Two Cape triplefins
Photo Adriaan Johnson
Cape triplefin with the three segments of the dorsal fin highlighted
The super klipfish (Clinus superciliosus with its tall dorsal crest breaking the dorsal fin into two segments.
The speckled klipfish (Clinus venustris), a klipfish with no dorsal crest or break in the dorsal fin.
The lace klipfish (Blennioclinus brachycephalus) with a slight dorsal crest, but a distinct raised rear section of the dorsal fin, giving the impression of three segments. It is rare, however, and compared to the Cape triplefin less "squat". It also lacks any tentacles above the eyes, unlike those found on the Cape triplefin.
The horned blenny (Parablennius cornutus with its continuous dorsal fin. Note the steep head profile - nearly vertical.
Photos Guido Zsilavecz
The triplefins (family Tripterygiidae), klipfishes (family Clinidae) and blennies (family Blennidae) ocurring in Cape Town are generally all small, cryptic, well camouflaged fishes. Hiding on well-grown-over reefs, many move only when accidentally approached too closely. A few species are often seen, but the majority require careful searching and a good measure of luck to find. Of the three families the klipfishes are the dominant group locally, both in numbers and species, with at least 24 species ocurring in the area (out of about 40 country-wide), whereas there is only one triplefin (out of only about 12), and only two blennies (out of about 45). Initially it is often hard to tell the various families, let alone species, apart. While there are a few species which are really so similar only comparing a photo of one with photos of correctly identified ones allows for moderately certain identification, it is not too hard to learn the differences between species and families.
Triplefins The name of this family refers to the dorsal fin which is divided into three segments, with a deep notch between the segments. The Cape triplefin is a small, somewhat depressed (flattened dorsally) fish with a broad head. Colouration varies, with most a drab mottled pattern in browns and occasionally nearly all over black, but some (possibly males?) have a bright band around the head, in deep yellows and oranges, occasionally extending over most of the body. The dorsal fin is always mostly see-through, and this makes it hard to see the three segments, especially as it is often folded back. The fish in the second image has the dorsal fin raised and the three segments are indicated. These fish prefer walls and overhangs, although they can be found on most reefs, and are remarkably common, yet not often seen.
Klipfishes The more common klipfishes tend to be larger than the Cape triplefins, and are more compressed (flattened ventrally), and hence appear less "squashed". With at least 24 species, this is somewhat of a generalisation, but it is true for the more abundant species like the super and speckled klipfish. The main difference is that the dorsal fin has at most two segments, with only one exception: the lace klipfish has a deep notch towards the rear of the dorsal fin, and a slightly raised front section - this could be mistaken for a separate section, hence giving the impression of three segments. The head profile, being nearly vertical, does set it clearly apart from the Cape triplefin. The other klipfishes have either a continuous dorsal fin, as shown in the image of the speckled klipfish, with some species having a slight crest but no notch behind the crest, or, as with the super klipfish, have a tall crest with a very distinct notch. The overall appearance of either super or speckled klipfish, compared to the Cape triplefin, is quite different, and the species can be readily distinguished from earch other.
Blennies The blennies, a family with many tropical members, is poorly represented in Cape Town waters with only two species. Both are, on top of that, rather rare. Neither has a segmented dorsal fin - at most a slight notch towards the middle, and both have near vertical head profiles. Both local species also have a rough skin, and are easier to confuse with some klipfish than with a triplefin.
For images and descriptions of all klipfishes, blennies and the lone triplefin found in Cape Town, refer to Coastal Fishes of the Cape Peninsula and False Bay, available from SURG.
Coastal fishes of the Cape Peninsula and False Bay, a divers' identification guide, G Zsilavecz, 2005.
Smiths' Sea Fishes, MM Smith and PC Heemstra, 1986.