Caves or Similar Hiding Places: 1.25" teracotta tubes
Spawning mop: N/A
Substrate: white play sand from home depot
Food Fed to Parents and How Often: hikari algae wafers daily, occasionally cucumber slices, bloodworms, or unsalted canned green beans
Food Fed to Fry and How Often*: alternating between cucumber slices and hikari algae wafers, daily
male trapping female in cave
mom with "her" kids
one of the fry today, currently around 3/4 of an inch long
Comments and Additional Information
I have always had trouble breeding plecos. However, this time around, I had 4 females to a male, and constantly gave them something to eat. Tank was kept warm and always clean, and flow from the output of the canister ran in front of the caves. There were dried oak leaves in the tank for the first month of them being in there, but they made short work of them. Between feedings they can be found rasping on the manzanita wood or any other flat surface. Admittedly the canister wasn't always on there, but within a week of me setting it up, I got my first spawn. This spawning report details the last spawn before the canister's impeller shattered, putting it out of commission for about a month. The tank is also inhabited by a shoal of gold dust mollies and red crystal platies, 99% of which born in the tank as well. I have heard the presence of actively reproducing livebearers can help trigger some pleco spawns, but am not sure if this applies to common ancistrus.
The tank is heated by a Tetra 100W preset heater and runs between 78-80F. The sponge is just one of those ribbed double sponge sponge filters you get in 4 packs off amazon, hooked up to a Tetra Whisper 60. The Whisper 60 has two output nozzles, and the other nozzle is hooked up to a bare length of airline tube with a piece of slate tied to the end by a rubber band to keep it secure on the bottom of the tank. I do water changes with the Aqueon knockoff of the Python hose that hooks up to the sink, 50% twice a month, though it bumped up to weekly waterchanges when the canister broke down. The canister contains 4 layers, the bottom contains seachem matrix, the one above it is eheim substrat, the one above that contains biohome biogravel, and the top layer has the stock two layers of fine sponge with a coarse sponge on top, except I sandwiched a thin layer of Marineland Black Diamond Carbon inbetween the two fine sponges. The tank is lit by a random screw on gooseneck LED I got off Amazon. I use teracotta tube caves bought from various sellers at swap meets and conventions.
I personally just kept them warm, clean, and well fed, and they started to spawn once the flow of the canister was applied. If you don't want to buy an entire canister for the purpose of breeding ancistrus, I would buy a small powerhead wrapped with mesh to prevent fry from scooting their way in and... well, you can imagine the result. Though a canister would help, given their bioload and the sheer amount of fry they produce. However, certain triggers you can do would be to feed bloodworms or other high protein foods to fuel egg production, and feed vegetables such as cucumber or unsalted canned greenbeans to give them something to constantly chew on. Most fish will spawn when they acknowledge there is an abundance of food and subsequent energy that not only they can put towards egg production and fry rearing, but that the fry can also use to grow and develop. Cold water changes also help, as it simulates rain after droughts. This triggers spawning, as they are genetically coded to understand that rain, and subsequent flooding, means there will at the very least be more access to food that they and their fry can take advantage of. If you want to go the extra mile with this, you can let the tank evaporate over the course of a week or two, and top it off by dripping cold water back into it through PVC pipes with holes drilled in them to simulate rain. This applies to most fish that spawn based on rainy seasons. However, domestic ancistrus are more likely to just spawn with the prevalence of food and flow. As for caves, teracotta and bamboo are your best bet. I have tried and had slight success with PVC pipes, though I have heard they don't like the smooth texture of PVC as opposed to the texture of teracotta or bamboo. For the most success, the opening of these caves should only be big enough to fit your male, or big enough for him to lodge himself into. This will allow him to trap females and have more of a chance at breeding. I have seen people have success with breeding them in normal caves you'd use for cichlids and the like that still were spacious on the inside but still had openings big enough for just the male, though if you want guaranteed success, tube caves are your friend. Fry hatch in around 3-5 days, and become free swimming at around 4-7 days old. Most pleco fathers are good enough to keep their fry until they're able to fend for themselves at around 2 weeks to a month old. If you want optimal growth and more fry however, you can take the fry right before or right as they become free swimming and put them in a breeder box or their own tank. You may check on the fry/eggs in the cave with a flashlight, though I have heard they are photosensitive for the first few days, so I wouldn't do it too much or for too long. Moving caves with males and fry inside doesn't really do much unlike substrate spawning cichlids, if you want to get a better look at them. In cichlids, if you mess with the nest too much they may eat the eggs and try again somewhere else. With plecos, a good example is one video I saw on YouTube, where a guy moved the entire cave with eggs inside to a breeder box without the male. The male climbed into the breeder box and went back to fanning the eggs. Once you have separated the fry and they are free swimming, begin feeding them things like Repashy gel food, algae wafers, cucumber slices, unsalted green beans, or other vegetables. Bare minimum requirement is that they always have something to chew on. In spite of their relatively slow growth, they have very high metabolisms and loose weight very fast. Adding a small piece of tank matured driftwood or dried leaves to the fry container would help supplement this requirement. Once you take a batch of fry, expect another batch of eggs the next day. In the event that your male is not a good father and kicks the eggs out of the nest, given you reach them before the other fish in the tank do, you can take the cluster (they spawn in clusters, kind of like frogspawn) and put it in a tumbler or breeder box, subsequently running aeration nearby to keep circulation on them to keep them oxygenated and prevent debris from settling on them.
