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Ruby Rasbora - Paedocypris progenetica : Complete Fish Profile & Care Guide

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Prior to 2012, when the tiniest frog was discovered, the Ruby Rasbora held the title of smallest known vertebrate. The Ruby Rasbora still holds the world-record title for being the smallest freshwater fish capable of living in a home aquarium. Since Ruby Rasboras are incredibly fragile and require such low water acidity, even if you are experienced in fishkeeping, these are expert-level fish and should not be kept by beginners. Also, these fish do not tolerate elevated nitrates or fluctuations in water chemistry, so be sure to acclimate them carefully. A decent-sized group of 12 or more will help give these peaceful fish confidence since they can be pretty timid. The best aquarium is a species-only aquarium, but if you plan to keep other aquatic species with them, make sure they are also small and serene. For example, Neon Tetras, Micro Rasboras, small Caridina and Neocaridina shrimps are all suitable tankmates. Small aquariums with heavy plants are ideal for Ruby Rasboras. In addition to mature water and dense vegetation, there should also be floating plants that diffuse light and create numerous hiding places. Broad-leaved plants can encourage spawning, and filtration should be effective, but water movement should be gentle. It is highly recommended that RO water is used and that this is filtered through aquarium peat to reduce the pH. It may also be beneficial to add dried Indian almond leaves or blackwater extract. As a result of the tannins released, the water will have a natural tea colour. This won't harm the fish but will allow them to show their most vibrant colours. A Ruby Rasboras body is thin and somewhat transparent with rather peculiar pelvic fins with clutching pads that males use to hold the females during mating. Spawning males will become a crystal red colour and will display a red mark on their heads that are used as a blinking light to lure the females to the spawning ground.

Ruby Rasbora Photos

Sexual Dimorphism

Differentiating a male and female Ruby Rasbora is relatively straightforward. In males, the pelvic fins are highly modified, with hypertrophied muscles and a keratinised pad in front. The female pelvic fins, on the other hand, are rudimentary or absent, and they also grow more significant than the males.

Quick Facts

Scientific NamePaedocypris progenetica
Year Described2006
Other NamesIndonesian Superdwarf fish, Sumatran Miniature Cyprinid
Max Size1 cm
Aquarium LevelMiddle
DifficultyIntermediate - Advanced
Best kept asGroups 10+

Water Parameters

Water TypeFreshwater
PH3.0 - 4.0
GH0 - 5
80 - 89
26.7 - 31.7

Natural habitat

Located within the peat swamp forests of Sumatra and Bintan, Ruby Rasboras are endemic to Indonesia. Close to the bottom half of the water column, these fish inhabit deeper, cooler water layers. Furthermore, they tend to live in shaded areas without much light. As a result of their small size, they are able to live in small puddles that remain after a drought. Habitat loss is a serious threat to them because of their small ranges and specialised habitats. As a result of habitat destruction in their wild ecosystem, they are now threatened with extinction.

How to breed the Ruby Rasbora

The Ruby Rasbora has only been bred in captivity a handful of times, making it a fantastic breeding project for an experienced hobbyist. To establish a breeding territory, male fish swim to the underside of a broad leaf when they are ready to spawn. In order to secure preferred spawning sites, rival males may engage in minor scuffles. It has been observed that this behaviour occurs when the morning sunlight hits the aquarium glass or when the tank lights are first turned on. Under the leaf, when spawning territories have been established, the male fish inverts itself so that its belly faces the underside of the leaf. After a short interval, and often when females are in close proximity, he will detach himself from the leaf and return to the swimming position before darting back into place under it. He will occasionally move up and down in this position, and then after a short interval, he will re-attach himself to the leaf and resume swimming normally. Every few seconds, he repeats this motion, and he will position himself so that an iridescent spot on his head faces the female. A willing female will eventually join the male at the same spot beneath the leaf, also inverted and positioned next to him. However, mating occurs exceptionally quickly, and the exact method is still unknown. On the underside of the leaf, spherical, translucent, adhesive eggs are laid and hatch in approximately 30 hours, depending on the temperature. A newly hatched larva is tiny and motionless, attached to the underside of the leaf or aquarium's glass. Due to the microscopic foodstuffs required, raising the tiny fry is extremely difficult.

Diet & feeding

Ruby Rasboras will require tiny foods such as decapsulated brine shrimp eggs, baby brine shrimp, rotifers, microworms, crushed flakes and micropellets.

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