Can someone with admin privileges move this to the Loricaridae location...
Ok, so "a pleco", means something like 400 different species of fish in some 30 odd genera, so maybe you could be a little bit more specific about which one you mean. I'm going to talk about "Common pleco", since that's probably what you meant.
are they always shy?
The natural habitat of these fish have many dangers, and they are generally shy and nocturnal.
are they active during the daytime?
Most common pleco's aren't very active during "light" hours. Other plecos vary greatly from "You'll never see it" to "You may well see it most of the day".
I've got some
which are almost always visible as I walk to the tank. If they aren't, they'll come out as soon as I feed the fish. They are however not very good algae eaters.
do they have a personality?
Absolutely. Each individual will have it's own behaviour, and will show different behaviour from others.
do they recognise/become unfearful of their owner?
Yes, almost certainly. I had two (one at a time) that learned to recognise me and come out "begging for food", whilst if anyone else walked into the room, the same fish would go into hiding.
why do so many people love them?
Because they are lovely fish.
Actually, I think they are very fascinating fish. But each person has his/her own reasons why they like or dislike anything, so that's my individual opinion. Some people love them because they are good algae eaters meaning the owner doesn't have to keep cleaning the glass of the tank every week.
On a final note: Common pleco is the name in the trade for some three or so different species of pleco's. All of these are good algae eaters, but they also grow QUITE large, at least 10 inches (250 mm) and maybe quite a bit more than that, which means that they are not quite suitable for anything but the bigger of the home aquaria.
There are several other species from the Loricaridae family that are better suited for small/medium size tanks, such as the common bristlenose
, which is a good algae eater, but doesn't grow much bigger than 5-6" (120-150mm). They are also quite active during daytime.
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Mats