The hypoxia adaptation strategy of the big-belly seahorses (Hippocampus abdominalis) with tuft gills

Abstract

Hypoxia tolerance is a critical trait in fish breeding, however, the mechanisms underlying hypoxia regulation in the tuft gills of seahorses remain unclear. In this study, we compared the gill structures of the big-belly seahorses (Hippocampus abdominalis, BBS) with lamellae gill fish and evaluated the effects of hypoxia on BBS. The average oxygen tension threshold for loss of equilibrium (LOEcrit) of BBS (2.68 mg·L−1) was higher than that of the common hypoxia-sensitive fish. Compared with the normoxia group, the duration of stationary, irregular swimming, curled tail, lying down behaviors, and respiratory rate significantly (P 0.05) changes were observed in the medial and proximal regions. Ultimately, we identified 5 significantly (P < 0.05) down-regulated (itgav, itga6a, itga1, pcna, and adcy9) and 5 significantly (P < 0.05) up-regulated (gusb, src, cdc20, ccnb1, and plk1) core hub genes related to gill remodeling. This study demonstrates that BBS is sensitive to hypoxia, and its unique tuft gills respond to hypoxia through local gill remodel, providing valuable insights for the breeding of hypoxia-tolerance seahorses.

Keywords

• Big-belly seahorses
• Hypoxia
• Tuft gill
• Local gill remodel
• Oxidative stress