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The Realities of Spawning Zebra Plecos

By Larry Vires (Tropical Fish Hobbyiest, August 1998)

Since its original import in 1989, the zebra pleco has maintained the status of one of the most popular- and misunderstood- Loricariidae available. There have been several successful spawnings of this fish reported; however, even with an accurate article explaining the event, the most successful aquarists still have had very little success replicating them. There are several reasons for that, and neither the author nor the hobbyists are at fault.
After I read the article in the January 1996 issue of this magazine, I became convinced that I was going to jump on this ticket to fortune. It wasn't until after I had gotten my group of five of these fish that I found out that it was not going to be as easy as it looked in type. Although I followed every detail listed in the article to the letter, I was also unable to get a spawning. With my reputation at stake, I decided to start a more in-depth study of this amazing fish.

Water Treatment

Fish Fur Feather sm2

Careful attention to water chemistry is a key element in the successful
captive propagation of zebra plecos. Photo by Mike Thielle.

Coming from a fairly stable environment, zebra plecos are not
extremely tolerant of changes in water chemistry or temperature. Photo by Mark Smith.

I have always been a firm believer of duplicating the natural environment of a fish to get them to spawn, but the biotope seemed to vary depending on who you talked to. The only thing that everyone agreed upon was that the water was very soft. With that little bit of information, and a few books, I started reading about as many other fish as I could from the same region, searching for spawning successes of them all. After several weeks of that, I found out that I had taken on a fairly futile quest. At that point, I was ready to give up on the idea of ever raising my first fry of this species. Luckily, I already had a great deal of experience with spawning other members of this family, and that was where my success began.

The first pleco that I ever spawned was Peckoltia vittata. In most of the general books published, this fish is reported to come from the Amazon basin to the Rio Xingu. In a stroke of ignorance- I later found out that the group I had were from the Amazon- I assumed that this fish came from the same area. The only sensible thing to do was to try the same set of parameters.

Then on Christmas day, while I was setting up a new tank on the same stand, under theirs, I looked up and saw two half-inch fry. One of them was very unusual in that it didn't have the first stripe on it. However, it did have a gorgeous pure white body.

Over the last seven years, I have learned that several factors are important to spawning any
of the Loricariidae. I get a lot of questions about the "why" of my methods, and this fish is a perfect example of why I do most of them.

The first, and probably most important, step to success is maintaining very stable conditions in the spawning tank. There are several things which are tied into saying this. You have to constantly monitor temperature, pH, hardness, ammonia, nitrites, nitrates, and dissolved oxygen. Most aquarists are familiar with all of these parameters, and probably test all of them, except dissolved oxygen, on a regular basis. I believe the reason that people are not testing this is because a lack of understanding of exactly what it does.

The natural habitat of the zebra pleco is one of huge currents-for which the suckermouth is a definite advantage.
To spawn these fish, you must attend to the position and velocity of water currents in the aquarium. Photo by M. Carletti

Although it is necessary for respiration, it also acts as a chemical buffer against ammonia spikes. Ammonia can be found in two different forms, NH3 and NH4+. Both of these are involved in the nitrogen cycle. The problem at higher temperatures is that proteins form ammonia very quickly and there is not enough oxygen to maintain a large colony of the beneficial bacteria. By maintaining an excess of oxygen, it is not a problem for the bacteria to reproduce very rapidly and take care of any unusually high amounts of ammonia.

It should be realized that a strong current is not always going to equal a high level of dissolved oxygen. My breeders are kept in a 29-gallon tank with 400 gallons per hour of filtration, and the oxygen levels still drop when I am too busy with my life to do water changes. It is possible to buy devices, sold as aquarium oxygenators, from pet shops. They may have to special order them, but they definitely make it easier if you have a busy schedule. If I have convinced anyone of the importance of oxygen, a proper level for this fish would be anything above 6.0 ppm. Oxygen will not stay in the water very long at the required temperature, so you may find yourself refilling the oxygenator very often.

