[jbernsteiniv]

"Marine Cryptophytes are Great Sources of DHA and EPA" - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5793051/

"Like humans, fish obtain EPA and DHA from their diet, basically from microalgae, some of which could be used in commercial PUFA production."

[adrian_b]

Few fish eat directly unicellular algae or other unicellular protists, which are indeed the main producers of DHA and EPA.

Those unicellular living beings are normally eaten by small animals, e.g. copepods, which are eaten by small fish, which are eaten by big fish.

Thus all of them get the required DHA and EPA.