There is a new acoustic transmitter that is smaller than anything on the market and can be used to tag smaller fish than ever before. It is called the Eel-Lamprey Acoustic Tag (ELAT). Although the technology is ready to use, we cannot deploy it in the field until the biological proof of concept is tested in the lab. As such, we conducted two laboratory studies to evaluate the tag effects of surgical implantation in small (30–95 mm fork length [FL]) fry and smolt sized juvenile salmon. The first study was a survival, transmitter retention, and growth holding study and the second was a swimming performance study. Our goal was to identify a minimum size threshold for Chinook Salmon that can be implanted with an ELAT where survival, ELAT retention, growth, and swimming performance would not be affected compared to an untagged population. In the survival and growth study, fish were held for 50 days. At the end of the study we found that fish as small as 55 mm FL had a 95% survival rate. There was no difference in growth between tagged and untagged fish. The swimming performance study identified a minimum size threshold of 51 mm FL. This indicated the swimming performance of a tagged fish was not different from an untagged fish once the fish was 51 mm or longer. Using the results from the two laboratory studies, 55 mm FL was identified as a minimum size threshold where growth, survival, ELAT retention, and swimming performance were not affected compared to untagged fish. This research confirmed we can tag a smaller size class of fish and provided a minimum size threshold for use in tagging guidelines.