ABSTRACT
Nidification and Spawning Few studies have investigated the reproductive biology of tropical freshwater Gobiidae, particularly in their natural habitat. Th ose species that have been studied live in various habitats, including middle reaches of rivers (Dotu and Mito, 1955; McDowall, 1965; Auty, 1978; Kim and Han, 1989; Daoulas et al., 1993; Han et al., 1998), streams with fast current (Delacroix, 1987; Kinzie, 1993a; Fitzsimons et al., 1993; Ha and Kinzie, 1996; Takahashi et al., 2001), lakes (Hidaka and Takahashi, 1987a; Hidaka and Takahashi, 1987b; Ito and Yanagisawa, 2000), estuaries or lower reaches (Hirashima and Tachihara, 2000; Takahashi, 2000; Tamada, 2000; Tamada, 2005a, b; Yamasaki and Tachihara, 2006, 2007 and others). Some amphidromous goby species are semelparous, others are annual spawners (Ego, 1956; Harrison et al., 1991), while others spawn repeatedly (Torricelli et al., 1985; Meadows and Meadows, 1988). To date, there are few studies of the mating systems in amphidromous gobies. In the non-Sicydiine goby species studied, polygamy appears to be the commonest pattern, with males guarding nests containing eggs laid by several diff erent females (Hidaka and Takahashi, 1987a; Daoulas et al., 1993; Takahashi and Yanagisawa, 1999; Ito and Yanagisawa, 2000; Tamada, 2000). For Sicydiines gobies, aquarium based studies indicate that they are not polygamous (Kinzie, 1993b). Th ey show no hermaphroditism, nor sex changes or other alternative sexual strategies, and this might also be the case for other freshwater gobioids. However, Watson (1991) reported two distinct phases in males of Stenogobius caudimaculosus Watson, 1991 from the Marquesas Islands. Th ough he added this was the only case of male dimorphism he had ever observed. Clutch size is known for few amphidromous species (Mizuno, 1960; Timbol et al., 1980, McDowall, 1994), such as Sicyopterus lagocephalus (Pallas, 1770), on the island of La Reunion, where the female fi sh produces 50 000 to 70 000 ova (Delacroix, 1987; Keith et al., 1999), or [in Japan] Sicyopterus japonicus (Tanaka, 1909) which produces up to 225 000 ova (Dotu and Mito, 1955). In general, the eggs are laid on the substratum, oft en on the underside of various supporting structures such as stones, rocks, crevices, but sometimes also on, or among, the vegetation. In Lentipes concolor (Gill, 1860) found in Hawaii, nests are situated preferentially under a large rock, away from
the main river channel, close to the banks where they are safe from the full strength of the river current. Th e eggs are found from October to June, with a peak occurrence in February. Th e number of eggs in the ovaries varies from 12 000 to 14 000 (Kinzie, 1993a). Following the courtship display, the male fi sh leads the female to the spawning site (Fitzsimons et al., 1993; Way et al., 1998). In Okinawa Island, southern Japan, Stiphodon percnopterygionus Watson and Chen, 1998, the spawning season was estimated as being from May to December. Standard length at maturity was approximately 20 mm in both sexes, and batch fecundity was approximately 1000-10 000 eggs per female (Yamasaki and Tachihara, 2006). Th e egg masses, guarded by the male, were laid on the undersurface of stones in freshwater. Th e pyriform eggs had long-and short-axis diameters of 0.54-0.58 mm and 0.49-0.50 mm, respectively. Newly hatched larvae (1.20-1.32 mm notochord length (NL)) were poorly developed, with large yolk sacs and unopened mouths. Th ree days after hatching (1.87-2.05 mm NL), eyes were fully pigmented and mouths were opened. In Awaous guamensis (Valenciennes, 1837) from the Pacifi c area, the adult fi sh normally migrate downstream to the spawning grounds, which are situated in general in the fi rst shallow rapids encountered upstream from the river mouth (Ego, 1956; Kido and Heacock, 1992). Th e females lay the eggs in the latter location, where they hatch within 24 to 70 hours (Kido and Heackock, 1992; Lindstrom and Brown, 1994). Th e females lay a vast number (up to 700000) of rather small eggs (0.23 cm in diameter) between August and December (Ego, 1956; Ha and Kinzie, 1996). The females usually leave the nest unattended, or are driven away by the male fi sh, immediately aft er releasing the eggs. Th e male fi sh care for and guard the eggs as in many other species of goby (Th resher, 1984; Gibson, 1970; Cole, 1982; Lindstrom and Brown, 1994). In Awaous melanocephalus (Bleeker, 1849), each nest contains 40000 - 220000 eggs guarded by males (Yamasaki and Tachihara, 2007). In the rivers of Martinique (West Indies), Lim et al. (2002) showed that the female of Sicydium punctatum Perugia, 1896 produce 50000 to 60000 ova. Th e breeding season of Sicydium plumieri (Bloch, 1786) from Puerto Rico begins in early September and fi nishes in January with the end of the rainy season (Erdman, 1961; Lim et al., 2002). Bell (1994) has shown that larvae were present virtually continuously, indicating that river gobies reproduce at all seasons.
