There are certain foods and nutrients that may boost male fertility. This cross-sectional study which was published in the Fertility and Sterility journal shows that semen motility and morphology are affected by antioxidant intake.
If you want your swimmers to be Michael Phelps gold medal winners, then upping your daily intake of carotene rich fruits and vegetables on the list below will give you a better chance to be standing on the podium at the end of the race to the egg.
On the other hand, lycopene rich foods help maintain structural integrity in the pool.

Carotene Rich Foods for Sperm Motility: sweet potato, kale, carrots, greens (spinach, mustard, turnip, collard), butternut squash, red leaf lettuce.

Lycopene Rich Foods for Sperm Morphology: tomatoes (sun dried are best, raw and cooked are also good), guava, watermelon, grapefruit, parsley, basil, asparagus, liver, red cabbage.

Link to the full study here: https://www.ncbi.nlm.nih.gov/pubmed/24094424