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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.

1. 1. The patterns of expression of the glucose-6-phosphate isomerase loci in the differentiated adult tissues and in the early embryonic stages (1.30–180 hr post-fertilization) of curimbata, Prochilodus scrofa, were investigated. 2. 2. As in other teleost species, two bidirectionally divergent GPI loci, GPI-A ∗ and GPI-B ∗ were differentially expressed among the tissues and sequentially during the embryogenesis of this species. The GPI-B ∗ locus was expressed predominantly in white skeletal muscle, and the A ∗ locus in all other tissues examined. 3. 3. GPI-A 2 was present throughout embryogenesis and it was the only GPI isozyme until 12 hr and 30 min after fertilization (pre-hatching). The GPI-B subunits were first detected only later in development, varying in the different mating types in their first appearance from stage 5 to 7 (12 hr 30 min–34 hr after fertilization), mainly as a very low activity heterotetramer form suggesting the concomitant synthesis of both subunits at this time. 4. 4. The timing of the appearance of the B subunits which predominate in adult skeletal muscle coincided with the first visible muscular contributions of the curimabata larvae. 5. 5. One genetic variant at GPI-A ∗ locus, A ∗ 87 , and three at the B ∗ locus, B ∗ 500 , B ∗ - 200 and B ∗ - 400 were detected in adult curimbata. In the A1002 B100/-200 and A100/87 B100/-200 heterozygous embryos (offspring from mating type II and III, respectively) both paternal alleles were asynchronously expressed. 6. 6. Following stage 6 (hatching) there was a marked increase in total GPI activity and its maximal levels were obtained 60–105 hr post-fertilization, when the yolk sacs of the larvae were reduced (60 hr) or totally reabsorbed (105 hr), and the larvae were free swimming and feeding.