Fish cognition: a primate's eye view

Abstract

We provide selected examples from the fish literature of phenomena found in fish that are currently being examined in discussions of cognitive abilities and evolution of neocortex size in primates. In the context of social intelligence, we looked at living in individualised groups and corresponding social strategies, social learning and tradition, and co-operative hunting. Regarding environmental intelligence, we searched for examples concerning special foraging skills, tool use, cognitive maps, memory, anti-predator behaviour, and the manipulation of the environment. Most phenomena of interest for primatologists are found in fish as well. We therefore conclude that more detailed studies on decision rules and mechanisms are necessary to test for differences between the cognitive abilities of primates and other taxa. Cognitive research can benefit from future fish studies in three ways: first, as fish are highly variable in their ecology, they can be used to determine the specific ecological factors that select for the evolution of specific cognitive abilities. Second, for the same reason they can be used to investigate the link between cognitive abilities and the enlargement of specific brain areas. Third, decision rules used by fish could be used as 'null-hypotheses' for primatologists looking at how monkeys might make their decisions. Finally, we propose a variety of fish species that we think are most promising as study objects.

Explaining brain size variation: from social to cultural brain

“…It seems reasonable to assume that small-brained organisms cannot afford to support domain-general cognitive abilities. Indeed, evidence available so far is consistent with the idea that invertebrates and poikilothermic vertebrates, with relatively smaller brains [1,33,36,48], do not show much of them [21]. On the other hand, domain-general abilities are found in both birds and mammals, whose brains are an order of magnitude larger for their body size than those of fishes, amphibians or reptiles [33,36].…”

“…However, we know that this is not universally true, as shown by the existence of modular abilities, such as food caching in birds, tactical deception in small fishes, tool use in ants or social communication in bees [21,44]. Moreover, if it were true, we would never know in which domain selection has favored the cognitive abilities.…”

“…The more organisms rely on domain-specific socio-cognitive adaptations, the more they may be able to perform these tasks with relatively small brains. In extreme cases, domain-general abilities trained on socio-cognitive challenges may be absent, such as perhaps in cleaner fishes [21], whereas at the other extreme, perhaps, for instance, in humans, the dedicated modules play a minor role. This prediction can be tested by examining the species concerned for evidence of domain-general cognitive abilities (Box 2).…”

“…First, it does not explain the existence of grade shifts, in that some lineages exhibit equally high socio-cognitive abilities with much smaller brains, both within primates [19] and other mammals [20], and most spectacularly, fish [21]. Second, recent studies suggest that primates and some other organisms show evidence for general intelligence, and it is not immediately obvious how selection on modular cognitive abilities (i.e., abilities limited to a specific domain) could have produced more general cognitive abilities.…”

“…When the comparison is extended to non-mammal and non-bird species, the discrepancies become even more marked. Several small fish species show socio-cognitive abilities rivaling those of primates [21,24], despite having relatively minute brains. (Because the fish case can be linked to the modularity debate, its discussion is postponed until the next section.)…”