SUNBLEAK (Leucaspius delineatus)! My first. Huge shoal. South Drain, Shapwick Moor, Somerset Levels

A huge shimmering shoal of SUNBLEAK (Leucaspius delineatus) was my prize for persisting in swimming down South Drain at Shapwick Moor in the Somerset Levels, through a relative dead zone caused by recent evident vegetation clearance (confirmed by a lady on the bridge remarking that she had noticed busy machinery working here last week). Their refuge was, predictably, under some overhanging willows. Having never met any Sunbleak before, I was puzzled, taking them at first - with their blunt head, big eyes and horizontal stripe - for Sand Smelt (Atherina presbyter) which is a marine/brackish species common on the neighbouring coast, whereas South Drain is freshwater. Although it was exciting to see a new fish species, it is a bad sign as it is an invasive alien species in the UK, native to continental Europe and West Asia, where it is considered rare or vulnerable. It was brought to the UK by the ornamental fish trade and as well as Somerset has become established in Hampshire. It was first recorded in Somerset in 1990 but may have colonised a decade or two earlier. It is not clear how much of a problem the Sunbleak may be to the native UK ecosystem, for example in out competing native fellow cyprinid fish such as Roach or Dace, although it has been shown to be a new host for the non-native parasitic copepod Neoergasilus japonicus, and a PhD study suggests its social behaviour may help non-native parasites spread faster in communities it has invaded. A Wikipedia entry also says it has been implicated in transmitting a new fluke species to otters and American mink in the Avalon Marshes. It is interesting for me, used to swarms of Bitterlings    • Bleak, Bitterling, Silver Bream, Rudd, Per...   being the dominant alien invasive fish in the Fens, here in the western equivalent of the Fens, the Somerset Levels, finding swarms of Sunbleak. They are mixed here with in this vast shoal of young fish with orange-eyed Common Roach (Rutilus rutilus), the dominant fish in this reach of South Drain, plus a few deep-bodied Silver Bream (Blicca bjoerkna), Common Rudd (Scardinius erythrophthalmus), Common Dace (Leuciscus leuciscus), a young Tench (Tinca tinca) and below, close to the riverbed, some small European Perch (Perca fluviatilis). Apart from these young fish, this cleared reach of South Drain was a desert. It was only once I swam upstream to a short reach spared the vegetation clearance that I found where the hoards of adult fish were taking refuge    • Most astonishing fish shoal have ever seen...  . (22 October 2026 1 GX012158 59 4K)