The Angelfish Chronicles

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© Warren Burgess (1979)

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One would think that the common aquarium fish should have no problems concerning their proper scientific names, especially if they have been in the hobby for many years. But in many of the popular aquarium fishes a name is generally applied, usually by a scientist, which is immediately accepted by all concerned, and no further inquiry is made. And after all, since they are common, specimens should be readily available for investigation by scientists in case some question arises as to their proper identity.

Unfortunately this is not always the case. Local breeders successful in propagating the initially high-priced imports, and domestic stocks soon are plentiful enough at low prices to satisfy most of the needs of aquarists. The imports naturally drop off considerably as domestic supplies increase and eventually stop altogether. In addition, easy-to-breed species that are genetically variable are selectively bred to produce any number of strains often quite different in appearance from the natural species. Wild-caught specimens are therefore not as available through the aquarium trade as one would think. Any inquiries into the systematic problems of such fishes would necessitate visits to museums where collections of the species concerned are held or travel to their natural habitats (as was done by Dr. Herbert R. Axelrod). The common angelfishes of the genus Pterophyllum seem to be one of these groups that has caused a great deal of trouble.

The first angelfish ever described was a species called Zeus scalaris by Lichtenstein in 1823. It was collected in “Brazil” and apparently deposited in the Berlin Museum. Cuvier (or Valenciennes) found the specimen there labeled Zeus scalaris and was probably unaware that Lichtenstein had already published its description. They therefore described it as new, kept the specific name scalaris, but decided that it was in the wrong genus, naming it Platax? scalaris. They apparently were not satisfied with placing it in the genus Platax (hence the question mark) and thought that when it became better known (the specimen was in a “mutilated” condition and only an incomplete description could be given) a new genus could be erected for it. This was apparently accomplished some nine years later (in 1840) by Heckel, who was able to see additional specimens from the Rio Negro. He called the new genus Pterophyllum (meaning fins like leaves), which included at that time the single species Pterophyllum scalaris. In 1855 Castelnau described a new genus and species of this same type fish, calling it Plataxoides dumerilii, seemingly unaware of the fish described by Cuvier and Valenciennes. Guenther, in his Catalogue of the Fishes in the British Museum (Natural History), simplified everything by synonymizing Plataxoides with Pterophyllum and placing all the species thus far described (Platax scalaris, Pterophyllum scalaris, and Plataxoides dumerilii, but not Zeus scalaris of which he was probably unaware) under the slightly modified name Pterophyllum scalare. There were then either one (P. scalare) or two (P. scalare and P. dumerilii) species of angelfishes depending upon whether one agreed with Guenther or not. At least they were finally placed together in a single genus.

In 1903 another angelfish species, Pterophyllum altum, was described by Pellegrin, and in 1928 a fourth species, P. eimekei Ahl, was added to the list. The most recent species described, Plataxoides leopoldi Gosse, was placed in Castelnau’s genus because Gosse believed that the name Pterophyllum was preoccupied by a genus of insects called Pterophyllum Harris. But Schultz, in reviewing the genus Pterophyllum in 1967, checked on the name and found that Harris consistently used the name Pterophylla, not Pterophyllum as erroneously reported. The genus name Pterophyllum was therefore free to be used (or available according to the terminology of the International Rules of Nomenclature).

At this point in time there were five named or nominal species: Pterophyllum scalare, P. dumerilii, P. altum, P. eimekei and P. leopoldi. But how many real species of angel-fishes were there?

It seems that Schultz was able to examine the holotype of P. dumerilii and the paratypes of P. leopoldi and concluded that they are one and the same species. Comparisons of P. scalare specimens with those of P. eimekei led Schultz to consider the latter species a synonym of the former. The remaining species, P. altum, he considered valid although casting some doubt on this decision with his statement "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 recent collections by Dr. Herbert R. Axelrod in the Rio Negro (see “The Heavenly Paradox”), some very interesting and, as it turns out, very important specimens of angelfishes were taken.* According to Schultz’ distributional map, the collecting sites for which he had data on the angelfishes were restricted to the Amazon River from its mouth to Manaus and then along the Solimoes (Amazonas) branch of the river to Peru. There were no collections reported on by him from the Rio Negro, which winds its way northwestward toward the Orinoco where Pterophyllum altum comes from! These specimens from the Rio Negro thus filled a very important gap. The question as to whether they would show (1) a close association with the Amazon and Solimoes forms and be as different from P. altum as they were, (2) a close association with the Orinoco forms and be different from the Amazon and associated forms, or (3) would they show a continuous gradient or cline from Manaus to the Orinoco, indicating that P. altum was really not very different after all, could at last be answered. According to Schultz, the differences between P. altum and P. scalare are the greater average number of soft dorsal and anal fin rays as well as the greater average number of oblique scale rows and vertebrae of P. altum. The color patterns were said to be identical and therefore of no use in distinguishing the two. Proportional measurements were made but considered unreliable due to the great variability “even at nearly equal sizes,” although photos of P. altum always seemed to show a fish with more elongate dorsal and anal fins.

*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 bittern 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 bit off their long trailing anal fins. Normally the two habitats are distinct and these physical anomalies are not apparent.

