Yongeichthys thomasi (Boulenger, 1916)

Family:  Gobiidae (Gobies), subfamily: Gobiinae
Max. size:  6 cm TL (male/unsexed)
Environment:  demersal; freshwater; brackish; marine, amphidromous
Distribution:  Africa: Senegal to Democratic Republic of the Congo (Ref. 7390, 57403, 79590, 80060).
Diagnosis:  Dorsal spines (total): 7-7; Dorsal soft rays (total): 8-9; Anal spines: 1-1; Anal soft rays: 7-9. Diagnosis: mouth broad, lower jaw slightly prominent; outer row of caniniform teeth in lower jaw distinctly larger than inner rows; lateral teeth of this outer row particularly enlarged and backward-pointing; interorbital space narrow; small, cycloid, predorsal scales extending anteriorly beyond level of preoperculum, towards rear edge of orbit, with anterior margin of scaled area convex in dorsal view; 11-16 predorsal scales; small scales at bases of pectoral fins and slightly reduced scales at base of caudal fin; flanks covered with large, weakly ctenoid scales; 23-27 scales in longitudinal series (including about 2 scales on caudal fin base), 7-9 in rearward transverse series; 1st dorsal fin: VI, sometimes with spines prolonged; 2nd dorsal fin: I,8 (rarely 9); anal fin: I,7-9; pectoral fins: 15-17 rays; caudal fin rounded or subacuminate, with 17-18 segmented rays; tips of pelvic fins not reaching to anus (Ref. 57403, 79590). Coloration: Preserved specimens, as well as live individuals, can be identified by their characteristic pigmentation patterns; head with a black ‘chinstrap’ band slightly narrower than eye, running behind jaw, ventrally from lower margin of eye to isthmus on ventral part of head; blackish spot on upper part of pectoral-fin base, and another on flanks immediately dorsal to this; 3 black lines running anteriorly along head, each starting at pectoral spot: one band runs anteriorly along dorsal margin of operculum and preoperculum towards eye, where it extends anteroventrally along lower margin of eye until it meets black chinstrap band; 2nd band runs anteroventrally on operculum towards preoperculum or rear of suborbital region; 3rd band runs ventrally over operculum towards branchiostegal rays; body brownish, paler on belly; several irregular bars on back, sometimes extending onto flanks; faint band along midline, emphasized into about 5 regularly spaced spots on midline; dorsal and caudal fins dusky; distinct black spot at base of caudal fin; pelvic and pectoral fins dark; ventral region of pectoral-fin base with oval black spots, sometimes confluent and forming a crescentric band along lower fin margin; anal fin dark, especially near distal margin (Ref. 57403, 79590).
Biology:  Endemic to brackish waters (Ref. 92840). Usually found in brackish waters of creeks close to river mouths, coastal lagoons (Ref. 4343, 7390, 57403, 79590), mangrove swamps (Ref. 7390, 57403, 79590), ponds and creeks (Ref. 4343). Rare reports of the species ascending rivers to freshwater, which it may tolerate for short periods (Ref. 57403, 79590). Maximum reported standard length 47 mm (=60 mm TL)(Ref. 79590).
IUCN Red List Status: Least Concern (LC); Date assessed: 20 October 2019 Ref. (130435)
Threat to humans:  harmless
Country info:   
 


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