Mystus seengtee (Sykes)

Prosanta Chakrabarty & Heok Hee Ng, 2005, The identity of catfishes identified as Mystus cavasius (Hamilton, 1822) (Teleostei: Bagridae), with a description of a new species from Myanmar., Zootaxa 1093, pp. 1-24 : 17-20

[[ Mystus seengtee (Sykes) ]]

Discussion

Pimelodus seengtee was originally described from the Deccan region in southwestern India from a holotype 6 inches (=152.4 mm) long (this length almost certainly refers to TL). There are two specimens in the Natural History Museum (London) attributed to Sykes (see Roberts, 1994): a dried, stuffed specimen 130 mm SL (BMNH 1857.6.13.154), and a wet specimen 113 mm SL (BMNH 1860.3.19.955). Before we discuss the identities of the two specimens, it is instructive to briefly review the history of the ichthyological material collected by Colonel William Henry Sykes during his Deccan survey. This material was initially deposited in two institutions: the Zoological Society of London (Greenwood, 1976; however, it is interesting to note that there are no written records that Sykes ever deposited fish specimens there, see Wheeler, 1997) and the Honourable East India Company's India Museum (sometimes also referred to as the "East India Museum " or the "East Indian Museum "; Whitehead & Talwar, 1976). The collections of the Zoological Society of London were sold to the Natural History Museum [then British Museum (Natural History)] in 1855-56 (Boulenger, 1906; Mitchell, 1929; Greenwood, 1976; Wheeler, 1997) and the collections of the India Museum were transferred to the Natural History Museum in 1859-60 (Boulenger, 1906). These may have been the reasons why BMNH 1857.6.13.154 (purchased from the Zoological Society of London) and BMNH 1860.3.19.955 (donated by the Honourable East India Company; such material is indicated in the registers as "...presented by the Secretary of State for India") were both regarded as potential types of Pimelodus seengtee (see Roberts, 1994).

Although the wet specimen (BMNH 1860.3.19.955) is closer in size to that of the holotype ( M. seengtee has a caudal fin of about 30% SL in length; this would make BMNH 1857.6.13.154 about 169 mm TL and BMNH 1860.3.19.955 about 146.9 mm TL), our examination of a photograph of this specimen shows that it is not M. seengtee , but M. cavasius (as the specimen has a gently-sloping predorsal profile making an angle of about 25° to the horizontal typically seen in M. cavasius ). This is confirmed by the gill raker counts (21) of this specimen (J. Maclaine pers. comm. to HHN), which correspond to M. cavasius (but not M. seengtee ). Therefore BMNH 1860.3.19.955 cannot be the holotype of Pimelodus seengtee .

The dried specimen (BMNH 1857.6.13.154) is also approximately the same size as that stated for the holotype. However, it is poorly prepared, having the head strongly arched backwards such that it is no longer possible to accurately determine the slope of the predorsal profile (Fig. 8). Furthermore, it is not possible to confirm the identity of the dried specimen by counting the gill rakers, because the gill openings have been sealed shut (J. Maclaine, pers. comm. to NHH); it also highly likely that the gill arches have been removed in the course of preparation. Given the uncertainty concerning the specific identity of BMNH 1857.6.13.154, we have refrained from identifying it as the holotype of Pimelodus seengtee . Since we are not even sure if it is conspecific with southern Indian material we have examined, we tentatively identify it as Mystus sp. incerta sedis .

Although it is frequently acknowledged that the fishes collected by Sykes (particularly the types of the species he described) are lost (e.g. Ferraris & Runge, 1999), our investigations uncover evidence that some of this material may still be extant. One other specimen (BMNH 1857.6.13.158) also acquired from the Zoological Society (and accessioned) at the same time bears the name Hypophthalmus goongorensis (most likely a misspelling of Hypophthalmus goongwaree ) in the register, and its status as the holotype of this species should be investigated. This is beyond the scope of this study, but we mention it here to draw attention to the problem.

Both M. seengtee and M. falcarius can be distinguished from M. cavasius by the differences in the number of rakers on the first gill arch. Although the gill raker counts can be variable among Mystus species (Roberts, 1989), the differences in counts as being indicative of interspecific differences are further supported by the presence of other characters in predorsal profile shape, dorsal fin shape, and coloration unique to the southern Indian, northern Indian and Myanmar populations of “ M. cavasius ”. Although some overlap exists between gill raker counts for M. cavasius (n=70) and both M. seengtee (n=25) and M. falcarius (n=29) combined, the overlap only occurs at the uppermost limit of the gill raker counts for M. cavasius (22) and only in one out of 70 specimens of M. cavasius examined. We note that because of this and the fact that gill raker counts can be useful in distinguishing species of Mystus (e.g. Roberts, 1992), the differences observed are treated as interspecific in nature. Furthermore, it is unlikely that the variation in gill raker counts is the result of clinal variation, as no clear geographic pattern exists (Roberts, 1994). The slope of the predorsal profile is consistent for all of the material we have examined and it can be reliably used to distinguish M. seengtee from M. cavasius . The shape of the humeral mark can be reliably used to distinguish M. falcarius from M. cavasius and M. seengtee . In M. falcarius , this mark is always crescent shaped (vs. ovoid). The ovoid humeral mark is also more prominent in nearly all of the M. cavasius material we have examined (except in UMMZ 238800, BMNH 1938.2.22.122, BMNH 1938.2.22.123 and BMNH 1938.2.22.124-128) when compared to that of M. seengtee . However, since we do not know the live coloration of M. seengtee (the humeral mark is prominent in the live coloration of M. cavasius ) and cannot rule out the faded condition in M. seengtee as a preservation artifact, we have refrained from using it as a diagnostic character. The dark spot at the base of the dorsal spine is very prominent in M. falcarius , more so than in either M. cavasius or M. seengtee . This is evident even in old material which has not been properly fixed and in which the color is considerably faded (BMNH 1891.11.210-219).

The species diversity and distributional patterns as observed in M. cavasius , M. seengtee and M. falcarius (with three distinct species distributed in northern India, southern India and Myanmar respectively) is fairly common among riverine catfishes in this region. For example, similar distributional patterns have been observed in other catfish genera, most notably Rita (see Ferraris, 1999) and Gagata (see Roberts & Ferraris, 1998).

A species of Mystus with a long-based adipose fin similar to M. seengtee (currently identified as M. cavasius ) is also found in Sri Lanka. A comparison based on a photograph of a Sri Lankan specimen in Pethiyagoda (1991) shows that it differs from M. seengtee in having a more falcate dorsal fin and the apparent absence of a dark spot in front of the dorsal-spine base. The identity of the Sri Lankan species is being further investigated in a separate study by the second author and colleagues.

Additional material examined

Mystus sp. incerta sedis :

BMNH 1857.6.13.154, 130 mm SL; India: purchased from the Zoological Society of London (photograph examined).