. ■■ ' ''}■/. ' 'i-V ':.■■■' ■■■■ > "^ "T V,'1 146 



■- ^^' Britski (1972) and Ferraris (1988) implied that dimorphism of the anal fin 

 and the barbels is characteristic of maturity, at least in some auchenipterid taxa. In 

 ageneiosids there is a definite seasonal, albeit prolonged, elaboration of sexually 

 dimorphic structures, as discussed by Britski (1972). During latent reproductive 

 periods, mature males have unmodified barbels and dorsal and anal fins, and 

 resemble females and immature males. I suspect that this is also true of at least 

 some auchenipterids. In the species of ageneiosids that I have examined, males are 

 in prenuptial or nuptial condition for a relatively extended period, ranging 

 approximately four to six months, and roughly corresponding to the middle or end of 

 low rainfall periods. Notwithstanding the objections of Roberts (1989b) in applying 

 a concept of seasonality to the reproduction of tropical fishes, it appears to me, from 

 the available evidence, that male ageneiosids are reproductively inactive during a 

 significant and predictable time of the year. Nevertheless, the ability of females to 

 retain sperm in their reproductive tracts for an extended period after insemination 

 supports Robert's (1989b) hypothesis that there may be temporal separation of 

 mating and oviposition. Perhaps, females ovulate and oviposit fertilized eggs when 

 ecological conditions (e.g., food availabiUty, reduced abundance of predators, etc.) 

 favor maximal survival of propagules, but, until ecological studies are done, such 

 predictions remain strictly conjectural. 



Britski (1972) and Ferraris (1988) considered sexual dimorphism to be one of 

 the prima facie characters supporting a hypothesis that auchenipterids and 

 ageneiosids share a common ancestry. I agree fully with this conclusion. There is 

 currently no evidence to support speculation by Roberts (1989b) that internal 

 fertilization may be widespread among catfishes. In fact, of the over 2000 species of 

 catfishes woridwide, internal fertilization has only been demonstrated in the 

 ageneiosids and auchenipterids. Furthermore, the sexual dimorphism exhibited by 

 these taxa is unparalleled among siluriforms (many others have additional forms of 

 sexual dimorphism, but in no case is there development of a gonopodium or similar 



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