Taxonomy & naming
Lacustricola gemma was described by Nagy in 2025 as part of a review of Cyprinodontiform fishes from the upper Congo drainage, a paper that simultaneously described four new species of the seasonal genus Nothobranchius and reorganised the placement of several lampeye taxa. The valid combination, Lacustricola gemma (Nagy, 2025), is recorded in Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong). The authority is presented without parentheses because the species was first placed in the genus Lacustricola, and no subsequent generic transfer is on record as of this writing; however, the original paper placed the species name in quotation marks — 'Lacustricola' gemma — flagging acknowledged phylogenetic uncertainty about whether the fish truly belongs within Lacustricola sensu stricto or within a related lineage of the family Procatopodidae.
Procatopodidae is the family of African lampeye killifishes, a group of small, non-annual egg-layers widespread across sub-Saharan Africa and distinct in both reproductive biology and anatomy from the annual killifishes (Nothobranchiidae) with which they often co-occur. Lacustricola itself is a broadly distributed African lampeye genus whose species range from West African forest streams to the East African rift systems. The type locality is the Kay system in the upper Lualaba drainage of the Democratic Republic of Congo, a tributary network feeding the upper Congo River basin.
Morphology
The gemstone lampeye is a small fish; FishBase records a maximum standard length of 1 in for males. Like all procatopodid lampeyes, the body is slender and laterally compressed, with the large, upward-tilted eyes characteristic of the group — the namesake iridescent eye patch, a reflective blue-green or turquoise blotch above the iris, functions as a species-recognition signal within schools and in courtship.
What distinguishes L. gemma from its congeners is the scale ornamentation of the flanks. Males bear iridescent, diamond-shaped light blue spots centred in the scales of the posteroventral flank, particularly below the mid-longitudinal scale series. On the dorsum, larger iridescent blue blotches form an irregular reflective mosaic in breeding males, intensifying the gemstone effect that inspired the species name. The median fins are yellow to hyaline with dark grey stripes running perpendicular to the fin rays. The dorsal fin carries a distinct light blue margin; the anal fin is edged in dark grey. These fin markings, combined with the scale patterning, distinguish gemma from other upper-Congo lampeyes and allow identification in the field.
Habitat
In the type locality, Lacustricola gemma was collected from a turbid remnant pool in the Lubule River, a watercourse 1–2 metres wide with grass margins. This habitat is characteristic of the seasonally inundated wetland margins of the upper Lualaba drainage: shallow, heavily vegetated, and subject to dramatic fluctuation in water volume and clarity between wet and dry seasons. The species is associated with the transitional zone between permanent and seasonal water — pools that persist through the dry season but are transformed in the rains into the flooded margins and backwaters of an expanding floodplain.
Unlike the annual Nothobranchius killifishes that share parts of this drainage, L. gemma is a non-annual species tied to permanent or semi-permanent water. The Procatopodidae as a family tends toward clear, well-oxygenated freshwater, but the turbid, shallow habitat recorded for gemma at the type locality suggests tolerance of reduced transparency and likely fluctuating oxygen conditions during the dry season. Water temperature, pH, and hardness figures specific to the Kay system collection site have not been published; conditions across the upper Lualaba watershed are generally warm (tropical plateau, 900–1,656 ft elevation) with soft-to-moderate water chemistry reflecting the granitic and sandstone geology of the basin.
Feeding
No dietary study specific to Lacustricola gemma has been published. In the broader context of African lampeye killifishes, the group feeds primarily on small aquatic invertebrates — microcrustaceans, chironomid larvae and pupae, small worms, and zooplankton — taken from the water column and surface film. The upward-tilted mouth and eye position of lampeyes are consistent with surface-feeding specialisation, and many procatopodids are effective mosquito-larvae predators in their natural habitats.
