Vegan sources are ALA, not EPA or DHA. ALA has no documented positive impact on human health.
"Like humans, fish obtain EPA and DHA from their diet, basically from microalgae, some of which could be used in commercial PUFA production."
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.
https://pubmed.ncbi.nlm.nih.gov/24679552/
“Conclusions: We conclude that vegans have low baseline omega-3 levels, but not lower than omnivores who also consume very little docosahexaenoic and eicosapentaenoic acids. The vegans responded robustly to a relatively low dose of a vegetarian omega-3 supplement.”
Look up Omega3 algae oil. It contains EPA and DHA.
https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.... See conclusions:
Specifically: "On the basis of the data available, the Panel concludes that a cause and effect relationship has been established between the dietary intake of ALA and the reduction of blood cholesterol concentrations."
linked to which is: "The Panel considers that the maintenance of normal blood cholesterol concentrations is beneficial to human health"