(Credit: Wix)
Ceviche is raw fish cooked through the process of marination in an acidic, pungent liquid. Through enzymatic reactions, the fish is chemically altered yielding a texture similar to regularly cooked fish. Ceviche typically uses fluke, flounder, sea bass, or shrimp in marinated in a citrus, bright, herb sauce. It is a Peruvian dish but is popular throughout Latin and South America and is an extremely popular menu item at really any mid to high end restaurant.
Other than for actual food safety, the dish is really hard to get right. As said earlier, one must perfect the ratio of citrus (acidity), spice, and aromatics. No one likes under-seasoned or salty fish. But when done perfectly, ceviche is a truly magnificent dish with the texture of soft, tender fish but maintaining the freshness and purity of the own fish's flavor.
Ceviche isn't traditionally cooked fish. The fish chemically reacts with the acid in the marinade which is why ceviche tastes like cooked fish, not gummy or soft. Much like heat cooks fish, the acid rearranges proteins yielding a product similar to seared fish except without a brown crusted skin.
The reaction that causes ceviche to resemble cooked fish is known as the process of denaturation. Here, the proteins lose their shape as the become less rigid and firm and relax yielding the tenderness of well-cooked seared fish. The most common example of this reaction taking place is through the process of cooking eggs. As eggs are beaten and mixed with salt, their proteins are broken down, yieldings a softer texture. The same is true for fish. Uncooked fish seems rubbery, gummy, and somewhat mushy. Cooked fish is flaky and crumbly.
Acid is used in this dish simply because it meets the best of both worlds. Ceviche is typically served earlier on in the meal. A bright, uplifting flavor is perfect as an appetizer. Additionally, citrus fruits are very abundant all throughout South and Latin America as this dish greatly exemplifies the utilization of surroundings, culture, and environment combined into one dish.