The increase in biofloc in the system was provided by the development
of heterotrophic bacteria which feed on ammonia and
organic carbon from molasses and the autotrophic bacteria that
consume nitrogen compounds (e.g., ammonia and nitrite), reducing
their concentration in the water while consuming inorganic carbon
(e.g., alkalinity). This biofloc, formed by the bacterial biomass
and other microorganisms present in the medium, has substantial
nutritional value that contributed to the diet ofthe cultured shrimp
in the present study, providing a feed supplement. The results of
this work suggest that substituting high (40%) with low-protein
(30%) feed in the shrimp nursery phase in a biofloc dominated
system may provide an alternative to improve biofloc technology.
Shrimp fed the high protein diet had significantly higher SGR and
final weight than those fed the low protein diet, but there were
no significant differences in shrimp survival or PER between the
two diets. Several advantages to using the low protein feed can
be shown. Firstly better water quality, as nitrite, nitrate and phosphate
were lower in the LP30 than in the HP40 treatment; second,
feed with lower protein content is cheaper; and third the use of
lower protein feed in this system can reduce the environmental
impacts from shrimp culture, through lower protein use and water
exchange requirement.