Comparative analysis of the heart histological structure, metabolic enzyme activities and transcriptome profiles of juvenile and adult yellowfin tuna (Thunnus albacares) in the South China Sea

The yellowfin tuna is a large marine carnivorous fish with high commercial value. It is known for its unique physiological characteristics and holds significant potential for aquaculture. However, research on this species' developmental biology and physiology remains limited, particularly regarding the structural characteristics and functional changes in the developing heart. To investigate the differences in cardiac tissue structure and function at different developmental stages in yellowfin tuna, we conducted comparative analyses of histology, metabolic enzyme activity, and transcriptomes. Hematoxylin and eosin (H&E) and Masson staining revealed that cardiac muscle fibers were thicker and more compact, and the area of collagen fibers was significantly increased in adult fish compared to juvenile fish (p < 0.001). Additionally, the enzyme activities of Na⁺K⁺-ATPase, Ca²⁺Mg²⁺-ATPase, carnitine palmitoyltransferase 1 (CPT-1), lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and malate dehydrogenase (MDH) were notably greater in adult fish compared to juvenile fish (p < 0.05). Comparative transcriptome analysis identified 1293 differentially expressed genes (DEGs) between juvenile and adult fish. Functional enrichment analyses indicated that these differential genes are primarily closely associated with heart development and metabolic regulation pathways. Furthermore, key metabolism-related DEGs, such as acsl3b, acsbg2, acsl1a, and cpt1ab, were further identified, and quantitative real-time PCR (qRT-PCR) validated the accuracy of the results. In conclusion, this study provides a systematic analysis of the differences in histology, metabolic enzyme activities, and transcriptomics between the hearts of juvenile and adult yellowfin tuna, providing foundational data for future research on heart development in the later stages of yellowfin tuna and contributing to the advancement of aquaculture practices for this species.