Not many people love African sharptooth catfish aka Clarias gariepinus. But, Leonard Flemming explains, as they spread across the Cederberg they appear to be destroying the smallmouth bass and bluegill populations. This may ultimately save the indigenous cyprinids.

We were on our way home, after spending a splendid weekend in the Cederberg, when Michelle and the kids nagged to stop at one last spot where they could swim and catch some fish. I was too happy to park at big pools where I had caught Clanwilliam yellowfish before, knowing there would also be lots of bluegill sunfish, bass and Mozambique tilapia to keep us busy.

I rigged up two rods and we strolled down white sandy banks to the inlet of a decent pool. The kids were in their element, running through the clear water while chasing big schools of fry in the shallows. I was fishing a small tadpole imitation on 5X fluoro, casting across the inlet and hoping for that “needle in a haystack” Clanwilliam yellowfish, while Michelle actively targeted big bluegills in sandy bays downstream of me. On about my third cast I got a very hard take and I stripped into the fish, gently setting the hook on the light tippet.

Needle in a haystack

The fish paused for a few seconds, shaking its head before moving slowly towards deeper water, as if it didn’t click what was going on. When the fish had taken up the slack and started pulling line off the reel, it obviously felt the constant pressure of the drag and it suddenly sped off and ran so much backing off that I got really concerned that I was going to run out of line. Convinced at this point that I was attached to a massive Clanwilliam yellowfish, I started wading after it.

The frantic fish made a huge boil on the surface over 50m away from me and then continued on its hurried journey towards the outlet of the pool. With so much line out, there was that danger that the powerful fish could either snap the light tippet due to line drag caused by the relatively fat fly line getting pulled through the water, or the line could easily get caught on structure between me and the fish that could also cause the 5X to break. At that point I had already waded so deep into the pool that I nearly started swimming after the trophy yellowfish.

The water was just about to touch my nipples and suddenly the fish stopped. Slowly, I started gaining some line back, until I could finally see the back end of my fly line appearing above the water. After about 30 minuntes into the fight, I finally got some of the fly line back on the reel, which felt like a milestone and got me very excited.

“Catfish!?”, I yelped out of horror and disbelief.

That was when the real torture started though… The yellowfish stayed in the deep river channel, continuously running across it towards the opposite bank where there was a fallen tree in the water. It was a nerve-racking ordeal to stop the fish from finding the structure every time it headed in that direction. Eventually, it did find those dead branches and swam deep into the sticks where the fight came to a stop. I nearly cried.

I gave the fish slack and loosened my drag to a “free spool” and slowly made my way across the deep channel to where the tree was. An hour into the fight, I started to feel the fatigue of the weekend and fight kicking in. My wrists were cramping, my arms felt like noodles and my heartbeats were heavy in my chest. It felt like a monstrous Clanwilliam yellowfish, over 20 pounds, and I couldn’t stand the thought of losing it.

When I got to the tree, I carefully removed the 5X tippet from the branches until I could feel the fish, still attached to the end of my line. I held my breath as I slowly lifted the head of the yellowfish to see how big it was, but instead of a metallic yellow head, a disgusting, flat, mottled grey cephalus with whiskers came up to the surface.

“I think the whole family was relieved”

“Catfish!?”, I yelped out of horror and disbelief. It was indeed a long, slender, river-grown sharptooth catfish (Clarias gariepinus), and as if it hadn’t punished me enough yet, it shot off like a bullet back into deep water. The entire fight lasted about an hour and a half before Michelle finally slipped the net over its ugly mug. I think the whole family was relieved at that point and even though it was a relatively big catfish for Western Cape standards, I wasn’t as pleased about it as I should’ve been.

A trophy Clanwilliam yellowfish that, surprisingly, turned into a sharptooth catfish at the end…

A bass killer

Although native to the Orange/Vaal River system in South Africa, sharptooth catfish was introduced as a sport fish in the Western Cape in the late 1900s. Humans slowly spread these fish throughout the province until all of our big reservoirs, including Theewaterskloof, Brandvlei, Misverstand and Clanwilliam Dam got ‘infested’ with sharptooth catfish. As it spread, both largemouth bass and smallmouth bass (and especially the latter) numbers started to plummet. But why?

Catfish are extremely adaptive and hardy predators that will target other fish species at any water depth. I’ve witnessed them harassing nesting bass in local waters, in which case multiple catfish were irritating the bass guarding the nest (the bass being completely outnumbered by several much larger predators). Scientific studies have indicated that male smallmouth bass guarding their nests are especially susceptible to disturbances and substantially greater rates of nest abandonment occurred when brood predation happened (Suski et al., 2011). Furthermore, catch-and-release events of bass guarding nests indicated that angling pressure reduced their ability to protect their eggs or fry.

“Smallmouth bass simply aren’t used to that level of disturbance and brood predation”

So I believe, and it is pretty clear in this case, that the sharptooth catfish being an opportunistic predator targets nesting fish for an easy meal and smallmouth bass simply aren’t used to that level of disturbance and brood predation (they have evolved by and large without the presence of large catfish species in their native waters in North America). Also, winter and spring ‘Bass Classics’ (bass competitions) or provincial bass fishing trials during the months of August, September and October could have a significant negative impact on the breeding success of these bass in the presence of sharptooth catfish.

Nevertheless, it is very obvious that the smallmouth bass numbers have declined significantly since the sharptooth catfish population exploded in the Olifants system. The result? Increasing numbers of threatened indigenous cyprinids, such as the Clanwilliam yellowfish – ultimately a positive spin-off?

Cranking up the heat

Netting surveys have shown that sharptooth catfish have already spread as high as the Olifants River gorge starting at Beaverlac. More recent catch records indicate that sharptooth catfish have also breached a weir on the lower Doring River and are spreading rapidly inland towards the Tankwa Karoo.

These things are spreading like wildfire and turning up the heat for nesting sunfishes, like smallmouth bass and bluegills. Ironically, an introduced species (i.e., the sharptooth catfish) is now threatening the survival of other introduced species. How will this impact the Clanwilliam sandfish, Clanwilliam yellowfish and sawfin? Interestingly, majority of these large cyprinids have evolved with the presence of sharptooth catfish (for example, moggel and yellowfish in the Orange/Vaal system – yes geology indicates that the Olifants River was a tributary of the Orange River many moons ago, when the sea level was much lower and that the Clanwilliam sandfish is related to the moggel, and Clanwilliam yellowfish comes from the same ancestor as smallmouth and largemouth yellowfish), so they already have some sort of inherent immunity against catfish predation.

Besides their African evolution, indigenous cyprinids don’t nest, they are scatter spawners and typically run up rivers in late winter or early spring (in the Western Cape now) to spawn in shallow riffles, areas at times of the year where sharptooth catfish are unlikely to be present.

The future?

What lies ahead? It’s not clear yet, but at this stage the sharptooth catfish ‘invasion’ seems to be exactly what our indigenous fishes in the Western Cape needed to make a comeback – freshwater scientists dubbed sharptooth catfish ‘The Silver Bullet’. Which brings me to final food for thought…By practicing catch and release fishing for bass (and bluegills) in river systems where threatened indigenous fish occur (naturally), you are purposefully doing harm to the environment. I will leave you to chew on that.

The future of smallmouth bass in the Olifants/Doring River system seems to be at stake, and in the mouths of sharptooth catfish that are rapidly spreading across the Cederberg.