Whole-larval innate immune-associated biochemical profiles during early ontogeny of silver pompano (Trachinotus blochii).

Understanding the developmental dynamics of immune system is essential for improving larval health management. This study examined the ontogenetic patterns of seven innate immune-associated parameters, viz. albumin, protease, antiprotease, sialic acid, nitrite, nitric oxide synthase (NOS), and alkaline phosphatase (ALP) along with a general clinical indicator of health (total protein content) from fertilized eggs (0 DPH) to the completion of metamorphosis (25 DPH) in a high-value tropical mariculture species, Trachinotus blochii. Among all parameters, protein content showed the least inter-stage variation (26.40%). All immune-associated markers displayed distinct, non-linear trajectories rather than a gradual, uniform progression. Larval development was marked by a steady rise in protease and NOS activities along with increasing nitrite levels. Metamorphosis was accompanied by marked changes in several immune-associated parameters, characterized by significant increases in albumin, nitrite, protease, and NOS, and simultaneous decreases in ALP, antiprotease, and sialic acid. These coordinated changes suggest intense modulation of innate immunity during the larva-to-juvenile shift. Post-metamorphic stages showed stabilization of several immune-associated markers, indicating the establishment of regulatory homeostasis. Multivariate analysis grouped early ontogeny into three clusters, with the greatest divergence observed between eggs and developmental stages undergoing metamorphosis. The present study also provides preliminary baseline reference values for innate immune-associated parameters during larval development of T. blochii. These findings contribute to the understanding of immune ontogeny in this species and may serve as a reference for future studies investigating larval immune development and hatchery management strategies following validation across multiple batches and functional immune assessments.