Journal
<p>The widely distributed amphidromous goby Sicyopterus lagocephalus needs drastic change of habitat to<br>
fulfil its life cycle: adults live and spawn in rivers, where eggs hatch into prolarvae that have to reach the sea to<br>
acquire characteristics of planktonic larvae. Postlarvae return to rivers where they recruit and grow to the adult<br>
reproductive stage. Here, we describe the prolarval stages, namely from hatching to first contact with sea water, as<br>
well as the first marine larval stages. The observations were made under experimental conditions. We described 3<br>
prolarval substages in freshwater (L1a–L1c). Prolarvae present a slight but visible ontogenetic development in<br>
freshwater, during which the yolk sac begins to reduce, the pigmentation increases on the body and in the eyes, and<br>
the lenses appear, although the eyes are not functional. Prolarvae need to reach the sea in a maximum of 96 h to<br>
pursue their development. Their transfer in sea water at a salinity of 36.5 induces important morphological<br>
modifications (i.e. yolk sac full absorption, appearance of pectoral fins, migration of the eyes in anterolateral<br>
position of the head, opening of mouth and anus), enabling the organisms to adapt to their new environment. This<br>
marine stage is divided into two substages: L2a corresponding to the organisation of the morphological structures<br>
adapted to the marine environment and L2b during which these morphological structures become functional.<br>
Whether it is in freshwater or sea water, the duration of the substages depends on the water temperature, but is<br>
similar for all individuals for a given temperature.</p>
