Rigour mortis is the Latin term for stiffness of death; the stiffening of an animal body after death. Because it is a Latin term it is conventional to italicise 'rgor mortis'; 'rigor', (not to be confused with the American spelling of 'rigour'), exists as meaning stiffness and is not usually italicized. Typically, vertebrate fish start to go into rigour 8-24 hours after death, but this period can be shorter or longer, and rigour is resolved after a further 1-3 days. Time into, time in, and strength of rigour varies with several factors, the main ones being species, nutritional status, amount of exercise by the fish immediately before death, and the ambient temperature of the fish.