The differences between sardine and pilchard species are not always easy to identify, because the two terms are often used interchangeably. Sardines and pilchards are in the same species, though various sub-species exist of each type. In general, sardines and pilchards vary in size, colour and habitat.
The main difference between sardines and pilchards is their size. Sardines tend to be smaller, with the smallest sub-species growing only to 13 cm (5 1/2 inches). On the other hand, the smallest pilchard subspecies grows to be about 25 cm (10 inches). Though sardines are usually smaller, some sardine and pilchard sub-species are similar in size, like the European pilchard and the Gilt sardine.
The habitats of sardine and pilchard sub-species are largely similar, though some sardines tend to survive in deeper waters than pilchards. For example, the Sardinella aurita can live up to 350 metres (1,148 feet) deep, while the deepest dwelling pilchard sub-species -- the Clupanodon pilchardus and Clupea pilchardus -- live a maximum 55 metres (180 feet) deep.
Pilchard sub-species only appear in black, green and olive tones, with silver and gold bellies, while sardines can be a wider variety of colours. Sardines can be black and green, but can also be brown, speckled and iridescent blue and green. Sardines often have darker scales on their bellies, including brown and bronze.
Sardines and pilchards are both plentiful in the Atlantic ocean and the Mediterranean sea, though exact locations can vary. The Alausa pilchardus, for example, tends to be found in the more western areas of the Mediterranean, while the Clupanodon pilchardus lives further east. Several sardine sub-species populate the North Atlantic, while others are largely migratory.