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Comprehensive Description

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Key to the species of Pseudoplatystoma ZBK

1. (a) More than 50 spots in the caudal fin, anterior projection on the lateral ethmoid (Fig. 8), ventral flange on the anterior process of the interopercle, tooth patch of infrapharyngobranchial # 5 covers only the dorsal region of that bone, width of the lateral ethmoid at the joint with infraorbital 1+2 (io 1+2) very narrow (as much as 3/4 narrower than the width of the lateral ethmoid in P. fasciatum , P. punctifer , P. orinocoense , P. reticulatum ZBK , P. corruscans and P. magdaleniatum ..............................2

(b) Fewer than 45 spots in the caudal fin, no anterior projection on the lateral ethmoid, absence of ventral flange on the anterior process of the interopercle, tooth patch of infrapharyngobranchial # 5 covers dorsal and extends over 2/3 of ventral region of that bone, wide lateral ethmoid at the joint with infraorbital 1+2 (io 1+2)............................................................................3

2. (a) Dark loops or reticulated bars along the side of the body (Fig. 15), no spots on the lateral region of the body............................................. P. tigrinum ZBK (Amazon River and tributaries).

(b) Dark vertical bars and few spots (no more than 10) randomly distributed along the side of the body. .................... P. metaense , n. sp. (Orinoco River and tributaries in Colombia and Venezuela).

3. (a) Nuchal plate # 1 expanded, posterior region of the metapterygoid wider than in the other species... ........... P. magdaleniatum , n. sp. (Magdalena and Cauca rivers, north-central region of Colombia).

(b) Nuchal plate # 1 reduced and not expanded.............................................4

4. (a) Thick loop-like or reticulated bars on the side of the body, dark loop-like bars join those in the dorsal region of the body forming distinct cells, dorsal region of head has either loops or spots............. ................................................. P. reticulatum ZBK (Amazon and Paraná rivers)

(b) No loop-like bars on the side of the body; spots or pale vertical bars common and located close to the dark vertical bars....................................................................5

5. (a) Spots distributed regularly in six to eight rows from the posterior margin of the opercle to the tail... P. corruscans ( Paraná and São Francisco rivers, in Argentina, Paraguay, Uruguay and southeast Brazil).

(b) Straight dark vertical bars along the side of the body.....................................6

6. (a) Well-defined straight dark vertical bars on the side of the body, longer than those in P. fasciatum and P. punctifer , vertical bars of the anterior region also straight and extending below the dorsolateral dusky area, bars do not form spots as seen on other species, usually no spots below lateral line, some individuals have two or three spots ................................................................ ............... P. orinocoense , n. sp. (Orinoco River, and its tributaries in Colombia and Venezuela).

(b) Dark vertical bars form spots below the lateral line, well -defined pale vertical bars, distinct demarcated boundary between the dusky dorsolateral and pale ventrolateral regions of the body ............... 7

7. (a) First spinelet of the anal fin contacts the haemal arch of the 24th vertebra, some specimens have spots below the laterodorsal dark region, 43-45 vertebrae .......................................... ...................................... P. fasciatum (Rupununi, Essequibo and Suriname rivers).

(b) First spinelet of the anal fin contacts the haemal arch of the 22nd vertebra, 37-40 vertebrae, free discrete dark spots below the laterodorsal dark region (Fig. 15), adipose fin with fewer (6 or 8) spots than on P. fasciatum ...................................... P. punctifer (Amazon River and tributaries).

