Fish Oil has, in general, not been studied directly as an aid to erectile dysfunction.
However, one European study found that it helped endothelial function and nitric
oxide output (in diabetic pateints) and both of those are the stuff of erections
as you know. 
Yet another study showed that it improved arterial elasticity which will do
nothing but help with erections.
Furthermore, fish oil is long-term protective of the entire cardiovascular
system including your endothelium. For those battling high triglycerides, one of the prime predictors
of heart disease, fish oil would be a strong contender as it is recognized
for substantialy lowering triglycerides. Fish oil also raises good cholesterol,
HDL, by a few percent while it's at it. Its only negative is that does also
raise LDL, the bad cholesterol by 5-10% in some cases. The net effect of fish oil,
however, is definitely good. Triglycerides, in particular, are a strong
predictor of heart disease (probably via ADMA) and a plague of Western societies with all of their
One recent study shows that taking fish oil capsules
dramatically increases the risk for advanced prostate cancer - this is the kind you don't want! - and significantly
increases it for all prostate cancers. See this
article for more details.
Based on this, the authors recommended eating just one or two meals of fish per week instead. Keep in mind that this is
just one study, but the results were so pronounced that it should be carefully considered. For a nice rebuttal to this study,
discussion for more information.
Fish Oil also
helps with mental state, warding off depression and feelings of melancholy.
And avoiding depression is critical for your brain, neurons and testosterone.
One study of middle and senior aged men also found that Fish Oil lowered levels
of SHBG  , the protein that binds to testosterone. Increasing levels of SHBG is
one of the curses of increasing age in males as it leaves less and less
testosterone available to do all. In other words, Fish Oil should increase free (but not total)
testosterone in aging males. (See my link on
How Fish Oil Help with
Testosterone for more details.)
Fish oil is also known for its inflammation-lowering properties and inflammation
is recognized as a key ingredient to heart disease and autoimmune disorders. A fatty
acid in fish oil, called human resolvin E1, does this by inhibiting both the migration
of inflammatory cells to sites of inflammation and the turning on of other inflammatory
cells. . Fish oil has done very
well in multiple studies with lowering fibrinogen, a key predictor of heart disease
and a kind of inflammatory marker related to clotting. But, strangely
enough, fish oil has had mixed results in lowering one of the key inflammatory markers associated
with heart disease, CRP (C-Reactive Protein).
Fish consumption is also associated with decreased dementia. Considering how
good fish is in warding off depression, this should come as no shock.
Fish's brain-saving properties may also be because Alzheimer's and dementia,
like so many other health problems, seems to have an inflammation component.
One recent large study of Asia and Latin American participants found that fish
consumption was significantly correlated with lowered rates of dementia. 
By the way, meat consumption showed the opposite: increased rates of
The bottom line is that fish and fish oil consumption are good for heart, penis,
brain and skin. (It is also good for
Raising and Protecting Free Testosterone.) One recent large meta-analysis recommended fish oil
because it both prevents heart disease and reduces the risk of heart attack. 
yet another huge endorsement for omega-3's, because the researchers
looked at multiple studies over the last 30 years, aggregated the results and
concluded that fish oil could "reduce the risk of hardening of the arteries
(atherosclerosis), irregular heartbeat (arrhythmia), heart attack, sudden
cardiac death, and heart failure". Not bad, eh?
NOTE: Many guys are plagued by DES, or Dry Eye Syndrome. This can be
quite bothersome and even debilitating depending upon how bad it is.
Researchers recently found that the higher the omega-3 fatty acid intake (and
tuna consumption), the less the likelihood of DES. This is just one study,
but it makes sense that fish and fish oil will very likely help this condition.
By the way, you will find some criticism of fish oil because, unfortunately, it
has had mixed results with the mortality studies. For an excellent summary
of the research as of a few years ago, see the following summary from the
prestigious journal  at this
link. But I think this is too rigorous of a
requirement: what supplement or food is so powerful that it can overcome all other
aspects of lifestyle and diet? (Green tea is the only one that comes to
mind.) Again, many of the miraculously healthy
cultures in our world eat fish and it is endorsed by, in my opinion, one of the
greatest researchers of our day.
Fish Oil - Safety
If you do decide to take fish oil, please read my link on
The Triglyceride versus Ethyl
Ester Forms of Fish Oil. Rancidification of fish oil is a significant issue and
this link discusses that in detail. You can do more harm than good if
you're not careful.
Studies have shown that fish oil, at high doses of 2 g DHA/day, does decrease
the body's Vitamin E to unacceptable levels.  It may be advisable to take
additional Vitamin E. I discuss this in more detail at the bottom of this
link on How to Buy Fish Oil.
Also, if you are wondering about contamination: Consumer Labs did a study recently
and found that all 41 fish oil brands they tested were safe from mercury and PCBs.
(This is contrast with actually eating fish to get fish oil, because almost all
fish, especially those on farms, are unacceptably contaminated.)
Fish Oil - Dosage
A recent study  broke cohorts up into varying dosages of DHA and then
followed various known markers of heart disease to find the optimal dose.
What they found was that only relatively small dosages, 200 mg of DHA per day,
were needed to achieve very high levels of protection. We don't have the
details yet on this study, but the results line up with
previous studies that found that only eating fish 1-2 times per week was
sufficient to achieve substantial gain. You may want to consider taking
more than 200 mg (of DHA) due to fish oil's
Free Testosterone Raising Powers.
NOTE: You may also want to read my link on How Fish Oil Can Help with
NOTE: Be very cautious about using flax seed to get try to get
your omega threes. First of all, it does not have all the properties of fish oil,
and, more importantly, it has been tied to a possible increase in prostate cancer.
For example, Mayo Clinic's
site states this: "Flaxseed oil
contains only the alpha-linolenic acid component of flaxseed, and not the fiber
or lignan components...Preliminary evidence suggests that alpha-linolenic acid may
be associated with an increased risk of prostate cancer".
1) Diabetologia. 1993 Jan;36(1):33-8
2) Life Science 2006 April 18;78(21):2523-32
3) Jour Exper Med, Mar 2007, 201(5):713-722
4) Circulation: 2002,106:2747
5) Nutr Cancer, 2000, 38(2):163-67
6) Amer J Clin Nutr, Received for publication February 3, 2009. Accepted for
publication May 21, 2009; Emiliano Albanese, et al; "Dietary fish and meat
intake and dementia in Latin America, China, and India: a 10/66 Dementia
Research Group population-based study"
7) J of the Amer Col of Cardiology, Aug. 11, 2009; 54:585-594, Lavie, C., News
release, American College of Cardiology.
8) FASEB Journal, 2009, 23: 2909-2916, "Increasing intakes of the long-chain -3
docosahexaenoic acid: effects on platelet functions and redox status in healthy
9) Brit Jof Nutr, Jul 1992, 68:163-173, "The influence of a fish oil high in
docosahexaenoic acid on plasma lipoprotein and vitamin E concentrations and
haemostatic function in healthy male volunteers"
10) Amer J of Clin Nutr, Oct 2005, 82(4):887-893, "Relation between dietary n–3
and n–6 fatty acids and clinically diagnosed dry eye syndrome in women"