Did this frog eat my fry?


Bob Mehen advises a reader who is suspicious of a frog that has set up home in his breeding set-up.

Q) I moved 10 White Cloud Mountain minnows outside for the summer into a large container filled with Java moss and duckweed. While they conditioned beautifully and I saw sparring and breeding behaviour I did not see any fry. But I noticed that a large frog has set up home in the tub, so could this have had anything to do with my lack of new minnows?


A) BOB MEHEN REPLIES: Common frogs, Rana temporaria, are predatory, but their hunting instinct is triggered by movement, and largely on land. I’d think they would be unlikely to eat fish eggs and the fry would probably be too small to attract their attention. If anything was at risk then I would expect it to be the adult fish. The frog is just taking advantage of some much-needed water to keep itself wet and healthy.

Far more likely culprits for disappearing eggs and fry would be newts, efts (juvenile newts) and a host of predatory aquatic insects and insect larvae such as damselfly nymphs which may well also be resident in your tub, but far harder to spot than the frog.

Similarly, the actual minnows themselves are not adverse to a bit of aquatic cannibalism. Depending on the size of the tub and the density of the planting in it, you may even find when you come to empty it at the end of summer that you actually have a number of extra minnows — it can be next to impossible to count them accurately with plants in situ.