Gunther's Nothobranch (Nothobranchius guentheri)

Gunther's Nothobranch (Nothobranchius guentheri), also called the Redtail notho, is a compact annual killifish with an unusually rich natural history. It comes from seasonal freshwater habitats on Unguja, the main island of the Zanzibar archipelago. Its wild life cycle is built around rain: adults grow and reproduce while temporary waters remain, then embryos persist in the substrate when those habitats dry. That adaptation makes this a rewarding fish for an aquarist who wants to understand the animal as well as admire it.

This page is for one unsexed live fish supplied at approximately 2.5-3.5 cm. It is not a male, female, pair, trio, group or packet of eggs unless the live variant selector explicitly says otherwise. Sex, mature colour and compatibility with another individual are not guaranteed. The current price and availability shown by the buy box are the live source of truth.

The species is small, but its care is specialist rather than disposable. A secure lid, stable warm water, gentle filtration, suitable small foods and restrained social planning matter much more than squeezing it into the smallest possible aquarium. This guide separates published species evidence, current batch facts and our conservative retailer planning advice so that you can see where each recommendation comes from.

What exactly does this listing include?

Each quantity in the basket represents one live fish. The current trade record gives an approximate supplied size of 2.5-3.5 cm and does not certify sex. At that size a fish may be close to the published adult standard length, but colour and sexual development can still vary. Do not plan a breeding pair, a one-male-to-several-female ratio or a mixed-male display from one or two random unsexed fish.

The product carries a quantity-pricing setting that can reduce the per-fish price when the qualifying quantity is selected. That is a commercial discount only. It does not turn two unsexed fish into a confirmed male-female pair, and it does not promise that two individuals will live together without conflict. Plan the aquarium for the number of fish you order, then manage individuals according to the behaviour you observe.

Identity, accepted name and the Zanzibar label

The accepted scientific name is Nothobranchius guentheri, described by Pfeffer in 1893 and placed in the family Nothobranchiidae. Gunther's Nothobranch and Redtail notho are useful common names. Current taxonomic work distinguishes this species from Nothobranchius melanospilus, a wider-ranging East African species with a history of confusion in collections. That distinction is why we use the full scientific name rather than relying on a broad trade label.

Scientific sources describe N. guentheri as endemic to Unguja Island in the Zanzibar archipelago. The historic product name also used "Zanzibar". On this page, Zanzibar therefore explains the species' documented natural range and the inherited trade context. The current batch record does not include a collecting code or evidence that would certify a particular wild locality, population or aquarium strain. We will not invent one.

What annual killifish means

Annual does not mean that every individual lives for exactly one calendar year. It describes a life-history strategy shaped by temporary water. In the wild, adults occupy seasonal pools and related shallow habitats while water is present. They mature quickly and spawn into the substrate. Embryos can pause development through diapause and survive conditions that the free-swimming adults cannot.

Peer-reviewed reviews describe post-hatch life in the genus as ranging from weeks to months, with marked variation among species, populations, laboratory lines and conditions. Studies using N. guentheri as an ageing model have reported different average and maximum lifespans. Those figures are research context, not a guarantee for a retail fish whose age and history are not known. Buy this species because its complete life story interests you, not because a fixed lifespan has been promised.

Natural habitat and ecological context

FishBase records the species from temporary pools, swamps, ditches and small streams. These are not fast, open rivers. They can be shallow, warm and changeable, with soft sediment and seasonal plant material. In an aquarium, the useful lesson is not to copy a drying pool literally. It is to provide calm water movement, cover, a safe substrate and a strongly secured top while maintaining modern standards of filtration and water quality.

The species is benthopelagic, so it is not confined to the surface. It will explore the lower and middle water, especially around feeding and spawning areas. A dark base, leaf litter used with care, fine plants, mops and wood can create useful visual structure. Leave clear feeding space as well: dense decoration that traps food and waste works against the stability this fish needs.

Adult size, colour and sex differences

FishBase records a maximum of 3.5 cm standard length for male or unsexed fish and 3.2 cm standard length for females. Standard length excludes the tail fin, so a total measurement can appear longer. The supplied range of 2.5-3.5 cm should therefore be treated as young-to-adult-sized stock rather than an assurance that every fish has more growing to do.