In the aquarium, small live and frozen foods are the appropriate choice for this size of fish: Artemia nauplii, Daphnia, micro-worms, and finely chopped chironomid larvae. Dry foods of suitable particle size are usually accepted after acclimation. Because males reach only 1 in SL, food particle size must be kept small throughout the life of the fish.
Mating
Lacustricola gemma is a non-annual lampeye killifish and reproduces by the continuous-spawning strategy characteristic of the Procatopodidae. Males display their iridescent flank markings and the bright blue dorsal-fin margin actively to rival males and to females, using the scale spots and fin edges as optical signals in the broken light of shallow, vegetated water. In schooling lampeyes, such visual signals serve both for species recognition — critical where multiple congeners may co-occur — and as honest indicators of male quality; the intensity of the iridescence is linked to body condition and light-catching angle.
Pairing is typically brief and repeated: a male manoeuvres alongside a receptive female, the two fish orient in parallel, and eggs and milt are released simultaneously in the shelter of fine plant growth or root masses. Spawning bouts are short, producing a small number of adhesive eggs at each event, and a healthy pair will spawn repeatedly over many days and weeks rather than in a single concentrated clutch event.
Breeding
As a non-annual procatopodid, L. gemma lays adhesive eggs that do not require desiccation or diapause to develop. Eggs are deposited singly or in very small numbers at each spawning bout, attached to fine-leaved vegetation, moss, or root tangles in the water column. Development proceeds continuously in water at tropical temperatures — exact incubation data for gemma are not available in the published literature, but related lampeye species typically hatch within 10–14 days at 75–79 °F.
In aquarium conditions, a clump of fine-leaved plants or a spawning mop placed in a small breeding tank will collect eggs from a conditioned pair. Because the adults do not guard eggs or fry and may consume both, the plants or mop should be moved to a separate shallow rearing vessel with aged water when eggs are visible. Fry are tiny at hatching and require infusoria or very fine commercial fry foods for the first days before graduating to baby brine shrimp nauplii. Growth is steady in warm, clean water; young fish develop the adult colouration progressively over the first few months of life.
In the aquarium
Lacustricola gemma is a very recently described species and, as of 2025, is not established in the mainstream ornamental trade. It is likely to appear in the collections of specialist killifish hobbyists, particularly those associated with the American Killifish Association and African killifish study groups, through direct collection trips or captive breeding chains originating from the description work.
For husbandry, the principles that apply to small African lampeyes generally will serve: a well-planted nano or species tank of 10–15 US gal, clean and well-oxygenated water, a tight-fitting lid (lampeyes are capable jumpers), and a peaceful community of similar-sized fishes if kept in a community setting. The turbid collection habitat suggests tolerance of imperfect water clarity, but clear, soft-to-moderate water at 73–79 °F is the appropriate aquarium target pending species-specific data. The fish's schooling nature means a group of eight or more individuals, with more females than males to distribute male courtship attention, will show the best natural behaviour and the most consistent display of the striking flank iridescence that makes the gemstone lampeye an appealing subject.
Conservation
The IUCN has not evaluated Lacustricola gemma; the species was described only in 2025 and carries Not Evaluated (NE) status. Its known range at the time of description is limited to the Kay system in the upper Lualaba drainage of the Democratic Republic of Congo, a region that encompasses part of the vast Congo Basin — the world's second-largest tropical rainforest and one of the most biologically diverse freshwater systems on Earth.
The upper Lualaba is subject to increasing pressure from artisanal and small-scale mining (cobalt, copper, and coltan extraction dominates parts of the Katanga plateau), agricultural expansion, and deforestation. Turbid remnant pools in seasonal riverbeds — the precise habitat type where gemma was collected — are among the most vulnerable freshwater microhabitats: they can be eliminated by stream diversion, deforestation of riparian vegetation, or a single season of unusually severe drought. For a species known from a single locality with no data on population size, these pressures constitute a plausible threat even in the absence of a formal assessment. Formal collection and conservation-status evaluation are warranted as part of ongoing survey work in the upper Congo drainage.