An experiment was carried out in the backyard hatchery of Bangladesh Fisheries Research Institute (BFRI), Riverine Station, Chandpur to observe the effects of high and low-cost feeds of Macrobrachium rogenbergii broods on their hatching and survival rate. A local feed was formulated using 21% fishmeal, 45% mustard oil cake, 28% rice-bran, 5% wheat flower and 1% vitamin-mineral premix (Table la and lb). This feed contained 30% protein which similar to Saudi-Bangla prawn feed. Three Treatments were designed for feeding with three replications as follows: Treatment T1, Saudi-Bangla prawn feed 100%, Treatment T2, Saudi-Bangla prawn feed 50% and low cost feed 50% and Treatment T3, low-cost feed 100%.
The experiment was carried out in a 135 m2 pond, partitioned into nine units by bamboo fencing covered with nylon mosquito net. Average effective water depth was about 1 m. The pond was drained out and treated with lime and cowdung at the rate of 1 and 10 kg/decimal, respectively. It was then filled with underground water and fertilized at the rate of 100g urea and 75g TSP/decimal for enhancing the natural food production prior to stocking. After fertilization, prawns were released into the pond compartments.
The prawns were stocked at a density of 2/m2. The average length and weight of the prawns was 10.3±0.86 cm and 20.5±0.94 g respectively. Feeds were supplied to the prawns at 3 % of their body weight. Three types of feeds were supplied to respective treatments. The culture period was four months. The physico-chemical parameters of the plots were recorded fortnightly. Temperature was recorded by a Celsius thermometer. The pH, DO and ammonia were measured by a portable water test kit.
Determination of hatching rate Fecundity was estimated by gravimetric method. Hatching rate was calculated from the previously calculated total number of eggs (fecundity) (Ali, 2002) using the following formula:
Hatching rate = Total no. of hatched larvae / Total no. of eggs x 100
Determination of survival rate After hatching of eggs, larvae of Zoea-1 stage (New and Singholka, 1985) were transferred to the larvae rearing chari containing 12 ppt saline water. Nine cemented charis were used for rearing of larvae from three different feeding treatments. Stocking density for larvae in the chari was 60/L. Aeration was maintained in the chari continuously from a centrally connected air pump and aerator. The larvae were fed only Artemia nauplii twice a day up to 10 days. After 10 days, artificial feed (egg custard) was also fed at the rate of 30% of the body weight together with the live food. The larvae were reared up to post-larval stage (PL), when they took the shape of adult prawn and started swimming changing from backward to forward movement and changing from upside down to normal position. At the end of the experiment, all prawns were collected and counted to find out the survival rate. It was calculated as:
Survival rate (%) = No. harvested PL / No. of stocked larvae x 100
Statistical analysis
One way analysis of variance (ANOVA) was performed to determine the treatment effects. Significant differences between treatments were determined by using Duncan's multiple range test (DMRT) at 5% level of significance