As I mentioned earlier, stability is very important, so this may be a good time to explain an important detail of water changes. I use reverse osmosis water, and treat with trace elements to raise the Total Dissolved Solids to 90 ppm. This reading is not important, but is what I use on all of my softwater fishes. It keeps it simple, and all of them seem to do fine in it. The one thing that I have found that is important is the temperature of the water. For the aquarists who have never seen the Rio Xingu, I'll describe it. It's huge, about half a mile wide and 60 feet deep in some places. Therefore, in nature they are never going to get a sudden cold shock, and in an aquarium that will put a stop to any hopes of a spawning for several weeks. It is not necessary to put a heater in your mixing bucket, but at least allow the water to rise to room temperature. It is also much easier on the fish if 10 percent water changes are done daily rather than a large one weekly.

The other values should be very well known by every reader of this magazine, so it should suffice to say "keep it in check and you will get eggs." Yes, I said eggs. I have never had a male guard a fry to the point that the yolk sac was gone-about 11 days post hatch. The longest they have ever kept them was two days post hatch.

I do, however, have a theory about this situation. In the wild, these fish have been reported to live in the back part of Scobiancistrus aureatus, L14, or goldy pleco nests. After I was told about this, I figured that they were using the larger pleco to guard their fry. This is only a theory, and may be wrong, but it would explain why a fish which has the general shape of a marble with a needle laying on top of it is kicked out of the nest. In a heavily decorated tank, there will usually be survivors. However, if you happen to see any fry hiding in the rocks, by all means, separate them. The adults will make short work of them if they find them.

The eggs of H.zebra.

Back to the general chemistry of the water; my best successes have been at a pH of 6.0-6.5, a general hardness of less than 1 ppm, and a temperature of 86°F (30°C).

Feeding is another subject that should be discussed. There has been a lot of controversy about the nutritional requirements of these fish. Some people say they are vegetarian, and others insist that they are omnivores. I can sum this argument up in one sentence: They eat anything that you offer. Mine will spawn on two daily feedings of high protein spirulina flakes, but do not condition as fast as they could. In the past, I have also used bloodworms, blackworms, and brine shrimp. The females come into condition much quicker if they are offered the flakes along with a tray of blackworms kept in the tank. Protein is definitely a must, and they will not spawn without it.

Because of space limitations, I have found that it is possible to I keep a breeding group of these in the same tank. Each male should have a cave to call his own. The females are left to fend for themselves, and will try to enter the males' cave for no other reason than shelter. The male will not allow this unless the female is ripe, in which case they will spawn before he kicks her out.

A zebra pleco hatchling.

When a female is in good condition, this is one of the few plecos that will allow you to watch the courtship. The female will sit at the front of the cave and try to attract the male to the front. At this point, she will start swimming back and forth until she has managed to coax the male completely out of his cave, and will enter as soon as he leaves. This is when she lays her first batch of eggs. The male will then force her out of the nest to fertilize them and resume his position guarding the entrance, and she has to get him outside again to finish depleting her supply. I have also seen the female just swim into the cave without this ritual and have a successful spawn; however, it is not very common. I have never witnessed what goes on inside the caves, but have seen them up to this point. For the best results, you should give them till the next morning and remove the eggs to artificially hatch.

With the small amount of eggs- 15 is a huge spawn- it is very easy to hatch them. I use convalescent homes, the plastic box that shops use to net fish, hung in the parents tank. An airstone placed on the other side of the container will give enough circulation to keep any sediment from settling on the eggs. One very important factor is water changes in the container. These should be done at least twice daily, and more often after the fry are eating. The good news is, they are very large once the yoke sac is gone- just over a quarter inch and can eat brine shrimp nauplii almost as fast as you can put it in the tank. At about a month of age, the fry will be almost 3/4 inch and can be placed in the tank with their parents, but I prefer to transfer them to a 10-gallon tank of their own to grow out.

At this point, I would like to explain why I think this method works so well. The 400 gallons per hour of filtration is used to mimic the very strong currents in the natural river setting. It is very important that there are no calm areas on the surface, and a canister filter outfitted with a spray bar works very nicely for this. Also, because of the turbulent surface, gas exchange is increased greatly. One very important point that should be made is that the current should not be aimed directly at the spawning cave. This will cause the male to abandon the cave. I was asked about this recently and decided to experiment with it. It was several weeks before the male would go back to the site.

