Fish and fishes
People often ask about how the terms 'fish' and 'fishes' should be used. In fact it is often said that there is no such word as 'fishes'. This is not true.
A group of fish of the same species are called 'fish'. Two or more species of fish are called 'fishes'.
For example, a number of Eastern Australian Salmon swimming together can be called a school of fish. But if one Tarwhine starts swimming with the Eastern Australian Salmon they are called fishes.
Books such as the Sea Fishes of Southern Australia and Coastal Fishes of South-Eastern Australia use the term 'fishes', because more than one species of fish are included in the book.
For more information, view the Wikipedia comment on Fish or Fishes?
Mark McGrouther , Collection Manager, Ichthyology