One of the first wild fish that a child is most likely to catch in a net in small streams and ponds is the three-spined stickleback, Gasterosteus aculeatus, a remarkably tough species that will eat any other unwary smaller passing creature.
At this time of year the breeding males – maximum length 8cm (3in) – turn from silvery fish into red-chested, green-sided, blue-eyed warriors. They build a nest in shallow oxygen-rich water in preparation for being an attentive and protective father.
