Threatened species of shark are being sold as flake in some South Australian food outlets, a university study has found.
Prompting calls for clearer labelling laws, the research revealed that up to nine species of shark are being offered to customers when guidelines suggest only two - the gummy shark and the New Zealand rig - should be sold a flake.
Among those found on offer in SA were the short-fin mako shark and the smooth hammerhead shark, both considered threatened.
University of Adelaide researchers analysed the DNA of flake fillets from more than 100 fish and chip retailers across Adelaide and regional areas of South Australia.
"Only 27 per cent of all samples were identified as gummy shark, a species that has a sustainable population, and is one of only two species that is recommended to be labelled as flake in Australia," study author Ashleigh Sharrad said.
The study also found that only one in 10 retailers could correctly identify the type of fish being sold as flake, while 20 per cent of the fillets were mislabelled and the rest had ambiguous labelling.
However, the researchers noted that smaller retailers were most likely unaware of what they were selling after buying processed or frozen fish fillets in bulk.
The Australian Fish Names Standard for the use of the term "flake" is also only a guideline and not mandatory.
Professor Bronwyn Gillanders, from the university's School of Biological Sciences, said food fraud in the seafood industry was a growing concern.
"It can have potential implications on human health, the economy and species conservation," she said.
Ms Sharrad said the study highlighted the need for clearer labelling laws for shark fillets.
"This is the key to building trust across the supply chain, boosting demand for local, sustainable catch and, importantly, empowering consumers and retailers to make informed choices," she said.