Published identification notes describe males with a red caudal fin and a black posterior margin. Male pattern and intensity can change with maturity, condition, light, substrate, social context and lineage. Females are normally much less ornate. None of those general differences allow us to certify the sex of a specific fish from this unsexed batch. A pale arrival may colour further after settling, while an individual may never match a representative image.

Who is this fish suitable for?

This is a good choice for an attentive aquarist who enjoys small specialist fish, can keep water stable, and is willing to feed suitable small foods. It is less suitable for somebody seeking a guaranteed male, a ready-made pair, an effortless mixed community fish or a long-lived centrepiece. A first-time keeper can succeed, but only with a fully cycled tank, reliable testing and a willingness to respond to individual behaviour.

Before ordering, check your source water, available floor space and cover. The water matcher helps compare species needs with your planned conditions, and the tank-volume calculator helps translate internal dimensions into real water volume. These tools support planning; they do not override the needs of multiple territorial fish.

Tank size and footprint planning

There is no single scientific minimum-tank number for this retail batch. Our conservative planning floor for one fish is a mature, covered aquarium around 45 litres with roughly a 60 cm horizontal footprint. This is retailer guidance designed to provide water stability, feeding room and usable structure, not a claim taken from a field study. A larger footprint is better when ordering several fish or keeping any male that proves territorial.

Do not multiply a litre figure mechanically. Two males may need separation even in a larger tank, while a carefully observed group may use visual barriers effectively. Because this listing is unsexed, the safest plan is to have a spare cycled enclosure or divider strategy before ordering multiple fish. Never rely on a hoped-for sex ratio.

Water parameters: evidence and operating target

FishBase gives 22-25 C, pH 6.0-7.0 and 4-10 dH for the species. These are the evidence-led ranges used on this page. They are narrower than the old generic listing values. Aim for a stable point within the range that your source water and acclimation plan can support; repeatedly forcing chemistry up and down is usually worse than maintaining a sensible stable value.

Temperature influences metabolism in an annual fish. Avoid using the warmest limit as a permanent target simply to accelerate growth or breeding. A practical everyday target around 23-24 C leaves room within the published range, but the best arrival match also depends on the water in which the fish has been held. Measure ammonia, nitrite and nitrate rather than judging water by clarity.

Filtration, oxygen and the non-negotiable lid

Use a mature sponge filter or a well-guarded filter with a gentle output. The goal is biological stability and good gas exchange without turning the tank into a high-flow stream. Direct the return so the surface moves, but preserve calm zones. Intake protection is important if breeding or rearing fry. Clean media in removed aquarium water when needed so that maintenance does not destroy the biological community.

A tight cover is essential. Killifish can use very small gaps around cables, feeding flaps and filter pipes. Check every opening and maintain a safe space between the water and lid. A cover also moderates evaporation and sudden chemistry changes. The fish's small size does not make an open-top tank safe.

Substrate, plants and visual structure

For a display aquarium, use smooth sand, fine rounded gravel or a bare-bottom layout that can be kept clean. Darker surroundings often make a small fish feel less exposed. Floating plants can soften overhead light, while fine-leaved plants and spawning mops create refuge. Any wood, stone or leaf material must be aquarium-safe and arranged without trapping a fish.

For more than one individual, build broken sight lines from the start. Structure should let a chased fish leave the aggressor's view rather than merely hide in one dead end. Keep an open feeding lane where every fish can be observed. Count fish at feeding time and inspect all sides of the body; dense planting should not conceal chronic exclusion.

Feeding an annual micro-predator

N. guentheri is adapted to small animal prey. A controlled study found juvenile fish preferred mosquito larvae over chironomid larvae and rotifers under the tested conditions. That result supports the species' predatory feeding biology, but it does not make mosquito larvae a complete diet. Captive fish benefit from variety, safe sourcing and portions that do not foul the water.

