Homeopathy

Fish (Oil) has benefits...
The scandi's have shown a link (using their supreme medical records) between high fish diet and reduced Alzheimer's onset.
Nurk, E., Drevon, C.A., Refsum, H., Solvoll, K., Vollset, S.E., Nygård, O., Nygaard, H.A., (...), Smith, A.D. Cognitive performance among the elderly and dietary fish intake: The Hordaland Health Study (2007) American Journal of Clinical Nutrition 86 (5), pp. 1470-1478

I'll just point out the obvious here (ie: I am not disagreeing or agreeing with you.)

A link between a high fish diet and and reduced Alzheimer's onset means one thing, that there is a possible causal link between a high fish diet and and reduced Alzheimer's onset.

It does not mean there is a causal link between fish oil and reduced Alzheimer's onset.