Impact of Temperature Manipulations on Growth Performance, Body Composition, and Selected Genes of Koi Carp (Cyprinus carpio koi)

Aquatic organisms face substantial challenges from climate change, particularly due to rising water temperatures, which significantly impact their growth and survival. This investigation utilized 960 Koi carp (Cyprinus carpio koi) (Initial Body Weight, 0.304 +/- 0.005 g). After a 10-day acclimatization period, the fish were distributed equally across 12 glass aquaria (80 x 40 x 45 cm), with three replicates per treatment. This study encompassed two phases. The first phase (10-60 Days Post-Hatching, dph) involved four temperature regimes: T1 (26 degrees C), T2 (28 degrees C), T3 (30 degrees C), and T4 (26/30 degrees C daily fluctuation). The second phase (60-120 dph) maintained all groups at 30 degrees C. Initially, T1 exhibited the best growth performance, indicated by the highest Final Body Weight, Weight Gain, Specific Growth Rate (SGR), and Thermal Growth Coefficient (TGC), along with the highest survival rate. Gene expression analysis revealed that HSP70, HSP90, SOD, BCL-2, and FASN were upregulated in T3 and T4, indicative of stress, while MYOD was highest in T1. During the second phase, T4 displayed superior growth and a healthier body composition with elevated moisture and protein, and reduced fat content compared to T1 and T2. HSP70, HSP90, and BCL-2 expression increased significantly in T1, suggesting thermal stress, whereas MYOD levels rose across all treatments, peaking in T4, which correlated with its growth. Further, there were strong relationships among growth parameters, gene expression, and body composition, with T4 exhibiting the highest essential and non-essential amino acids and a unique fatty acid profile. Overall, the results suggest that manipulated temperature significantly influences Koi carp's characteristics, making it more adaptable to future environmental stress.