Detecting Perkinsus-like organisms and Perkinsus marinus (Myzozoa: Perkinsidae) within new bivalve hosts in the southeastern Gulf of California.

Perkinsus marinus, a parasite myzozoa native from the Atlantic Ocean, has spread across various bivalve species in the Pacific Ocean. In the Gulf of California, clams like Larkinia grandis and Leukoma grata have become a secondary fishery, experiencing demand. During annual sampling (August 2017 - July 2018, n = 30/month), the Ray's fluid thioglycollate medium (RFTM) revealed presumptive hypnospores of Perkinsus sp. in L. grandis, with a low parasite prevalence (4.16%) and density (≤ 3.14 hypnospores g^-1 tissue). From summer 2020 to summer 2021, P. marinus was seasonally identified in L. grata via staining and PCR tests, showing mean prevalence and density of 48.33% and 48 hypnospores g^-1 tissue, respectively. The infection level was light in both clams. This parasite's presence in these new hosts within the southeastern Gulf of California confirms its ability to expand into non-native places, signaling a need for intervention strategies in managing and transporting mollusk species within the region.