Diagnosis: The absence of a dark submarginal band in the dorsal fin distinguishes Petrotilapia xanthos from P. microgalana, P. genalutea, P. nigra, P. chrysos, P. mumboensis, and P. pyroscelos which have such a band (Ref. 87181). Adult males of P. xanthos are yellow, which distinguishes them from P. tridentiger, which are light blue with dark blue bars; they are also distinct from those of P. flaviventris, and P. palingnathos; males of P. flaviventris are yellow on ventral and mid flank with scales outlined in blue; the dorsal one-third is blue to gray with yellow and orange highlights; cheeks and throat yellow to orange; adult male, and female, P. palingnathos have distinctly retrognathous jaws and can thus be distinguished from those of P. xanthos (Ref. 87181). Females of P. xanthos are light brown, which distinguishes them from those of P. tridentiger, which are brown, from P. chrysos and P. microgalana, which are golden yellow, from those of P. flaviventris, which are yellow brown with interrupted black stripes and fading to dark brown dorsally; the melanin pattern in females of P. xanthos have both horizontal and vertical elements, which distinguishes them from those of P. chrysos, which lack a distinct melanin pattern and are completely yellow, and from P. microgalana and P. flaviventris, which have no vertical elements in their melanin pattern (Ref. 87181).

Description: Body depth at origin of dorsal fin 32.3-39.2% of standard length; dorsal head profile concave between snout tip and interorbital (Ref. 87181). Horizontal and vertical eye diameters 29.8-35.5% of head length and 30.1-36.9% of head length respectively; preorbital depth 22.6-28.3% of head length; snout 33.4-38.6% of head length; isognathous jaws and thickened lips; teeth on lower jaw in 10-17 rows with outer and inner rows tricuspid (Ref. 87181). Dorsal fin with XVII-XIX spines and 6-10 rays; anal fin with III spines and 7-9 rays; first dorsal-fin spine about half length of eighth spine; caudal fin subtruncate to emarginate; depressed pelvic fin not reaching anal fin in females, reaching second to third anal spine in males; pectoral fin round and paddle-shaped (Ref. 87181). Flank scales large, ctenoid; cheek with 2-5 rows of scales; lateral line with 29-31 pored scales (Ref. 87181).

Colouration: Live males with gold head and green opercular spot; flank and breast gold with white to pale yellow belly, gold dorsal fin; caudal fin with gold rays and blue membranes; anal fin proximal 1/4 yellow, distal 3/4 blue to gray with 1-5 yellow ocelli; pelvic fin with light blue to white anterior margin, gold to clear posteriorly; pectoral fin with gold rays and clear membranes (Ref. 87181). Females with brown head; white to light brown throat, and purple highlights on cheek; black opercle spot with green highlights; flank light brown with 5-8 dark brown bars and narrow horizontal mid-lateral and dorso-lateral stripe, and light brown breast and white belly; dorsal spines and rays clear, membranes clear with brown spot between spines and black spots between rays; proximal half of caudal fin brown, distal half light gray and membranes with light gray spots; proximal 3/4 of anal fin dark brown, distal 1/4 clear, anal fin membranes with narrow orange margin and 1-3 small faint orange ocelli; pelvic and pectoral fins clear (Ref. 87181). Preserved males with yellow to light brown head, black opercle, and yellow to brown throat; flank yellow with sometimes 7-8 light brown vertical bars and yellow breast and belly; dorsal, caudal, anal, and pectoral fins faint yellow; pelvic fin yellow with yellow to clear membranes (Ref. 87181). Preserved females with dark to light brown head, black opercle, and yellow throat; flank light brown to yellow with two horizontal dark stripes and 5-8 dark bars; breast and belly yellow to whitish (Ref. 87181).