Electroretinographic Analysis of Night Vision in Juvenile Pacific Bluefin Tuna (Thunnus orientalis)

We used electroretinogram recordings to investigate visual function in the dark-adapted eyes of the juvenile scombrid fishes Pacific bluefin tuna (Thunnus orientalis) and chub mackerel (Scomber japonicus) and the carangid fish striped jack (Pseudocaranx dentex). Despite the fast swimming speed of the Pacific bluefin tuna, analysis of flicker electroretinograms showed that visual temporal resolution in this species was inferior to that in chub mackerel. Peak wavelengths of spectral sensitivity in Pacific bluefin tuna and striped jack were 479 and 512 nm, respectively. The light sensitivity of Pacific bluefin tuna was comparable to that of chub mackerel but lower than that of striped jack. The Pacific bluefin tuna may not need highlevel visual function under dim light conditions in natural habitat because it is a diurnal fish. However, this low temporal resolution and light sensitivity probably explain the mass deaths from contact or collisions with net walls in cultured Pacific bluefin tuna.