Why not flaxseed oil? There's no mercury to worry about, and it does contain omega-3 fats...but not the best kind.
D004281:Docosahexaenoic Acids / Q000008:administration & dosage / Q000378:metabolism; D015118:Eicosapentaenoic Acid / Q000008:administration & dosage / Q000378:metabolism; D015525:Fatty Acids, Omega-3 / Q000008:administration & dosage*; D005395:Fish Oils / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D008043:Linseed Oil / Q000008:administration & dosage* / Q000009:adverse effects; D017962:alpha-Linolenic Acid / Q000008:administration & dosage / Q000378:metabolism
D015525:Fatty Acids, Omega-3; D005395:Fish Oils; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids; D008043:Linseed Oil; D015118:Eicosapentaenoic Acid