A morphometric and meristic investigation of Lusitanian toadfish Halobatrachus didactylus (Bloch and Schneider, 1801): evidence of population fragmentation on Portuguese coast

Abstract

A total of 207 specimens of Lusitanian toadfish Halobatrachus didactylus from six different localities were analysed in terms of morphometric and meristic characters in order to investigate the hypothesis of population fragmentation on the Portuguese coast. This study confirmed the relative isolation between the Algarve populations and those from the western estuaries, which also showed a high degree of discrimination among them. Morphometric characteristics were much more adequate than meristic characters for a good separation of these populations. The most relevant morphometric characteristics for separation between H. didactylus populations were head width, interorbital width and pelvic fin length. These three variables were very useful for separation between western populations and seem to play an important role in species feeding activity. The caudal peduncle development is mainly related to the specimen´ swimming ability and was particularly relevant for discrimination between northern and southern populations and between estuarine and adjacent marine populations, apparently due to differences in hydrodynamic conditions. Meristic variation is mostly of a latitudinal nature (mainly nasal tentacles and pores on the lower jaw) but some differences between estuarine and marine populations (principally fin rays counts) related to water temperature were also observed.