FishBase in the context of Ecological pyramid

Ichthyology, from Ancient Greek ἰχθύς (ikhthús), meaning "fish", and λόγος (lógos), meaning "study", is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 35,800 species of fish had been described as of March 2025.

Sardine and pilchard are common names for various species of small, oily forage fish in the herring suborder Clupeoidei. The term "sardine" was first used in English during the early 15th century; a somewhat dubious etymology says it comes from the Italian island of Sardinia, around which sardines were once supposedly abundant.

The terms "sardine" and "pilchard" are not precise, and what is meant depends on the region. The United Kingdom's Sea Fish Industry Authority, for example, classifies sardines as young pilchards. One criterion suggests fish shorter in length than 15 cm (6 in) are sardines, and larger fish are pilchards. The FAO/WHO Codex standard for canned sardines cites 21 species that may be classed as sardines. FishBase, a database of information about fish, calls at least six species pilchards, over a dozen just sardines, and many more with the two basic names qualified by various adjectives.