Bot fish back in the spotlight

By Sue Matthews, Overstrand Estuary Management Coordinator

A fish discovered in the Bot River estuary 30 years ago has been the focus of renewed attention of late, as taxonomists try to figure out its evolutionary history. 

The species was originally described in 1983 by Bruce Bennett, then doing his PhD on the use of inshore and estuarine habitats by fish in the south-western Cape. His research activities included monthly seine-netting of the Bot River estuary, and the fish, which he recognised as a klipfish, was the fourth most abundant species in his catches. Klipfish belong to the genus Clinus, all of which have a supraorbital (above the eye) tentacle, although it is more obvious in some species than others. In this one it was long and spade-shaped, so Bruce named his find Clinus spatulatus, and dubbed it the Bot River klipfish. 

More recently, it has come to be known as the estuarine klipfish, because it bears the distinction of being the world’s only truly estuarine member of the genus. It also occurs in the Klein River estuary in Hermanus, where – according to Dr Steve Lamberth of the Department of Agriculture, Forestry and Fisheries, who conducts fish surveys in both estuaries twice a year – it is actually more abundant. 

But it is its murky relationship to similar looking fish that has put it back in the spotlight. It shares so many features with the ‘super’ klipfish Clinus superciliosus that questions were raised as to whether it is indeed a separate species. Wouter Holleman, a taxonomist with the South African Institute of Aquatic Biodiversity in Grahamstown, heads up a project to establish the who’s who of klipfish society. 

“Klipfish are the largest endemic group of fishes we have in southern African waters, with close to 50 species,” he says. “But Clinus superciliosus is complicated because it comes in a bewildering array of colours. We suspect it may be like some Californian clinids, where the juveniles adopt the colour of the substrate they settle on.” 

He explains that all South African klipfish are viviparous, giving birth to live young, rather than laying eggs. The juveniles are born as quite mature larvae, and spend a short time in the plankton before they settle out into a benthic existence. Klipfish in weedy areas tend to be green, those on sand are pale, while many rockpool residents are mottled brown and purple, camouflaging them amongst the intertidal algae. 

This colour variation resulted in many different species being described over the last century and a half, but subsequently they were all lumped together as Clinus superciliosus. Initial genetic testing even indicated that spatulatus and superciliosus were one and the same species. 

“Now we’ve found that what we thought was Clinus superciliosus is actually six species,” says Wouter. “One of these is spatulatus, which did show some clear differences to superciliosus in both physiology and appearance, so our molecular biologist - Sophie von der Heyden of Stellenbosch University - went back and started looking at the genetics in more detail.” 

“The six species all had a common ancestor, but the history between it and where they are now is still obscure. We don’t know exactly who’s related to who, but in that complex superciliosus and spatulatus are very closely related – so closely that the genetic differences are very fine. We suspect that the speciation event is quite recent – in the last 10 000 years, say.” 

While Clinus superciliosus does also occur in estuaries, it is limited to those that stay open for much of the year and where the salinity remains high. Our own Clinus spatulatus can survive salinities as low as 2 parts per thousand (seawater is 35 ppt), as recorded by Bruce Bennett in his description of the species. He noted that a period of prolonged closure of the Bot River estuary’s mouth – from the end of 1977 - caused a mass mortality of fish in October 1981, yet no Clinus spatulatus appeared to have died as a result of the extremely low salinity. 

Bruce also described the different appearance of males and females, mature males typically being uniformly dark grey or brown, but often with small pale patches, while mature females are mottled green and brown over an olive base. In both sexes the first three spines on the dorsal fin elevate to form a crest, but it is considerably higher in mature males than females. The sex ratio appears to be skewed towards females, with one male to approximately 15 females. In the Bot the diet is dominated by gastropods (marine snails), followed by amphipods and isopods (both tiny crustaceans), insect larvae and small fish. Few individuals survive for more than 18 months, by which time they have reached a tip-to-tail length of approximately 130 mm. 

It is highly likely that the ‘Bot River klipfish’ occurs in estuaries even beyond the Overberg, just waiting to be brought to light. But what has become of its discoverer? Like a modern-day Livingstone, he disappeared into deepest Africa. Although a well-respected scientist who later pioneered South African research on marine protected areas, Bruce was always a fisherman at heart. After stumbling upon the virtually pristine populations of linefish in Angola – protected from exploitation through the years of civil war – he upped and left, and now runs a fishing lodge at the mouth of the Kwanza River, 70 km south of Luanda.

Sue is contracted to the Overstrand Municipality in a position funded by The Table Mountain Fund, an associated trust of WWF-SA.