G. mossambica had been first formally described in 1957 by the South African ichthyologist James Leonard Brierley Smith with its type locality given as Pinda in Mozambique.

The family Lethrinidae is classified by the 5th edition of Fishes of the World as belonging to the order Spariformes.

[5] Wattsia has a deep, approximately rhombus shaped body with its depth being about half of its standard length.

The colour of this fish is a yellowish hued silvery grey, with some vague bars and blotches sometimes apparent.

[2] Wattsia is found from the eastern African coast off Mozambique, the Seychelles, Maldives and Sri Lanka and into the Pacific Ocean east to Fiji and north to Japan, south to Australia.