| dc.description | The giant freshwater prawn Macrobrachium rosenbergii is indigenous to the whole South
and Southeast Asia, together with the northern Australia and some Pacific islands (New,
1988). This indigenous species has been introduced initially to aquaculture in the coastal
areas and few other areas of Bangladesh in 1970s, but the farming practice expanded
widely in rice fields (gher) in Khulna, Bagherhat and Satkhira districts in the late 1980s
(Mazid, 1994) depending on naturally collected seed. It inhabits in tropical freshwater
environments and its larval development takes place in brackishwater environments (Ling
and Merican, 1961; Sandifer et al., 1975). Bangladesh enjoys an ideal environment for
this species due to her vast inland open freshwater areas and adjacent brackishwaters with
sub-tropical climate and fertile soil. | en_US |
| dc.description.abstract | A study on stimulating pond production through enhancement and linkage of the biotic food webs in the
prawn farming system was carried out at the Fisheries Field Laboratory, Bangladesh Agricultural
University, Mymensingh (1° and 3 experiment) and at Boilor Union under Trishal Upazilia of
Mymensingh district, Bangladesh (2°° experiment) during 2009 and 2010. In the first experiment, the
production performance of giant freshwater prawn Macrobrachium rosenbergii, with monosex male
tilapia Oreochromis niloticus, was evaluated in C/N controlled periphyton-based polyculture (C/N-CP)
system. The experiment had three treatments: Ctrl, CN (carbon: nitrogen 20) and CN+P (CN plus
substrate for periphyton growth) with three replications for each. Prawn (individual weight 0.23g) and
tilapia (individual weight 14.97g) were stocked at the same density of 3 m™ and 1 m”, respectively in all
treatments. Bamboo branch (mean diameter 2.8 cm and 15 branch m”) were posted vertically into the
pond bottoms as periphyton substrate. Prawns were fed twice daily with locally formulated and prepared
feed at 10% of body weight at the beginning of study (up to 30 days), and assuming 80% survival, feed
application was gradually reduced to 3% in the last month. Additionally maize flour was applied to the
water column separately as carbohydrate source for increasing the C/N ratio 20 in CN and CN+P
treatment ponds. Water quality parameters, except total alkalinity did not differ significantly (P>0.05)
among, the treatments. Both the organic matter and total heterotrophic bacterial (THB) loads in the
sediment were significantly (P<0.05) higher in treatment CN+P followed by treatment CN and Ctrl with
a significant (P<0.05) increase over time in different treatments. Periphytic biomass in terms of dry
matter and chlorophyll a values constantly decreased during the culture period. The feed conversion ratio
(FCR) was significantly (P<0.05) lower (2.02) in CN+P treatment than Ctrl (2.96) and CN (2.63)
treatments. The addition of substrates did not influence prawn and tilapia size at harvest as well as
specific growth rate (SGR), while CN ratio had influence on harvesting size and SGR of prawn. Again,
the addition of substrates improved survival of prawn by 20% from CN ratio treatment. Substrates
contributed 66% significantly (P<0.05) higher net yield of prawn resulting in 24% significantly (P<0.05)
higher combined net yield (both prawn and tilapia).In the second experiment, the comparison of
performance between hybrid Red tilapia strain (Mutant, O. niloticus x O. mossambicus ) and GIFT strain
of Nile tilapia was evaluated in C/N-CP -based prawn farming system. The experiment had two
treatments namely, TR and TG with three replications for each. Hybrid Red tilapia (individual weight
12.10 g) and GIFT tilapia stain (individual weight 11.98 g) were stocked with prawn (individual weight
2.47 g) in TR and TG treatments, respectively at the same density of prawn and tilapia followed in the
previous experiment. Management practices were same for two treatments. Water quality parameters did
not differ significantly (P>0.05) between the treatments. The abundance of total benthos and periphyton
as well as total periphytic biomass differed significantly (P<0.05) between the treatments, and among
different months with a decreasing trends (exception to some extent) over the experimental period. The
individual harvesting weight, individual weight gain, specific growth rate ((SGR, % bw d°), survival,
gross and net yield, combined gross and net yield, economic return (BCR 0,82) were significantly higher
(P<0.05) in TG than TR treatment. In the third experiment, the effects of stocking density of tilapia with
the inclusion of silver carp (Hypohthalmicthys molitrix) was evaluated in C/N-CP prawn farming system
The experiment had three treatments namely, Tyo000, T 15000 and T2900 (named according to the stocking
density of tilapia with an individual weight of 0.42g) with three replications for each. Prawn (individual
weight 5.27g) and silyer carp (individual weight 9.21g) were stocked at 30,000 and 1,250 ha”,
respectively. Management practices were same for all treatments. Water quality parameters, except
transparency and chlorophyll a did not differ significantly (P>0.05) among the treatments. The periphytic
abundance and biomass differed significantly (P<0.05) among the treatments, and even among the
different months. Although the individual ‘harvesting weight, individual weight gain, SGR “were
significantly higher (P<0.05) in Tjo000 treatment compared to T1500 and T9000 treatments, respectively,
but the gross and net yields of tilapia were significantly higher (P<0.05) in treatment T20000 followed by
T5000 and T1oo09 treatments resulting in higher combined gross and net yield of both prawn and tilapia
(16.05% and 16.92%, 32% and 33.59% from the later two treatments, respectively) with higher economic
return (BCR 0.53) during a 122 days culture period. As a whole, the study revealed that prawn, tilapia and
silver carp with a stocking density at 30,000, 20,000 and 1,250 ha", respectively was found to provide an
optimum and sustainable production as well as economic benefit in the C/N- CP based culture system. | en_US |
