36 



are probably convergent (Regan 1911). Ageneiosus and Helogenes are 

 rather similar and may resemble the Siluridae and Schilbeidae in their 

 habits. (Alexander 1965:122) 



With his description, Alexander proposed that the compressed shape of 

 silurids (Cryptopterus) and schilbeids (Schilbe, Eutropiella) was related to their 

 pelagic swimming habits. To the above list Howes (1983) added Hypophthalmus, 

 Ompok (a schilbeid), and the famiUes Pangasiidae and Auchenipteridae (i.e., 

 Auchenipterus). Alexander (1966) further included descriptions of the 

 hydrodynamics of a generaUzed pelagic schilbeid. His suggestion was that free- 

 swimming catfishes tend to exhibit this morphology, in contrast to the more common 

 depressed body shape characteristic of most sedentary, benthic catfishes. 



Howes (1983) compared the body shape oi Ageneiosus to that of 

 Hypophthalmus, and also commented on the ramified lateral line, the reduced 

 swimbladder, the high fat content, and other characters shared between the two 

 taxa. With regard to Hypophthalmus, Howes (1983:5) was hesitant to classify this 

 genus as pelagic, but he did conclude that the "schilbeid morphotype" described by 

 Alexander was probably independently derived within several Hneages, and that 

 within each group it represents a derived feature with concommitant modifications 

 of the swimbladder and acousticolateraUs system. Moreover, Hypophthalmus 

 exhibits morphological features unlike most other catfishes, and its body shape may 

 in part be related to its planktivorous feeding habits (Howes 1983). 



Although the above comparisons characterize the generalized body shape of 

 a pelagic siluroid, there is unquestionably strong convergence in body shape 

 between several unrelated taxa. As suggested by the above authors, this condition 

 may be correlated with the semipelagic habits of the various genera. Although 

 ageneiosids are generally confined to large river charmels and may migrate great 

 distances (Smith 1979), Uttle is known of their behavior. In captivity they have been 



