Spinous dorsal fin darkly pigmented, appearing slightly spotted or streaked in 

 some specimens due to lightly pigmented areas of interradial membranes. Adipose 

 fin uniformly black throughout, except for unpigmented thm band along posterior 

 margin. Caudal fin dark brown, spotted at base, uniformly dark throughout lobes, 

 except for broad, unpigmented distal margin, which appears yellowish in preserved 

 specimens. Paired fins heavily pigmented, slightly mottled, with black band along 

 distal margin. Anal fin heavily spotted or mottled at base, pigment extending 

 throughout fin as u-regular spots. The intense, dark coloration of this species is 

 attributed in part to its occurrence in the clear and blackwater habitats prevalent 

 throughout its range. .-,^. 



Distribution 



Ageneiosus pofystictus is found only in the Rio Negro drainage of Brazil, 

 including at least the lower reaches of the Rio Branco (Fig. 54). Some specimens 

 have been taken from near Manaus, Brazil, in the vicinity of the mouth of the Rio 

 Negro. However, the species does not apparently enter the Rio Amazonas proper. 

 The extent of its distribution in the upper Rio Negro and upper Rio Branco is not 

 known because of poor collecting efforts in these areas. Presumably, it may enter 

 the Rio Casiquiare in northern Brazil and southern Venezuela. 



Ecology :, / 



Nothing is known about the ecology oi A. pofystictus. Since this species 

 appears to be confined to the Rio Negro, draining the southwestern portion of the 

 Guiana shield, it presumably is in some way adapted for the nutrient-poor, 

 blackwater hydrology characteristic of that system. The Rio Negro has a fair degree 



