Investigating photoreceptor densities, potential visual acuity, and cone mosaics of shallow water, temperate fish species

• Compares the eye anatomy and retinal structure of eight different fish species.
• Rod densities increased with the maximum habitat depth.
• All shallow water species had a regular square cone mosaic structure.
• There was a 3.9-fold difference in potential visual acuity among species.
• Species with high rod density and potential visual acuity may react most to visual cues.

The eye is an important sense organ for teleost species but can vary greatly depending on the adaption to the habitat, environment during ontogeny and developmental stage of the fish. The eye and retinal morphology of eight commonly caught trawl bycatch species were described: Lepidotrigla mulhalli; Lophonectes gallus; Platycephalus bassensis; Sillago flindersi; Neoplatycephalus richardsoni; Thamnaconus degeni; Parequula melbournensis; and Trachurus declivis. The cone densities ranged from 38 cones per 0.01 mm2 for S. flindersi to 235 cones per 0.01 mm2 for P. melbournensis. The rod densities ranged from 22 800 cells per 0.01 mm2 for L. mulhalli to 76 634 cells per 0.01 mm2 for T. declivis and potential visual acuity (based on anatomical measures) ranged from 0.08 in L. gallus to 0.31 in P. melbournensis. Higher rod densities were correlated with maximum habitat depths. Six species had the regular pattern of four double cones arranged around a single cone in the photoreceptor mosaic, while T. declivis had only rows of double cones. P. melbournensis had the greatest potential ability for detecting fine detail based on eye anatomy. The potential visual acuity estimates and rod densities can be applied to suggest the relative detection ability of different species in a commercial fishing context, since vision is a critical sense in an illuminated environment for perceiving an oncoming trawl.