Vitamin K occurs in two natural forms, phylloquinone (K₁, plants) and menaquinone (K₂, microorganism), and a synthetic form, menadione (K₃). Vitamin K is required for normal blood coagulation in animals and may be associated with electron transport and oxidative phosphorylation (energy metabolism). Requirement of vitamin K by shrimp is questionable. Sources of vitamin K include liver meals and fish meal. Supplementation level of vitamin K in commercial feeds is 5 mg/kg (Akiyama et al., 1992).