The Hawaii Larval Fish Project
Larval rearing of the oval chromis, Chromis ovalis
November 01, 2014
Family: Pomacentridae > Genus: Chromis > Species: C. ovalis
The Pomacentridae are mostly small (2”-4”), colorful and highly territorial coral reef fishes. They occupy a variety of important ecological roles as territorial algae farmers, detritivores, grazers, schooling planktivores, prey for reef piscivores and even facultative parasite pickers. The family comprises 29 genera/360 species. Of these, two genera, Amphiprion sp. and Premnas sp., are commonly referred to as anemonefishes or clownfishes, while the remaining genera are referred to as damselfishes. Damselfish and anemonefish make up over 40% of the global trade in marine aquarium fish. Close to half of all traded anemonefishes are aquacultured while most damselfishes (Chromis, Chrysiptera and Dascyllus sp.), which are more difficult/costly to culture and naturally abundant than anemonefishes, are collected from reefs.
Oval chromis (Chromis ovalis) were cultured once for this project in March 2014. This Hawaiian endemic damselfish forms large schools, sometimes high in the water column, where it feeds on plankton. Though juveniles are colorful, oval chromis are not popular aquarium fish because adults are large (up to 7”) and relatively unattractive.
Oval chromis spawn from February through May. Reproductive behavior begins with males forming temporary territories and clearing nest sites on rocks, spaced at least 3 feet apart. Males take on courtship colors and repeatedly swim up into the water column to entice females to spawn.
Female oval chromis will typically lay thousands of eggs that hatch in 3-4 days. The eggs are oval and very small, measuring just 450x500um and are usually attached to macro algae on the nest site. A small portion of the nest was removed and incubated in a 5-gallon bucket until just before hatching. About 100 larvae hatched in the larval tank when the eggs were exposed to light.
The larvae measure 2.2 mm TL (total length) at hatching and lack pigmented eyes and a mouth. They feed on very small copepod nauplii 2 days after hatching at 2.4 mm TL. The critical flexion period occurs between 13 and 18 dph (days post hatch) at 3.9-4.3 mm TL. The larvae begin to settle (associate with tank sides) near 33 dph at close to 8 mm TL. Juvenile transition is rapid and completed in 2-3 days. The larvae were raised on wild and cultured copepods and the juveniles were grown out on artemia, cultured copepods and frozen foods. The small food size requirements of the first feeding larvae, sporadic mortality events during first feeding and flexion and the relatively long larval stage makes C. ovalis one of the more difficult damselfish species to culture.
Twelve cultured 1” juvenile C. ovalis were released onto a coral head to assess their survival instinct on the reef. Most of the fish failed to seek shelter and lacked predator recognition and an escape response. It was surprising to see how quickly the surrounding predatious reef fish (Parupeneus insularis, Iniistius baldwini) detected this behavior and preyed on the released fish. The result highlights the importance of training hatchery-raised fish destined for restocking.