Single target acuity in the common sunfish (Lepomis gibbosus).

Vision contributes to foraging, territorial and reproductive behavior in sunfish. In these contexts, sunfish need to perceive single targets, such as prey items or body markings from either conspecifics or individuals of other sunfish species, from some distance. We determined the single target acuity of six common sunfish in a behavioral experiment to assess whether the visual abilities of sunfish correspond with behavioral observations or reactive distance measures, and thus assessed the limits of vision for the mentioned behaviors. Single target acuity for full-contrast single targets amounted to 0.17 deg (0.13-0.32 deg). When contrast was reduced to Weber contrasts of 0.67 and 0.41, single target acuity dropped to 0.34 deg (0.31-0.37 deg), and finally to 0.42 deg (0.34-0.54 deg). Single target acuity would thus allow common sunfish to perceive biologically relevant stimuli at reasonable distances even when contrast is reduced.