[Solving of simple problems by a fish (free water experiments with Balistes fuscus)].

The problem-solving behaviour of Balistes fuscus was investigated in the Red Sea by under-water observation of three tame animals. The foraging behaviour of Balistes is adapted to moving objects aside with the mouth to get at hidden prey. In test problem situations with familiar objects, obstacles were deliberately and expediently removed in order to reach the prey (sea urchins). In test situations with unfamiliar objects (flat lid, glass cylinder: Fig. 2) it was also evident that the animals have a grasp of spatial connections and can solve arranged problems forthwith. If a once-solved problem is again presented the successful action sequence unwinds very quickly in the new situation. Modified tests for delayed action show that Balistes can retain short-term information for up to about 3 mins. The analysis of behavioural sequences makes it probable that, according to the criteria of Yerkes and Hassenstein, we are dealing with problem-solving behaviour guided by regrouping of engrams. The behaviour is interpreted as ecologically occasioned adaptation to an intensely structured habitat. The solving of problems by the moving of environmental objects seems to have evolved, in vertebrates, in interaction with their habitat, and independently of their systematic position.