Research cruises were carried out between 1990-92 to study the demersal macrofauna of the shelf off the Sinaloa-Nayarit area and in the Gulf of Tehuantepec. Synodus spp. were frequent in the Sinaloa-Nayarit area, tending to be more abundant further from the coast. In the Gulf of Tehuantepec the largest catches were obtained off Salina Cruz. S. evermanni length composition ranged from 6 to 29 cm, while S. scituliceps ranged from 7 to 43 cm total length. There were differences in abundance and length composition depending on the depth and area. Both species were found below 30 m deep except S. scituliceps in the Gulf of Tehuantepec. S. evermanni was more abundant at depths greater than 90 m. S. scituliceps showed a preference for shallow waters (30-60 m) independent of the length. The fish were from 0 to 4 years old for S. evermanni and from 0 to 9 for S. scituliceps. S. evermanni is characterised by a relatively small maximum size, rapid growth and distribution at greater depths than S. scituliceps, whilst the latter species is distributed at lesser depths, reaching considerable sizes with slow growth.