A small Indonesian fish, Paracheilinus nursalim belongs to a genus commonly known as flasher wrasses due to their vivid colouration, which is ‘flashed’ by the males during courtship displays. This colourful fish was first discovered in 2006 during a survey by Conservation International, and was formally described as a new species in 2008 (2).
The male Paracheilinus nursalim is usually dull reddish overall, fading to yellow on the belly and with a dusky grey area on the top of the back. There is also a black rectangular patch on the underside of the body, just before the tail. Each side of the male’s body has five narrow, red-brown stripes running along it, while a blue to purplish stripe runs below the eye, from the lip to the lower part of the operculum. The eyes of Paracheilinus nursalim are yellow (2).
As in other members of the genus, males of Paracheilinus nursalim have long, tapering, filamentous extensions on around four to six of the rays of the dorsal fin. In this species, the dorsal fin is reddish-orange, with pinkish-red fin rays, while the pelvic fins, tail fin and broad anal fin are largely reddish. The tail fin of the male Paracheilinus nursalim has unusually long, trailing, filamentous extensions (2).
During courtship, the male Paracheilinus nursalim undergoes a dramatic colour change, becoming orange overall and fading to whitish or pink on the upper side of the body. The conspicuous dark patch near the tail develops a bright blue stripe along its upper edge, and a second, less distinct dark patch becomes apparent on the upper back. In addition to the faint red stripes along the sides, the male Paracheilinus nursalim develops several bright blue stripes on the body and head, including one along the base of the dorsal fin (2).
The dorsal fin of the male Paracheilinus nursalim turns yellowish to pinkish-white and has a sky blue margin during courtship, while the anal fin and pelvic fins become wine red, with a blue edge to the anal fin. The tail becomes translucent, with blue speckling and with pinkish-white filaments, and the pectoral fins turn a translucent yellowish colour (2).
In contrast to the male, the female Paracheilinus nursalim is largely pinkish-red with yellow mottling, and has a series of yellow blotches along the base of the dorsal fin. Each side of the female’s body has four to five bluish or violet stripes, with irregular rows of blue or violet spots in between. Two blue to violet stripes extend backwards from the eye, and the female also has a light blue line running below the eye to the side of the breast. The dorsal fin and tail fin of the female Paracheilinus nursalim are yellowish with narrow blue bands and spots, while the anal fin is red with blue spots and the pelvic fins are whitish to pink (2).
Paracheilinus nursalim is most easily distinguished from other members of its genus by the dark patches on the back and near the tail of the adult male, which are not present in other species (2).
- Length (excluding tail): up to 5.1 cm (2)