FRESH-WATER FISHES OF SIAM, OR THAILAND 285 



While the fish is primarily and essentially an inhabitant of moun- 

 tainous regions, it nevertheless is sometimes found in the sluggish 

 waters of the plains and may occur there in great abundance, as in 

 Bung Borapet. A noteworthy extension of range into the coastal 

 plain streams is seen in the records for the Menam Tachin (Fowler, 

 1937) and the Menam Chao Phya at Nontaburi and near its mouth at 

 Paknam. 



It is a strict vegetarian. Its long coiled intestine is usually found 

 crowded with amorphous green material representing algae that is 

 cropped from stones. This feeding habit is accounted for by the 

 absence of pharyngeal teeth, which are unnecessary because the small 

 oral opening does not permit the taking of food that requires masti- 

 cation. The scraping of the algae from stones is facilitated by the 

 rasplike folds of the inner surface of both lips. 



The same peculiar mouth structure enables the fish to adhere to hard 

 surfaces, and thus to maintain itself in swift water. The use of the 

 mouth as a sucking organ is, however, not confined to flowing water but 

 is regularly seen in fish in balanced aquaria. Numerous observations 

 on such fish indicate that when resting they j3ref er to attach themselves 

 to the bottom or to the vertical sides up to several feet above the 

 bottom, even in the complete absence of any current. 



The tip of the snout, with its strong spines, is rather freely movable, 

 and in handling live specimens a person may have his fingers severely 

 pinched between the movable group and the fixed median band. 



A fish imperfectly described and inaccurately figured by Tirant in 

 1883 under the name Psilorhynchus aymonieri remained a puzzle until 

 Hora (1935) , having obtained photographs of the type in the Museum 

 of Natural Sciences of Lyons, was able to decide that the fish is not 

 a Psilorhynchus but a Gyrinocheilus^ identical with G. Jcaznakovi 

 Berg (1906). The type of G. aymonieri came from the basin of the 

 Mekong near Phnom-Penh, Cambodia ; the type of G. haznakovi came 

 from a stream flowing into the Tonle Sap, Mekong basin, at Pailin, 

 then in Thailand, now in Cambodia. 



The fish bears several vernacular names in different parts of its 

 range. In the Paknampo region, including the upper Menam Chao 

 Phya, the lower Menam Nan, and Bung Borapet, it is called yla rak 

 Muey. A name in use at Lampang and on the Mekhan in Northern 

 Siam is pig, mood. Fishermen on the Mekhan employed also the name 

 pla yalu. On the Meklong in the Potaram section and in the west 

 branch of the Meklong above Kanburi, the designations are pla piing 

 (bee fish) and pla Ink piing (young bee fish), perhaps in allusion to 

 the dense swarms of fish about 5 cm. long found along the shores in 

 August to November. At Udon on the Menam Pong in Eastern 

 Thailand the fish is recognized under the name pla plak lai (lower- 

 mouth fish). 



