Many, perhaps most, of the what I call the Super Cultures (in terms of health and longevity) eat fish as a staple. I covered in another link How Fish Protects Your Heart (and Therefore Penis). But did you know that Fish is extremely protective of your testosterone as well? That's right - no other supplement that I know works in so many ways at protecting your testosterone. You could rightly call Fish Oil Anti-Andropause.
First of all, fish oil has many studies showing that it combats insulin resistance. Insulin resistance, as you hopefully know from my link on Metabolic Disorder, is the hallmark sign of Metabolic Disorder and Metabolic Disorder is associated with decreased testosterone (and erectile dysfunction). The reason is that fish oil has long chain omega-3 fatty acids, which improve insulin response.
In fact, fish oil can protect you from the insulin resistance that is brought about a high fat diet or saturated fats.  This is one of the big problems with modern cattle and pork: they are very fatty (25-35%) versus their wild game equivalents (~4%) and, even worse, their fat has very little omega-3's because they are grain fed not grass fed. In other words, their muscle ends up extremely fatty and laced with insulin resistance-inducing saturated fats. And then, as if to add insult to injury, ranchers make sure that the one ingredient, omega-3's, that could take care of the insulin resistance are completely missing!
NEWS FLASH: 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, read this discussion for more information.
Protecting your testosterone from insulin resistance is just the beginning. Fish oil has also been shown to lower SHBG.  Again, this is anti-andropause because andropause is known for slowly raising SHBG levels with age, which means that more SHBG is bound to your testosterone leaving you less free testosterone.. The net effect of taking fish oil, then, is the opposite and will leave you with more free testosterone.
Fish Oil has also been shown in one study to increase Luteinizing Hormone (LH).  Luteinizing Hormone (LH), you may remember from other threads, is the hormone that triggers or signals testosterone production. It is particularly strong in young males, but is important for us old guys as well.
So, again, fish oil is definitely not a panacea to solve your low testosterone problems. But it likely will boost your free and total testosterone a little and preserve your total testosterone from the ravages of andropause. When you consider what fish oil does for the brain, the heart and your penis, it is a supplement well-worth the money in my opinion. (Read also about How Fish Oil is Good for the Heart, lowering triglycerides, inflammation and clotting, all significant risk factors for heart disease.)
CAUTION: 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.
NOTE: Some have argued that fish oils are oxidative upon digestion and that fish oil thus probably does significant aging and cellular damage internally that we may not yet understand. However, several studies suggest this to be a relative non-issue.  In addition, one study also found that additional Vitamin E can protective help overcome most of the small amount of oxidative damage that is done anyway. The study authors found that oxidative products in the urine "more than doubled when the fish oil capsules were introduced but then dropped by a factor of four when vitamin E was added. The vitamin E concentration in the red blood cells dropped very significantly when fish oil was ingested but more than recovered with the vitamin E supplement". 
Also, I recommend that you take a mixed tocopherol blend of Vitamin E, rather than the standard alpha tocopherol Vitamin E used in this study, even though it is more expensive. Pure alpha tocopherol can lower your body's other tocopherols.
You may also want to check out my link on Arthritis, as it documents how fish oil can significantly help with knee and joint pain.
1. J. Nutr, Nov 2005, 135:2634-2638
2. Nutr Cancer, 2000, 38(2):163-67
3) Alteration of the Lipid Composition of Rat Testicular Plasma Membranes by Dietary (n-3) Fatty Acids Changes the Responsiveness of Leydig Cells and Testosterone Synthesis; Elena Sebokova, Manohar L. Garg, Antoni Wierzbicki, Alan B. R. Thomson and M. Thomas Clandinin; Manuscript received 13 July 1987. Revision accepted 27 November 1989
4) Pharmacological Res, 57(6):451-455, Jun 2008, "Polyunsaturated fatty acids as antioxidants", Richard D Kefi, et. al.
5) Amer J of Clin Nutr, 58:98-102, July 1993, "Dietary fish oil-induced changes in the distribution of alpha-tocopherol, retinol, and beta-carotene in plasma, red blood cells, and platelets: modulation by vitamin E"