412 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



Figure 92. — Modified ventral fins of female Thailand catfishes (Tachysurus). The 

 "claspers" are developed on the pelvic fins to assist in holding the large eggs. The eggs 

 are extruded one at a time, so that the male fish may take them in his mouth, a, Left 

 pelvic fin of Tachysurus argyropleuron; b, left pelvic fin of Tachysurus venosus. 



The local iBshermen called the fish pla hot lueng {lueng, yellow), 

 reported that it attained a slightly larger size, and said its food value 

 is very good. 



TACHYSURUS ARGYROPLEURON (Cuvler and Valenciennes) 



Figure 92a 



Arius argyropleuron Cuvieb and Valenciennes, 1840, vol. 15, p. 104 (Java). 



In the Dutch East Indies this fish is known from sea, estuaries, and 

 rivers, but the specimens collected by the writer in Thailand were 

 from Langsuen and Singora, on the western side of the Gulf of Siam, 

 and from Cham Ham Bight, on the eastern side of the gulf. These 

 were taken in iVugust, September, and October, and ranged from 13.5 to 

 33 cm. in length, as against a maximum of 46 cm. recorded by Bleeker. 



TACHYSURUS LEIOTETOCEPHALUS (Bleeker) 



Arius leiotetocephalus Bleeicee, 1846 (4), p. 292 (Batavia). 

 Tachysurus leiotetocephalus Smith, 1934b, p. 299 (Gulf of Siam). 



The published records for this fish include Celebes, Java, Singapore, 

 and Malacca, in sea and estuaries, as well as the Gulf of Siam. It is 

 the most abundant of the sea catfishes of Thailand and is a schooling- 

 fish, usually going in very large numbers along both rocky and muddy 

 shores, and often being caught in immense quantities in bamboo traps. 

 As many as 5,000 fishes were taken in one day in February 1924 in a 

 single trap off Bangplasoi, at the northeast corner of the Gulf of 

 Siam. The appearance of the fish in a given section is irregular and 

 the abundance varies greatly from month to month or year to year. 



The species may be readily recognized by the large ovate occipital 

 process that completely occupies the space between the head and the 

 basal bone of the dorsal spine. This process is easily detached and 

 may often be seen in numbers on sandy or gravelly beaches, where 

 carcasses of the fish have disintegrated. 



