Big shoal of European Minnows (Phoxinus phoxinus) in shallows of River Little Ouse, Santon Downham

In the clean, sandy shallows of the River Little Ouse, a chalk stream on the Norfolk/Suffolk border, a huge shoal of Minnows were relaxing on a hot, gusty July day. Individuals would frequently produce flashes when they moved, for example making vertical dashes down, or horizontal wiggles as if itching their bellies on the sand, causing their specular (mirror-like) scales to catch the sunlight. These reflective scales contain tiny guanine crystals. Perhaps these movements were signals to other fish or predators (though they did not seem concerned about me or any other potential predator), or feeding, but the shoal did not seem in feeding mode (if they were birds you'd describe this as a roosting site). Many have taken on pale colouration to blend into the sandy substrate. Those over adjacent patches of algae or out feeding among the macrophytes in the main water column of the river have darker more vibrant colouration, especially those in full spawning colours. At this warm, open, bright site, the water is rife with mesmerising "caustics". These dancing underwater light patterns, sometimes strobe like, found in clear shallow water are caused by the moving waves bending sunlight. Surprising to see when there is a particularly strong blast of wind, near the end of the video, it causes a panic in the shoal. A few young Common Dace (Leuciscus leuciscus) and perhaps a young Bleak (Alburnus alburnus) can also be seen among the Minnows towards the end. For more details on this swim see: https://bsky.app/profile/numenini.bsk... or https://x.com/numenini/status/2091463... (7 July 2026 P7062353 40 GX011858 59 60) .