B 



Fig. 33: Dorsal view of gas 

 bladder of (A) Phoxinus 

 erythrogaster (KU 3895, 63.1 

 mm SL) and (B) P. issykku- 

 lensis (P- 10696, 42.4 mm 

 SL). Scale bars = 1 mm. 



a long tube-like structure; its anterior portion is not broader than its posterior portion in 

 some species of Phoxinus. 



Morphological variation of the gas bladder among the species of Phoxinus is found in the 

 shape of anterior and posterior chambers, the relative length of the two chambers, the 

 length of the constriction, and the position where the pneumatic duct connects with the 

 gas bladder. 



The gas bladder is long and slender in P. phoxinus (TS 30[1]; Fig.34B). The gas bladder 

 is very short and broad in P. issykkulensis (TS 30[2]; Fig.33B). Other species are similar 

 to the outgroups in having a gas bladder that is broader and shorter than that in P. pho- 

 xinus, but narrower and more slender than that in P. issykkulensis (TS 30[0]). 

 The relative length between the posterior and anterior chambers also varies. Three diffe- 

 rent conditions can be recognized in the relative length of the two chambers. 



(1) The anterior chamber is about 70% of the posterior one in length (TS 3 1 [0]; Fig.34D). 

 In P. neogaeus and erythrogaster, the anterior chamber is about 75% of the posterior cham- 

 ber. In P. tennesseensis, oreas, cumberlandensis, brachyurus, and eos, the anterior cham- 

 ber is about 70% in length of the posterior one. 



(2) In P. phoxinus, the anterior chamber is less than 50% in length of the posterior one 

 (TS 31[1]; Fig.34B). 



(3) In P. issykkulensis, the anterior chamber is almost equal in length to the posterior one 

 (TS 31[2]; Fig.33B). 



