title: Development of gas exchange and ion regulation in two species of air-breathing fish, Betta splendens and Macropodus opercularis.
abstract: Aquatic air-breathing anabantoids, a group of fish species characterized by the presence of a labyrinth organ and some gills, exhibit morphological variations. This study aimed to examine whether unequal gill growth begins during the early stages and described the sequence of the early gill developmental events in Betta splendens and Macropodus opercularis. To determine when the ion regulatory and gas exchange abilities first appear in the gills, mitochondria-rich cells (MRCs) and neuroepithelial cells (NECs) were examined in young B. splendens. To evaluate the relative importance of the gills and the labyrinth organ under different levels of oxygen uptake stress, the levels of carbonic anhydrase II (CAII) and Na(+)/K(+)-ATPase (NKA) protein expressions in 2 gills and the labyrinth organ were examined in M. opercularis. We found that the first 3 gills developed earlier than the 4th gill in both species, an indication that the morphological variation begins early in life. In B. splendens, the MRCs and NECs clearly appeared in the first 3 gills at 4 dph and were first found in the 4th gill until 11 dph. The oxygen-sensing ability of the gills was concordant with the ionoregulatory function. In M. opercularis, the hypoxic group had a significantly higher air-breathing frequency. CAII protein expression was higher in the labyrinth organ in the hypoxic group. The gills exhibited increased NKA protein expression in the hypoxic and restricted groups, respectively. Functional plasticity in CAII and NKA protein expressions was found between the gills and the labyrinth organ in adult M. opercularis.
authors.affiliation: Department of Life Science, Tunghai University, Taichung 40704, Taiwan; Department of Chemistry, National Taiwan Normal University, Taipei 11677, Taiwan; Center for Tropical Ecology and Biodiversity, Tunghai University, Taichung 40704, Taiwan.
authors.forename: Chun-Yen
authors.initials: CY
authors.lastname: Huang
authors.affiliation: Department of Chemistry, National Taiwan Normal University, Taipei 11677, Taiwan.
authors.forename: Cheng-Huang
authors.initials: CH
authors.lastname: Lin
authors.affiliation: Department of Life Science, Tunghai University, Taichung 40704, Taiwan; Center for Tropical Ecology and Biodiversity, Tunghai University, Taichung 40704, Taiwan. Electronic address: hclin@thu.edu.tw.
authors.forename: Hui-Chen
authors.initials: HC
authors.lastname: Lin
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D029941:Fish Proteins / Q000378:metabolism; D005399:Fishes / Q000033:anatomy & histology / Q000254:growth & development*; D005880:Gills / Q000254:growth & development / Q000648:ultrastructure; D008297:Male; D010100:Oxygen / Q000378:metabolism; D012119:Respiration; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D029941:Fish Proteins; D000254:Sodium-Potassium-Exchanging ATPase; D010100:Oxygen
keywords: Anabantoidei; Development process; Hypoxia; Labyrinth organ; Mitochondria-rich cells; Neuroepithelial cells