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THE RIO NEGRO ANGELFISHES (1976)
© Warren Burgess (1976)

The second species of angelfish, P. dumerilii, with the characteristic black spot at the base of the dorsal fin.

Dr. L. P. Schultz, in his 1967 "Review of South American Freshwater Angelfishes-Genus Pterophyllum" (Proc. USNM, Vol. 120, #3555) came to the conclusion that there were at least two species (P. scalare and P. dumerilii) in the genus, with a third (P. altum) as possible. The dubious species, P. altum, according to Dr. Schultz, had a color pattern identical with that of P. scalare, but different on the basis of counts. He concluded that, "undoubtedly P. altum represents the P. scalare type of angelfish in the upper Orinoco, and in having a higher average number of dorsal, anal, oblique scale rows and vertebrae than P. scalare, it might be considered to represent only a subspecies of P. scalare: however, since P. altum has been taken so far only in the upper Orinoco basin, I prefer tentatively to recognize it as a distinct species."

In Dr. Axelrod's recent collection from Igarape Anapichi and Igarape Apania of the Rio Negro, nine specimens of angelfish, varying in size from 28.4 mm to 101.5 mm standard length, were brought back for examination. The specimens were undoubtedly not P. dummerilii on the basis of color pattern and counts, but the identification with either P. altum or P. scalare was uncertain. In fact, the counts seemed to be intermediate between the two forms.

Fig. 2 Map of the Amazon basin showing selected areas of the angelfishes' range (1-11).

They ranged from 25 to 27 rays in the dorsal fin and 27 to 30 rays in the anal fin. All had VI anal fin spines, and eight of the nine had XII dorsal fin spines. The ninth had XIII spines. The scale rows ranged from 34-43 from the rear of the head to the midbase of the caudal fin. In P. altum there are reported XI-XIII dorsal fin spines (though normally XII) with 27-31 dorsal fin rays (mostly 28), and VI anal fins spines with 28-32 rays (usually 29-30). P. scalare had XI-XIV dorsal fin spines (mostly XII or XIII) with 21-28 rays (mostly 22-26) and V-VII (usually VI ) anal fin spines with 22-30 rays (mostly 24-28). It had 28-44 scale rows (more normally 31-39). Since Schultz gave the number of specimens from each locality for each of the counts in his Table 3, it was an easy matter to plot the mean of the counts from each locality on a map and compare them (Fig. 2 above).

A wild caught angelfish from the Orinoco River. This is the Pterophyllum altum of Schultz.

The results of this graphic representation were quite interesting. In proceeding up the Amazon River from Santarem through Manaus to the Rio Negro and on to the Orinoco, the mean number of dorsal and anal fin rays and scale rows increased. The specimens in the Manaus to Tefe area were almost alike in these counts, but moving upstream in the Solimoes system to the Peruvian Amazon the counts decreased again. Heading to the Atlantic coast from Santarem there is another increase in mean counts. The Guyana specimens agreed quite well with the Porto do Moz specimens. Right: A wild caught angelfish from the Orinoco River. This is the Pterophyllum altum of Schultz. It appears, then, that P. altum is the end of a cline of the Rio Negro populations of P. scalare. Another group of 6 specimens taken above the Igarape Anapichi and Igarape Apania region, which were identified as P. altum, had counts which fell nicely into this clinal sequence (see fig. 1).

Captured farther up the Rio Negro (proceeding in a northwesterly direction along the Rio Negro from Manaus).

On the basis of these findings it seems that there are only two valid species in the genus Pterophyllum.. P. scalare and P. dumerilii, with P. altum not valid. P. dumerilii is sympatric with P. scalare and differs in color pattern. There are generally fewer dorsal and anal fin rays (D. XI-XIII, 18-24, but usually 19-21; A. VI, 19-28, but usually 20-22), and fewer scale rows 26-33 (but usually 27-31).

Wild-caught angelfish taken from the Rio Negro at different points in the river. The fish to the left (Fig.4) was captured a two-days journey farther up the river (proceeding in a northwesterly direction along the Rio Negro from Manaus) than the fish below-right (Fig. 5), which was caught in the area of Igarape Anapichi and Igarape Apania.

Caught in the area of Igarape Anapichi and Igarape Apania.

Because of Dr. Axelrod's report on the short anal fin, I examined the rays carefully under a microscope. It seems fairly certain that the trailing anal rays and sometimes the caudal and pelvic rays were torn or bitten off and have started to regenerate. When I explained this to Dr. Axelrod he surmised that the exceptionally high waters conjugated the habitats of the angelfish with those of the piranhas, thus enabling the piranhas to bite off their long trailing anal fins. Normally the two habitats are distinct and these physical anomalies are not apparent.

 
 
 
 
 
 
 
 
 
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