Abstract 1. 1. The patterns of expression of the lactate dehydrogenase loci in the differentiated adult tissues and in the early embryonic stages (0.8–180 hr post-fertilization) of curimbata, Prochilodus scrofa, were investigated. 2. 2. As in other Characiformes species, only two bidirectionally divergent LDH loci—LDH-A∗ and B ∗ were differentially expressed among the tissues and sequentially during the embryogenesis of this species. The LDH-A∗ locus was expressed predominantly in white skeletal muscle, and the B ∗ locus in all other tissues examined. 3. 3. LDH-B4 was present throughout embryogenesis and was the unique LDH isozyme until 20 hr post-fertilization (post-hatching). Ldh-A subunit activity, however, was detected only 34 hr post-fertilization (stage 7) and then, only as heterotetramers containing Ldh-B subunits. This later development detection of A subunits and the appearance of both subunits under heteropolymeric forms suggest the concomitant synthesis of these two subunits at this time of development. 4. 4. The A subunits, which predominate in skeletal muscle where they presumably play an important biochemical role in anaerobic energy production, are first detected when curimbata larvae show more accentuate swimming motions. 5. 5. Three allelic variants for LDH-A∗ locus, A ∗ 300 , A ∗ 1000 and A ∗ -400 were detected in adult curimbata. In heterozygous embryos (offspring from matings type II, III and IV), heteropolymers with maternal and/or paternal A100 and A1000 subunits are synchronously expressed 34 hr post-fertilization.