Similar looking fish species. A coincidence? Maybe not..

[yikai]

Ever wondered why a group of fishes within a genus look so similar? while they look so different from others in the genus?

take for example the very popular dwarf angel fishes, genus centropyge.

why do argi, flame backs, resplendent, all look so similar? while they look so different from flame, coral beauty etc.

or take butterflies for example. pearl scale butterfly? there's at least 4 that look so similar.

wrasses too. are these all coincidence? maybe not.

We define these fishes as a complex.

what is a complex and how is it formed? I'm not exactly sure too. many scientist believe these fishes within a complex are allopatric species.

allopatric species? this means that many of the species within the complex only originated from 1 fish and then slowly evolved into many other closely related one due to intrinsic forces.

Let us take centropyge argi for example. the cherub/argi angel. the other related fishes in the "argi complex" are C. aurantonotus, C. acanthops and C. resplendent.

It could be that C. argi was the only one sole member of "argi complex". but because of forces like strong waves, shifting plates, these argi angels are separated into different locals in the world, and started evolving. from there we see the argi angel evolve into resplendent (in the ascension islands), flameback angels (in brazil) etc.

that's how allopatric species originate.

i'm still learning more about this so my post will lack some information, but i just find it too interesting so i will share it with you guys. (provided anyone is interested lol..)

on a side note, a complex should not be confused with a genus.

a complex is a group of fishes within a major family that bear striking resemblance. more information below.

a genus or subgenus, is a collection of fishes with confirmed DNA evidence such that they can be classified in their own genus.

in a way, a complex is an un-confirmed "genus" from the main family.

[yikai]

From the genus centropyge, we have the argi complex. A group of dwarf angels bearing very close resemblance to Centropyge argi.

We have here,

C. resplendent, C. aurantonotus, C. acanthops and C. argi

there are other very closely similar species of dwarves but i don't know if they can be consider complexes. such as

C. multicolour and C. nachyaki

C. colini and C. narcosis

C. multispinnis, C. bispinosa, C. nox and C. flavipectoralis

[yikai]

From the wrasse family, genus cirrhilabrus, we have the temminckii complex. A group of wrasses bearing very close resemblance to Cirrhilabrus temminckii.

We have here,

C. temminckii, C. balteatus and C. katherinae. there might be more within this complex that i'm unaware of

All very closely related species. that said, even C. temminckii is highly variable and 1 species can look very different from each individual.

[yikai]

We have here the "rubriventralis" complex. A group of fairy wrasses very similar to Cirrhilabrus rubriventralis.

Members of this complex includes C. rubriventralis, C. naokoae, C. joanallenae, and C. morrisoni

here are the pictures in order from left to right. i can't find a picture of C. morrisoni.

As for the genus Cirrhilabrus (fairy wrasse),

i'm not sure if the following are considered complexes

C. rhomboidalis, C. pylei, and C. lineatus

C. roseafascia, C. lanceolatus, C. cf. lanceolatus, C. blatteus

[yikai]

Butterflies, we have the "xanthurus" complex. Called the xanthurus complex because of a group of similar looking butterflies belonging to the family chaetodon, bearing very close resemblance to chaetodon xanthurus.

it's debatable that this group of butterflies should be placed in the subgenus Exornator, or a distinct subgenus of Rhombochaetodon.

here we have C. xanthurus, C, madagascariensis, C. paucifasciatus, C. mertensii, C. argentatus

[yikai]

Next in butterflies, we have the "quadrimaculatus" complex. a group of butterflies similar to Chaetodon quadrimaculatus.

C. quadrimaculatus, C. pelewensis, C. punctatofasciatus, and multicinctus. possible candidate for this could be the lemon butterfly and milletseed butterfly. C. citrinellus and C. miliaris.

[yikai]

And my favourite complex in butterflies, the "tinkeri" complex.

comprising of C. tinkeri, C. declivis, C. mitratus, C. burgessi and C. flavocoronatus.

this complex is placed in the subgenus "roaops"

[yikai]

Chaetodon sensu stricto, or the capistratus complex.

C. capistratus, C. ocellatus and C. striatus.

[yikai]

The "bennetti" complex. placed in subgenus Tetrachaetodon

C. bennetti, C, andamanensis, C. speculum, C. plebius

[yikai]

Fremblii complex! these are two of my favourites

Chaeotodon fremblii and Chaetodon blackburnii

[yikai]

i think you guys get the idea now. on what a complex is. So the next time you hear this word, don't need to get confused! learn something new everyday

i realiesd that the family chaetodon (butterflyfish) is just too complicated with too many subgenus and complexes. if i were to do it here i no need to sleep at all.

just take a look at how complicated it is

[Digiman]

So a complex is purely due to physical resemblance and no scientific and DNA difference? Seems like only genus with any species contains complexes. Example centropyge genus has many complex groups whereas the smaller chaetodontoplus genus has no complex groups.

So i wonder how do one categorize fishes within the same genus into complex groups, solely by physical resemblance only? Then why not categorize all the genus then. For example the genus prognathodes also has no known complexes, but if we look at physical differences, then there can be complexes as well:

(Prognathode Dichrous and Prognathode Obliquus) compared with (Prognathode Marcellae and Prognathode Aya)

[yikai]

So a complex is purely due to physical resemblance and no scientific and DNA difference? Seems like only genus with any species contains complexes. Example centropyge genus has many complex groups whereas the smaller chaetodontoplus genus has no complex groups.

So i wonder how do one categorize fishes within the same genus into complex groups, solely by physical resemblance only? Then why not categorize all the genus then. For example the genus prognathodes also has no known complexes, but if we look at physical differences, then there can be complexes as well:

(Prognathode Dichrous and Prognathode Obliquus) compared with (Prognathode Marcellae and Prognathode Aya)

i think for prognathodes, the whole genus is a scientifically recognised complex. that's why it's elected into it's own genus, prognathodes.

imagine if all prognathodes were actually chaetodon. then we will be classifying all of them into a chaetodon "aya" complex. but this complex will soon be elected into prognathodes..

that's why i said in my first post i dunno much about this but it's so interesting to know. so what is the clear defining line between a complex and a genus? i've spent many nights thinking about this and searching on RC. but no one can tell me the answer

i think as long as the complex is scientifically recognised and backed up with proof, it can be elected into a genus level.

take the xanthurus complex for example. they are being placed in and out of exornatus and rhombochaetodon on and off. how come? this is also a subgenus. but maybe because not yet confirmed by evidence? thats why they are on and off referred to as the xanthurus compelx, and not the exornatus.

same for the corallochaetodon, comprising of ornate, trifascialis etc. why we don't see corallochaetodon as a distinct confirmed genus, but an on and off one? maybe coz it's not confirmed yet, so they refer to them as a ornate complex for now.

same for roaops. i think the tinker complex may actually be confirmed as a roaps genus in the near future. so in future this complex will no longer be a complex, but actually a genus.

chaetodon tinkeri no more. it shall be roaops tinkeri. perhaps? i dunno.

perhaps you or someone here could enlighten me.