Offer appropriately sized live or frozen foods such as daphnia, Artemia, cyclops and other suitable aquatic invertebrates. Bloodworm can be part of a rotation but should not become the only food. A high-quality micro-predator granule may be useful if the individual accepts it. New arrivals may recognise moving food sooner than dry food, so confirm actual intake instead of assuming food has disappeared.

Feed small portions once or twice daily according to condition, temperature and filtration. There is no benefit in leaving a permanent cloud of food. Remove leftovers, vary the diet and track body shape. A fish that rushes food but loses weight may need closer health assessment rather than simply larger portions.

Behaviour and social signals

Expect an alert fish that investigates food and may display strongly as it matures. FishBase records male aggression toward other males in aquaria. Display is not automatically a crisis, but persistent pursuit, fin damage, hiding, refusal to feed or a fish being pinned to one area are intervention signals. A small species can still exert serious social pressure.

Unsexed fish complicate social planning because colour and behaviour may develop after purchase. Observe individuals rather than applying a generic ratio. A fish kept alone is not being denied a mandatory shoal; this species does not need a conventional schooling group. Its welfare depends on security, enrichment, feeding opportunity and freedom from chronic attack.

Tank mates and species-focused care

A species-focused aquarium is the most predictable choice. Community keeping is possible only when water needs, food size, pace and temperament align. Avoid boisterous surface feeders, fin nippers, large predatory fish and any companion likely to monopolise live food. Small shrimp and fry may be treated as prey. Similar-looking killifish can also compete or hybridise, which matters if eggs are collected.

If you are comparing options, browse the killifish hub before deciding. The Gunther's Zanzibar Gold Nothobranch is another presentation of the same accepted species, while Rachovi's Nothobranch is a different annual species. Aphyosemion australe represents a different, non-annual style of killifish care. These links are comparisons, not automatic tank-mate recommendations.

Arrival, acclimation and observation

Prepare the aquarium before dispatch. Test the water, secure the lid, dim the light and make sure the filter is mature. On arrival, follow the instructions supplied with the order and avoid prolonged exposure to open transport water. The acclimation timer can help organise the sequence, but visual observation and source-to-tank parameter differences still matter.

Keep the first hours calm. Offer a small appropriate meal only after the fish has had time to settle, and do not panic if feeding is delayed. Record respiration, balance, fin position, skin, waste and response to food. A dedicated observation tank is valuable, especially before introducing the fish to established stock; use mature filtration and conditions appropriate to the species rather than an uncycled temporary container.

A practical maintenance rhythm

Maintenance should preserve stability without allowing waste to accumulate. The exact water-change percentage depends on stocking, feeding, nitrate, source water and filter maturity. Smaller frequent changes may suit a compact specialist tank, provided replacement water is prepared and closely matched. Never let a calendar replace test results and observation.

Breeding overview: a substrate-spawning annual

Breeding is possible, but this sale is a live unsexed fish rather than eggs or a confirmed pair. A proper project begins with correctly identified, mature fish and clear records. Annual Nothobranchius typically spawn into soft substrate. In nature, embryos persist through the dry phase and hatch when suitable water returns. In captivity, keepers reproduce parts of that cycle by collecting damp spawning medium and managing incubation.

Male courtship can be persistent. Females need room and refuge, and a guessed sex ratio should never be forced to work. If breeding is your goal, establish sexes through development, separate incompatible fish, condition them with a varied diet and maintain a second plan for eggs and fry. Do not mix species or unrecorded lines in a breeding tank.

Egg collection, diapause and incubation uncertainty

Egg handling is where annual killifish differ most from familiar mop spawners. Keepers use an appropriate spawning medium, collect it without crushing eggs, and store it damp rather than submerged. Temperature, moisture, parental line, embryo state and other conditions affect development. Not all embryos in one batch necessarily progress on the same schedule.

FishBase mentions a three-to-four-month incubation reference, while broader annual-killifish research shows that diapause and development can vary. Treat any fixed number as context, not a timer that guarantees readiness. Experienced breeders inspect embryos and maintain dated batch records before wetting. This listing does not supply eggs, and it should not rank for egg-shopping intent by pretending otherwise.

