‘Chloride Cells’ in the Gills of Fresh-Water Teleosts
0
(From the Department of Zoology, Banaras Hindu University
,
Varanasi-5
,
India)
Specialized cells of several kinds, namely, (a) mucous-gland cells, (b) large bi- or tri" nucleate glandular cells, and (c) mast cells occur in the gills of some species of freshwater teleosts. The typical 'goblet' type of mucous glands are present in large number in freshwater species, such as Catla catla, Labeo rohita, Ophiocephalus punctatus, and Mastacembalus armatus. In Catla catla, these glands respond to the 'chloride test'. This indicates that, besides discharging mucus, they also play some part in the elimination of chloride. In Ophiocephalus punctatus, Clarias batrachus, and Heteropneustes fossilis only some of the mucous cells give a positive reaction with the AgNO3/HNO3 test for chloride. This may mean that a few of them are in a state of active secretion of chlorides, while others are in a non-secretory phase.
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'Chloride cells' in the gills of fresh-water teleosts
I T has been claimed that the bulk of the sodium, potassium, and chloride
absorbed in the gastro-intestinal tract of marine teleosts is excreted by the
'chloride-secreting' cells in the gills (Smith, 1930; Keys, 1931, 1933; Keys
and Willmer, 1932); but Bevelander (1935, 1946) believed that the supposed
excretory cells are nothing but intra-epithelial mucous glands and that the
general respiratory epithelium
might be a site of chloride excretion.
Liu (1942) attempted to acclimatize the fresh-water air-breathing fish,
Macropodus opercularis, to different concentrations of salt solution. He stated
that even an exclusively fresh-water fish can tolerate a salt solution nearly as
saline as sea-water by virtue of the enormous development of latent
'chloridesecreting cells'. From this experiment he concluded that fresh-water teleosts
possess 'chloride-secreting cells' in the gills in a dormant condition.
Copeland (1948a, b) noted cytological changes in the chloride cells of
Fundulus heteroclitus during adaptation to varying degrees of salinity, and by using
the Leschke test demonstrated the presence of a copious amount of chloride
in the secretory cells of fishes adapted to the salt-water condition, but only
a limited amount of it at the free ends of the cells in fishes adapted to
freshwater life. Getman (1950) working on Anguilla rostrata came to a similar
conclusion.
More recently Vickers (1961) has said, with reference to the gills of Lebistes
reticulatus (a fresh-water teleost), that after subjection to hypertonic-salt
solutions of varying concentrations, its mucous cells become functionally
transformed into chloride cells.
The present studies on gill epithelia of fresh-water teleosts were undertaken
in order to remove some of the ambiguities and deficiencies in our knowledge.
Materials and methods
Fishes were collected from the river Ganges and the local ponds. Pieces of
their gills were immediately fixed in Zenker, Helly, chrome-Bouin, alcoholic
Bouin, Gilson's mercuro-nitric, or Carnoy's fluid after gently removing the
adhering mucus with a cotton swab and rinsing them in river water. Sections
of the gills were stained with Heidenhain's or Delafield's haematoxylin or
Mayer's haemalum, and counterstained with eosin. Mallory's triple stain,
borax-carmine followed by picro-indigo-carmine, and other stains were also
employed.
Parts of the gill lamellae were dissociated in several different fluids such as
sodium-chloride solution, Ranvier's alcohol, and borax solution. The
dissociated cells were stained with methylene-blue and examined with the
microscope.
Thionin was used to demonstrate the presence of mucus and
mucusproducing cells and mast cells (the latter by their chromotropic reaction).
Sections were stained in a 0-2% aqueous solution of thionin, quickly passed
through acetone to xylene, and mounted in balsam. The PAS technique was
used to demonstrate the mucus-producing cells. Fresh tissues of the gill
lamellae were also studied supravitally with neutral red.
The Leschke silver technique, as modified by Copeland (1948a, b), was also
used to detect the presence of the chloride in the so-called branchial glands.
Histological studies were made on the following species of fishes:
1. Hilsa ilisha (Ham.)
2. Gadusia chapra (Ham.)
3. Catla catla (Ham.)
4. Labeo rohita (Ham.)
5. Rohtee cotio (Ham.) Family Clupeidae Cyprinidae
6. Glorias batrachus (Linn.)
7. Heteropneustes fossilis (Bloch)
8. Wallago attu (Bl. & Schn.)
9. Rita rita (Ham.) 10. Mystus aor (Giinther) Group D
11. Ophiocephalus punctatus (Bloch)
12. Ophiocephalus striatus
13. Anabas testudineus (Bloch)
14. Trichogaster fasciatus (Bl. & Schn.)
Anabantidae
Osphronemidae
The chloride test was only applied to nos. 1, 3, 6, 7, 9, 11, 12, and 15 in the above list.
Results
The principal findings are summarized in tables 1 and 2 (see appendix,
p. 88), and illustrated in figs. 1 and 2.
The structure of the gills of Labeo rohita, Hilsa ilisha, Rita rita, and
Ophiocephalus striatus ha (...truncated)