The most common word for a baby fish is "fry," but other words are used as well. For example, depending on the age of the fish, a young salmon can be referred to by four different names before reaching adulthood.
Newly hatched salmon are called alevin. At this stage, the young fish is still feeding off the nutrient sac that nourished it while it was in the egg. At five to 10 weeks, baby salmon become fry. Fry swim free and feed themselves. After several months, fry become parr. After anywhere from one to three years, parr become smolt. Some of these terms refer only to salmon, but the word fry can be used as a generic term for baby fish.