Background
The Bronze Catfish (Corydoras aeneus) which is a member of the Callichthyidae Family is a bottom dwelling scavenger fish that is approximately 2-1/2 to 3 inches long (adult size). The Bronze Catfish has the typical Corydoras shape. Sexually mature specimens are easy to distinguish since the female has a stouter body (approximately 3 inches long) when viewed from above, and the male (approximately 2-1/2 inches long) has a larger more pointed dorsal fin. The body coloring varies from pale brown to brownish yellow to copper/green for the adults. The head and sides have a metallic sheen which appears green, golden or copper depending on the lighting. There is also an albino “colored” variety that has “pink” eyes.
The Bronze Catfish is a peaceful shoaling fish native to the Amazon River in various South American countries. Since they are a hardy community type fish and easy to care for, a school of Bronze Catfish is a good choice for the beginner aquarist. In addition, the Bronze Catfish is considered an easy fish to spawn once they have reached sexual maturity at one year old. A ratio of two males to each female is recommended for spawning.
Prior to spawning, the males and female will clean a hard surface (e.g., a flat rock, inside glass surface of the tank) that will be the deposit site for the eggs. During spawning, the female may produce over 100 very adhesive eggs which are transferred by the female a few at a time to the previously cleaned surface. Since the parents do not attend to the eggs, it is best to remove either the eggs or the parents after spawning before any eggs are eaten. The fertilized eggs take 2-4 days to hatch depending on the water temperature.
Discussion
Unlike Homo sapiens (Latin for “wise humans”), most species of animal will only mate/breed/spawn when the environment (and food supply) is sufficient to support an increase in the local species population. My experience with spawning the Bronze Catfish is a prime example of how animals only breed when they consider their environmental conditions to be “just right”.
Before attempting to breed the Bronze Catfish, I prepared the spawning tank based on various “on line” articles and the books listed in the Bibliography below. I did not expect to have any problem since the Bronze Catfish is considered the easiest of the Corydoras catfish to breed. Various techniques were identified in the literature to condition or “trick” the catfish into spawning, if necessary. I tried almost all of these techniques with no success.
Tank & Equipment
- Spawning Tank: 10 gallon (20” x 10” x 12”)
- Spawning Tank Water:
Approximately six gallons of “aged” water (pH = 6.8, Ammonia = 0 ppm, Nitrites = 0 ppm, Nitrates = 10 ppm, General Hardness = 5 dGH, Carbonate Hardness = 2dKH, Temperature = 76oF).
- Spawning Tank Accessories:
One Sponge Filter plus Air Pump and Tubing
One 10 gallon tank divider
One 50W Heater (to maintain the water temperature between 76oF - 78oF) plus a thermometer
One Air Stone, Tubing, and Control Valves
Aquarium gravel (1” deep)
Plants - Java Ferns (attached to rocks) and Java Moss
Full hood reflector with two 15 watt helical fluorescent bulbs
Tank Setup
Approximately 50% of the water was drained from the 10 gallon tank and tap water was added to bring the water level up to 7 inches. The tank divider was installed to separate the tank approximately 40%-60%. A breeding pair of Gold Zebra Danio (Brachydanio rerio) had been placed in the 40% (volume) side of the tank. The 60% side of the tank contained the sponge filter, the heater, the air stone, and my six Bronze Catfish (2 females and 4 males) to begin conditioning for breeding. The side of the tank with the catfish had about 1 inch of gravel. Both sides of the tank contained rocks with Java ferns and free floating Java moss.
The Bronze Catfish normally resided in a 20 gallon community tank where they had been performing pre-spawning “glass cleaning” (as discussed above) for a couple days. The females were very plump with eggs. I feared the spawning would occur in the community tank and the eggs would be eaten by the other residents (tetras, danios, snails, shrimps, corydoras, etc.). I had originally purchased the six catfish from Oddball Aquatics in January 2007 when they were about 3 months old. They were now over a year old and sexually mature.
The catfish were fed live black worms and frozen blood worms to get them into breeding condition. However, even though the catfish ate the offered live and frozen foods, most of the time they would hide behind the sponge filter and plants. I thought this was very strange considering how active they usually were in their home tank. I did not think they were overly crowded in the 10 gallon “conditioning” tank. The catfish seemed very shy for some reason.
The Gold Zebra Danio subsequently spawned (11/03/07) and the eggs began to hatch on 11/07/07. I moved the six Bronze Catfish to a different 10 gallon tank to prevent predation of the danio fry. The “new” breeding (10 gallon) tank contained approximately seven gallons of aged water (pH = 6.8, Ammonia = 0 ppm, Nitrites = 0 ppm, Nitrates = 5.0 ppm, General Hardness = 5 dGH, Carbonate Hardness = 2dKH, Temperature = 75oF). The “new” tank contained a sponge filter, air stone, heater, gravel, Java Ferns on rocks and free floating Java Moss similar to the previous tank that had housed the six catfish. The only difference was the new tank only had one 15 watt helical fluorescent bulb in the hood.
