Biofilm developed on plant substrates enhances growth and survival of post larvae of Macrobrachium rosenbergii.

Abstract

A five-week laboratory experiment was conductedto evaluate the efficacy of plant-based substrates forbiofilm production and their effect on water qualityas well as growth and survival of freshwater prawnMacrobrachium rosenbergii (De Man, 1879) post-larvae. The experiment consisted of three treatmentswith a control, each with three replicates followinga completely randomized design. The substratesevaluated were dried sugarcane bagasse (T1), paddystraw (T2) and Eichhornia (T3). Tanks withoutsubstrates acted as control. Seven days after theintroduction of substrates at the rate of 300 g /tank,post-larvae were stocked at 40 nos/m2. The meaninitial length and weight of the post-larvae was10.3 mm and 0.008 g, respectively. The post-larvaewere fed with commercial pellet feed (30% protein)at 20% of initial biomass. Results revealedsignificantly higher (p<0.05) levels of total ammo-nia-nitrogen, nitrite-nitrogen and nitrate-nitrogen inthe control tanks (0.07 ±.004 mg L-1; 0.03 ±.01 mgL-1; 1.40 ±.05 mg L-1, respectively) compared totreatment tanks. Addition of natural substratesenhanced survival and growth of post-larvae withhighest growth recorded in paddy straw (0.15 ±0.05g) followed by sugarcane bagasse (0.14±0.04 g) andEichhornia (0.10±0.01 g) treatment. The enhancementof growth of PL in natural substrate corresponds tothe heterotrophic bacteria that are using thesubstrate, probably as a food resource and as aprobiotic. Further, there was no water exchangeduring the experimental period, which indicatedthat the presence of a biofilm reduces the necessitiy of water exchange and saves water during the post-larval rearing of M. rosenbergii at this density.