Prawn

Studies were conducted to observe the effects of different types of feeds on the gonado-somatic index (GSI) and fecundity of freshwater prawn Macrobrachium rogenbergii. Three different treatments (T1 T2 and T3) were designed with three types of feed as follows: (i) Saudi-Bangla Prawn feed 100% - T1 (ii) SaudiBangla prawn feed 50%+ local feed 50%- T2 and (iii) local feed 100%- T3. The results showed that the average value of gonado-somatic index (GSI) was 14.39, 14.35 and 14.36 and the average fecundity of M. rogenbergiiwas 99,741, 98,125 and 97,911 in T1 T2 and T3 respectively. No significant difference (p>00.5) was between gonado-somatic indices (GSI) and fecundities of M. rogenbergii among different feeding trails. The price of Saudi-Bangla prawn feed was very high (Tk. 23/kg) than the local feed (Tk. 14/kg). So, use of local feed was recommended for M. rogenbergii brood rearing.

Effects of high and low cast feed on the hatching and survival rate of freshwater prawn Macrobrachium rogenbergii larvae were observed. Three different treatments (T1, T2 and T3) were designed with three types of feeds as follows: T1, Saudi-Bangla Prawn feed 100%; T2,Saudi-Bangla prawn feed 50% + low cast feed 50%; T3, low cast feed 100%. The prawns were reared from February to May 2001 until they became mature enough to breed. The results showed that the average value of hatching rate was 90.14%, 89.69% and 89.29% and the average survival rate of larvae was 39.44%, 38.88% and 38.33% in Tl, T2 and T3 respectively. There were no significant differences (P>0.05) between hatching and survival rate of M. rogenbergii from different feeding trails. The price of Saudi-Bangla prawn feed was very high (Tk. 24/kg) than the local feed (Tk. 14/kg). So, use of local feed was recommended for M. rogenbergii brood rearing.

The aim of this study was to compare two rearing systems for freshwater prawn Macrobrachium rosenbergii: one with use of a recirculating aquaculture system with biofilters (RAS) and another with use of microbial flocs (F). Thirty postlarvae of freshwater prawn with an initial average weight of 0.13 ± 0.05 g were randomly stocked in six experimental units with 0.20 m² and volume of 50 L. The experiment lasted thirty days. Dissolved oxygen, temperature and pH were monitored daily; ammonia concentration was determined three times per week; nitrite concentration, alkalinity and hardness were measured weekly. For the formation of microbial floc, molasses was used to keep the ammonia concentrations within safe levels for prawn farming. The variables of water quality remained within the suitable range for the production of the species, except for ammonia concentrations at the F treatment, which exceeded the safe levels. At the end of the experiment, the following parameters were evaluated: survival, specific growth rate, weight gain and feed conversion rate. Differences were found only in feed conversion rate with better values on RAS treatment. The microorganisms present in the RAS and F treatment were also evaluated. The densities of rotifers, amoebas and total bacteria were higher at the F treatment although the same organisms were found at the RAS treatment. The results of this study showed the possibility of rearing M. rosenbergii in biofloc system technology.

Effects of high and low cast feed on the hatching and survival rate of freshwater prawn Macrobrachium rogenbergii larvae were observed. Three different treatments (T1, T2 and T3) were designed with three types of feeds as follows: T1, Saudi-Bangla Prawn feed 100%; T2,Saudi-Bangla prawn feed 50% + low cast feed 50%; T3, low cast feed 100%. The prawns were reared from February to May 2001 until they became mature enough to breed. The results showed that the average value of hatching rate was 90.14%, 89.69% and 89.29% and the average survival rate of larvae was 39.44%, 38.88% and 38.33% in Tl, T2 and T3 respectively. There were no significant differences (P>0.05) between hatching and survival rate of M. rogenbergii from different feeding trails. The price of Saudi-Bangla prawn feed was very high (Tk. 24/kg) than the local feed (Tk. 14/kg). So, use of local feed was recommended for M. rogenbergii brood rearing.

This study was carried out to evaluate the effect of heat and cold on the microorganisms existing in prawn. Roasting for 5 min, boiling for 10 min and storage at -18 degrees C for 10, 20 and 30 days were applied on raw prawn to study the effect of each treatment on the bacterial load. The average counts of APC (aerobic plate count) at 25 degrees C and 0 degree C, Enterobacteriaceae, Coliforms and Staphylococci were 1.3 x 10(7), 6 x 10(4), 2 x 10(2) and 3 x 10(3) organisms per gram raw prawn sample, respectively, then reduced to 10(4), 8 x 10(2), 3 x 10(3), less than 3 and 3 x 10(2) organisms per gram roasted prawn in shell, respectively. Such counts were more reduced in roasted peeled samples. Boiling reduced the average counts of APC at 25 degrees C and 0 degrees C, Enterobacteriaceae, Coliforms and Staphylococci from 8 x 10(8), 2 x 10(5) 2 x 10(7), 3 x 10 and 3 x 10(4) organisms per gram raw prawn sample to 2 x 10(5), 3 x 10(3), 2 x 10(2), less than 3 and 4 x 10(2) organisms, respectively. Concerning freezing storage, it could be observed that the average counts of APC at 25 degrees C and 0 degree C, Enterobacteriaceae, Coliforms and Staphylococci were reduced from 4 x 10(7), 5 x 10(5), 3 x 10(5), 10(3) and 3 x 10(2) organisms per gram raw sample to 5 x 10(4), 10(3), 3 x 10(2), 10 and less than 2 x 10(2) organisms per gram after freezing storage for 30 days.