Unfortunately, the change in scenery did not have a positive effect on the six Bronze Catfish. They continued to hide and only come out to eat the live black worms and frozen blood worms when the lights were off. They now had an entire 10 gallon tank to themselves (no other fish), but did not exhibit any pre-spawning behaviors.
In the wild Bronze Corydoras usually spawn in the spring when their native water is cooled by a combination of melting snow that flows down from the mountain peaks and the spring rains. Based on corydoras breeding information I gathered from reference books, on-line articles, and fellow aquarists, I tried each of the following to simulate their native environmental conditions. None of these attempts (in the order listed) met with any success:
- Lowered the level of water in the 10 gallon tank to a 3 inch depth. I left the water at the 3 inch depth for 2 days at a temperature of 75oF (using the heater).
- Unplugged the heater and raised the water depth back to 6 inches using tap water (pH = 7.0, Ammonia = 0 ppm, Nitrites = 0 ppm, Nitrates = 10.0 ppm, General Hardness = 7 dGH) that was 65oF. The heater remained unplugged for 12 hours.
- With the water level at 6 inches and the temperature at 76oF (the heater had been plugged in for 2 days), I floated 18 ice cubes in the tank.
- Three days after placing the ice cubes in the tank (with no success), I unplugged the heater and let the water temperature adjust based on the room temperature. The room temperature ranged from 70oF down to 63oF at night. The water temperature would subsequently fluctuate between 68oF and 63oF. I unplugged the heater on November 14, 2007. The water depth was approximately 6 inches.
During each of these attempts to simulate “cooler spring-time” water conditions, the six catfish continued to hide and only come out to feed after lights out. During this approximately 10 day period the females continued to grow plumper.
On November 18, 2007, I decided to try a new approach. Since the Bronze Catfish were hiding all the time in the sub-70oF water, I introduced my six “cold water loving” White Cloud Mountain Minnows (Tanichthys albonubes) to act as dither fish. Amazingly, within 30 minutes of releasing the acclimated White Clouds into the tank the catfish were swimming about. Within 3 hours after the White Clouds appearance, all six catfish began performing pre-spawning “glass cleaning” on the front and right side of the tank. Two days later (November 20, 2007) I discovered approximately 100 eggs in small bunches on the aquarium glass (front, left, and right sides). Each bunch contained between 5 and 15 white eggs that were approximately 1-2 mm in diameter. One of the females was noticeably smaller in girth. Since there were also signs that some of the eggs may already have been munched from the glass (by the catfish and/or White Clouds), I decided to remove the remaining eggs to a plastic shoebox.
Egg and Fry Care
November 20, 2007
5:00 PM – I washed a hard plastic container (13” x 8” x 4” deep) and placed approximately 2 inches of water from the spawning tank into this “hatching” box. An air pump and air stone were setup to aerate the water in the box. I initially tried to carefully scrape the adhesive catfish eggs from the aquarium glass with a razor blade. However, I quickly found out how sticky they really were. It was almost impossible to shake/rinse/dislodge them from the razor blade into the shoebox water without using my finger. Since I was trying to minimize the chance of contaminating the eggs by touching them, I tried using a small very thin sheet of semi-hard plastic to scrape the eggs off the glass. This worked much better since the eggs did not adhere very tightly to the plastic and would fall off into the hatching water.
Approximately 100 eggs were transferred to the hatching box. The air flow rate was adjusted to create a current but not strong enough to move the eggs. The lid was loosely placed on the plastic box and terrycloth towels were wrapped around the box. The heavy towels served two purposes: to prevent air drafts from causing excessive temperature changes in the hatching container and to minimize the amount of light into the container. Light increases the growth rate of bacteria and fungus in the hatching water since the eggs provide a prime source of nutrients for these single-celled organisms.
November 22, 2007
6:00 PM – Approximately 10 fry were scooting along the bottom of the hatching box and other eggs were in the process of hatching. I placed a plastic livebearer breeding trap in the 10 gallon tank containing the Gold Zebra Danio fry which were now about 15 days old. After acclimating them to the 10 gallon water temperature, I released the newborn catfish fry and remaining eggs into the breeding trap. Most of the newly hatched catfish fry (approximately 1/8 inch long) quickly found the slits in the trap and escaped to settle on the bottom of the 10 gallon tank.
NOTE: Before transferring the eggs and fry to the breeding trap, I removed about 10 eggs that had succumbed to fungus.
November 24, 2007
All of the remaining eggs in the breeding trap had hatched and most of the fry managed to escape through the slits in the trap to the bottom of the 10 gallon tank. Since the Bronze Catfish fry usually take 4-7 days to absorb their yolk sacs, no food was provided for them to avoid “fouling” the water.
