Hemigrammus erythrozonus (Glowlight Tetra)

by David Snell

Ever since I started keeping fish back in ’93 I have been keeping tetras in at least one of my tanks. It was not until the summer of ’00 that I decided to try and spawn them.

I was in the Centreville Aquarium store in early June when I noticed a nice tank of various fishes including a number of adult Hemigrammus erythrozonus. It was very easy to distinguish the males from females. The male Glowlights were more slender in the middle and the females were much more round in the mid-section. I decided to purchase two pair.

I had a 10-gallon tank set up in my fishroom that was divided into two sections so that I could separate the males and females. The tank’s temperature was kept at about 78°F. I fed various foods, but mostly frozen bloodworms, live blackworms, and newly hatched brine shrimp. In about two weeks, I noticed that the females had become very large in the midsection. They had been filling up with eggs.

Spawning tank

I had set up a 5.5-gallon tank that was filled with about 2 gallons of RO water, with a hardness of 2DH and a pH of 6.0. The water temp was about 78-80°F. The water was treated with a double dosage of Kent Blackwater Extract. I attached a small piece of Java moss to a small lettuce clip that was attached with a suction-cup to the back glass panel. On the bottom of the tank was a homemade spawning grate that would allow the eggs to fall to the bottom of the tank and be separated from the adults above.

My first spawning attempt

I took one of the two pairs and put them into the spawning tank. The tank was completely covered with a towel to block out any light to the tank. Tetra eggs can be very light sensitive, and some believe the light contributes greatly to the eggs fungusing. On the second day the pair had spawned, as I noticed there were about 100 eggs on the bottom of the tank. Unfortunately, all the eggs had fungused within 24 hours. I removed the pair and returned them to my conditioning tank.

The second spawning attempt

I immediately took the other pair and put them into the spawning tank. Unfortunately, they did not spawn in the 5 days that they were in the tank. This pair was also returned to the conditioning tank.

The third spawning attempt

After spending another week in the conditioning tank, the first pair was returned to the spawning tank on June 29. Within 24 hours, the pair had spawned. There were about 200-300 eggs. By July 1, I noticed that there were a few wrigglers/jumpers. I could see the fry wiggling on the bottom of the tank. When a light was shined in on the fry, the fry would jump up or dart up off the bottom and then drop back down. On the second day, I noticed that there were about 17 or so fry stuck to the side for the glass in a vertical position. By day three there were 60+ fry free-swimming in the tank. Most of the fry at this point were swimming at the top of the tank, just under the surface. An air stone was added to the tank to provide a very mild circulation of the water. The remaining eggs in the tank had fungused.

The fry were extremely small and they looked like small slivers of glass. The fry were so small that I started them out on paramecium. I fed the fry a one-cup portion from my paramecium culture. By shining a flashlight into the tank I could see that the tank was filled with paramecium, making the food available to them continually.

I continued feeding the fry paramecium to make sure the fry had a continual supply of food. By the 4th day, I started to add a very small portion of newly hatched brine shrimp. By the 5th day, I also added microworms as a source of food.

On the 6th day, I performed a 25 percent water change and carefully removed the spawning grate. I continued to perform water changes about once a week. The fry grew well. By the 12th day, the fry appeared to show signs of a silver coloring.

At three weeks of age, the fry started showing their characteristic red line of the Glowlight tetra. Their size had grown to about 1cm. By two months, I still had about 50 or so fry, with sizes up to about 2cm. The remaining Glowlight tetras were moved to my 75 gallon planted tank. At the PVAS November 2000 auction I sold off the adults and a few bags of juveniles. By seven months, the 40 remaining Glowlights reached their adult size of 4cm.

This article first appeared in PVAS’s Delta Tale, Vol 32, # 2