Impact of lipids modulation on growth, histology, structural integrity, and thermo-biochemical profile of Cyprinus...

The preparation and formulation of larval diet to meet the nutritional requirements of fish is crucial to enhance growth at advanced phases of life. A 56-day growth assessment experiment was conducted in triplicate to find suitable amount of fish oil incorporation for Cyprinus carpio postlarvae. Four nanosized feeds with equal nitrogen content (40%) were formulated by graded lipids incorporations, L3 (3%), L6 (6%), L9 (9%), and L12 (12%). These diets were fed to four separate groups of C. carpio. Following the trial, key parameters including growth performance, gills histology, structural stability (Fourier transform infrared spectroscopy), and thermo-biochemical (thermogravimetric analysis) profile of common carp were assessed. The results indicated that there was no marked distinction in survival rate of four dietary groups. But lipid incorporation had a marked impact on final weight, weight gain, and specific growth rate of fish across all treatment groups. Post hoc test revealed that the L12 group, which received the highest lipid level, achieved the highest growth performance, followed by L9 and L6 groups. The lowest growth was observed in the L3 group. Gills histological analysis showed mild to moderate tissue alterations in gill structures at suboptimal lipid levels, indicating stress and potential physiological compromise. The FTIR spectra for fish feed and muscles were in the approximate wavenumber ranges of 3300 to 2800 and 1750 to 500 cm^-1 respectively and confirmed significant variations in protein and lipid profiles. Differential scanning calorimetry analyses revealed that feeds with higher lipid content showed altered thermal stability, with Diet L3 and L6 displaying greater resistance to thermal degradation, suggesting denser, more stable formulations. DSC for fish muscle showed that L3 retained the highest residual mass (28.90% at 665.23 °C), indicating greater thermal stability, possibly due to a denser protein matrix and lower lipid interference. While L6 exhibited the lowest residue (24.76% at 691.99 °C), suggesting higher organic loss and potentially more efficient thermal degradation. Moreover, L9 and L12, resulted in no recorded data beyond 416 °C, showed intermediate stability with weight percent around 34.5%, implying a comparable degradation profile up to that temperature. These results indicate that increasing dietary lipid levels influences the thermal degradation behavior of fish muscle, with moderate lipid levels (L6, L9) showing the most significant breakdown of organic matter. Overall, the study highlights the importance of optimizing dietary lipid levels in nano-formulated larval feeds to enhance growth, nutrient utilization, and tissue integrity in C. carpio. The integration of histological, spectroscopic, and thermal analyses provides a robust framework for developing sustainable, thermostable, and effective early-stage feeds for common carp. This study incorporated graded lipid inclusion in larval feeds and evaluated their effects not only on growth, survival, and histological integrity but also documented a novel tool to asses spectral and thermal properties of larval feed and fish meat quality for its potential aquaculture usage.