The acid in the marinade reacts with the proteins in the seafood changing the molecular structure in much the same way as heat does. It will work with any meat but using delicate foods like seafood or chicken works better.
Any acid will work the way the lime and lemon juice does in this recipe. You can use a sweet citrus juice like orange or grapefruit. It will be acidic enough but may be too sweet and using a small amount of vinegar helps balance the flavors. I like to use rice vinegar because it is not as acidic.
Any combination of fish will work. Because each type of fish will “cook” at a different rate, firmer fish like shrimp should be marinated longer. Using vegetables or fruits can really make your seviche but the same rule applies (marinate the firmer produce longer).
Use the freshest of ingredients when making Seviche because the final recipe doesn’t keep well for long.