How to differentiate similar fish species
Below are some notes I made when first coming to grips with how to tell similar species apart. On my PC with a large screen, I found it useful to open up tabs of fishbase.org thumbnails for each of the difficult species below, so that I could figure out which features of a fish were the actual differentiators between similar species. I am not sure that I have properly learnt how to do this, and I have marked my contributions with a "-JFB" to warn of my lack of expertise. I suggest you open each thumbnails link below in a new browser tab (e.g. by Ctrl+Clicking it) so that you can get an accurate idea of how to tell these similar species apart. (I set up these links by copying the Column C entry from the source spreadsheet into the Tiki text.)
| Species | Common Name | Notes |
|---|---|---|
| Heniochus acuminatus | Longfin Bannerfish | Compared to the Schooling Bannerfish, the bottom-rear fin of the Longfin Bannerfish is longer and has a rounded end, unlike the Schooling Bannerfish which has a smaller and more angular end. Other differences: H. acuminatus has a longer snout than H. diphreutes, and the spots on its snout are darker. |
| Heniochus diphreutes | Schooling Bannerfish | see above |
| Heniochus monoceros | Masked Bannerfish | usually darker in lower half of face (lower half may start above eyes). - JFB |
| Heniochus chrysostomus | Pennant Bannerfish | 3 distinct parallel brown bands, with last at trailing edge |
| Heniochus varius | Humphead Bannerfish | humphead and two distinct white bands in almost meeting upside-down V. - JFB |
| Variola | Lyretails | I don't think you can tell the 2 species of this Genus apart just by looking at photos of them. - JFB |
| Cephalopholis argus | Peacock grouper | very difficult to distinguish from the Blue Spotted - JFB |
| Cephalopholis cyanostigma | Blue spotted grouper | very difficult to distinguish from the Peacock - JFB |
| Coradion altivelis | Highfin Butterflyfish | Generally, H. altivelis has a high fin, V-ish bands, and it might have a false eye. - JFB |
| Coradion chrysozonus | Orange-banded Butterflyfish | Generally, C. chrysozonus has a top false eye with a white border, and often has a black spot at the base of its tail. Generally the first two bands are very close and touch at the bottom. - JFB |
| Coradion melanopus | Two-eyed Butterflyfish | Generally: distinct/close/V-ish bands, distinct top false eye with white border. It often has a lower false eye, and lacks orange at its front. - JFB |
| Parachaetodon ocellatus | Ocellated Coralfish | Generally: distinct bands, with a top false eye. - JFB |
| Chelmon muelleri | Blackfin Coralfish | Generally: black lower fin, distinct bands except rear 2 bands meet at top with tan in between them; orange band over gills and below eye - JFB |
| Chaetodon auriga | Threadfin Butterflyfish | Generally, C. auriga has 90 degree marks like C. vagabundus, but with a threadfin and orange/yellow rear quarter. - JFB |
| Chaetodon vagabundus | Vagabond Butterflyfish | Generally, C. vagabundus is like C. auriga, but with two vertical black stripes on yellow rear quarter. - JFB |
| Chaetodon semeion | Dotted Butterflyfish | Generally, this fish has a threadfin and has black dots on yellow and a blue forehead and a black eyepatch. - JFB |
| Chaetodon selene | Yellow-dotted Butterflyfish | Generally, this has yellow diagonal dots on white background, then black & then outside yellow rear border. -JFB |
| Chaetodon ocellicaudus | Spot-tail Butterflyfish | Generally: black & white diagonal lines with yellow rear border and black spot on tail. - JFB |
| Chaetodon melannotus | Black-backed Butterflyfish | Generally: diagonal black and white dots, then _black_ & then outside yellow rear border. - JFB |
| Chaetodon lineolatus | Lined Butterflyfish | Generally: black lines on white, then black & then outside yellow rear border. - JFB |
| Chaetodon mertensii | Yellow-backed Butterflyfish | Generally: black verticle thru eye and above, chevroned black dots with 150 degree angle, then yellow white yellow. - JFB |
| Chaetodon adiergastos | Panda Butterflyfish | Generally: black around eyes and a black nape, but with diagonal lines of black dots on white leading to a yellow border. -JFB |
(Note to BC; everyone else can ignore this: Reverse image search of BC photo BC_B041 for "Heniochus acuminatus" instead suggests Chaetodon burgessi a.k.a. Black-barred butterflyfish (or Chaetodon tinkeri, also discussing Chaetodon flavocoronatus and Chaetodon declivis).)
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