Many animal species share the ability to discriminate between sets with different quantity of food items. In fish, this ability has rarely been investigated, although findings have been obtained do indicate a preference, as in other animals, for sets with large over small quantities. The role played by food item size has also been found to be important in the discrimination. However, another potentially important non-numerical variable, food density, has not been investigated. In this study, we examined the influence of density (inter-item distance) in the decision-making process of food discrimination in angelfish (Pterophyllum scalare). In a binary choice task, we kept the number and size of food items constant, but contrasted a set containing food items spaced further apart (sparse set) to another set with food items spaced more closely (dense set). We conducted this analysis with sets in the small (3 vs 3 food items) and in the large number range (5 vs 5 food items) and also varied the specific spatial arrangements of the food items in the sets. Contrary to expectations, angelfish showed a preference for the sparse sets over the dense sets in the five vs five contrasts irrespective of the specific spatial arrangement, but exhibited no preference in case of the three vs three contrasts. Subsequently, we slightly lengthened the inter-item distance in the dense sets, and found preference for the dense over the sparse sets. Last, we further examined the potential effect of spatial configuration of the items in the sets, but found no effect of this latter factor. Overall, these results indicate that higher density of the contrasted food item sets significantly influences choice in angelfish, which prefer denser sets if a clear discriminability of each individual item within the sets is provided.

中文翻译：

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食物密度和首选数量：区分神仙鱼中的小数量和大数量（Pterophyllum scalare）。

许多动物物种具有区分食物数量不同的食物的能力。在鱼类中，很少研究这种能力，尽管已获得的发现确实表明，与其他动物一样，它们偏爱大数量而不是小数量的鱼。人们还发现，食品大小所起的作用在歧视中很重要。但是，尚未研究另一个潜在的重要非数字变量食物密度。在这项研究中，我们研究了密度（项目间距离）在神仙鱼（Pterophyllum scalare）食物歧视决策过程中的影响。）。在二元选择任务中，我们使食物的数量和大小保持不变，但是将一组包含距离较远的食物（稀疏集合）与另一组距离较近的食物（密集集合）进行了对比。我们对小型（3个食品与3个食品）和较大范围（5个食品与5个食品）的组合进行了分析，并且还更改了组合中食品的特定空间布置。与预期相反，神仙鱼在五对五对比中表现出对稀疏集的偏爱，而不对密集组偏爱，而与特定的空间布置无关，但在三对三对比的情况下则不表现出偏爱。随后，我们稍微延长了密集集中的项目间距离，并发现相对于稀疏集合，优先选择密集。持续，我们进一步检查了集合中项目空间配置的潜在影响，但没有发现后者的影响。总体而言，这些结果表明，对比食品组的较高密度会显着影响神仙鱼的选择，如果提供了组中每个单独食品的明显可辨别性，则更喜欢密集组。