Abstract
The development of improved brood stock of freshwater prawn Macrobrachium rosenbergii (De Man 1879) through gender and feed management was studied under six experiments. In Expt-1, an assessment of the problems faced by the prawn hatcheries was carried out by survey during Aug-Oct 2011. Freshwater prawn hatcheries were randomly selected from all over the country belonging to private, GO and NGO sectors, under three production capacities, i.e. small (<3.0 million PL), medium (3.1-6.0 million PL) and large (>6.1 million PL). The survey revealed, none (0%) of the prawn hatcheries had their own brood development programme, about 73% hatcheries used natural berried females collected from different coastal rivers and 27% used broods from farmers' cultural farms beside natural broods. None of the hatcheries could reach to the target of production capacity. Most private hatcheries identified inadequate broodstock, lack of technical manpower as the major problems. Marketing channel was found weak where the PL traders mostly control the prawn seed markets. In Expt-2, a survey was carried out during Oct-Dec 2011 to evaluate the growth performance of hatchery produced post larvae (HPL) in the grow-out farm conditions. Thirty-five farms and gher (traditional prawn farms) owners from six upazilas of Bagerhat, Khulna, Jessore and Norail districts were interviewed to understand the performance of HPL in the grow-out farming system. A few numbers of farmers cultured HPL alone other than they stocked both HPL and natural post larvae (NPL) together in different proportions. About 38% farmers expressed dissatisfaction, 53% showed moderate satisfaction and 9% stated satisfaction about HPL. Expt-3 was carried out during Jul-Oct 2012, to explore the possibility of formulating as well as screening of better feed for prawn brood development. Three selected commercial feeds, treatment F1- (commercial feed Mega with Crude protein of 33.49%, Lipid 5.38%, Carbohydrate 30.31%), treatment F2 (feed SABINCO with Cp of 26.70%, Lip. 5.50%, Carb. 34.34%), treatment F3 (feed CP with Cp of 38.90%, Lip. 8.09%, Carb. 25.37%) and F4, (prepared feed with Cp of 33.00%, Lip. 11.13%, Carb. 25.43%) were fed for 120 days to NPL collected from the Kocha river. The weight of prawn at harvest were 57.99 ± 9.75 g, 56.01 ± 10.62 g, 67.00 ± 8.44 g and 47.00 ± 4.87 g in the treatments of F1, F2, F3 and F4, respectively. The SGR (%) were 3.41 ± 0.14, 3.19 ± 0.16, 3.85 ± 0.11 and 3.85 ± 0.11 and survival was estimated as 60.83 ± 4.32%, 74.16 ± 6.66%, 70.83 ± 4.16% and 64.83 ± 4.56% in F1, F2, F3 and F4, respectively. Feed F3 was found to show an apparently better performance in terms of survival and growth, and thus used to prawn brood development. In Expt 4, the reproductive performance of broodstock grown on diets F1, F2, F3 and F4 was carried out during Aprl-Sept 2013. Females, fed on commercial feed F3, was found to produce the maximum number of eggs (59,640 ± 5,270/female) followed by feed F1, with the egg numbers 53,889 ± 1,054/female. The hatchery performance of berried females was studied in the backyard prawn hatchery at Bangladesh Fisheries Research Institute, Mymensingh. The weight of berried females used in the hatchery operation were 66.67 ± 1.53g, 55.00 ± 2.83 g and 67.33 ± 3.51 g in F1, F2 and F3, respectively which were significantly different (P<0.05). The newly hatched larvae were counted to be 2,433.33 ± 40.41 L-1, 238.00 ± 4.24 L-1 and 265.00 ± 9.71 L-1 in treatments F1, F2 and F3 respectively. The total incubation period was recorded during the operation cycle, which were 27.67 ± 1.52 days, 27.00 ± 1.41 days and 28.33 ±0.58 days for F1, F2 and F3 respectively. The PL were produced at the completion of cycle between 27 to 28 days. The number of PL 35.00a + 3.00 L-1, 18.00b ± 4.24 L-1 and 10.33 ± 2.08 L-1 were obtained in treatments F1, F2 and F3 and was significantly different (P<0.05) among the treatments. Expt 5, effects of feed enriched with cod liver oil on the growth and survival of M. rosenbergii was carried out during Nov 2013-Feb 2014. The juveniles fed on cod liver oil (CLO) enriched selected diet (CP feed) were produced from the developed brood of previous Expt 4. The juveniles of an average length and weight of 8.62 ± 1.05 cm and 5.40 ± 2.13 g were cultured for 90 days in three treatments during winter period. The prawn was fed with three levels of cod liver oil added during treatment T1 0.0 ml CLO kg1, treatment T2 1.0 ml CLO kg-1 and treatment T3 3.0 ml CLO kg-1. The length of prawn at harvest was 11.85 ± 1.81 cm, 12.20 ± 1.43 cm and 11.64 ± 1.20 cm and weight was 15.28 ± 7.68 g, 16.50 ± 7.10 g and 11.63 ± 4.84 g in T1, T2 and T3 respectively. The survival rate was 36.00 ± 19.08%, 48.00 ± 10.00% and 54.67 ± 2.31%, while, the SGR (%) was estimated as 1.18 ± 0.06, 1.22 ± 0.03 and 1.11 ± 0.06 in T1, T2 and T3, respectively. The estimated male female ratio was 1.83 ± 0.76, 1.60±0.69 and 1.27 ± 0.44 in T1, T2 and T3 respectively. The treatment T2, fed with 1.0 ml Cod Liver Oil kg-1 feed showed a comparatively better performance in respect of growth and SGR %. Expt 6, performance of broodstock in four sex ratios of male : female (natural selection, 1:1, 1:2 & 1:3) was carried out during Nov 2013-May 2014 to understand the performance of brood stock stocking in natural and manipulated sex ratios. The juvenile of male (10.50 ± 1.29 cm, 15.60 ± 2.89 g) and females (8.02 ± 0.82 cm; 3.60 ± 1.05 g) were stocked at ratio 1:1, 1:2 and 1:3 and natural selection in the treatments T1, T2, and T3 respectively, except T4 and fed with CP feed. After rearing for 210 days, the berried females were 39.00 ± 1.4 g, 35.00 ± 11.35 g and 58.00 ± 11.31g in T1, T2 and T4, respectively. The number of eggs was obtained 28,000 ± 3535, 28,333 ± 9292 and 32,500 + 7778 in T1, T2 and T4, respectively, but no berried females in the treatment T3 during the period of investigation. The egg numbers did not differ significantly (P>0.05) among the treatments. The injured males and females increased with the increasing number of males. The research revealed the existing struggles of the prawn hatcheries along the lack of trained technical hands. Quality brood was identified as an urgent need. Policy should be adopted to short the PL supply chain. The responses of the prawn farmers towards the use of hatchery produced PL have been understood well. The development of prawn broodstock through gender and feed management in favour of prawn production is highly potential.