New stud­ies sug­gest an­gelfish can as­sess food quan­ti­ties, and wrasse recog­nise their own re­flec­tion

Practical Fishkeeping (UK) - - Contents -

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.

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