It is banned in the UK also. [ 6 ] Aquatic animals  metabolize  malachite green to its leuco form. Being non-polar, LMG is retained in  catfish  muscle longer (t 1/2  = 10 days) than is MG ( 1/2  = 2.8 days). Toxicity The  LD 50  (oral, mouse) is 80 mg/kg. Rats fed