Use of Pangasius Fish in Restaurants

Pangasius fish, mainly Pangasius hypophthalmus (tra/swai) and Pangasius bocourti (basa), which belong to the Pangasiidae family of catfish, are imported farm-raised freshwater fish from Asian. Nowadays, the U.S. is one of the largest importers of Pangasius fish worldwide. As mounting quantities of Pangasius fish being imported every year, the names of "tra/swai" and "basa", however, seldom appear on restaurant menus. Since processed fish products in restaurants are not subjected to the requirement of labeling species/origins, it is unclear how and to what extend Pangasius are used in restaurants. The overall objective of this study was to investigate if Pangasius fish has been used as a substitute for domestic catfish (Ictaluridae family), high valued fish species, e.g. grouper and snapper, and fish products without specifying the species on the menu from local restaurants. In total, 47 different fish products from 37 local restaurants in a medium size city were sampled and a commercialized rapid lateral flow strip assay (EZ PangasiusTM kit) were used to identify Pangasius fish. The results showed that 26.7% of domestic catfish tested was substituted by Pangasius, and 22.2% of high-valued fish, grouper, was verified to be Pangasius while no cases of substitution for snapper, sea bass and sole samples tested were found. In addition, a high percentage (66.7%) of dishes displayed under the general name of "fish" on the menu were identified as Pangasius, revealing the favorable choice of imported Pangasius for various fish products due to its sensory quality and cheap price. Isoelectric focusing (IEF) was further conducted to characterize protein patterns of each sample in comparison with authentic fish standards, and the results showed that all the Pangasius positive samples were exclusively tra/swai rather than basa. One year later 7 tested Pangasius positive dishes, including 4 in catfish group and 3 without specifying the species, were sampled again as follow-ups. Indirect non-competitive enzyme linked immunosorbent assay (iELISA), which applied a Pangasius-specific monoclonal antibody (mAb) T7E10, was used to analyze these follow-up samples. The results revealed the continuous use of Pangasius as substitutes for domestic catfish (4 out of 4) and as "anonymous" ingredients for the products without labeling the species. This study exhibited the prevalence of Pangasius in restaurants and also revealed the existence of dishonest behaviors in restaurant business, which called for the need to set up specific measurements and regulations to discourage the fraudulent practice using tra/swai or basa.