Nothing will ruin a fishing trip like getting seasick. You can take steps to avoid seasickness and things you can do if you start to feel yourself getting seasick.
The best option is to take a few simple steps to avoid getting seasick in the first place. Start with the basics; stay hydrated, eat a mild light meal, avoid acidy drinks, be prepared for the hot sun.
Next, consider over-the-counter motion sickness medication. Bonine (marezine) and Dramamine (dimenhydrinate) are two major ones. On Grand Cayman these can be found at Fosters, Kirks, Hurley’s and at the local pharmacies. 
Scopolamine skin patches are very effective and are available by prescription. Be sure to follow the directions as it is usually necessary to start a day before.
Consider natural remedies. Many people have had good results with sea bands. These are inexpensive, soft, comfortable wrist bands that work by applying slight pressure to the underside of the wrist (pressure point). There is no downside to this simple solution and the effectiveness is high. Herbal solutions work well for some folks. Ginger and mint are the most popular and can be used in many different forms like infused in water (great for hydration) or candied ginger or mints work too. Both can work as aromatherapy.
Here are some other things you can do to avoid getting seasick. Sit or stand facing forward. Stay above deck. Keep off the bow; that’s where the boat’s motion is worst. Look at the horizon. Avoid the exhaust on diesel-powered boats. Seek shade to avoid too much sun. Don’t read or start at your phone for long periods. Also, try to relax and breathe deep.
If you have a history of motion sickness, it makes sense to take steps ahead of time. You don’t want to suffer or ruin the trip for others. Once you start to feel the effects of motion sickness, it is often too late. Medication (over-the-counter or prescription) is the most effective. If you only occasionally get seasick or just feel minor effects, try sea bands or herbal remedies. You may want to consider these even if you have never felt motion sickness, as there is no downside.
