Albinism in biology is the "Congenital absence of any pigmentation or coloration in a person, animal or plant, resulting in white hair and pink eyes in mammals." Varied use and interpretation of the terms means that written reports of albinistic animals can be difficult to verify. Albinism can reduce the survivability of an animal, for example, it has been suggested that albino alligators have an average survival span of only 24 hours due to the lack of protection from UV and their lack of camouflage to avoid predators. Albino animals have characteristic pink or red eyes because the lack of pigment in the iris allows the blood vessels of the retina to be visible. Familiar albino animals include in-bred strains of laboratory animals (rats, mice, guinea-pigs and rabbits), but populations of naturally occurring albino animals exist in the wild, e.g. Mexican cave tetra. Albinism is a well-recognized phenomenon in molluscs, both in the shell and in the soft parts. It has been claimed by some, e.g. that "albinism" can occur for a number of reasons aside from inheritance including genetic mutations, diet, living conditions, age, disease, or injury, however, this is contrary to definitions where the condition is inherited.