Fumarylacetoacetase involved in the tyrosine degradation pathway. 4-fumarylacetoacetate + H2O = acetoacetate + fumarate + H(+) Amino-acid degradation; L-phenylalanine degradation; acetoacetate and fumarate from L-phenylalanine: step 6/6. Highly expressed in the intestine and the hypodermis. RNAi-mediated knockdown from hatching results in stunted growth, reduced fertility, progressive destruction of the intestine by adulthood characterized by the thinning of the intestinal wall and loss of intracellular lipid droplets, which eventually culminates in lethality (PubMed:18227072). RNAi-mediated knockdown results in activation of cellular stress pathways, and thus the intestinal damage is most likely due to activation of oxidative stress responses and ER stress responses in the intestine (PubMed:18227072). The reduced fertility phenotype is enhanced in response to exogenous tyrosine or homogentisic acid (PubMed:18227072). RNAi-mediated knockdown together with tatn-1 RNAi, hpd-1 RNAi or hgo-1 RNAi rescues the impaired growth and fertility defects in the single fah-1 RNAi mutant (PubMed:18227072). Belongs to the FAH family.