Polyunsaturated fats consist of two main types called omega 3 and omega 6.  Most Americans consume way too much omega 6 relative to omega 3. Fish and fish oils are the richest source of omega-3 fatty acids; the main two are called EPA and DHA.  Omega 3 fats have been shown to have positive effects on heart health including decreasing inflammation and fat levels in the blood. Since chronic elevations in inflammation are linked to many disease states and also to proper recovery from exercise,
omega 1250
more info about omega 1250

 there are obvious applications of fish oil supplementation for strength athletes.  Recent studies have indicated that omega 3s enhance insulin sensitivity, regulate muscle growth, augment blood flow to muscles during exercise, and decrease muscle soreness and swelling after damaging exercise.  Given all these potential benefits of fish oil on muscle it seems reasonable that improving omega 3 status would have a positive effect on strength gains.  That was the goal of Brazilian researchers who had older women perform 90 days of strength training with or without fish oil (2 grams per day).  As expected the fish oil group had a significant increase in blood levels of EPA (+45%) and DHA (+20%).    The fish oil group also showed significantly greater improvements in a spectrum of strength and power tests including peak torque, muscle activation, and functional capacity.  The mechanism of how fish oil improved strength performance was speculated to be related to improved membrane fluidity and potential effects on nerve conduction velocity and activation of muscles.  These results provide evidence that supplementing with fish oil during resistance training can have a positive effect on neuromuscular adaptations.  
Rodacki CL, Rodacki AL, Pereira G, Naliwaiko K, Coelho I, Pequito D, Fernandes LC. Fish-oil supplementation enhances the effects of strength training in elderly women. Am J Clin Nutr. 2012 Jan 4.