Abstract
The eye of Brama japonica, which exhibits eyeshine, contains a retinal tapetum composed of guanine. The total amounts of guanine in the eyes of two specimens measuring 19.5 and 51.4 cm in standard length were 7.4 and 70.5 mg, respectively, the respective retinal surface areas being 4.9 and 39.9 cm2. The mean guanine content was almost identical (1.5 and 1.8 mg/cm2, respectively). A locus tapetalis, with guanine values exceeding 2.5 mg/cm2, was developed in the ventrotemporal region of the retina, where it cooccurred with the area centralis. Evidence is presented that sound functional reasons exist for both the development of the locus tapetalis and its position in the retina. A plea is made for future examination of the retinae of additional pelagic and nonpelagic species for the presence and location of a locus tapetalis.
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