Hatching Corydoras & Fry raising
by Ian Fuller


here are several methods to successfully hatch and raise Corydoradinae fry. Here I will show some of the equipment that I have used over the last 40 years.

 

 

Floating Container

The Floating Container

 

Floating Container: This is the easiest method of hatching eggs away from the parent fish and once the fry hatch and become free swimming they should be moved to a larger stage one growing on tank or container.

 

Outside Hanging Container

Outside Hanging Container

 

Outside Hanging Container: This container can either be a hang on the outside of the tank type as shown, or one that floats on the surface of the spawning tank. An air stone is added to create water movement and maximise oxygen absorption.

 

Inernal Hatching Nursery

Internal Hatching Nursery

 

Internal Hatching Nursery: The internal nursery is the same type of container as shown above but has been modified to take the poly filter on one side and a fine meshed covered outlet 6 mm above the base line on the opposite side. This has a big advantage over the external container in that although it keeps the eggs and fry in a fairly confined space, they are actually still in the same water in which the spawning took place. As the picture shows the small poly filter that is attached to the nursery not only filters the water going into the container, but it also creates a constant flow over the eggs, preventing any particles of debris from settling on them and causing contamination.

 

Egg Hatching Unit

Egg Hatching Unit

 

Egg Hatching Unit: This was the hatching unit I used until recently (2019), prior to scaling back my facility. The smaller containers hold 3 litres and the larger ones hold 4.5 litres. Each container has its own air supply and a close-fitting lid with just a narrow gap at the front to cut down on evaporation.

 

Egg treatment and hatching.

Corydoras eggs are sticky and depending on the species the stickiness will vary from just a light tackiness, which is sufficient to hold the egg in place where the female had decided to deposit it, and usually in the aquarium these will be placed all over tank, on plant leafs, on solid objects and the aquarium glass. At the other end of the sticky scale a few species produce very sticky eggs, these species usually deposit their egg close together in a tight clump, sometimes even on top of each other. When we look into the natural conditions these fish live in we usually discover that they inhabit fast moving rivers and streams and the extra stickiness ensures that the eggs remain where they have been deposited until the fry are ready to emerge.

 

A batch of very sticky Scleromystax. sp. CW147 eggs

A batch of very sticky Scleromystax. sp. CW147 eggs

 

Corydoras habrosus eggs deposited in a polyester spawning mop.

Corydoras habrosus eggs deposited in a polyester spawning mop.

 

The eggs of the majority of species are not overly sticky and can easily be removed from where they have been laid, by gently rolling them off the object with a finger. Eggs that have laid on the aquarium glass can be removed with the aid of a razor blade; this is the usual method for the very sticky eggs. The process I use for hatching eggs is to put the harvested eggs into a small 3 litre hatching tub containing water from the spawning tank that has a depth of 35mm – 45mm, an air stone is added and one or two Alder cones. The Alder cones release tannins which over a few hours will coat the eggs protecting them from fungal attack. For species that come from clear waters and are not naturally subjected tannins, I will treat the eggs in the container with 5 or 6 drops of Methylene blue, after 10 or 15 minutes the eggs are rinsed through a fine net and the Methylene blue water is discarded this is replaced in the container again with water from the spawning tank. In the cases where Alder cones have been used, theses are removed after 24 hours and again the water in the container is replaces with spawning tank water.

 

Fry feeding and raising.

Once the fry have emerged from the egg membrane it takes up to two days for them to absorb the contents of their yoke sac, during this time there is no need to offer any food, I do however change up to 90% of the water in their container, and always replace with water from the spawning tank. Once the fry are free swimming I will start to introduce a little food, usually in the form of Micro or Walter worm, depending on the size of the fry. Walter worm is about 50% smaller than Micro worm and suitable for even the smallest of Cory fry, it also lives longer in water than Micro worm, lasting to 30 hours in suspension, making it ideal for the tiny fry to browse in it for longer. I normally feed twice daily and before each feed I make 90% water changes, again replacing the water with water from the adults spawning tank.

 

Corydoras sp C139 at three days

Corydoras sp. C139 at three days

 

After three or four day on Walter worm I will start to add the larger Micro worm and a little pre-soaked crushed tablet food. This is prepared by powdering down a Corydoras tablet and adding a little water making it into a paste, then when it is fed to the fry it forms a very fine cloud, which they can graze on I usually feed the crushed tablet paste in the morning and live micro worm in the evening. As the fry develop and grow larger particle foods are given, I start to add the larger size Grindal worm and newly hatched artemia to their diet, and will add crushed tablet or flake, both pre soaked so that it sinks easily.

 

Walter Worm

Walter Worm

 

Micro Worm

Micro Worm

 

Freshly hatched Artemia

Freshly hatched Artemia

 

At around four to five weeks fry are usually showing fully formed fins and looking like tiny versions of the adults and will be constantly searching for food. At this time if available I will add sifted Daphnia and or finely grated frozen blood worm or tubifex. I will also feed frozen Cyclops but no longer use it live, as I have found some Cyclops forms are parasitic and although generally not a danger to Cory fry they carry a sting which can irritate the fry and tends to stop them feeding.


This article was first pulished in CorydorasWorld 2020.

 

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