Cichlid Room Companion

Editorial

The feeding behavior of Perissodus straeleni

By , 2015.
Last updated on 24-Sep-2015

Ad Konings, 2012

" A recently published paper on the mimicry of P. straeleni is discussed. The authors find scales from many different species, mostly cichlids, in the stomachs of 38 P. straeleni specimens, but very few coming from C. frontosa, the species which is thought to be the model of the mimicry. So it seems not a case of aggressive mimicry as the authors claim it to be "

Male at Kalugunga A male of Perissodus straeleni at Kalugunga, Lake Tanganyika [Tanzania]. Photo by Ad Konings. determiner Ad Konings

Boileau, Nicolas & F. Cortesi, B. Egger, M. Muschick, A. Indermaur, A. Theis, H.H. Büscher & W. Salzburger. 2015. "A complex mode of aggressive mimicry in a scale-eating cichlid fish". Biology Letters. v. 11, pp. 20150521

To start off, the paper now proves with DNA signatures that P. straeleni (the authors still use Plecodus as the genus) feeds on a host of cichlid species and just rarely on C. frontosa which it appears to mimic. This would have been fine enough for a publication, but it is bizarre, however, that the authors claim that “the prevailing view” is that P. straeleni would “primarily attack its model”. The only reference they give to support their understanding is Pierre Brichard’s first "Fishes of Lake Tanganyika" book which was published in 1978! We are talking 37 years ago! They couldn’t refer to his second book (Brichard, 1989) because he then no longer held the belief that P. straeleni mainly attacked C. frontosa. The results Boileau et al. present were already known through the published works of Yanagisawa et al. (1990) and Nshombo (1994), both papers which they also refer to! Baffling! Everybody knew that P. straeleni feeds on any species it encounters and also that it rarely attacks its assumed model, C. frontosa. Already for at least 23 years.

Another bizarre quote: “There are indeed reports that P. straeleni blend in schools of Cyphotilapia frontosa […] (Brichard, 1978), suggesting a protective mimicry function.” Protective mimicry means that the mimic would suffer fewer attacks from predators. This would further mean that the model is toxic or has another character that would protect it from being eaten. I have eaten frontosa myself — they taste pretty good actually, not toxic at all — but in my opinion this so-called schooling behavior (I think it is just coincidence most of the time) does certainly not suggest a protective mimicry.

Another quote: “…mimicry in P. straeleni apparently involves two models and a whole species community as dupes, making it one of the most complex aggressive mimicry systems known to date.” Already in 1992 (Konings, 1992:24) I tried to explain why it would be illogic to think that P. straeleni is mimicking Neolamprologus sexfasciatus, and I have repeated these thoughts in books published later. Apparently no author could find a fault in these thoughts else it would have been mentioned at some point. This is what I wrote 23 years ago:

" It has also been said that it (P. straeleni) may mimic not only C. frontosa but also Neolamprologus sexfasciatus and N. tretocephalus. There are several reasons why this seems unlikely. First of all P. straeleni resembles C. frontosa to such an extent that it is easily mistaken for its model, even at close quarters. It goes to great lengths to copy C. frontosa, so much so that the population at Kapampa has a much bluer coloration (like C. frontosa) than that at Rutunga, Burundi. Secondly, there are many places in the lake where there is no N. sexfasciatus or N. tretocephalus, which would of course not exclude the theory that P. straeleni’s colour pattern could have developed in mimicry of those species, but it would make the extreme resemblance to C. frontosa at locations where these two species are found inexplicable. Thirdly we could argue that other scale-eaters, especially the abundantly present Perissodus microlepis, do not mimic their prey. If we combine this with the observation that P. straeleni attacks other cichlids than C. frontosa then it seems unlikely that P. straeleni needs its coloration to be able to exist predominantly on scales of C. frontosa.

C. frontosa roams about in the rocky biotope but it has never been seen hunting prey. Other species inhabiting the same biotope probably know its peaceful manners and thus give P. straeleni, dressed in a “sheepskin”, a good opportunity. Feigning to be a good-natured C. frontosa, the scale-eater comfortably closes in on its prey and before the victim recognizes the wolf it has lost some of its scales. "

Claiming that P. straeleni mimics two models — and all the time we are just talking about the male, because the female is all-brown — is a little far-fetched. The authors even make an effort in comparing the color patterns of N. sexfasciatus, C. frontosa, and P. straeleni, and then state that that of N. sexfasciatus is a better match than that of C. frontosa. Be that as it may, when diving in Lake Tanganyika one doesn’t have to look twice to see whether it is P. straeleni or N. sexfasciatus, not even close in my opinion, but to immediately tell C. frontosa apart from P. straeleni is a different matter. And again: “… making it one of the most complex aggressive mimicry systems known to date.” I don’t believe it is complex, am not even sure it is a case of aggressive mimicry because P. straeleni is not attacking C. frontosa much at all. For all we know it may just have evolved its color pattern separate from its feeding behavior. Nobody claims that N. sexfasciatus is mimicking C. frontosa to get better hunting results.

References (6):

Citation:

Konings, Ad. (September 23, 2015). "The feeding behavior of Perissodus straeleni". Cichlid Room Companion. Retrieved on January 23, 2019, from: https://www.cichlidae.com/section.php?id=287.