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DNA ANALYSIS OF CYTOCHROME OXIDASE 1 TO CONFIRM THE IDENTITY OF LOCALLY PURCHASED FISH
Introduction
Matthew Chrostek and Alex Doan; Carleton Summer Science Institute 2013, Carleton College, One North College St., Northfield, MN 55057
In 2011, Americans spent 80.2 billion dollars[1] on
seafood. A comprehensive study by Oceana found that
within the United States, an estimated 33% of
commercially bought fish and shellfish were mislabeled[2].
Cheaper fish such as the Escolar ($13/lb) are frequently
mislabeled, either intentionally or accidentally, as more
expensive varieties, such as Albacore Tuna ($18/lb).
Beyond a monetary loss, cheaper fish can also cause a
variety of adverse health effects, for example, in the case
of Escolar, distressing gastrointestinal effects[3]. We
sought to verify the identity of 6 Northfield area fish
samples using analysis of the mitochondrial DNA subset
Cytochrome Oxidase 1.
Albacore Tuna
Discussion
Results
Sequences of Fish
Mislabeled Fish
Example of DNA Sequence Alignment of
Fish 1 [Labeled Red Snapper]
Comparative sequences between two mislabeled fish
Red Snapper vs. Nile Tilapia [Fish 1]
Forward and reverse sequences were compared using ClustalW2
to compare sequence similarity and to ensure accuracy of
sequencing reaction.
Of the six samples of fish we analyzed, two were found that did not corresponded to the species
of fish they were labeled as. Mislabeling frequently occurs for one of two reasons, either for
monetary gains or simply by accident. In the case of the Oreochromis niloticus (Nile Tilapia), this
fish species was mislabeled as Lutjanus campechanus (Red Snapper). These two species of fish
are not found in the same location, do not resemble each other in appearance, and are not from
the same family of fish. Moreover the large price difference between an Oreochromis
niloticus and Lutjanus campechanus may make the mislabeling a lucrative mistake for the
company selling these mislabeled fish. The other fish that was found mislabeled was the Sander
Canadensis (Sauger) that was incorrectly labeled as a Sander vitreus (Walleye). In this case the
two species of fish shared similar appearances, could be found in the same location, and came
from the same family of fish.
In this case of mislabeling it seems probable that a simple mistake was made. By mislabeling fish
the health of the customer can be put in jeopardy. Mislabeling may also give the seller an unfair
advantage over competitors by allowing them to sell their fish for far cheaper than others. While
our conclusions would implicate restaurants or supermarkets, these may not be the guilty parties
at all. The mislabeling could occur anywhere in the path of the fish while it moves from ocean to
plate.
Walleye vs. Sauger [Fish 5]
Escolar
Methodology
1.DNA was extracted from six fish samples collected
from pet stores and restaurants in Northfield and
Proteinase K was used to break down cells, and a
DNeasy spin column was used to isolate DNA.
2.DNA was amplified through Polymerase Chain
Reaction to isolate the mitochondrial DNA segment
of Cytochrome Oxidase 1, about 600 base pairs long.
3.Purified the PCR product to remove unincorporated
nucleotides.
4.DNA was sequenced by Elim Biolabs.
5.We compared sequences using the Basic Local
Alignment Search Tool, a program which compared
our sequences to known sequences to determine
fish species.
*N indicates unknown base pair [sequencing error]
Red Snapper ($15/lb)
Labeled as
Matched
Base Pair
Base Pair % Similarity
Identified as
Matched
Base Pair %
Base Pair
Similarity
Red Snapper
91%
440/480
Nile Tilapia
99%
594/595
99%
647/649
Halibut
99%
647/649
100%
618/618
Goldfish
100%
618/618
100%
615/615
Greenland
Cod
100%
615/615
99%
628/631
Halibut
Hippoglossus
Hippoglossus
Goldfish
Carassius
auratus auratus
Cod
Genus: Gadus
Oreochromis
niloticus
Hippoglossus
Hippoglossus
Carassius
auratus
auratus
Gadus Ogac
Walleye
Sander vitreus
Tilapia
Oreochromis
niloticus
92%
100%
Sauger (Unknown Price)
Conclusion
Actual Fish Species
Lutjanus
campechanus
Nile Tilapia ($4.5/lb)
Walleye ($17/lb)
582/627
626/626
Sauger
Sander
Canadensis
Nile Tilapia
Oreochromis
niloticus
100%
626/626
In conclusion, we found that our results, like those of the Oceana study,
indicated incidents of mislabeling occur. Two of the six fish analyzed did not
match the labels. Analyzing the Cytochrome Oxidase 1 Gene was a very
efficient way to determine fish species, because even within the same genus,
in the case of the Walleye and Sauger, there was a 7% difference in their COX
1 DNA sequences. Despite our small sample size, we found it notable that we
discovered one instance of both what seemed to be intentional mislabeling
and accidental mislabeling. Going forward, we would suggest further studies
with more samples across a larger area.
Acknowledgements:
We would like to thank the Carleton Summer Science Institute, and Carleton
College, Northfield, Minnesota. We would especially like to thank Professor/Men’s
Tennis Coach/Biology Chair Stephan Zweifel Ph.D., and Research Assistants/Bagel
Deliverers Drew Holmen and Madeline Arnold.
References
[1]: Consumer Reports Magazine. “Mystery Fish”. December, 2011. http://www.consumerreports.org/cro/magazine-archive/2011/december/food/fake-fish/overview/index.htm
[2]: Warner, Kimberly; Timme, Walker; Lowell, Beth; Hirshfield, Michael. “Oceana Study Reveals Seafood
Fraud Nationwide”. Oceana. February 2013. http://oceana.org/sites/default/files/National_Seafood_Fraud_Testing_Results_FINAL.pdf
[3]: Daily Mail Reporter. “Fish mislabeling widespread in the U.S. and 84% of ‘white tuna’ is a species which causes distressing gastrointestinal side effects”. Daily Mail Online. 24 February 2013,
http://www.dailymail.co.uk/news/article-2283880/Fish-mislabeling-widespread-U-S-84-white-tuna-species-causes-distressing-gastrointestinal-effects.html