As for the number of caves, I believe I should give both sides of the story and let you decide. The Rio Xingu has been reported in the past to have an almost rift lake layout. This can easily be created in an aquarium by layering several rocks on top of each other. My original breeding set-up was done in this fashion, but it was a lot of trouble netting fry and the males could not establish any kind of territory because of the amount of openings in such a design.

Using a single cave per male is an adaptation of my usual pleco spawning tank. The only real difference is that with any other species I would only have one male per tank. This idea was taken by an article that I read in a scientific journal several years ago. As explained in the article, most Loricariidae will spawn year-round in nature. The only factor that prevents this is the number of available nesting sites. It also had a great deal of information about how to place the caves to make them breeding caves, and not just decorations. The opening of the cave should be placed opposite the water flow and the back should be completely sealed. After seeing the benefits of this, it is almost self explanatory. The back of the cave is where the eggs are laid, probably for defense reasons, and the strong current would cause them to be battered fiercely.

A ventral view of a zebra pleco, illustrating the characteristic suckermouth.

With this same principle in mind, this may be a good time to explain what I believe is the best way to get accurate chemical parameters for spawning. Several conservationist groups give grants every year to ecologists for limnology research. They get vital information about natural rivers and lakes which they can use in allocating funds for wildlife reserves and other things. The point is, by collecting this information through their publications or on the Internet, we can become aware of the water chemistry of our fishes' natural habitat during that time of the year. By using that small amount of knowledge, combined with the information that plecos will spawn year-round in their natural habitat, it should stand to reason that they will spawn in that water.

When I first started trying to spawn plecos, late 1991, there was no information available about the different types of sexual dimorphism in this family except Ancistrus sp. Nowadays, there are several people who are specialists, and this is finally starting to change. In mature fish, there are several different ways to tell who is what. Males of most species will show longer interopercular odontodes, pectoral odontodes, or caudal odontodes. Odontodes are the bristles which they tend to get hung in our nets with. Males will also tend to have a larger head profile. This shows extremely well in zebras. The male is almost half again as wide as the female. usually, you can make an accurate hypothesis of the dimorphism of a genus with a little experience, and I will cover this when I write about each of them.

There are a few observations that I have made over the last two years that I believe may come in handy for anyone else who feels the need to work with these fish. First, although these fish are generally not extremely territorial, females will fight for the right to sit outside a males cave. I lost my largest female by ignoring this fact. Because of this, I have made one vital assumption. These are not haremspawners like a lot of the other Loricariidae; therefore, with their diminutive size, it should be possible to breed them in a smaller aquarium. I have not had the chance to research this yet due to the fact that my apartment does not have the space to add another tank. Second, I am repeating this one to stress it, never add more caves than you have males. This is a surefire way of slowing or stopping any chance of a spawning. Third and final, as mentioned in the 1996 article, color variations in this fish are extremely common. I have seen colors that span the entire spectrum between pearl white to jet black. Since I am still trying to raise a batch of F2's, I cannot comment about whether or not these will breed true, but it is a project that I am planning as soon as time allows.

In closing this article, I would like to make a single plea to anyone who is, or plans to be, working with these fish. Over the past several years, since I started studying the spawning habits of Loricariidae, I have had a lot of problems show up because of the very small amount of information available. I have succeeded with 19 different species, but it was not easy. If these are ever going to become reasonably priced, we are going to have to start exchanging information. At first, I did not want to write this article because the possibility of losing a large portion of my income. However, I realized that by sharing my information someone else may be able to use it to start raising some of the expensive fish that I would like to have and in the process lower the price. Is there a pleco that you would like to have? All you have to do is tell as many people as you can about how you came to your spawning successes, maybe even try writing about them.

Seidel, January 1996. Tropical Fish Hobbyist, Pp.10-28.
Moodie and Power, 1982. Environmental Biology of Fishes Vol. 7, No 2, Pp. 143-148.