Koi keepers often have stories to tell of how their koi disappeared for some unknown reason. First to be blamed is normally the resident cat, or the next door family dog. Fact is that your ordinary house cat will be so well-fed that he will hardly bother a mouse, let alone a koi.
In South Africa the main reason for koi disappearing is aerial attacks from predatory birds. Kingfishers and cormorant must surely be rated as the most effective fish predators. Since they feed almost exclusively on fish, they will, if given the opportunity, return every day for their meal until there is none left in your pond. The bright coloured ones will be taken first. The red and white Kokaku’s and yellow Ogons and the tri-coloured Sanke. Perhaps a brown or black koi will remain too elusive for these birds.
Other birds like the hammerkop, grey heron and hadeda are less likely to take fish since they prefer other small prey like frogs, platanna, lizards and insects, but should a fish come into view they will most certainly try to catch it. The most disconcerting thing is that these birds do not know their own limits and will actually try to catch fish to large for them to handle and will leave wounds that could cause their death or leave them on dry land to dry. In suburban areas these birds can quickly switch to an all fish diet if that is the only food they can easily prey on.
Ponds that are in rather quiet parts of the garden are better targets for aerial attacks, while ponds that are shallow will leave your collection easy prey. Cover the pond with bird net of some sort. The larger your koi the larger the mesh size can be and the less unsightly it will look. Some keepers prefer to provide natural hiding places for their fish. Plants like water lilies, a ledge or a pipe can be used. These obstacles in the water are not recommended. It can hurt you fish, tend to make they skittish and hide all day. Besides, quite a few fish need to be caught before the others get the message.
In the rural areas keepers must also be content to do battle with the clawless otter, water mongoose and terrapins. Platanna will eat fish with a great appetite while sometimes even your pet duck may not turn to eating small fish. And then we should not forget about man, the ultimate predator who sometimes can do the most inexplicable things to a koi collection.
Written for Animal Talk magazine
Servaas de Kock & Ronnie Watt