Rovers (Emmelichthyidae) are slender, reddish, small to medium sized, planktivorous, schooling fishes with protrusible, toothless or nearly toothless jaws, long dorsal fins, and forked tail fins with lobes. The family comprises 3 genera and 16 species. Juveniles occur near the surface, often with other schooling fishes, and adults live near the ocean bottom, at depths of 300-1200 feet. Rovers are commercially fished for human consumption, bait and for fish meal but have not been aquacultured.

Rover species – Emmelichthyid sp.  (May 2012)

A rover species present in Hawaii waters was reared from a small number of eggs collected in waters off the west side of Oahu in May, 2012.

Pelagic Juvenile Hawaii Rover (Emmelichthyid) species reared in the laboratory.
Pelagic Juvenile Hawaii Rover (Emmelichthyid sp.) species reared in the laboratory.

Rover larvae (Emmelichthyid sp.) are rather featureless and have limited specializations for pelagic life, aside from weak head spination. They look similar to the larvae of some damselfish (pomacentrid) and jack (carangid) species but are less pigmented in the early larval stages, e.g., pre-flexion and flexion. The pelagic juveniles have dark vertical bands on the body. The larval development of this rover species is quite rapid with a larval period of only about 20-25 days. The larvae have a large mouth at first feeding and easily feed on copepod nauplii. They do not have any special rearing requirements and can probably be raised quite well on a rotifer/artemia diet.

Hawaii Rover (Emmelichthyid) larvae reared in the laboratory.
Hawaii Rover (Emmelichthyid sp.) larvae reared in the laboratory.

Rovers could make good candidates for aquaculture based on their excellent flesh quality, their short larva period, fast growth and uncomplicated rearing requirements of the larvae. Further studies to evaluate the efficacy of captive spawning adults, raising the larvae in numbers and growing out the juveniles to market size are needed.

Karnella’s rover – Emmelichthys karnellai  (April 2013)

The Karnella’s Rover (Emmelichthys karnellai) is one of three rover species found in Hawaiian waters at depths of 400-900 feet (120-270 m). This species also has been reported from Guam and Easter Island. The largest individuals reach about 12 inches (30 cm).

Pelagic juvenile Karnella's Rover (Emmelichthys karnellai) reared in the laboratory.
Pelagic juvenile Karnella’s Rover (Emmelichthys karnellai) reared in the laboratory.

A single E. karnellai juvenile was raised from a batch of eggs collected in coastal waters off Oahu, Hawaii in March, 2013. Rover larvae appear similar to the larvae of some damselfish (Pomacentrid) and jack (Carangid) species in the early larval stages (pre-flexion, flexion) but are less pigmented. This individual was first identified seven days after hatching by it’s relatively large size, calm behavior and unique morphology relative to the other larvae in the rearing tank. It was feeding on copepod nauplii at the surface.

Karnella's Rover (Emmelichthys karnellai) larvae reared in the laboratory.
Karnella’s Rover (Emmelichthys karnellai) larvae reared in the laboratory.

The larva underwent notochord flexion between 15 dph (6.5 mm TL) and 21 dph (8.7 mm TL). The dark bands, characteristic of juvenile rovers, were first observed on 32 dph (16 mm TL). Juvenile growth was rapid, averaging slightly over 2 mm per day.

This species appears easy to culture with a similar growth rate and morphology (but different pigmentation) to the Emmelichthys sp. previously raised for this project in May 2012.