Waitrose has launched an investigation into one of its trout suppliers after an animal rights group released footage it claims shows serious fish welfare failings during slaughter.

Animal Equality UK said covert footage filmed on 17 July aboard the Tiffany II, a harvest vessel operated by Scottish trout producer Kames, showed fish being crowded and facing delays before slaughter.

The campaign group also alleged that some fish were not stunned correctly, while others were left for extended periods before stunning and bleeding. It claimed that in at least one instance a fish was neither stunned nor bled before death.

Kames, which supplies Waitrose and has farmed trout on Scotland’s west coast for more than five decades, is certified under the RSPCA Assured scheme.

The supplier said it was carrying out a “thorough internal investigation” into the footage and allegations and had shared the material with the RSPCA.

Kames managing director Andrew Cannon said fish health and welfare were taken “extremely seriously” by the business, adding that it would seek independent input and address any shortcomings identified in its procedures or operations.

Waitrose has also opened its own investigation.

A spokesperson for the supermarket said: “Animal welfare is vital to us. We are investigating this and will take any necessary action.”

The allegations come as Waitrose continues to make animal welfare and responsible sourcing a central part of its seafood strategy.

The grocer states that it only sources from approved aquaculture farms that meet its animal welfare standards, while all farms supplying its own-label salmon and trout are audited by Waitrose aquaculture experts before being accepted into its supply chain.

RSPCA Assured said it was also reviewing the footage and investigating the allegations, but declined to comment further while its inquiry remained ongoing.

The assurance body said it takes complaints concerning poor welfare or potential breaches of its standards seriously.

Animal Equality UK executive director Abigail Penny said the footage demonstrated the welfare problems farmed fish can face during slaughter and called for tougher regulation.

The group is urging the Scottish government to introduce species-specific slaughter legislation for farmed fish, arguing that current guidance does not provide sufficient protection.

The organisation has previously campaigned for stronger legal protections around trout slaughter, arguing that more prescriptive and enforceable rules are needed to govern how farmed fish are killed.

Sign up here to get the latest grocery and food news each morning