmis chui showed better growth at salinities ranging from 25 ppt to 30 ppt but failed to grow at salinities from 5 to 10 ppt. The maximum cell density (458X 10 4 cells / ml) of Tetraselmis chui was observed at 30 ppt on the 24Ul day. Chaetoceros muelleri did not tolerate a salinity of 5 ppt but grew well at the salinity range of 20-30 ppt and the highest cell density (395 X 10 4 cell/ ml) of this alga was found at 25 ppt.
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