Ontogeny of swimming behaviour in sardine Sardina pilchardus larvae and effect of larval nutritional condition on critical speed

The ontogeny of swimming behaviour in sardine Sardina pilchardus larvae was studied, from hatching to 75 days post-hatch (dph), by measuring the critical swimming speed (Ucrit) and observing locomotory behaviour. In addition, the effect of larval nutritional condition on Ucrit at the onset of their swimming abilities (20 to 25 dph) was evaluated by rearing larvae under 4 different feeding treatments. Diets consisted of different concentrations of dinoflagellates, rotifers and the copepod Acartia grani, and a wild plankton assemblage. Recently hatched larvae were mostly inactive, but from 2 dph onwards larvae started to swim freely in the rearing tank, and time spent swimming increased throughout ontogeny. Larvae younger than 20 dph (i.e.