Never had it before. Maybe missing out on something good.

Is ceviche like Mexican sushi?

Well not exclusively Mexican, most latin-american countries have their own version which of course is "the best". Might not sound that good, but it's addictive. Essentially, you soak the fish chunks in an acid, usually lime juice. Along with that you add other flavors like onion, hot chile pepper (habanero and jalapeno for me), cilantro, cellery, tomato. Again, recipes vary and their arent' rules. Usually eaten with crackers or chips of some sort. In places like Panama you can buy this stuff in little stores in styrafoam cups to pick up along with your beers.

Fresh water parasites are much more prolific than saltwater parasites. There is a reason you don't ever, EVER, see freshwater sashimi served in a sushi restaurant. Fresh water parasites can and will penetrate the lining of your stomach if you ingest one. The whole argument that they cannot survive your stomach acid is a complete myth. The main parasite that most people contract from eating under-cooked or raw fresh water fish is the tapeworm. There are plenty of other nasty critters that can wreak havoc on you or kill you for that matter from eating any type of raw freshwater fish, including eating ceviche made from freshwater fish. The reason is because ceviche is still very much raw fish. The citrus bath does turn the meat opaque, giving it the appearance of being cooked, and it does kill some of the parasites present in raw foods that can make you sick, but the ceviche-making process will not protect you from the worst of the parasites, ranging from salmonella to parasites and worms. The best practice is to always cook freshwater fish. You may have eaten raw freshwater fish before with no ill affects but like Bear Grylls says: "You can get it right a thousand times, you only need to get it wrong once". Essentially, you're taking an enormous risk by doing this and if you do happen to ingest one of these parasites, it will be the last time you take that kind of risk, I guarantee.

Play is safe, don't take that chance. Cook everything from the freshwater... my 2 cents.