Pelham PR replaces Abchurch Communications on the account, which will see the agency advising a firm in a state of flux.
The AIM-listed firm, which replaced its chairman last month, posted operating losses of £1.65m on Friday. Its share price has dipped from above eight pence last November to under 1.5 pence.
Chairman Ranjit Murugason, who has held the role since Hot Tuna's admission to AIM, stepped down last month. He was replaced by David Lenigas, the former owner and the executive chairman of African investment company Lonrho.
City watchers said the brief was an investor relations and PR 'nightmare', but 'a great challenge nevertheless'.
Hot Tuna CEO Niels Juul, who joined last year and is the executive behind the successful street brand Von Dutch, said: 'An extremely challenging trading environment, coupled with restructuring of the group's supply chain, slow brand recognition in the US and adverse trading conditions, have impacted trading results.'
Hot Tuna has experienced a failed rebrand in the US in the past year, and suffered supply chain problems.
The company has already moved manufacturing to China in an attempt to lower costs and cut overheads in the UK and the US.
Hot Tuna was one of the first surf-fashion brands, born in Australia in 1969. It grew in popularity and reach through the 1980s, and is now headquartered in the UK, the US and Australia.
Account leader Kate Catchpole also looks after brands such as Walpole, Portmeirion and Savile Row.