FRESH- WATER FISHES OF SIAM, OR THAILAND 329 



The fish is unique among the Thailand representatives of the genus 

 NoeTnacheilus in having no cross bands on body but is characteristically 

 marked with a narrow sharply defined black stripe extending from 

 head to base of caudal fin; from the stripe, above the middle of the 

 pectoral fin when depressed, two short black bars extend vertically 

 about halfway to the median line of the back, the bars occupying a 

 bright yellow area, and there is a round black spot on the base of the 

 central raj'S of the caudal fin. A black area extends from gill opening 

 to eye and is continued as a well-defined stripe from eye to tip of snout 

 and thence to dorsal surface of the four rostral barbels. The body 

 is slender, the head is long, the dorsal fin is high, the caudal fin is broad 

 and moderately forked, and the lower fins are comparatively small. 



Order Nematognathi : Catfishes 



The catfishes are very numerously represented in Thailand. They 

 fall into 10 families, 34 genera, and about a hundred species, ranging 

 in size from 5 centimeters to 3 meters.^ 



The great majority of the species live only in fresh water. The few 

 that are strictly marine have fresh-water relatives and are herein 

 referred to in order to make the family and generic treatments com- 

 plete. 



In the adaptation of the local catfishes to the peculiar physical con- 

 ditions that have to be overcome, some remarkable habits and struc- 

 tural features have developed. Thus, in one large family (Tachy- 

 suridae) most of the members practice oral incubation, and in another 

 family (Clariidae) all the members have special air-breathing appara- 

 tus to supplement the gills. In some mountain-stream catfishes (fam- 

 ily Sisoridae) there is a thoracic adhesive organ to aid in maintaining 

 themselves in swift water. 



The catfishes are important as food, especially for the people of 

 interior districts. Every species, regardless of size, is eaten. 



The families of this order may be differentiated as follows: 



la. Dorsal fin absent or, if present, spineless ; no adipose fin. 

 2a. Dorsal fin few rayed, rudimentary, or absent. 



3a. Two pairs of barbels (maxillary and mandibulary) ; breathing apparatus 



of ordinary type Siluridae 



3&. Four pairs of barbels (nasal, maxillary, mandibulary, and mental) ; 

 breathing apparatus highly modified, a pair of cylindrical air sacs 

 extending fi'om gill cavity through muscles of back to tail. 



Heteropneustidae 



^ The richness of this fauna may be better appraciated when it is stated that continental 

 United States, with fifteen times the area of Thailand, has in its fresh and coastal waters 

 only one-third the number of catfish species. India and Burma, with nine times the area 

 of Thailand, have about the same numbei- of catfish genera and only about 12 percent 

 more species. 