When the average number of dorsal and anal fin rays and oblique scale rows were plotted on a map of the Amazon system, it was found that Belem specimens had an average of 24.9 dorsal fin rays, 27.5 anal fin rays and 36.7 oblique scale rows. The average numbers dropped as one headed up-river to Porto do Moz and Santarem (to 23.3 and 22.6 dorsal fin rays, 25.3 and 24.9 anal fin rays and 33.2 and 33.1 oblique scale rows respectively) but increased again (to 24.6, 26.8, and 35.4) by the time one reached Manaus. At this point the branching off of the Rio Negro occurs. If one follows the Solimoes (Amazonas) the counts stay about the same at least as far as Tefe (24.6, 27.1, and 35.5) but start to drop again upstream at Tonantins (23.6, 24.9, and 33.1). With the new specimens available it was discovered that if one follows the Rio Negro from Manaus, the counts increase with distance from the Amazon so that at Igarape Anapichi and Igarape Apania in the upper Rio Negro the average soft dorsal ray count for nine individuals was 26.2, the average anal fin soft ray count 28.3 and the average number of oblique scale rows 38.1. The identification of these specimens as either P. scalare or P. altum on the basis of counts was not immediately obvious, although they seemed to favor the latter species. Another group of six specimens collected further up the Rio Negro fell nicely into this sequence, with an average number of soft dorsal fin rays of 28.0, anal fin rays 29.8 and oblique scale rows 40.3.* When compared to the counts for P. altum from the Orinoco (28.6, 29.7 and 42.6 respectively) it could be seen that they were extremely close. The Rio Negro angelfishes appear to bridge the gap between the Orinoco populations.

 *The counts that appeared in position 2 on the map appearing in T.F.H. Magazine for January 1976, p. 95, were in error.

Fig. 1. Map of the Amazon basin and adjacent areas showing the locations of the samples (1-13).

Map of the Amazon basin and adjacent areas showing the locations of the samples (1-13). At each locality the range of soft dorsal (D.) and soft anal (A.) fin counts are indicated along with their mean average, as well as the mean average of the longitudinal scale rows.

When one looks at the color pattern of these fish very little can be seen to separate them at first glance. On closer examination, however, certain distinctions become evident. If one were again to compare the extremes (Rio Orinoco with the Amazon or Guyana specimens) one would observe that the Amazon and Guyana specimens possess a dark band that extends from the chest (where it is joined by the corresponding opposite band) through the eye to the first spines of the dorsal fin. The Orinoco forms have a similar band that starts from the same spot on the chest, passes through the eye and ends on the nape. A second band starts from the first few spines of the dorsal fin and extends toward the pectoral fin base but is considerably faded, almost absent, below the first few millimeters. There is a distinct gap between these two bands. The question then arises, how are these bands arranged in the Rio Negro angelfish? It appears that they are similar in position to those of the Orinoco angelfish. The difference in these two types of banding is not all that great. All it takes to move from one to the other is some melanophores to bridge the gap between the eye band and the band from the first dorsal spines-which apparently occurs in the Guyana populations and those from the Amazon. Not enough wild-caught specimens are available to me to be able to extrapolate further in the nuances of the different types of head banding. It is interesting to note at this point that P. dumerilii goes one step further in that there is another “short” band between the eye band and the band on the first dorsal fin spines, the eye band itself simply crossing from one eye to the other directly across the interorbital space.

Finally, there seems to be a more vertical appearance to the Rio Orinoco individuals. Schultz considered the proportional measurements as too variable and that comparison of specimens even at “nearly equal sizes suggests that little reliance can be placed on measurements for identification purposes.” The Orinoco and Rio Negro populations show a tendency to be slightly deeper bodied than the Amazon and Guyana populations in the limited material at hand. Body depth of the former ranges from 1.2-1.3 in standard length whereas that of the latter ranges from 1.3-1.5 in standard length.

Repeating the question asked before, how many real angelfishes are there? Answer-two, Pterophyllurn scalare and P. dumerilii. But P. scalare is considered here to consist of two subspecies, P. scalare scalare from the Amazon and Guyana and P. scalare altum from the Orinoco and Rio Negro. These two subspecies are separable on the basis of color pattern as described above, a tendency towards higher meristic counts (at least in the dorsal and anal fin soft rays and the lateral scale rows) and perhaps a deeper body. P. dumerilii differs from P. scalare in having lower counts in the dorsal and anal fin rays and the lateral scale rows. These meristics are summarized in the accompanying table.

Fig. 2. Pterophyllum species meristics sumerization.

In addition, there are color pattern differences which can be used for distinguishing P. scalare and P. dumerilii. In P. dumerilii there is a conspicuous black spot located just below the dorsal fin base between the two black bars. In P. scalare there is a bar or the remnant of a bar in the same position, its distinctness depending a great deal upon the mood of the individual fish. As noted before, there is a separate bar between the eye band bar and the one originating at the first few dorsal fin spines. This would seem to be more similar in appearance to P. scalare altum from the Orinoco and Rio Negro and more distinct from the Guyana and Amazon populations. Since P. dumerilii has only been found in the main Amazon and Guyana regions with P. scalare scalare, they are more easily separated by this character from the specimens found there.

As far as known, P. scalare scalare has a broad range over the Amazon basin from the area of the mouth to Peru (Ucayali R., etc.) and from Guyana (Schultz also listed French Guiana in his list of specimens examined) to the Araguaia River (almost 15 0S latitude near Brasilia). Dr. Axelrod was able to extend the range to the Madera River as far as Humaita.

Counts recorded for Pterophyllum species at various localities in the Amazon basin and adjacent regions. Data from Schultz, 1967 and new material.

P. scalare altum appears to be restricted to the area from the Orinoco (at Atabapo) to the Rio Negro at least as far as Igarape Anapichi and Igarape Apania. The Orinoco and Rio Negro may have some connection through the Casiqulare River (where P. s. altum has also been found).

P. dumerilii seems to be restricted to the Amazon River from its mouth to Tonantins on the Solimoes, as well as occurring in Guyana. Its distribution seems to follow that of P. scalare scalare, although it is not nearly as widespread or common. Perhaps as the species becomes better known its distributional pattern will become clearer.

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