Wriiten by Jon Tarn(cup)
Right. So, while I have had most of my successes with what one might consider "dwarf" plecs, I'm fairly convinced that these things are applicable for all cave spawning ancistrinae--not for aberrant species such as glass spawning chaetostoma, hypostomines, or loricariinae. These are just some tips I've accrued both from personal experience and contact with world class breeders, and is written assuming that you, the aquarist, already has some amount of know-all regarding the spawning of these animals. If you're confused in any way, check out the excellent breeding section here (shameless plug). Also, you might have different observations than I--if so, go write your own article.
Yeah, that's what I thought.
1) Caves. I swear that this is THE most important thing as far as spawning is concerned (well, short of, having the fish and the tank and whatnot). Only a male who is satisfied with his dwellings will spawn, and we've all had females who've popped in, seemed trapped, and pop back out. I have no concrete evidence, but it seems like there is some female choice involved here, and if she doesn't like what she sees inside, she'll try and get the hell out. So, you know, it can't hurt to make sure your male's pad is as nice as possible. Here are my guidelines for caves:
-tight. I mean, really tight. Tight enough so that you think to yourself "there's no way this male bit'll fit in there" (innuendos abound). I would say just slightly larger than the diameter of your male's body, minus all finnage.
-oddly shaped and rough. I know all you guys out there rave about the golden standard of the square slate cave. Nah. Throw em away. These hand rolled caves give the male unparalleled fry security, and henceforth, an unparalleled opportunity for them to spawn. Sure, they may look like something you just pooped out, but if we cared about aesthetics, we wouldn't be keeping fish that are jammed into their caves 23 out of 24 hours a day. They do make getting fry out next to impossible, so see number six on this list.
-the entrance of the cave should be covered. An arch of driftwood over the top, a piece of slate, or just an overhanging cave entrance--whatever. These are the sites which my males stake out. I see a correlation.
2) temperature. Important for both fry development and spawn triggering, water temperature is admittedly important. I personally spawn all my warm water fish at a comparatively freezing 78-80F for longevity of the fishes, and this seems sufficient with established groups (length between broods is not limited by willingness to breed, but rather, extended length of fry development). HOWEVER, nothing gets a group in the mood like cranking up the thermo a few notches. Or maybe down a few notches then up a few notches. Either way, when speaking about triggering through rapid cool water changes and all that good stuff, in my experience it's not during the influx of cool water that they start to exhibit spawning behavior, but during the rising of the temperature. Again, pure speculation, but it doesn't seem like a great idea to spawn while the raging melt and rainwaters are surging down the mountainside. Rather, its when the storm clears, and things are normalizing that we get some action going.
3) water quality. Unless your water is liquid rock, I wouldn't worry about much in this aspect save for your nitrogenous contaminant levels, and maybe phosphate. Hardness is a relative nonissue for these fish, and anything within 200 uS is probably sufficient--even for most soft, blackwater species. They say that soft water changes help, and it's logical that they would, but I haven't had any luck. It couldn't hut, though, so I guess keep on truckin' with the RO changes if they aren't spawning.
4) current. Not important. Next.
5) tankmates. I have never found fish to be more apt to spawn in the presence of dithers--or, for that matter, large cichlids or anabantoids, or other seemingly capable predators of fry. Some fish, especially fish specialized in raiding nests (crencichla, certain tangs, etc), should definitely be avoided, though. There is speculation that having too many fry around reduces spawn activity. That's possible, but it's never happened with me. This category includes other members of the same species. Pairs or trios are always my favorite spawning groups. Too many males usually ends up in having too many squabbles for me, but giving the females a choice can be beneficial. Usually, as far as women go, female plecs are pretty loos--I mean, unpicky. Also, MTSs are some of the best things to have around. They clean up the substrate, are reasonably attractive as far as snails go, indicate overfeeding, and are superb fry trap companions in every step of the process. They clean eggs almost as good as a male will (but don't eat them--if you have a clearly infertile one, poke it with a sewing needle, and the MTSs will clear it right up for you), don't touch fry, clear food, and help keep the sides and bottom free from nasty biofilms and crap.
6) Do NOT ever ever ever disturb the male. Quickest way to prevent spawning activity, stop a spawn in progress, and screw up a spawn that has already occurred is to mess with the male. I've even heard of stories where males just stop breeding altogether because they were repeatedly mishandled during attempted spawns, releasing fry, and whatnot. Leave the fish alone, and more often than not, they'll spawn for you. This is always my most important piece of advice I can give prospective owners. This includes trying to get a clutch from a male. The only time you should be handraising is if your male is a known brood-eater or he kicks out his clutch. Unscientifically speaking, fry always seem to do much better for me when they're naturally raised and subsequently released by the male.
7) Substrate. A fine layer of pea gravel is great. It greatly increases surface area for nitrification traps food for consumption in those high gradient tanks (even though I told you current doesn't matter. for shame.), gives young fry and probably your plecs a sense of security, and looks better than a bare bottom. As long as the substrate is properly maintained, it is not any more difficult to clean than a bare bottom. I know there are die hards that like this kind of thing. Suck it, guys.
8) Filtration. Just make sure it works.
9) conditioning. I really hate this aspect of spawning, but in all honesty, if you're looking exclusively to spawn your fish, you can't beat power feeding with meaty foods. Females berry up so fast it's astounding, and once the ladies are filled, it's only a matter of time. Problem is, this greatly increases the wear an tear on the 'ol GI tract. If you want to enjoy your fish for years to come, I say caloric restriction is the way to go.
10) decor. They say I barren tank speeds up spawning. This, in my experience, is very true. Whereas males might otherwise prefer a nice notch in the driftwood if provided with a full layout, if you only give them one cave, they'll take it. As long as you have a small corner of the tank so that the female will be okay with the arrangements, it should be fine. In fact, females, given no other choice, will probably opt for caves as well. So a suitable setup would be to have just a bunch of caves littered all over the place and nothing else. That's jsut not the way I like to keep my fish, though.
11) So important that I had to reiterate. Don't touch the tank. Drop a few water changes, and just let them sit. One of the biggest mistakes people make are when they get so concerned about the lack of breeding activity, they start messing with everything. Think about it--is that really going to make the male more receptive to spawning?