Catfish Corner: Lake Tanganyikan Synodontis--- the Revision

Author: Lee Finley

Catfish Corner: April 2007

In recent columns I have discussed two recently published studies on the Lake Tanganyikan Synodontis species. Both of the works covered were based on mitochondrial DNA and indicated the presence of undescribed species. Now the standard taxonomists have had their go at these fishes and a revision based on the examination of 312 specimens has recently been published (Wright, J. J. and L. M. Page, 2006. “Taxonomic revision of Lake Tanganyikan Synodontis[Siluriformes: Mochokidae].” Bulletin of the Florida Museum of Natural History, 46(4): 99-154). What follows are some notes, of varying length, based on the revision.

Notes on Non-Endemic Species

First noted will be the non-endemic species Synodontis melanostictus, which is sometimes referred to as S. nigromaculatus. The latter fish is a valid species, but it is not found in the lake. S. melanostictus from the vicinity of the lake is not very important hobby wise, and it is rarely imported.

Commentary on the Ten Endemic Species

That takes care of the easy part. Now to the endemic species, which have a far greater complexity. The new revision recognizes 10 endemic species, with three of them being described as new. In addition, one species that was previously placed in synonymy is resurrected. Some situations are clarified by the paper, but others (from the point of the catfishes in the hobby) are a little less clear.

1. Synodontis multipunctatus

This is arguably the most popular and widespread in the hobby of the Lake Tanganyikan Synodontisspecies. It is—or, better said, was—also one of the most easily recognized of the species. But this has changed due to the presence of…

2. Synodontis grandiops

This is one of the new species of Wright and Page. In color pattern it is in all ways identical to S. multipunctatus. It is interesting comparing the coloration sections of the paper on this new species and S. multipunctatus. Except for three words (which change nothing) and one small punctuation difference, the coloration sections for these two species are identical. Where do we go from here?

Small Differences

There are a number of small physical differences that separate these two species, but many of them can be difficult to work with on living catfishes. There are two features that can be used to differentiate the species and these are usable on living fishes. The first of these is the number of soft rays in pectoral fins. In S. grandiops this number is reported to be consistently seven. In S. multipunctatus it is reported to always be eight.

The other feature for identification is the difference in the size of the eye. S. multipunctatus has a smaller eye size (noted to be 44.9 to 62 percent of the snout length). In S. grandiops the eye size is 64.2 to 81 percent of the snout length. The snout length is defined as the distance between the very tip of the forward part of the head (snout) and the anterior margin of the eye. So basically, S. grandiops has a much larger eye in relation to the snout length. Interestingly, the species name grandiops means large (or big) eye.

Based on some snout length/eye diameter measurements made on photographs, it is clear that this species, which is noted to be common, has been imported into the hobby.

There are also size differences between the two species, but these would only be helpful in the case of having a large S. multipunctatus. The maximum sizes provided for the two species are 280 mm TL (11 inches) for S. multipunctatus and 150 mm TL (5.9 inches) S. grandiops.

The description of S. grandiops does bear out my contention that there was hidden diversity in the fish we have historically called S. multipunctatus.

3. Synodontis dhonti

Interestingly, in the 312 fish used for the revision only one S. dhonti was identified. This was the large type specimen which was collected in 1912 and measures 395 mm TL (15.5 in.). So, what smaller fish possibly seen in the hobby might look like is anyone’s guess.

4. Synodontis irsacae

S. irsacae, which has been considered a synonym of S. dhonti, has been resurrected to species rank. This smaller species (190 mm TL, 7.5 inches) has been known as S. dhonti in the hobby and aquarists keeping it have wondered why it never got as large as it was supposed to. Now we know…it wasn’t supposed to get any larger.

5. Synodontis granulosus

This very distinctive species, which reaches a reasonably decent size of 270 mm TL (10.6 inches) is more than distinctive enough so that it needs little description—beyond “stunning!”

6. Synodontis tanganaicae

This is the largest of the endemic species of Lake Tanganyikan Synodontis. In table 2, Wright and Page list the maximum length of this fish as 585 mm TL, but on page 147 they make note of Poll’s holotype of S. lacustricolus (601 mm TL, 23.7 inches), which is a synonym of this species, which increases the maximum length by a bit.

