Taxonomy & naming
Fundulopanchax arnoldi (Boulenger, 1908) is the valid name in the Catalog of Fishes. The parentheses show that Boulenger originally described it in a different genus. It belongs to the family Nothobranchiidae and the African killifish genus Fundulopanchax.
Morphology
FishBase gives a maximum of 3 in TL for males or unsexed fish. Males are the more colourful sex, as is usual in the genus. Detailed meristics are in Boulenger's description and later revisions.
Habitat
The type locality is Warri, near the mouth of the Niger River, in southeastern Nigeria (about 5°31'N, 5°45'E), a low-lying coastal delta of swamps and creeks. FishBase describes the species as living in temporary swamps and swampy parts of smaller brooks in the coastal rainforest, in freshwater at 72–77 °F and pH 5.8 to 7.2. It is non-migratory and lives in southern Nigeria.
Feeding
Killifish of this genus are carnivores taking small invertebrates, and in aquaria accept live and frozen foods such as brine shrimp, daphnia and bloodworm.
Mating
Males display to females with fin spreading and body quivering, and spawning takes place close to the substrate or in plants and mops.
Breeding
FishBase describes F. arnoldi as a bottom spawner with an incubation of about two months. Hobbyists collect eggs from peat or mops and incubate them out of water.
In the aquarium
Sold by Wet Spot. It has a long history in the hobby, and a pair or trio does well in a small, softly lit tank with a peat or mop spawning site. The usual hobby advice is to keep a lid on killifish tanks, since they jump.
Conservation
The IUCN Red List lists Fundulopanchax arnoldi as Endangered (EN), meaning it faces a very high risk of extinction in the wild; FishBase does not give the assessment year. The Niger Delta is under heavy pressure from oil extraction and development.