New studies suggest angelfish can assess food quantities, and wrasse recognise their own reflection
Studies into fish intelligence, cleaner shrimps’ healing hands, and an outbreak of the notifiable disease KHV.
Two recent scientific studies into the cognitive abilities of fish have again shown what many fishkeepers already know – that they are far more sophisticated than most people give them credit for.
the first study involved aquarium favourites angelfish, Pterophyllum scalare, and set out to see if they could ‘count’. researchers offered the fish two or more small portions of the same food at the same time, and the angels usually went for the largest-sized portion. Interestingly the study also seemed to show the fish were ‘rounding off’, as when four or more portions of food were offered, they became less picky about which one they ate.
Many vertebrates, including humans, show this ability where low numbers of something are counted or assessed exactly, but larger numbers are roughly estimated. Fascinatingly, both angelfish and humans seem to swap systems at around four. while this doesn’t show counting in the strict ‘one, two, three...’ sense, it does show fish are able to discriminate between food quantities, which would clearly be a evolutionary advantage.
In a second study, cleaner wrasse, Labroides dimidiatus, have joined a small group of mammals and birds found to be able to identify themselves in a mirror, suggesting a level of self-awareness previously
Cleaner wrasse were first put in an aquarium witha mirror, which most soon attacked
thought to be beyond fish.
the wrasse were first put in an aquarium with a mirror, which most soon attacked, thinking a rival was in their territory. this aggression lessened over a few days, to be replaced by various other curious and odd swimming behaviours.
the researchers then marked the fish with a small coloured gel spot on their head. At first the fish were left to recover and swim without the mirror in their tank, and no odd behaviour was noted. However, once the mirror was returned, all the fish spent more time in front of it in positions where the spot was visible, as well as more time rubbing the spot against things in their environment. to try to rule out physical irritation being a factor in this behaviour, the scientists also ‘marked’ some fish with a colourless gel in the same way, and found their behaviour did not change when the mirror was reintroduced.
while the findings are fascinating, it’s too early to assume these charming fish are self-aware in a manner similar to humans.
Cleaner wrasse seem to be self aware.