November 27, 2007
6:10 AM – There were approximately 70 more catfish eggs in the 10 gallon spawning tank and the second female was much slimmer. I again removed the eggs using the small very thin sheet of plastic and placed them in the breeding trap in the 10 gallon “growout “ tank (after acclimating them to the warmer water temperature). There were now Gold Zebra Danio fry, Bronze Corydoras fry, and Bronze Corydoras eggs in the “growout” tank.
November 30, 2007
4:00 PM – All of the remaining eggs from the November 27 spawn that were placed in the breeding trap had hatched and most of the fry had escaped to the bottom of the 10 gallon tank. Since beige/tan colored gravel covers approximately 80% of the bottom of the 10 gallon tank (that now contains both Gold Zebra Danio and Bronze Corydoras fry) it is impossible to tell how many baby catfish are lurking on the bottom of the tank. The ones that could be seen were approximately 1/8 to 3/16 inches long and had darker coloring than when they first hatched.
December 2, 2007
8:00 AM – After releasing the remaining catfish fry, the breeding trap was removed from the 10 gallon nursery tank. The larger/older catfish fry have become darker colored with distinctive dorsal fins and barbels. Their bodies have dark brown colored spots that look like army camouflage.
Initial Food Source - Some of the catfish fry had been free-swimming for a day or two (i.e., their yolk sacs had been absorbed). Based on the size of the catfish fry, I was able to provide live microworms and First Bites (powdered fry food) for their initial food source three times a day. By comparison, the Gold Zebra Danio fry were not big enough for microworms or First Bites until they were free-swimming for about 10 days.
December 9, 2007
The largest catfish fry are at least 1/4 inch long with numerous dark brown spots from head to tail. The camouflage pattern and coloring make it difficult to spot them among the gravel when they are not moving. The smallest fry are still only 1/8 to 3/16 inch long. The three a day feedings (live microworms, powdered fry food, plus decapsulated brine shrimp eggs) continued. Water changes of approximately 20% were performed once per week being careful not to siphon out any of the catfish or zebra danio fry.
December 21, 2007
The catfish fry from the first spawn are now one month old. The largest catfish are approximately 1/2 to 5/8 inch long and have changed color over the past week. Most of the largest fry have the bronze body coloring of their parents with only a trace of the camouflage spots remaining near their caudal fins. Some of the smallest fry are still less than 1/4 inch long with overall camouflage spots and no bronze areas. The three a day feedings continued with a diet consisting of live microworms, decapsulated brine shrimp eggs, and finely crushed flake food. I estimated approximately 100 catfish fry, but it is still difficult to spot any that are not moving and even more difficult to quickly count the ones that are moving.
January 11, 2008
I continued to alternate between live microworms, decapsulated brine shrimp eggs, assorted flake foods, and Hikari ® Multi-Vitamin Enriched Daphnia (a type of freeze-dried powdered food) for the three daily feeding. Twenty-five of the catfish fry were transferred to another 10 gallon tank with White Cloud fry to help “clean” their tank. All except a few of the fry are 1 inch to 1-1/4 inches long and have the same coloring as the parents.
January 24, 2008
At 2 months the majority of the “older” fry are 1-1/4 to 1-1/2 inches long. Approximately 80 catfish fry have survived to reach their two month birthday. Their diet remains a rotation of live microworms, decapsulated brine shrimp eggs, Hikari ® Daphnia, and assorted flake foods. I continued three feedings per day with the above assortment.
Summary
Once my six Bronze Corydoras turned one year old and began displaying “pre-spawning glass cleaning behaviors” I figured the BAP certificate and points were just around the corner. However, my challenge to get these “supposedly easy breeders” to spawn was just starting. Literally using almost every trick in the book, including live food diets and changes in water temperature to get these catfish to spawn, didn’t work. What it came down to was using dither fish to show the Bronze Corys that the environment was indeed safe for them to spawn and start a family. Having the opportunity to see the fry hatch from their eggs and go through body color and pattern changes (that provided protection during their early development) was well worth the effort to spawn these “supposedly easy breeders”. Watching the Bronze Corydoras (a.k.a. the clown princes of the aquarium) start out as tiny fry and grow to achieve their parents’ coloring was an incredible thrill. Maybe my next attempt to breed Corydoras will provide the chance to actually see the mating ritual and the female depositing her very sticky eggs.
Bibliography
Bailey, Mary, and Gina Sandford. The Ultimate Encyclopedia of Aquarium Fish & Fish Care. New York: Hermes House, 1998.
Lambert, Derek. A practical guide to Breeding Your Freshwater Fish. New York: Barron’s, 2001.
Mills, Dick. You & Your Aquarium. New York: Alfred A. Knopf, Inc., 1986. |
