The Bronze Corydoras

The Bronze Corydoras

Corydoras aeneaus, known more commonly as the bronze corydoras due to its colouring is a native of South America, Colombia and Trinidad, although those seen in the global aquarium fish trade will be almost exclusively captive bred. Corydoras is one of several genera of the armoured catfish group, a feature that unites all of these fish is the presence of hard bony plates over the skin instead of more usual scales. There are many species of corydoras available to tropical fishkeepers, but the C. aeneaus remains one of the hardiest, commonest and most popular.

In the wild, bronze corys will form shoals of 20 – 30 fish which will roam running river beds and backwaters with a soft substrate, looking for food. They are an omnivorous fish, feeding on a range of invertebrates and plant matter. Spawning occurs during the wet season, when the growing fry can take advantage of the bounteous quantities of food available. So what can we learn from this and how can we ensure we meet the environmental requirements of these lovely fish in our aquaria?

Water chemistry conditions in the native habitat of bronze corys are highly variable due to differing geophysical conditions of the numerous rivers they inhabit and seasonal variations, however, the predominant preferred water type for these fish is soft acidic water. They are happy over a pH range of 6.0 – 8.0, but prefer a value tending towards the lower end of the range, especially before spawning. A General Hardness range between 5 and 19′dH is fine, but again tending towards the lower end when conditioning fish for a successful spawning. A stable temperature in the range of 24 – 28′C is ideal.

A minimum tank size of 60 cm is required and as these fish prefer company, a collection of at least 5 individuals is needed. As Bronze corys can attain a maximum size of 7 cm from nose to base of tail, a happy shoal of 5 bronze corys will form half of the stocking density of a well planned 60L aquarium. (Assuming a stocking density of 1 cm fish standard length per litre of water).

The substrate of the tank should be either a soft sand or small particle rounded gravel, this allows the corys to forage without damaging their delicate sensory barbles.

The omnivorous diet of Corydoras and benthic feeding habits mean it will take a variety of formulated and natural fish foods. As with all fish, variety of foodstuffs is the key, base the diet of your corys on a quality sinking tablet or wafer food but offer additional treat foods of frozen bloodworm, daphnia, tubifex and brineshrimp. Some fishkeepers find it hard to get food onto the bottom of the tank without the other occupants of the tank intercepting the food as it falls! Thus try feeding the corys at night as caters for their nocturnal habits otherwise adding a flake food at the same time as the sinking diet distracts the upper water swimmers.

As mentioned above, Corydoras spawn during the wet season, and fishkeepers can mimic this by performing large water changes, preferably with cool RO water and allowing the water temperature in the tank to drop by a couple of degrees. The fish must be conditioned beforehand which involves holding in a species tank and increasing feed rates to allow females for build energy reserves prior to spawning. Most breeders prefer to transfer 6 or so corys to a breeding set up rather than waiting for two fish to pair up.

The breeding tank should be a minimum of 60L, and should have a fine gravel or sand substrate, cover should be provided by a areas of broad leaved planting. Male fish start courtship by rubbing the females backs with their mouths. Courtship climaxes with the males releasing their sperm into the females mouth, this then passes through the gut of the female to be expelled from her anus over the newly laid eggs – a truly unique spawning behaviour!

Fry hatch after 4 days and need their first meal after a further 3 days, they should then be fed newly hatched brine shrimp and will rapidly move onto a powdered fry diet.

One final interesting fact about the corydoras, like all fish in the genus, it can extract oxygen from air using a highly vascularised portion of the gastrointestinal tract. Thus corys will often dart up to the water surface and grab a gulp of air. Once the oxygen is extracted the fish then passes the air out of its gut! If you notice corydoras frequently darting to the surface of your tank, this is a sign that there is not enough oxygen present in the water, oxygen tests should be conducted and aeration devices such as air pumps and filter outlets should be inspected and possibly uprated.