Plecos
A suckermouth catfish in armour plates. The common pleco reaches a foot and a half, so the small one on a shop shelf is not the fish you end up with.
Photo by Motu purkait, CC BY-SA 3.0
Overview
Pleco covers a great many suckermouth catfish, and the size range across them runs from about 40 mm to 450 mm. That matters because the fish sold plainly as a common pleco is at the top of that range, and it is the one most often bought for a tank it will outgrow.
They are also facultative air breathers, taking oxygen at the surface when the water will not supply it, and they are algae eaters that do not stay algae eaters as they grow.
Temperament
Nocturnal, retiring and territorial with their own kind. A pleco spends the day attached to wood or glass or wedged under something, and does most of its work after the lights go out.
One to a tank is the usual arrangement, since two will compete for the same cave. Larger species can be rough on slow moving, flat sided fish at night. Cave spawning is the breeding pattern, with the male guarding the eggs on his own.
Care and grooming
Algae, small crustaceans, detritus and wood. The wood is not decoration: many plecos rasp on driftwood and need it available, and a tank without any is missing part of the diet.
Algae on the glass will not feed an adult. Sinking wafers, blanched vegetables and some protein make up the rest. FishBase gives a temperature range of 20 to 28 degrees C, which is 68 to 82 F, and a pH of 6.2 to 8.2, which is wide enough that water chemistry is rarely the problem.
Living and exercise
Thirty gallons suits the small species. A common pleco needs a great deal more, along with filtration sized for a fish that produces a substantial amount of waste.
Driftwood, caves and shaded ground are what the tank needs, and open swimming space is largely wasted on them. Anyone deciding between species should check the adult size of the exact one on the label before buying, because on this shelf that number varies by more than tenfold.
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