Integrative study of acute ammonia exposure on the skin of the Striped catfish (Pangasianodon hypophthalmus).

Abstract

Ammonia can rapidly accumulate in a water body and pose a serious threat to fish health. Striped catfish is a key species in Southeast Asia. Climate change and intensive farming waste pose significant risks of ammonia stress to this species in both natural habitats and farming ponds. As a vital immune-related organ and a significant surface barrier, the fish skin plays a crucial role in defending against ammonia; however, little is known about skin response to acute ammonia exposure. In this study, Striped catfish were exposed to 40 mg L-1 concentration of total ammonia for 24 hr to evaluate skin responses. In general, we found inflammation in the skin. However, the skin tissue showed subtle to no signs of damage, with tissue ammonia concentration accumulating and then decreasing over the challenge duration. Subsequent transcriptomic analysis of skin gene functions suggests that overall ammonia regulation may occur along with specific cellular components. Transmission electron microscopy then revealed accumulated exosome-like vesicles near the epithelial surface of the skin's superficial layer during challenge. Using the established Striped catfish skin epithelial cell line along with an exosome inhibitor, we confirmed the presence of exosomal vesicles and their role in ammonia excretion. In conclusion, while acute ammonia exposure induces inflammation in the Striped catfish skin, active ammonia excretion along with exosomes may alleviate accumulation, thereby maintaining skin tissue integrity. This study explores the Striped catfish skin responses to acute ammonia exposure and highlights the ammonia regulation system that maintains skin integrity.