Tuna species substitution in the Spanish market: a knock-on effect

Scientists at the CEAB-CSIC have surveyed the tuna commercialized in Catalonia in order to find out if there are cases of species substitution. This is a widespread problem, together with the deficiency of labeling. It happens particularly with high-valued species and has negative effects on the market. DNA Barcoding techniques can help to establish routine controls.


Small pieces of tuna in a fish market in Barcelona.The study, led by scientist Ana Gordoa, at the Centro de Estudios Avanzados de Blanes of the CSIC, analyzes the case of tuna. The results are published in the PloS ONE magazine.

The scientists did examine tuna mislabelling, deliberate species substitution, types of substitution and its impact on prices. The survey has been done during a year, and covered the commercial chain, from Merca-Barna (where the central fish market of Barcelona can be found) to the fishmongers and restaurants in the Spanish autonomous community of Catalonia.

The samples were taken monthly. The results showed a high deficiency in labelling: 75% of points of sale and 83% of the restaurants did not specify the species, and in those cases the name of the species had to be asked.

¿What it is in the generic name of “tuna”?

More than half of the time, consumers don’t know what they are buying, says Ana Gordoa. The problem is the labeling, which is deficient, and in the fact that labeling normally indicates a generic name not the species. In Spain, regulations allow the generic commercial name of “tuna” only for some species which are rarely found in the Spanish market: the longtail tuna (T.tonggol), Blackfin tuna (T. atlanticus), Pacific bluefin tuna (T. orientalis), southern bluefin tuna (T. maccoyii) and Slender tuna (Allothunnus Fallai). Nevertheless, the identified species in the survey were yellowfin tuna  (Thunnus albacores), Atlantic Bluefin Tuna (Thunnus thynnus) and Bigeye tuna (Thunnus obesus).

Spanish regulations allow the generic commercial name of “tuna” only for some species which are rarely found in the Spanish market

Besides, because its big size, tuna is usually commercialized in small parts and consumer will rarely see the whole fish. Also, the lack of the bluefin catch document –which is obliged in every stage of the commercial chain until the consumer buys the product-makes very hard to know which is exactly the specie one is buying.

The study shows that species substitution begins at suppliers, with 40% of observed cases, which has a knock-on effect and increases to 58% at fishmongers and 62% at restaurants. The substitution was mainly on bluefin tuna (T. Thynnus) which was replaced by other species in the 73% of cases.
But at restaurants and during the bluefin fishing season, scientists observed a decrease of Bluefin tuna substitution and an increase of reverse substitution, revealing some probable illegal fishing.

DNA Barcoding techniques  

The scientists made the analysis with the DNA Barcoding technique, a quick method to identify species and which, in the future, could be cheap enough to enable routine controls.

Species substitution conceals illegal fishing and jeopardizes

the sector

The effect of species substitution is important, whether it is intentional (fraud) or not (mistake). It affects the market prices, generates unfair trade, conceals illegal fishing and jeopardizes the sector. The effects on price are relevant: T. obesus increased its price by around €12 kg-1 when it was sold as bluefin. As a matter of fact, the survey made by the Centro de Estudios Avanzados de Blanes (CEAB-CSIC) was made on request of a company which was suspicious of the fraud.  

From an environmental point of view, DNA Barcoding techniques can help to avoid the commercialization of protected species.