ABSTRACT
INTRODUCTION Oceans cover about 70 percent of the earth's
surface and account for 97 percent of its waters. Exactly how many species of fishes exist is difficult to determine, for new species are or will be described as our knowledge of fishes expands and is refined. Nearly 25,000 species of fishes are currently known. About 14,500 species live all their lives in marine waters; 9,966 live in freshwaters of the world. Perhaps 200 marine species are diadromous, living part of their lives in freshwaters and part in marine waters (e.g., American eels, Anguilln rostrata). Many marine fishes (10,465) may venture into fresh waters to spawn, feed, etc. (e.g., salmon, sturgeon) or are tolerant of brackish waters (a mixture of fresh and saline waters) into which they are carried by various currents or may follow for food.
