Differences in head shape of the European eel, Anguilla anguilla (L.)

Abstract

Differences in eel, Anguilla anguilla (L.), head shape were the result of greater increases in head width, rather than changes in head length. The ratio of head width:total length (HW:TL) increased significantly (t‐test, P < 0.05) from the glass‐yellow eel stage. Cultured yellow eels were exclusively narrow headed (mean HW:TL = 0.027, range = 0.023–0.032), while wild yellow eels displayed an array of head shapes (mean HW:TL = 0.033, range = 0.023–0.046). Therefore, broad heads (HW:TL 0.033) occurred only among wild yellow eels sampled and may have resulted from diet. Cultured yellow eels consumed only small pellet material. Of wild yellow eels stomachs containing food, 78% of broad‐headed eels consumed large and/or hard‐bodied organisms (e.g. beetles, fish, molluscs and Notonecta sp.), while 83% of narrow‐headed eels consumed exclusively small/soft‐bodied prey (e.g. amphipods and chironomids).