Background:
Fish is a vital source of high-quality animal protein, essential nutrients, and livelihoods in developing countries, contributing significantly to food security and local economies. Fish growth performance is strongly influenced by feeding regimen, dietary protein level, nutrient utilization efficiency and growing conditions. Unlike column-feeding carps, Cirrhinus mrigala primarily feeds near the pond bottom, which may alter its interaction with suspended microbial communities and organic solids under intensive culture conditions. These species-specific dietary and habitat preferences of Cirrhinus mrigala suggest that the response to advanced aquaculture systems may differ from that of other carps, requiring targeted investigation.

Objectives:
The aim of this study was to systematically evaluate the response of Cirrhinus mrigala to growth, survival, feed utilization, and water quality in biofloc-reared fish with varying dietary protein levels. By clarifying the interactions between feeding strategies and biofloc systems in Cirrhinus mrigala, this study aims to generate new species-specific data to advance scientific understanding of efficient and sustainable biofloc-based carp production methods.

Methods:
To achieve this objective, three experimental treatment groups were established under controlled rearing conditions: (i) Cirrhinus mrigala cultured in a conventional clear-water system and fed a diet containing 25% protein; (ii) fish cultured in a control system and fed a 30% protein diet; and (iii) fish cultured in a biofloc-based system and fed a 30% protein diet. Growth performance was evaluated using standard length, fork length, total length, total weight gain, standard growth rate, and survival rate.

Results:
Fish reared in the biofloc system with a 30% protein diet exhibited significantly higher growth across all measured parameters, achieving a final total length of 13.0 cm and a biomass increase from 117.4 g to 130.9 g (specific growth rate: 11.49%), with 100% survival. In contrast, fish receiving the same protein level without biofloc showed reduced growth (final length: 12.4 cm; growth rate: 7.12%), despite equivalent survival. The lowest performance was recorded in the 25% protein clear-water treatment, which showed reduced survival (92%) and minimal growth (6.17%).

Conclusion:
These findings demonstrate, for the first time in Cirrhinus mrigala culture, that biofloc technology provides a distinct growth advantage beyond dietary protein enhancement alone, confirming a synergistic interaction between biofloc-derived microbial nutrition and formulated feeds. The results provide new experimental evidence supporting biofloc systems as a biologically efficient strategy for improving carp growth performance while potentially reducing reliance on higher protein inputs.