their structure while in the testis, suggesting that they may be bound by an 

 encapsulating layer. ,. , . ; . 



Based on cytology of the gonads, I speculate that fertilization in ageneiosids 

 occurs near the time of ovulation. The spermatozeugmata are probably retained in 

 the ovary for an extended period, since oviposition may not occur for several weeks 

 after insemination (Burgess 1982, Kopke 1986). Studies of the gonad morphology 

 and reproductive behavior are needed to confirm this speculation. 



Evolutionary Significa nce of Internal Fertilization in the Ageneiosidae 



Possible selective factors that have led to the evolution of sexual dimorphism 

 and internal fertilization in ageneiosids and auchenipterids remain unknown, in the 

 absence of meaningful ecological data. A fair amount of attention has been given to 

 a general correlation between migratory patterns of tropical fishes and seasonal 

 rainfall patterns (e.g., Lowe-McConnell 1987, Smith 1981, Goulding 1980). Roberts 

 (1989b) speculated that many tropical freshwater fishes may in fact have prolonged 

 reproduction, and he suggested that generalizations about reproductive life-history 

 patterns may have to be considerably modified and revised as more ecological data 

 are obtained. Roberts specifically stated that discussions of reproductive seasonahty 

 in tropical freshwater fishes should be avoided, since in many cases there is no clear 

 correlation with seasonal ecological or climatological phenomena; he speculated 

 that other factors, such as food or mate availability, may be the proximate factors 

 responsible for the evolution of unique reproductive patterns in tropical fishes. 

 With respect to auchenipterids, Roberts (1989b) further remarked that internal 

 fertilization could allow for temporal and spatial separation of mating and spawning, 

 potentially leading to a more prolonged reproductive period. He stated that 

 internal fertilization may be more widespread in catfishes than is presently known. 



I 



