From Wiktionary, the free dictionary
From mid- + side.
midside (plural midsides)
- The middle of the side of something.
- 2018, Robert H. Robins, Lawrence M. Page, James D. Williams, Fishes in the Freshwaters of Florida (page 439)
- Row of scales along midside (usually along lateral line) from rear edge of gill cover to base of caudal fin