Hatching and fry planning

Fry can emerge small and need immediate access to suitably tiny live food, clean water and gentle filtration. Newly hatched Artemia may become useful as they grow, but the first food must match mouth size. Prepare cultures and rearing space before wetting eggs. Rapid growth is part of the annual strategy, yet heavy feeding without waste control can quickly undermine a fry tank.

Sort by size if bullying or cannibalism appears, protect filter intakes, and make frequent observation the centre of the plan. Keep batch labels through to adulthood. Good records protect both welfare and identification, especially when similar species or colour forms are kept in the same fish room.

Lifespan, ageing and realistic expectations

Search results often reduce the answer to "one year", but the evidence is more nuanced. Reviews describe annual-fish adult life in weeks to months, and N. guentheri research has reported different averages and maxima under controlled conditions. Aquarium lifespan depends on the fish's age at purchase, line, temperature, diet, social stress, disease and husbandry. Its prior age is not encoded in the supplied size.

Expect a shorter life cycle than that of many non-annual community fish, while recognising that no exact death date can be forecast. Watch for gradual changes in appetite, body condition, activity and recovery rather than labelling every symptom as age. Treatable water or health problems still require attention.

Health signals and first responses

A healthy settled fish should balance normally, respond to food, breathe without persistent distress and maintain open, intact fins. Warning signs include clamped fins, rapid breathing, flashing, spots, damaged skin, continued hiding, progressive weight loss, swelling or stringy waste. Start with water tests and social observation before reaching for medication.

Use a separate treatment tank where appropriate and identify the likely problem before dosing. Medication choice depends on the condition and the animals sharing the system. Copper and other treatments can harm invertebrates, plants or biological filtration. Follow the product label for actual water volume and do not combine treatments casually.

Conservation and provenance honesty

FishBase currently reports an Endangered global assessment for the species. That status concerns wild populations and habitat; it does not by itself tell us whether a particular aquarium fish was wild-caught or captive-bred. The current product record does not provide origin documentation beyond the commercial species identity, so this page does not claim either source.

Never release aquarium fish, eggs, plants or transport water into the wild. If conservation breeding, locality preservation or exchange through a specialist association is your goal, request traceable provenance and a collecting code before treating stock as a population-preservation line. An inherited word such as Zanzibar is not enough.

Comparing nearby choices

The right alternative depends on what you value. Another N. guentheri colour presentation may offer a similar annual life cycle, while a different Nothobranchius species changes identity and sometimes husbandry. A non-annual killifish changes the life-history expectation more substantially. Compare the actual listing's sale unit, size, water range and sex promise rather than choosing from colour alone.

Ordering, delivery and first-order discount

Current stock, price and dispatch choices are shown by the live storefront controls rather than fixed inside this care text. Review the delivery page for the current service area, packing process, dispatch schedule and Live Arrival Guarantee terms. The guarantee applies to live animals when its evidence and notification conditions are followed.

New customers can use WELCOME10 for 10% off their first order, subject to the live promotion terms at checkout. Discount pricing does not change the sale unit: each selected quantity remains one unsexed fish. Prepare the tank before ordering and choose a delivery date when somebody can receive the parcel promptly.

Why buy this listing from Tropical Fish Co?

The value of a specialist listing is clarity. We tell you what the quantity represents, what the current commercial record does and does not certify, how the gallery was produced, and which husbandry figures come from published sources.

This fish is covered by our Live Arrival Guarantee, and the page links directly to planning tools and current policy details. The title remains clean and species-led, without a supplier stock code. Care is designed around the animal's biology, while price, inventory and delivery remain connected to the live systems that can change safely.

Sources and evidence boundaries

Species identity, distribution, maximum standard length, water range and core biology were checked against FishBase. The distinction from N. melanospilus and Zanzibar endemism were checked against Costa's 2017 taxonomic revision. Annual-life-cycle context comes from the peer-reviewed Nothobranchius review, and feeding context from the controlled prey-preference study.

The 2.5-3.5 cm supplied size and unsexed sale unit are batch-specific commercial facts. Tank footprint, maintenance and community guidance are conservative retailer recommendations derived from the evidence and practical welfare planning; they are labelled as such rather than presented as experimental findings.