Questions raised over influx of fish in Menai Strait

An influx of fish suspected to be farm escapees in the Menai Strait has prompted concern among local anglers and environmental groups, with uncertainty over how they ended up there.

North Wales Live initially reported that anglers were “flocking” to the area hoping to catch some of the increased numbers of fish on 26 March (2026).

The fish, presumed to have come from a recent farm escape in Scotland, are now believed by Natural Resources Wales (NRW) to be rainbow trout.

The trout were identified from photos provided by anglers, and are being caught between the Menai and Britannia bridges that connect Ynys Môn to mainland Wales.

Under the assumption that they were salmon, and as it is illegal to ‘take’ wild salmon in Wales, many bass anglers in the strait returned the fish to the waters.

The secretary of the Seiont Gwyrfai and Llyfni Fishing Society, Huw Hughes, told North Wales Live that other anglers had gutted the fish and found they had been eating sandeels, and said he hoped to send scale samples to NRW.

The fish are suspected to have come from a farm due to rings on their scales which indicate artificial rearing processes that encourage fast growth.

Huw Jones, NRW environment team leader, told North Wales Live: “It is possible these fish have escaped from a local fishery or a fish rearing facility, although at this stage we do not know which one.

“The fin irregularities visible in the images are characteristic of stocked trout and suggest the fish will not have travelled far from their point of release…

“If there is any doubt over species identification, the fish should be returned.”

Escapes of farmed fish into open waters are not uncommon in the UK, often linked to storm damage or failures at fish farms, raising concerns about potential impact.

In early October 2025, an estimated 75,000 farmed salmon escaped from a damaged cage at a site in Loch Linnhe following Storm Amy.

Many anglers intercepted the fish where possible to prevent them harming wild populations, according to reports.

Escaped farmed fish have previously been recorded in rivers in Wales following incidents elsewhere in the UK and Ireland.

As well as competing with wild fish for food and habitat, they may pose a disease risk, or threaten the genetic integrity of native populations.

Mr Hughes also raised concerns that the Menai’s fast-flowing currents mean wild salmon regularly pass through the area en route to rivers such as the Conwy, where they could be at increased risk from farmed fish.

NRW added that reports of the influx of fish had not been made to them prior to 26 March, though they have now been logged. Anyone with information can call 0300 065 3000 or visit the NRW site.