Mouth Growth and Prey Selection in Juveniles of the European Long‐snouted Seahorse, Hippocampus guttulatus

Seahorses are ambush predators that swallow the prey through their tubular snout. In order to better understand mouth growth and its effect on prey preference by juveniles of the seahorse Hippocampus guttulatus , experimental assays were carried out by feeding juveniles (0–30 – d after male's pouch release [dar]) on a mixture of rotifers, Brachionus plicatilis ; Artemia nauplii; and copepods; Acartia tonsa . Mouth development in juveniles was accomplished by growth of upper and lower jaws, which were linearly correlated with juvenile length, whereas mouth width ( MW ) and height ( MH ) grew exponentially with juvenile size. Additionally, MW and MH were exponentially correlated, so that the transversal section of the mouth increased linearly with juvenile age and length. Gut content and Ivlev' selectivity index demonstrated a permanent rejection of rotifers for the whole experimental period and a clear preference of juveniles for copepods from 0 to 15 dar and for Artemia nauplii afterwards. Results also suggest that juveniles are able to ingest larger prey than those provided as the limiting factor in prey ingestion was not MW , as for many marine fish larvae, but mouth area. A tentative feeding schedule to successfully feed H. guttulatus juveniles from 0 to 30 dar is proposed.