Assessment of different grass species extracts as source of micronutrients in prawn Macrobrachium rosenbergii feeds

The present research is an attempt to screen five perennial indigenous grass species for their biochemical constituents seasonally for one year in order to determine the exact season for the harvest of the target species which will be used as feed ingredient. Among them, Cynodon dactylon has shown better result compared to other grass species and was hence incorporated as micronutrient in the formulated feed. Macrobrachium rosenbergii culture was carried out by feeding conventional and formulated feed (prepared from grass species) in tanks and ponds filled with spring water for 180 days in 2020 in the Eastern Ghats region of Koraput district, Odisha, India. Two treatments namely T₁ and T₂ having four replications each were supplied with commercial feed and formulated feed. Feeds were applied as per the body weight of prawns at 20% for the 1st month, 15% for the 2nd month, 10% for the 3rd and the 4th month, 5% for the 5th month and 2% till the end of the experiment. The water temperature, pH, dissolved oxygen, transparency, nitrate, phosphate, silicate, Chl a in the culture tanks and ponds were monitored fortnightly. ANOVA results between all the water parameters for both culture tanks and ponds showed significant variation (P < 0.05). The survival rate (77.0% ± 0.89%), daily growth rate (0.233 ± 0.05) g/day, specific growth rate (4.657% ± 1.04%) per day and condition index (2.638 ± 0.05) were found to be highest in prawns fed formulated feed. The feed conversion ratio varied from (2.03 ± 0.05) to (2.68 ± 0.04). Benefit cost ratio of field culture were 1.46 with yield of 702 kg/ha in conventional feed and 1.75 with yield of 950 kg/ha in formulated feed respectively. The study proved grass extracts to be efficient micronutrients for prawn feed which can be easily adopted in prawn production.