Günther's notho (blue form) — Blau

Geographical Origin and Habitat: Endemic exclusively to the heavily localized coastal lowlands, isolated seasonal swamp systems, and ephemeral river plains of mainland Tanzania (and potentially the Zanzibar archipelago) in East Africa. Nothobranchius guentheri 'blau' (the selectively bred or naturally localized "Blue Form" of Günther's Killifish) natively colonizes intensely temporary, shallow rainwater depressions and mudholes. These micro-habitats are characterized by heavy organic load, high turbidity, dense marginal grasses, and a complete, absolute dry-out period during the seasonal drought.

Taxonomy and Morphology: Scientifically classified within the Nothobranchiidae family, it is an astonishingly vibrant, biologically fascinating, and specialized "annual" killifish. Morphologically, fully mature adult males reach roughly 4.5 to 5.5 centimeters (1.8-2.2 inches) in length, while females remain significantly smaller and notably plumper. It possesses the classic, deeply robust, highly compressed, and muscular body profile typical of the genus. Its absolute defining anatomical feature is an exceptionally massive, rounded dorsal fin and a large, fan-like tail evolved for sudden bursts of mating and combat speed.

Social Behavior: They are hyper-active, intensely territorial, and strictly temporary bottom-dwelling fish. Because they are biologically programmed for an incredibly short lifespan (often only 6-12 months total), their entire existence is dominated by an overwhelming, frantic drive to feed and spawn continuously. Males are intensely hyper-aggressive toward other males, engaging in constant, violent sparring that will end in death if confined. They strictly MUST be kept in a specialized "harem" setup: one spectacular male housed with 3 to 4 females to disperse his relentless breeding aggression.

Coloration and Sexual Dimorphism: Sexual dimorphism is spectacular, massive, and absolute. The 'blau' (blue) form is a breathtaking genetic variation where the typical red base is replaced by intensely glowing, deeply saturated metallic blue. Mature males are the indisputable stars: their entire body is an intense, iridescent sky-blue or dark sapphire, heavily overlaid with deep red or maroon edging on the scales. The dorsal and anal fins are stunningly patterned with dark red and yellow spots. Females are completely devoid of any color, exhibiting a perfectly uniform, pale grey-brown.

Aquarium Setup: The aquarium architecture MUST flawlessly accommodate their unique breeding biology and aggressive nature. A minimum 40-liter (10-gallon) dedicated species tank is required for a single male and his harem. The tank MUST feature significant line-of-sight breaks (like dense thickets of Java Fern or small driftwood) so females can escape the male's relentless pursuit. Crucially, because they are substrate spawners, the bottom MUST be completely covered in a deep layer of extremely soft, fine peat moss, which is an absolute biological requirement for preserving their eggs.

Diet and Feeding: They are highly specialized, intensely voracious micro-predators (carnivores) with an incredibly rapid metabolism (driven by their short annual lifespan). They are notoriously picky and will frequently reject commercial dry flakes or pellets. You MUST feed them a heavily varied, high-protein diet to fuel their relentless, continuous spawning. Daily, heavy offerings of live or high-quality frozen foods are absolutely mandatory: massive amounts of bloodworms, Daphnia, Artemia (brine shrimp), and mosquito larvae. Malnutrition will quickly halt breeding and lead to premature death.

Water Quality: Originating from temporary African rain pools, their water requirements differ completely from typical community fish. They thrive in warm tropical temperatures (23-28°C / 73-82°F). Crucially, they demand moderately soft to moderately hard water (GH 4-12) and a slightly acidic to neutral pH (6.5 - 7.5). They possess absolute zero tolerance for dissolved organic waste; rigorous weekly water changes are mandatory. The water flow MUST be extremely gentle; strong currents will violently exhaust them and completely prevent them from performing their delicate substrate-spawning dives.

Compatibility and Cohabitation: Compatibility is virtually non-existent for standard community setups. Due to their incredibly short lifespan, intense male-on-male aggression, hyper-aggressive breeding behavior, and specific requirement for a deep peat substrate, they MUST be kept exclusively in a dedicated, single-species breeding tank. They are NOT community fish. Housing multiple males in a small tank will result in lethal combat until only one remains. They should be kept strictly as one male to a harem of 3-4 females to prevent the females from being stressed to death.

Aquarium Breeding: Breeding is the entire purpose of keeping this species. They are "annual" killifish; the adults die when the pool dries, but the eggs survive encased in the baked mud. The male aggressively drives the female into the deep peat substrate, where they dive into the mud to deposit single, hard-shelled eggs. To hatch the fry, the aquarist MUST remove the peat, squeeze it damp-dry, seal it in a bag, and incubate it at room temperature for roughly 3-4 months before re-wetting it to trigger explosive hatching.

Risks and Diseases: The absolute greatest physical risk is lethal exhaustion and stress to the females caused by the male's relentless, hyper-aggressive mating drive; housing a single female with a male will result in her rapid death. A harem is strictly mandatory. The second major risk is lethal Velvet Disease (Oodinium), to which Nothobranchius species are uniquely and severely susceptible; adding a small amount of aquarium salt to the water is highly recommended. Finally, remember their lifespan is biologically fixed at roughly 6-12 months.