THE EYE OF THE BLUE ACARA (AEQUIDENS PULCHER, CICHLIDAE) GROWS TO COMPENSATE FOR DEFOCUS DUE TO CHROMATIC ABERRATION

By rearing fish in various monochromatic illuminations we investigated (1) the potential for compensation of refractive error due to chromat ic aberration, (2) the contributions of the chromatic channels to emme tropization, and (3) the role of color cues in the control of eye grow th. Cichlid fish (Aequidens pulcher) were reared for 6 months (12 h li ght/12 h dark) in monochromatic lights (623.5, 534.1, 485.0 nm; spectr al purity 5-10 nm). Light levels were isoirradiant at 1.1 . 10(12) qua nta/s/cm(2). Two control groups were reared in white light with down-w elling illuminances of 0.2 and 33 lx. Nasotemporal diameters (NTDs) of the eyes were measured in relation to lens size. Due to the oblique a xis of highest acuity vision in cichlids, NTD is considered to be a mo re important dimension than axial length. Variances in NTD were equall y small in all rearing groups. NTDs were enlarged with increasing wave lengths of the rearing lights with highly significant values over cont rols in the red-light group. The wavelength-dependent size of the eyes matched the changes in focal length due to longitudinal chromatic abe rration. Complete recovery from eye enlargement was observed after fis h reared in red light were exposed to a white light regime for 5 weeks . Small variances in NTD in all groups indicated stringent control of eye growth in the absence of color cues. The reversibility of the incr ease in NTD in fish reared in red light suggests that the eyes were em metropized by visually guided mechanisms. Eye size in fish reared in w hite light was intermediate between the values expected if only blue-s ensitive single or the red- and green-sensitive double cones contribut ed to the control of eye growth. This suggests that all chromatic chan nels participate in emmetropizing the fish eye.