Seasonal effects of protein levels on common carp (Cyprinus carpio) body composition

This study evaluated the growth performance and feed utilisation of common carp (Cyprinus carpio) fed diets with varying protein levels across summer (June-August) and winter (December-February). During these periods, fish were acclimated to temperatures of 25.3°C in summer and 18.7°C in winter. Four dietary treatments with protein levels of 30%, 28%, 26%, and 35% were tested on 900 juvenile carp per group. Significant differences (P < 0.05-0.001) were found in daily feed consumed (DFC), total feed consumed (TFC), daily protein consumed (DPC), and total protein consumed (TPC) across treatments and seasons. Higher protein diets (28% and 35%) led to better growth in both seasons. The protein efficiency ratio (PER) and net protein utilisation (NPU) were highest at 26% protein, indicating optimal protein utilisation. Specific growth rate (SGR), metabolic growth rate (MGR), and condition factor (FCF) were significantly higher with the 28% protein diet in summer, aligning with improved feed efficiency ratio (FER) and PER. These results highlight the importance of protein optimisation for season-specific growth, driven by temperature-dependent metabolic processes, essential for sustainable carp aquaculture.