The interactive effects of hypoxemia, hyperoxia, and temperature on the gill morphology of goldfish (Carassius auratus)

Abstract

Acclimation of crucian carp and goldfish to temperatures below 15°C causes covering of the gill lamellae by a mass of cells termed the interlamellar cell mass (ILCM). Here we explore the cues underlying gill remodeling (removal or growth of an ILCM) and specifically test the hypotheses that 1) depletion of internal O2stores in the absence of any change in external O2status can trigger the removal of the ILCM in goldfish acclimated to 7°C, 2) exposing fish acclimated to 25°C to an abundance of O2(hyperoxia) can reverse the gill remodeling (i.e., cause the covering of lamellae by an expansion of the ILCM), and 3) neuroepithelial cells (NECs) are involved in signaling the shedding of the ILCM. Hypoxemia induced by phenylhydrazine (anemia) or 5% CO caused a decrease in the ILCM from 80% to 23% and 35%, respectively. Hyperoxia exposure at 25°C caused an increase to 67% of total ILCM and a smaller decrease in the size of the ILCM when fish were transferred from 7 to 25°C. Daily sodium cyanide injections were used to stimulate NECs; this treatment led to a significant decrease in the ILCM. Thus, the three major conclusions of this study are 1) that gill remodeling can occur during periods of internal hypoxemia, 2) that O2supply and demand may be a significant driving force shaping gill remodeling in goldfish, and 3) the NECs may play a role in triggering the shedding of the ILCM during hypoxia.