I'm not a doctor and I'm assuming you asked your doctor about this. Perhaps you asked your Doctor and he was the one suggested fatty fish. But he should have added some more foods that are good for increasing your HDL. Those additional foods are all vegan.
According to AI those foods are nuts, seeds, avocados, olive oil, and whole grains.
These are all foods on Dr. Gregars Daily Dozen. So good to do no matter what.
Dr Gregar recommends you eat 1/4 cup of nuts each day. That's a couple of tbs or a handful. I used to buy peanuts for this. cause they are cheap but now I buy mixed nuts because different nuts have different nutrients. But be careful with Brazil nuts. they are supposed to be good for lowering cholesterol. Supposedly 2 a day are good for lowering TSH levels, too. Not all the mixed nuts blends include Brazil nuts but I get the kind that does.
A good way to the recommended amount of seeds by Gregar is just a Tbsp of ground flax seed. (easily added to oatmeal)
Three servings of grains are recommended by Gregar. Don't go over 5.
Avocados are great. but they are calorie dense. So portion size is important.
Same with olive oil. Here in America there is a fad of people adding olive oil to coffee. Just a spoonful. and it has to be Extra Virgin (EVOO.) Supposedly it's great. I've never tried it. In some Starbucks it's on the menu. They call it Oleato.
Regular exercise and maintaining a healthy weight are also key.
Just out of curiosity, how is your good cholesterol and how is your weight?
-------------------
The foods you eat can help improve your cholesterol. Here are some top choices.
www.mayoclinic.org
A checklist to inspire you to include some of the healthiest foods in your diet, based on the best available balance of evidence.
nutritionfacts.org
Nuts are nutritious and eating them regularly may be beneficial. What happens to your body when you eat nuts every day—here is what the research says.
www.eatingwell.com
This article lists 7 health benefits of eating avocados, supported by science, including more about nutrition, weight loss, and how to enjoy them.
www.healthline.com
Olive oil is the natural oil obtained from olives, the fruit of the olive tree. Learn more about 11 health benefits of olive oil that are supported by science.
www.healthline.com