In last month’s column I did a discussion on the spelling of the species name of this fish. I ended up noting that I was going to use the spelling “tanganyicae” until further notice. Wright and Page accept that this is a proper species, but revert to the spelling of the name in the manner of Borodin—tanganaicae. So for now I will follow this spelling in that it is part of such a major work.

7. Synodontis petricola

S. petricola is one of the two so-far-described species in which the dorsal and pectoral spines are colored white (The other is the new species S. lucipinnis) and all rayed fins have black roughly triangular markings at their base. S. petricola is one of the smaller species and reaches a length of 135 mm TL (5.3 inches).

8. Synodontis lucipinnis

This is a new species and its coloration is very much like that of S. petricola, with one main difference. With this species it is noted that there are “lightly colored windows” at the base of the black triangles on the fins. These “windows” are stated to be “most noticeable in dorsal and anal fins.”

S. lucipinnis is a smaller fish than S. petricola and reaches a maximum size of 100 mm TL (3.9 inches). This fish appears to be, at least in part, the so-called “dwarf petricola” of the hobby. I will emphasize the “in part” in that the widespread use (and misuse) of common names in the hobby can, and does, lead to a lot of confusion. Such names on the commercial level are many times bandied around with little rhyme or reason. Most often there is no malice involved, but it can nonetheless lead to confusion and make discussions on the various fishes involved somewhat problematic.

Note: Although the two above species are noted to be the only ones having white spine coloration, various imported fishes over the years do, to my mind, indicate that there may be greater diversity to be discovered in this group.

9. Synodontis polli

This is a fairly well-known species that reaches a maximum size of 180 mm TL (7 inches). Notable with this fish is its relatively broad mouth. The dorsal and pectoral spines are dark in coloration, but the pectoral spines are noted to have a “thin, light stripe along anterior margin.” In younger fish the caudal fin has a white posterior margin, but this becomes duskier with growth.

10. Synodontis ilebrevis

S. ilebrevis, a new species, bears some resemblance to S. polli. But it does differ in lacking the light stripe on the anterior margin of the pectoral spines. The spotted pattern is noted to consist of “small, regularly shaped, widely spaced black spots.” This is opposed to the pattern of S. polli which has “large, irregularly shaped black spots.” The lighter coloration on the caudal fin is noted to be consistently dusky. S. ilebrevis is smaller in size than S. polli and is reported to reach a maximum length of 150 mm TL (5.9 inches).

Differentiating S. petricola from S. lucipinnis

The above listings and brief comments will hopefully be somewhat helpful with the identification of the endemic species (or at least groups) of Synodontis from Lake Tanganyika. However, I know that at this stage this situation may be problematic. A good case in point is the similar species S. petricola and S. lucipinnis. While these form a “natural group” of sorts based on the white spines of the rayed fins (most notable on the dorsal and pectoral fins), other defining characters are not easy to demonstrate using standard aquarium type photographs (most typically a good side-view). A couple of the differences that are difficult to demonstrate in the manner are:

The shape of the humeral process. These are noted to be quite similar in both species, but some differences are evident on close examination.

Belly spots. In S. petricola these are noted to be small and irregularly shaped. S. lucipinnis is stated to have spots of a more regular shape.

Axillary pore. Herein lies a major diagnostic difference. This opening, located between the lower edge of the humeral process and the base of the pectoral spine, is small but present in S. petricola and lacking in S. lucipinnis. I have yet to see an aquarium-based photo (and I have looked at many in preparation of this piece) that shows any indication of this opening, which is not surprising.

Windows in the black fin markings. This is a tough area and needs more study. Although Wright and Page note this as a major difference between the species, their black-and-white photo of S. lucipinnisdoes not clearly illustrate this as much as I would like. Aquarium photos are mixed in regards to “illustrating” this aspect. Many photos of “S. petricola” that I’ve looked at show varying degrees of a lighter base on the dark areas of the fins. Interpreting this to the extreme would seem to indicate that photos of S. lucipinnis are actually more common than those of S. petricola. This area needs more study and I shall be on it. Hopefully you shall also be doing the same.

Questions and Answers

So this is the listing of Lake Tanganyikan Synodontis revisions based on the work of Wright and Page. Hopefully I have provided some answers in this discussion, but I know that I have created some questions. There will be more to follow in the months to come—hopefully, more answers than questions.