MatsP wrote:It's unlikely that it is purely "playing" in the human sense of the word - although in humans, a lot of play can be seen as practicing for some skill or other in life, so maybe we could say that it's similar... Depends on what you mean by playing.
I remember having read that 'being amused' is part of playing. True, almost all mammels play (in this sense) and practise in the same time (predators wrestle and chase each other, ungulates like to run, while primates like to climb trees) but I think fish are incapable of amusement.
However, regardless of being amused, or playing, I also thing cichlids are intelligent enough to be bored and frustrated.
I once obtained a 'Geophagus'steindachneri (7 cm / 3 inches) from a sandless tank. I placed at home in a 120 * 40 cm tank, in my bedroom at 11 hrs at night. The next morning (sunday, thus 9 o'clock) the whole tank was ploughed by it.
This one never ever dug this much, so I can only conclude that it has shaken of its frustration