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

Abstract

A five-week laboratory experiment was conducted
to evaluate the efficacy of plant-based substrates for
biofilm production and their effect on water quality
as well as growth and survival of freshwater prawn
Macrobrachium rosenbergii (De Man, 1879) postlarvae.
The experiment consisted of three treatments
with a control, each with three replicates following
a completely randomized design. The substrates
evaluated were dried sugarcane bagasse (T1), paddy
straw (T2) and Eichhornia (T3). Tanks without
substrates acted as control. Seven days after the
introduction of substrates at the rate of 300 g /tank,
post-larvae were stocked at 40 nos/m2. The mean
initial length and weight of the post-larvae was
10.3 mm and 0.008 g, respectively. The post-larvae
were fed with commercial pellet feed (30% protein)
at 20% of initial biomass. Results revealed
significantly higher (p<0.05) levels of total ammonia-
nitrogen, nitrite-nitrogen and nitrate-nitrogen in
the control tanks (0.07 ±.004 mg L-1; 0.03 ±.01 mg
L-1; 1.40 ±.05 mg L-1, respectively) compared to
treatment tanks. Addition of natural substrates
enhanced survival and growth of post-larvae with
highest growth recorded in paddy straw (0.15 ±0.05
g) followed by sugarcane bagasse (0.14±0.04 g) and
Eichhornia (0.10±0.01 g) treatment. The enhancement
of growth of PL in natural substrate corresponds to
the heterotrophic bacteria that are using the
substrate, probably as a food resource and as a
probiotic. Further, there was no water exchange
during the experimental period, which indicated
that the presence of a biofilm reduces the necessity of water exchange and saves water during the postlarval rearing of M. rosenbergii at this density.