Little is known of the appearance or ecology of white teatfish (Holothuria fuscogilva) juveniles, which are very rarely found in the wild. In this study we use juveniles cultured in Kiribati to describe their ontogenetic changes in colouration and morphology, which differ strikingly from those of the adults. Juveniles are mostly yellow and up to ~15 mm in length, then gaining more black blotching on the body and becoming brown with black blotches around 20–30 mm in length. At this size they have stout, spike-like, dorsal protrusions on the body. When they reach ~50 mm in length, the body becomes progressively smoother and often cream-coloured with dark blotching. We present a length–weight relationship (r2=0.95) from hatchery produced juveniles, which allows conversion of these measures among future studies. Our observations should assist in the identification of white teatfish when they are small, and shed light on suitable habitats for releasing them into the wild for restocking.