Scotopsin

The protein component of Rhodopsin. The protein can be paired with two different Chromophores, which results in one of two opsins:

• Rhodopsin – when paired with Retinal Vitamin A₁ has a Peak Wavelength at about 500nm. This form is dominant in land animals and marine fish.
• Porphyropsin – when paired with Retinal Vitamin A₂ has a Peak Wavelength at about 560nm. This form is common in freshwater fish and amphibians.

Some species that migrate between freshwater and saltwater will undergo a rhodopsin-porphyropsin shift, by replacing their Chromophores during their life cycle to best reflect their current environment.