Evolutionary trends of LDH isozymes in fishes

Abstract

1. 1. LDH characteristics (loci numbers, number of isozymes constituted by A and B subunits, and tissue specificity of LDH-C4) were reviewed for 245 fish species. 2. 2. The occurrence of different isozyme numbers among species of a single family (e.g. 3, 4 and 5 banded patterns), plus the existence of alleles generating 4 or 5 banded patterns in a single population indicate that the number of LDH isozymes constituted by A and B subunits might not be a character under selective pressure. 3. 3. The regulatory pattern of LDH-C* gene, i.e. its occurrence in several tissues of primitive fishes plus its highly restricted tissue distribution in advanced teleost, and even its absence in some intermediate groups (e.g. Characiformes and Siluriformes) suggest a possible selective pressure upon an ancient gene. 4. 4. Four evolutionary trends are suggested considering isozyme tissue distribution as well as LDH physiological role: (i) convergence of B to A subunit as in good anaerobes; (ii) restriction of B subunits in advanced teleost, resulting in the same pattern as in (i); (iii) non-divergence between A and B subunit as occurs in some Amazon fishes which are obligatory aerobes and (iv) the restriction of C subunit to specific tissues in advanced teleost reaching a high specialization degree, which physiological meaning is not explained yet. © 1993.