Discussion

Unrecognized species of Pseudoplatystoma ZBK have been included under the names P. fasciatum and P. tigrinum ZBK for decades. Considering the wide distribution of both species, at least as regarded in the current literature, this classification results in an underestimation of diversity. Comparative analysis of the morphology of P. fasciatum and P. tigrinum ZBK throughout their ranges supports the prediction that each major river basin of the region (e.g., Guyanas) represents a different species. Thus, the P. fasciatum and P. tigrinum ZBK clades represent six and two different species, respectively. This brings the total number of species recognized in Pseudoplatystoma ZBK to eight. Two species ( P. punctifer and P. tigrinum ZBK ) are sympatric in the Amazon Basin, two ( P. metaense and P. orinocoense ) are sympatric in the Orinoco Basin, and two others, P. corruscans and P. reticulatum ZBK , are sympatric in the Paraná . Pseudoplatystoma magdaleniatum and P. fasciatum each occur as the only species of Pseudoplatystoma ZBK in their respective individual ranges. Pseudoplatystoma reticulatum ZBK may be sympatric with the two other species in the Amazon Basin, but we have no records of them being captured together in the mainstem or tributaries. Herein we restrict P. fasciatum to the Essequibo, Rupununi and Suriname rivers. Whether P. fasciatum , as envisioned here, was fractured as a result of vicariance events is difficult to test because the Guyanan Shield antedates the formation of the major river basins in northern South America (see Lundberg et al., 2000). Dispersion, the other alternative, requires interconnections between Guyana -Amazonian as well as Guyana -Orinocoan rivers. Indeed, connections do exist among some of the rivers, i.e., Branco -Essequibo rivers (Guyana region) and some lowland interconnections in the state of Para (Brazil) that may have allowed Amazonian -Guyanan transfers (J. G. Lundberg, pers. comm.). Whether transfers occurred or still exist at the present time is not known. Pseudoplatystoma fasciatum may have evolved after dispersion from the Amazon River and in isolation during the last glaciation in the Pleistocene (2 Mya.). Pseudoplatystoma orinocoense , a species described here as new, resembles P. fasciatum and P. punctifer . The color pattern and anatomy characters are somewhat similar in these three species and they form a clade within Pseudoplatystoma ZBK ([ P. fasciatum + P. punctifer ] + [ P. orinocoense ] Buitrago - Suárez , 2005). The Amazon and Orinoco rivers are connected by the Casiquiare Canal; hence, fish species interchanges between these two basins are certainly possible. Furthermore, life history studies on P. orinocoense and P. tigrinum ZBK (Orinoco River basin) suggest that these two species make short migrations (Escobar et al., in prep.). Armbruster and Provenzano (2000) suggested that the Casiquiare canal has a recent origin. This suggestion coupled with observations of Escobar et al. (op. cit.) allows for a prediction that species of Pseudoplatystoma ZBK may have been isolated from one another for a much greater time period than previously thought. The same situation applies to P. tigrinum ZBK because it has been traditionally considered a widely distributed species throughout the Amazon and Orinoco rivers (Ringuelet et al., 1967; Mees, 1974; Schultz, 1944; Burgess, 1989), and has been confused with P. reticulatum ZBK (see below PCA).

PCA showed complete separation of P. magdaleniatum from P. orinocoense (Fig. 28A). PCA also showed an almost complete separation of P. magdaleniatum from P. fasciatum , but no separation between that species and P. puntifer . PC2 is most strongly and negatively affected by the dorsal fin base length and anal fin base length, and positively affected by the maxillary barbel length and the anterior chin barbel length.

FIGURE 28. Principal component analyses of the species of Pseudoplatystoma ZBK with similar pigmentation patterns. A, species with dark vertical bars; and B, species with loops.

PCA showed complete separation of P. reticulatum ZBK from P. tigrinum ZBK (Fig. 28B). PC2 is strongly and negatively affected by the dorsal fin base length and adipose fin length, and positively affected by the distance between the pectoral fin and pelvic fin. Separation of P. reticulatum ZBK and P. tigrinum ZBK is consistent with differences in morphology. These two species have similar pigmentation pattern represented by dark loops. PC analyses were not informative when P. fasciatum and P. punctifer were studied together. These two are presumed sister species and have a similar head and body shape. The same situation was observed when PCA was applied to P. corruscans ( São Francisco River) and P. corruscans ( Paraná River).

Cuvier and Valenciennes (1840) and Schomburgk (1841) commented on a structure noticed by Schneider on P. fasciatum from Suriname. Schneider (no date) observed a small hole on each side above the pectoral fin by which the abdomen presumably inflated. We did not find such a pore in the material examined, and moreover there is neither an internal organ associated with such a pore nor ducts connected to the skin that might allow any suggestion of the presence of external pores.

We have seen tiny young of Pseudoplatystoma ZBK being marketed in the ornamental fish trade in both North and South America. Individuals were too small for certain identification, but slight pattern and shape differences may indicate that more than one species is being imported. All the species are sold commonly in the numerous open fish markets throughout much of South America. Catch data from the different basins can now be better clarified to include all eight species of Pseudoplatystoma ZBK , and will allow for more accurate assessment of fishing impact on all the species.

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