Mechanism Of Numerical Discrimination In Fish Species

Collective living is one of the important survival strategies for fish.Animals often choose to stay with the group with proper size by numerical discrimination.The quantitative cues used in the process of animal numerical discrimination are divided into two categories: discrete quantity information(number of items et al.)and continuous quantity information(total area,density et al.).Two series of investigation were conducted based on spontaneous shoal choice test in this thesis:(1)the shoal preference and numerical ability of qingbo(Spinibarbus sinensis),curcian carp(Carassius auratus),zebrafish(Danio rerio)and guppy(Poecilia reticulata)based on continuous quantitative information;(2)the numerical ability of in singletons,conspecific and heterospecific dyads of crucian carp and qingbo,with particular to test the possible improvement in numerical ability through cooperation between individuals.The main findings are as follows:1.Qingbo showed no significant preference to either stimulus shoal at numerical contrast of 12 vs 12,12 vs 6 and 6 vs 6 when the densities of both stimulus shoals were the same.2.Qingbo showed significant preference to stimulus with higher density(the density ratio was 2: 1)at numerical contrast of both 12 vs 12 and 12 vs 6(p <0.05)but not at numerical contrast of 6 vs 6.3.Qingbo,curican carp,zebrafish and guppy all showed no significant preference to either stimulus shoal under a numerical contrast of 2: 3 when both stimulus shoals were manipulated with the same body shape area.4.When the stimulus shoals were manipulated with conflict between discrete and continuous information(i.e.shoal with less group member but larger accumulative body shape vs shoal with more group member but small accumulative body shape),all four selected fish species showed significant preference to the larger body shape area with less group member.5.Singletons of qingbo were able to discriminate a numerical contrast of 8 vs 12 but not 9 vs 12,whereas dyads of qingbo were able to discriminate numerical contrasts of 8 vs 12,9 vs 12,10 vs 12 and 11 vs 12.6.Both singletons and dyads of crucian carp showed poor numerical ability which could not decimate any of the numerical contrasts in the present study.Furthermore,qingbo in heterospecific dyads could only discriminate 8 vs 12 numerical contrast.The results show that:1.Fish species rely mainly on continuous quantitative information to perform shoal choice.2.The numerical ability and the possible improvement through inter-individual cooperation varied with fish species which possibly due to the difference of cognitive ability and(or)boldness among species.