Some alternative sources for long-chain W-3, may be:

Seafood as shrimp, crab, lobster, etc.

But another sustainable source of W-3 in specific ALA, may be:

Walnuts, Flaxseed, Flaxseed oil, Cod liver oil and Canola oil.

The idea behind this question was to highlight that we should find alternative sources of long chain omega 3 PUFA to cover the nutritionnal needs and fish is definitely not the best option for several reasons: decrease of wild resources, risk of contaminants...etc

There are big différences of biological activities between long chain and short chain omega 3 PUFA and the problems of ressources are also not comparable.

Algal sources of DHA are clean and sustainable. It can be provided as oil or as powdered algae. Martek has a popular product

Cecile, what do you consider a sustainable source? Are you considering non-animal products as sustainable? I understand that fish are decreasing, so then they would not be considered sustainable. Is this true for all varieties of fish? I agree that algae contains DHA and would be considered long-chained; however, flax oil ALA is only 2 carbons short of DHA - so why is it not considered long-chained? Older persons and people of certain ethnic groups do not synthesize ALA to DHA, so most vegetable products containing omega-3 such as flax oil and walnuts would not be an option for them.

A review on non-fish sources of long chain omega-3 fatty acids:

Lane K, Derbyshire E, Li W, Brennan C. Bioavailability and potential uses of vegetarian sources of omega-3 fatty acids: a review of the literature. Crit Rev Food Sci Nutr. 2014;54(5):572-9. doi: 10.1080/10408398.2011.

http://www.ncbi.nlm.nih.gov/pubmed/24261532

Poultry (and birds in general) are much better than humans at bio-converting the medium-chain omega-3 PUFA to long-chain omega-3's. Therefore there can be some benefit from feeding laying hens plant omega-3 PUFA sources and letting them bio-convert them and deposit them in the egg. Most recently we have tested a high-SDA flax (ALA to SDA is a key rate-limiting step in bio-conversion to long chain omega-3 PUFA's). While the long-chain omega-3 PUFA's were increased compared to using regular flax, there also a rate-limiting step right before conversion to DHA.

There have been some big developments in production of algal sources of DHA. In general, challenges in the field have been dealing with some of the anti-nutritive factors that can limit DHA transfer to the animal (I'm most familiar with enrichment of animal feeds, but this would also apply to humans). In addition to Martek (mentioned above), Alltech is another company producing algal DHA as a feed additive.

Fish oils, in general, are excellent sources for Omega-3 polyunsaturated fatty acids. One can find them in other plant sources like olive oil, wallnuts, almonds...etc

Joan -

Flax and other foods such as walnuts are not good sources for the conversion of ALA to DHA. It is well known ALA to DHA conversion is less than 0.5%, whether younger or elderly; therefore, ALA is not a dependable choice. Still misconceptions abound, and ALA sources are heavily promoted. If the rate of conversion of ALA to DHA were lower in certain groups, the question of how lower can it get arises.  In view of this very low conversion of ALA to DHA vegetarians need to depend on algal sources of DHA. Micronutrient deficiencies (zinc, vitamins B6, niacin, etc.)  also can hamper the conversion of ALA to DHA. Vitamin C, B6, magnesium, zinc, niacin, etc. are tsome cofactors required for this conversion.

http://fishcooking.about.com/od/howtochoosefreshfish/tp/omega3_list.htm

http://www.healthaliciousness.com/articles/high-omega-3-foods.php

http://nutritiondata.self.com/facts/finfish-and-shellfish-products/4120/2