Vol. 43 No. 4, 2004
Ionocyte Distribution in Gills of the Euryhaline Milkfish, Chanos chanos (Forsskål, 1775)
Chun-Nian Chen1, Li-Yih Lin2 and Tsung-Han Lee1,*
1Department of Life Sciences, National Chung-Hsing University, Taichung, Taiwan 402
2Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan 114
Chun-Nian Chen, Li-Yih Lin and Tsung-Han Lee (2004) As a marine euryhaline teleost, the milkfish, Chanos chanos,
is considered a good model fish for studies of ionoregulation. In
preparation for studies of the effects of seawater-freshwater
adaptation on the biochemistry and morphology of the milkfish gill, the
present investigation describes different distributions of ionocytes on
the gill epithelium of seawater- versus freshwater-adapted fish.
Paraffin sections of filaments revealed afferent, interlamellar, and
efferent regions of the epithelium. Round eosinophilic epithelial cells
(5~10 µm in diameter) were exhibited in the interlamellar epithelium
near the afferent side of the filament. Due to their identical size and
location, histochemical (osmium-zinc iodide) and immunofluorescent (Na,
K-ATPase) staining was used to demonstrate that these eosinophilic, Na,
K-ATPase-immunoreactive (NKIR) cells are ionocytes. It is thus hard to
examine the apical openings of ionocytes by scanning electron
microscopy in the gill epithelium of the milkfish as compared to those
in the other teleosts, because most ionocytes are distributed in the
interlamellar regions of the filaments. Further confocal micrographs
showed abundant NKIR cells on the filamental epithelia of both
seawater- and freshwater-adapted fish. However, NKIR cells were rarely
observed on the lamellar epithelia of gills in seawater-adapted
individuals, while they were commonly found in freshwater-adapted
milkfish.
Key words: Gill, Na, K-ATPase, Mitochondria-rich cell, Euryhaline, Milkfish, Teleost.
*Correspondence: Tel: 886-4-22856141. Fax: 886-4-22851797. E-mail: thlee@dragon.nchu.edu.tw

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