It is true that fish oil can help protect against manic depression?

Bipolar depression : Mixed, but mainly positive evidence has been found for omega-3 for bipolar depression, while no evidentiary support has been found for use in mania. Some believe omega-3 fatty acid deficiency to be a risk factor and possibly treatment in with omega-3 fatty acids in the prodromal phase may be of benefit. No one really knows for certain at this time. Unlikely to hurt though.

Statistically only: I agree with colleagues who have provided a qualified "yes" to which i will add a related qualification: the intensity and frequency of depression is statistically alleviated, it seems, in a large sample. This means that no one has their bipolar symptoms disappear entirely and not everyone benefits even some. No substitute has been found for mood stabilizing medications.