Can I feed earthworms to my fish?

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Neale Monks advises on what to look out for when feeding earthworms to your fish.

Q: How safe is it to feed earthworms from my garden to my fish? I used to do it when I was younger but someone recently told me that garden worms can be full of chemicals that can kill fish. Is this true, or can I still use them? 

SANDY DODDS, VIA EMAIL

A: Neale replies: Assuming your garden has not been sprayed with insecticides, herbicides, or some other poison, earthworms make a great food for carnivorous fish. It’s one of those situations where you need to use a bit of common sense. If you pick over the compost heap at the back of a suburban garden, far from any potential source of poisons, you should be fine. But if you’re collecting earthworms from off a flower bed that’s regularly sprayed with weedkiller, or a front garden close to a busy road, then that’s less wise.

The good thing about feeding earthworms is that they are gut-loaded with partially decayed plant material that’s full of fibre, minerals, and vitamins. In the wild, gut contents such as this are like vitamin pills for predatory fish, providing them with nutrients otherwise lacking in meat alone.
In captivity, where we tend to provide mostly ‘choice cuts’ of meat — such as shelled prawns or white fish fillet — we can end up short-changing our predatory fish a bit on the micronutrient front. So, supplementing such a diet with earthworms is really useful, and goes beyond merely providing variety.