Taxonomy & naming
Tateurndina ocellicauda was described by the American ichthyologist John Treadwell Nichols in 1955 from material collected in eastern New Guinea, and it remains the only species in the genus Tateurndina. The Catalog of Fishes — the authority for valid names — places it in the family Eleotridae, the sleepers and gudgeons. This is the first thing to understand about the fish: although the hobby sells it as the "peacock goby," it is not a true goby. The true gobies (Gobiidae and their relatives, the Gobionellidae and Oxudercidae) carry their pelvic fins fused into a cup-like sucker disc; the sleepers and gudgeons keep theirs separate, and that single character is the easiest way to tell the two lineages apart.
The two names sit side by side in the trade, but "peacock gudgeon" is the more accurate one. The fish belongs to the same broad assemblage as the purple-spotted gudgeons (Mogurnda), the carp gudgeons (Hypseleotris) and the larger sleepers (Oxyeleotris) — Australasian and New Guinea eleotrids — rather than to the Asian river gobies it superficially resembles.
Morphology
The peacock gudgeon is a small, deep-bodied fish that reaches around 3 in in total length, the males a little larger than the females. The body is a pale, almost translucent silvery-blue, overlaid with bars and washes of rose-red and yellow and scattered with fine iridescent spots, and the unpaired fins are edged in yellow and black. The name ocellicauda refers to the dark ocellus — an eye-like spot — at the base of the tail, a marking carried by both sexes.
The sexes are distinct once mature. Males grow larger and develop a pronounced nuchal hump, a swollen forehead that gives older males a blunt, high-browed profile, along with longer, more extended fins and stronger colour. Females stay smaller and rounder-bodied and characteristically show a bold yellow band edged with black along the margin of the anal fin, especially when in breeding condition. This clear dimorphism makes the fish easy to pair.
Habitat
Tateurndina ocellicauda is endemic to the eastern part of Papua New Guinea, where it lives in the slow, shaded fresh waters of the lowland and foothill rainforest — small streams, backwaters, rainforest pools and ponds rather than fast, open rivers. These are warm, soft to moderately hard waters, often tea-stained and densely shaded by overhanging vegetation, with plenty of leaf litter, submerged wood and plant cover.
This is a strictly freshwater fish: unlike the bumblebee gobies, the knight goby and the mudskippers elsewhere in this section, it neither needs nor tolerates added salt, and it is not amphidromous — its whole life cycle takes place in fresh water, which is one of the reasons it can be bred in an aquarium when so many of its relatives cannot. It is happiest in still or gently moving water with cover to retreat into.
Feeding
The peacock gudgeon is a micro-predator. In the wild it takes small aquatic invertebrates, insect larvae and tiny crustaceans from among the leaf litter and plants, hunting by sight in the shaded, slow water it favours. It is not an algae grazer and not a scavenger of flake — it wants small, meaty, moving food.
In the aquarium it does best on a varied diet of small live and frozen foods: bloodworm, daphnia, brine shrimp, cyclops, grindal worms and the like. Many specimens learn to accept good-quality dry foods, but a fish kept only on flake tends to lose condition and colour, and conditioning a pair for breeding really calls for live and frozen feeds. Its mouth is small, so foods should be sized accordingly.
Mating
Tateurndina ocellicauda is a resident freshwater cave-spawner with male parental care — the same broad strategy used by many of the small resident gobies and gudgeons, and the reason this fish is so much easier to breed than the amphidromous stream gobies whose larvae must develop at sea. A conditioned male takes up and defends a cave — a hollow, a length of pipe, a coconut shell or a crevice among wood and rock — and courts passing females there, intensifying his colour and flaring his fins.
Pairs form readily, and a tank that holds a small group will usually sort itself into spawning pairs. Courtship is gentle by cichlid standards; the male leads a ripe female, recognisable by her yellow-and-black anal-fin edge and full belly, into the cave to spawn.
Breeding
Breeding the peacock gudgeon is straightforward and one of the pleasures of the species. The female lays a clutch of adhesive eggs on the roof or wall of the chosen cave — often well over a hundred — and then leaves. From that point the male takes sole charge, guarding the cave and fanning the eggs with his fins to keep them oxygenated and clean until they hatch, generally in about a week to ten days depending on temperature.
The newly hatched fry are small and need tiny first foods — infusoria or other micro-foods at first, moving on to newly hatched brine shrimp and microworm as they grow. Because the parents do not eat the eggs and the male tends them attentively, a planted, mature tank with cover can yield fry with little intervention, though for higher survival many breeders move the egg-laden cave to a separate rearing tank once the female has spawned. It is among the easiest egg-guarding fish in this whole section to raise.
In the aquarium
The peacock gudgeon is an excellent community and nano-aquarium fish: small, peaceful, colourful and undemanding by the standards of its relatives. A modest tank suits a pair or a small group — give it warm, clean, well-filtered fresh water in the low-to-mid twenties Celsius, gentle flow, and plenty of cover in the form of plants, wood, leaf litter and small caves, which both reduce squabbling between males and provide spawning sites. It shows best over a darker substrate against green planting, where its colours stand out.
It mixes well with other small, peaceful fishes and is a fine dither-free centrepiece for a planted tank, though males will spar mildly over caves, so a group benefits from several retreats. It does not need salt and should not be kept brackish. Its main needs are simply stable water quality, a varied small-food diet and enough cover; meet those and it is hardy, long-lived for its size, and quick to breed — a rare easy fish in a family full of specialists.
Conservation
Tateurndina ocellicauda has not been formally assessed on the IUCN Red List, so it carries no conservation category here; we record it as Not Evaluated rather than guess at a status. It is a range-restricted endemic of eastern Papua New Guinea, which in principle makes any species vulnerable to local habitat change, but it is also extremely common in the aquarium trade and is bred in very large numbers in captivity.
That captive production is the key conservation point: because the peacock gudgeon breeds so freely, most fish offered for sale are tank-raised rather than wild-caught, which relieves pressure on the wild population. Buyers can reasonably seek out captive-bred stock — easy to do for this species — and so enjoy the fish with little impact on its New Guinea streams. The broader risks to those streams are the familiar ones of lowland deforestation and development, but there is no evidence of a trade-driven decline in this widely-propagated species.