Voyager: How do scientists collect tissue and DNA samples? Does a fish have to be alive or can it be dead or preserved?

Samples can be taken from fish species in a variety of physical states. In rare circumstances, Scripps Institution of Oceanography at UC San Diego researchers catch a live fish and take a small piece of its fin, and then return it to the ocean. This is similar to the practice of whale researchers taking small pieces of blubber for genetic and physiological analyses.

However, in most cases Scripps researchers need to have a voucher specimen remain in the Marine Vertebrate Collection to verify identification of the species. These voucher specimens are either fresh or frozen and are dissected to extract a small piece of muscle. This muscle tissue is placed in either 95 percent ethanol, an -80ºC freezer, or both.

The specimen’s tissue sample is used to extract DNA, information from which will be stored to create a barcode-style identification of the species in the future. The specimen eventually is placed into isopropanol for permanent storage, but occasionally the entire specimen will be stored in 95 percent ethanol.

To add a new sample to the larger collection of fish DNA being collected around the world, all researchers analyze DNA for the same gene, called “cytochrome c oxidase subunit 1,” also called CO1. Once that DNA has been extracted and processed, it creates a sequence of DNA that is unique to that species.

--H.J. Walker, manager, Marine Vertebrate Collection

To learn more about using barcodes to identify fish species, read our story “Life Behind Bars” at explorations.ucsd.edu/Features/2009/Life_Behind_Bars/.