Different Oxygen Stresses on the Responses of Branchial Morphology andProtein Expression in the Gills and Labyrinth Organ in the Aquatic Air-breathing FishTrichogaster microlepis

摘要

Organisms face direct challenges froma variety of abiotic factors in the environment. Changes in dissolved oxygen are one ofthe most common types of these challenges. The gills of some fish species can compensatefor ambient oxygen changes by exhibiting morphological and functional plasticity that givethe gill the ability to modify its structure. In the previous studies of aquatic air-breathing fish with an accessory air-breathing organ (the labyrinth organ), we foundmorphological and functional specializations between the 1st and 4th gills in the genus . This study investigated morphological and functionalchanges in the gills and labyrinth organ of the aquatic air-breathing fish over a 28- day period of oxygen uptake stresses. The experimentaldesign was as follows: (1) a control group (held under normoxia with air-breathingrespiration (ABR) allowed); (2) a hypoxic group (held under hypoxia with ABR); and (3) arestricted group (held under normoxia without ABR). We recorded the cumulative mortalityof the fish and the frequency of ABR between the control and hypoxic groups, conductedmorphological examinations of the lengths of gill filaments and lamellae of gills anddetermined the relative abundance of carbonic anhydrase II (CAII) and Na+/K+-ATPase (NKA).Mortality in the restricted group was higher than those in the control and the hypoxicgroups. The frequency of ABR in the hypoxic condition was higher than that in the control.The lengths of the lamellae in the 1st, 3rd and 4th gills in the restricted group weresignificantly longer than those in the control group after 14 and 28 days. In addition,the relative abundance of CAII was significantly increased only in the labyrinth organ inthe hypoxic group compared to the control group on day 3. The relative abundance ofproliferating cell nuclear antigen also was significantly increased in the 1st gill, 4thgill and the labyrinth organ in the restricted group compared to the control group on day14. This study showed, for the first time, that the 4th gill in , which is generally much-reduced compared to the other gills, canhave elongated lamellae when fish are subjected to the restricted group for 28 day. Therelative abundance of CAII in the labyrinth organ was significantly higher under hypoxicgroup than under control group on day 3