This study aims at fractionation of arsenic according to its polarity into water-soluble arsenic fractions, polar and non-polar arsenolipids in herring, capelin and blue whiting fish meal and edible seaweed dulse. Changing the sequential extraction order showed a significant labile fraction of the non-polar arsenolipids (AsLps) where species transformation is considered a more likely explanation than a partitioning problem in the compounds. The majority of non-polar AsLps were not stable through water extraction for three types of fish meal (71–93% for herring, capelin and blue whiting). The non-polar AsLp fraction was minor for dulse. In 27 samples of herring and blue whiting fish meal, arsenic was mainly present in the water phase: 71% (2.8 ± 0.8 mg kg−1) and 93% (17.2 ± 1.9 mg kg−1) for herring and blue whiting on average, respectively. The polar arsenolipids in the MeOH/DCM fraction accounted for 15% and 5% (0.5–1.2 mg kg−1 As) for both herring and blue whiting, respectively. Speciation analysis of arsenolipids was undertaken for herring meal, capelin meal and dulse (red seaweed) using simultaneous HPLC-ICPMS/ESIMS for quantification and identification. Among the known arsenohydrocarbons (AsHCs), arseno fatty acids (AsFAs) and arsenosugarphospholipids (AsPLs), a novel AsFA374 was identified in dulse by arsenic detection via simultaneous protonated mass, accurate mass as well as MSMS fragmentation. Additionally, recently reported AsLp groups, arsenic containing phosphatidylcholines (AsPCs) and arseno fatty alcohols (TMAsFOHs), have been reconfirmed to occur in marine samples.