Adults and behavior:
Probably should've put this bit before the breeding process, but nonetheless it is pretty straightforward. Very hardy and easy to sex. Males are usually the ones that have the bristles (odontodes), but while females can also get bristles along the edge of their mouth with age, they will not get any on top of their head, as males will. Bristles on males will also always be longer. When not breeding or actively attracting females, their bristles will be relatively shorter, though when breeding starts they will begin to grow significantly longer and branch. While I only have shortfins right now, the longfin gene also causes the bristles on longfin males to get extremely long in tandem with their fins.
Again, when preparing adults for breeding, always keep them fed, feed high protein foods such as bloodworms and have things they can chew on like dried leaves, matured driftwood, gel foods, algae wafers, or fresh/boiled vegetables. They also appreciate fruit such as melons, however this WILL heavily cloud and possibly cause algal blooms in your tank as they are high in phosphorus. Dried nori also makes a good snack for them, they love to chew on it, though the nature of how the nori is dried in tandem with how they eat causes it to flake off all over the tank. They can take a wide variety of water conditions and temperatures, realistically they will breed in anything from 6-8 pH and temps from 60-80+F. For the comfort of the other fish in the tank though, I have mine in a pH of 8 and a temperature of around 80F. They can handle very poor water conditions, which is good because of how messy they are, though as their keeper it is only courteous that you at least clean up after them. Again, along with my overfiltration, as an extra countermeasure I do 50% waterchanges with water that is either the same temperature as the tank or slightly cooler, twice a month. More if I feed heavier or if the filter stops.
For optimal fry production I recommend two females to a male, as while one female is still producing more eggs, the other can come and lay another batch after you've collected the first. However, with inexperienced males this can become troublesome, as the male will always be stuck in the cave and the stress of raising fry plus not eating can get to him. My male seems to be good at what he does, as he comes out to eat occasionally when he's on fry or eggs, and quickly returns back to the cave. However again, if you don't care about getting a large amount of fry out of them, a pair is fine. In my experience with multiple varieties of bristlenose plecos, the males don't seem to pressure the females into breeding, it's more the female who chooses when she wants to breed, and I've even seen my females fight over breeding rights. Males will stick their pelvic fins and tail out of their cave and wave the former up and down to advertise the fact that they are ready to breed. Females will come and investigate the cave, and the male will try to trap her in the cave. This may take several attempts, but it usually only takes one or two if the cave is the right size. Females can lay eggs every two weeks to a month. I also recommend having at least one to two caves per pleco.
Going back to fighting, they have little balls of spikes on their gills they can deploy to sort of "punch" eachother in disputes over breeding, territory, or food. I see my females do it a lot more, as they tend to be the more active sex. My two males spend most of their time waiting for females in their caves. However, when they do come out and encounter eachother, they can get in long fights over real estate and come out pretty tattered, however in optimal conditions they fully regenerate any torn fins or scratches in about a day. With the armor on their backs, their little "punches" don't seem to do much in most disputes. I however, only see my males fight at most, once a month. Without adequate numbers of caves, I would not have multiple males to a tank. They do not disturb their fry however, and I can often see older fry in the same cave as their father with a newer batch of eggs or fry, just sitting on his back.
They are prone to a strange bloating when tank conditions become suboptimal. In the off times it does occur, they usually sort themselves out within a few days of the tank's condition being restored, without medication. Be cautious medicating them, they may have armor on their backs, but their bellies are soft and scaleless. I have not noticed any other ailments in any bristlenose plecos I have ever kept, other than a mild infection a few years ago in an L144 that occurred as a result of a scratch on her belly from a decoration.