Corydoras San Juan
By Joseph Huisman
The San Juan Corydoras are not an easy fish to spawn. I worked on these fish for over a year and half before it finally happened. This took a lot of time, and trying many different tricks before I got it right. Yes you have to get it right, not the fish; they know what they are doing. They need all the right things. The trick is, you have to give them what they have in the wild. The biggest trick was the water. That is to get them to spawn. After the spawn comes the next trick. The eggs from these Cory’s are very small. You are talking about .8 mm in size, so when the fry hatch they are very small. The San Juan Cory’s I used to spawn were wild caught fish, so the fry are F1. Sometimes this can make spawning them easier, but I do not think that was the case for these fish. These fish are very slow growing, so the fish you spawn will have to be about 2 years old. That is enough about the fish; let’s get down to what I did.
Preparing your fish to spawn: The fish I used were 2 males and 1 female. The fish must eat high protein foods, so this is what I feed the trio of fish: baby brine shrimp, freeze dried Tubifex worms, micro worms, frozen adult brine shrimp and bloodworms. They receive this for about 2 weeks. At this time you should notice the belly on the female is getting larger. The fish are prepped to spawn. That is the first step you have to get through.
Tank information: I used a 10-gallon tank. In the tank I have a sponge filter. The bottom of the tank is bare. The tank is not filled all the way. I fill the tank leaving about 2” from the top. The temperature is set to be 78°. This heater is on a timer so it goes on when the lights in the fish room turn on. It shuts off at night, so the temperature goes down at night. One of the things I did was to use rainwater in the tank. I would change the water just before the lights would go off. The water was not the same temperature as the water I took out. In fact it was about 7°-10° colder then what was in the tank. I did this every night for the next three nights. After the third night the next morning they spawned. I finally got over that hump.
Hatching the eggs: Once the fish spawned then I removed the eggs from the tank. I do this by using an old metal thermometer to scrap the eggs off the tank side where the Cory’s place their eggs. I then put them in a small container that hinges over the outside of the tank. Then I add Methyblu to the container to turn it a light blue. Do not use a lot of Methyblu--it will get very dark blue. What I do is take a small cup of water, then I add the Methyblu to the cup, only one drop. Then I mix the water. Pour some of the water from the cup into the container with the eggs ‘til it is a light blue color. Then you want to add an airstone to the container to keep the water moving over the eggs. The eggs will hatch in about 3 or 4 days. This may take longer if the water temperature is below 76°. Once the eggs hatch, remove half of the water from the container. Replace it with fresh water that has been aged and treated. Make sure the water is the same temperature as what was in the container. Now the fun starts.
Taking care of the fry: If you remember, I said the eggs were quite small. Well the fry are even smaller. They look like a piece of sand with a very small tail. They are too small to eat Baby Brine Shrimp at first, so you need to feed Liquifry No1. This is how I did it. Remember when we changed the water in the container after the eggs hatch? That is when I first start using Liquifry No1. At that time I placed 1 drop into the container. You will continue to do that every day for the next 5 days. After the third day you will have to change the water every day. YES, every day at least 50% must be changed. Remember to replace the water with aged water that has been treated. The temperature must be very close to the same as what is in the container. After the fry have been eating for about six days you can start to feed baby brine shrimp or micro worms. This is fed at least twice a day. I feed in the morning and then after I eat supper at night. Do not forget to change the water every day, 50%. Stop using Liquifry No1 at this time. Baby brine shrimp or micro worms will be fed for at least 1 month. After that you can start to feed other types of food, like flake foods that are crushed very small. This Cory is not an easy fish to spawn. I now understand why it is a Class D 20 point fish in the BAP program.