Freshwater ecosystems are all unique. The geography that separates rivers, lakes and swamps results in species that may be found nowhere else on Earth except in one tiny mountain stream or living in a single lake. This is very different from the vastness of the oceans, and has resulted in freshwater and marine species being very different.
Our Freshwater Exhibit in the Penguin Exhibit, brought to you by Old Mutual Finance, offers a chance for the public to learn about some of the complexities of the Western Cape's freshwater ecosystems and the threats they face.
What is it like to work with freshwater fish?
Ayrton King is a young aquarist and presenter at the Two Oceans Aquarium who has taken responsibility of the Freshwater Exhibit and surrounding ecosystem over the past year. We asked him a few questions:
TOA: What does your job entail?
AK: My job is to look after the freshwater fish. Basically taking care of general husbandry, making sure they are fed and that the exhibit, including the plants, are clean and well looked after. I want the exhibit to be attractive to our visitors.
TOA: Other than their habitats, what do you think are the main differences between our saltwater and freshwater fishes?
AK: The freshwater fish on display here not as colourful as marine reef species, and tend to have shapes that resemble leaves and natural things. They blend more into their surroundings, which are usually darker or murkier waters than many marine species.
TOA: What do you think the public can learn from this exhibit?
AK: The Western Cape has lots of small rivers, but most people don’t know what's in them. This exhibit shows people what they should expect from a healthy stream that they might find in nature. It also shows that the plants on the shore are a part of the ecosystem, and that there are different elements to this ecosystem – like the awesome waterfall.
TOA: What’s your favourite part of your job?
AK: I enjoy cleaning the exhibit. On a hot day it is great to put on a wetsuit and climb into the water with a snorkel to clean the algae off of the glass.
What species can you see here?
The Freshwater Exhibit hosts a number of fish endemic to the Western Cape, as well as plants, alien species and other animals that affect their ecosystems.
Found nowhere on Earth except the Breede and Berg Rivers.
Migratory fish that travels along the Olifants River - threatened by dam construction.
Destructive alien species from Eurasia that damages local water systems.
Ancient fish that survived climate change by retreating to the streams of the Cape Fold mountains.
An ecosystem under threat
The Western Cape’s 18 species of freshwater fishes are under threat – 13 of these are found nowhere else on Earth but in the rivers here.
The restriction of freshwater species to isolated river systems has resulted in the extinction rate of freshwater life being as much as six times higher than that of other species. Like oceanic species, human activity is the top contributor to these extinctions: water pollution, climate change and over-fishing are the culprits.
The introduction of alien species, such as common carp, sharptooth catfish and bass as 'game fish' in the Western Cape has historically also been a major threat to these ecosystems. These aliens are just as adaptable as our local species, but have also brought diseases and parasites that local fish are not immune to.
Our Freshwater Exhibit tries to emphasise this threat by including all elements of a typical riverine ecosystem – including the invasive alien species (our only exhibit to do so).
The Freshwater Exhibit shares a space with our beautiful rockhopper and African penguins, and a host of the Aquarium's smaller, lesser known inhabitants. Pay a visit – you never know what new treasure you may discover.