Can angelfish (Pterophyllum scalare) count? Discrimination between different shoal sizes follows Weber’s law

@article{GmezLaplaza2010CanA,
  title={Can angelfish (Pterophyllum scalare) count? Discrimination between different shoal sizes follows Weber’s law},
  author={Luis M. G{\'o}mez-Laplaza and Robert Gerlai},
  journal={Animal Cognition},
  year={2010},
  volume={14},
  pages={1-9}
}
The ability to discriminate between larger and smaller quantities has been demonstrated in several mammalian and avian species suggesting the possibility of evolutionary conservation of this characteristic. Preference for the larger of two groups has also been shown in fish species, although this ability has rarely been systematically studied in lower order vertebrates, and thus the mechanisms of such ability are not understood. Here, we exploit the tendency of angelfish to seek protection in… 
Quantification abilities in angelfish (Pterophyllum scalare): the influence of continuous variables
TLDR
Investigation of whether angelfish can discriminate between shoals differing in numerical size using non-numerical attributes finds density to be a sufficient condition for discrimination between large shoals as the test subjects preferred the more dense shoal.
Spontaneous discrimination of small quantities: shoaling preferences in angelfish (Pterophyllum scalare)
TLDR
The results are compatible with the hypothesis of the existence of an object-file mechanism to discriminate small quantities in vertebrates and provide evidence for spontaneous discrimination of up to three elements in angelfish, a similar limit to that found in human and non-human animals.
Angelfish (Pterophyllum scalare) discriminate between small quantities: a role of memory.
TLDR
The results imply that angelfish form internal representations and demonstrate that these fish can make comparisons between small quantities of items while relying on their working memory alone, implying the robustness of the quantity discrimination abilities of this species.
The Role of Body Surface Area in Quantity Discrimination in Angelfish (Pterophyllum scalare)
TLDR
It is concluded that body surface may be an important continuous variable in shoal discrimination and the potential existence of different processing systems for large and small numbers in fish.
Quantity discrimination in angelfish, Pterophyllum scalare: a novel approach with food as the discriminant
The ability to distinguish between different quantities of items is fundamental in many ecological contexts, and it has been shown in different animal species. This ability may also be context
Discrimination of large quantities: Weber's law and short-term memory in angelfish, Pterophyllum scalare
The ability to discriminate between different quantities has important ecological relevance for animals when engaging in behaviours such as forming groups, foraging or trying to avoid predators.
Group-size preferences in a shoaling cichlid
TLDR
Test fish consistently preferred the larger of two shoals, irrespective of the ratios, indicating recognition of this parameter, and has fine-tuned discrimination skills, adding to the evidence that quantitative abilities are widespread in fishes.
Food Quantity Discrimination in Angelfish (Pterophyllum scalare): The Role of Number, Density, Size and Area Occupied by the Food Items
TLDR
It is concluded that food item number, density, and size may not be considered individually by angelfish, but instead, the fish respond to all these factors attempting to maximize energy gained from eating the food while minimizing energy expenditure collecting and/or protecting the food.
Continuous versus discrete quantity discrimination in dune snail (Mollusca: Gastropoda) seeking thermal refuges
TLDR
Investigating whether snails used numerical information or based their decisions upon continuous quantities, such as cumulative surface, density or convex hull, which co-varies with number leaves open the question of whether gastropod molluscans possess elementary abilities for numerical processing.
Quantity discrimination in angelfish (Pterophyllum scalare) is maintained after a 30-s retention interval in the large but not in the small number range
The ability to discriminate between sets that differ in the number of elements can be useful in different contexts and may have survival and fitness consequences. As such, numerical/quantity
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TLDR
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