ABSTRACT
The suborder Gobioidei (Teleostei, Perciformes) comprises about 270 nominal genera and more than 2000 species (Hoese, 1984), which are distributed worldwide except for Arctic and Antarctic areas. Gobioids are widespread in tropical and temperate seas from subtidal to more than 300 m deep waters, as well as in estuarine and freshwater environments (Nelson, 1994). Th e suborder includes relatively small fi sh ranging from 8 mm to about 50 cm SL, most of them being generally benthic dwellers as adult with planktonic larval stages. Some gobioid genera, however, exhibit a planktonic life mode throughout the whole life span. Among the diverse mode of life of gobioids, species living in the water column have been considered of particular zoological interest because of the persistence into adulthood of several larval anatomical characteristics (Miller, 1973), which are of adaptive signifi cance for a planktotrophic life in midwater (Brunelli
and Atella, 1914; Brunelli, 1919). Generally, they are characterized by transparent body, scarcity of melanophores, persistence of the swimbladder and short and straight alimentary canal (Miller, 1973, 1989). Th ere is also an evolutionary trend toward a reduction of the fi rst dorsal fi n, a change from ctenoid to cycloid scales and a more or less pronounced sexual dimorphism in dentition (Miller, 1973). Th e retention of larval morphology when adult, or paedomorphosis, is achieved through heterochrony, a rather common process of adaptation and radiation among gobioids, consisting of a change in the timing and/or rates of processes underlying the ontogenetic formation of morphological traits compared to the ancestral species (Gould, 1977). Among diff erent types of heterochrony (Reilly et al., 1997), paedomorphosis is produced by a slower development rate or deceleration (neoteny sensu Gould, 1977), an earlier off set time of shape or hypomorphosis, sometime coupled with early maturity (progenesis sensu Gould, 1977), or a later onset time of shape or post-displacement (Kon and Yoshino, 2002a). It is suggested that paedomorphic ontogeny of descendants, expressed as progenesis or neoteny, is constrained by seasonally restricted maturity (Kon and Yoshino, 2002b). Typical marine gobioid genera with paedomorphic traits when adult, such as transparent body, and planktonic life mode are the European Aphia Risso, Crystallogobius Gill and Pseudaphya Iljin, and the Indo-Pacific Paedogobius Iwata, Hosoya and Larson, Leucopsarion Hilgendorf and Schindleria Giltay. All these genera are monotypic, except for Schindleria, which includes three paedomorphic species, namely S. brevipinguis, S. praematura and S. pietschmanni (Johnson and Brothers, 1993; Watson and Walker, 2004). According to some authors (Miller, 1973, 1997; Dotsu and Uchida, 1979; Caputo et al., 2000; Kon and Yoshino, 2002a, b; Kitano, 2002), Paedogobius kimurai and Schindleria spp. are progenetic, whereas Aphia minuta, Crystallogobius linearis, Leucopsarion petersii and Pseudaphya ferreri are neotenic. Th e progenetic gobioids P. kimurai and Schindleria spp. are distributed in warm waters and inhabit coral reefs and muddy bottoms, respectively (Johnson and Brothers, 1993; Iwata et al., 2001; Kon and Yoshino, 2002a). Th e neotenic L. petersii and the three European paedomorphic gobioids are distributed in temperate and cold waters (Kon and Yoshino, 2002a), in shallow coastal areas over sandy and muddy bottoms (Miller, 1973, 1986; Matsui, 1986). Other than paedomorphosis achieved by heterochrony, all these species have in common similar lifehistory strategies, showing generally a short life span, a rapid achievement of sexual maturity (especially in progenetic species), a planktotrophic habit and, oft en, a sudden death of breeders soon aft er spawning.
