Acclimation to warm temperatures modulates lactate and malate dehydrogenase isozymes in juvenile Horabagrus brachysoma (Günther)

Differential expression of isozymes enables fish to tolerate temperature fluctuations in their environment. The present study explores the modulation of lactate dehydrogenase (LDH) and cytoplasmic malate dehydrogenase (sMDH) isozyme expression in the heart, muscle, brain, liver, gill, and kidney of juvenile Horabagrus brachysoma after 30 days of acclimation at 26, 31, 33, and 36°C. LDH and sMDH zymography were performed using native polyacrylamide gel electrophoresis. The zymography revealed five distinct bands of LDH isoenzymes (labelled from cathode to anode as LDH-A4, LDH-A3B1, LDH-A2B2, LDH-A1B3, and LDH-B4) and three distinct bands of sMDH isoenzymes (labelled from cathode to anode as sMDH-A2, sMDH-AB, and sMDH-B2), with considerable variation in their expression in the tissues. Acclimation to the test temperatures did not influence the expression patterns of LDH or sMDH isozymes. Densitometric analysis of individual isozyme bands revealed a reduction in the densities of bands containing the LDH-B and sMDH-B molecules, while the densities of bands containing the LDH-A and sMDH-A molecules increased in the gills and muscle, indicating the role of these organs in adaptive responses to thermal acclimation. However, the total densities of the LDH and sMDH isozymes increased with higher acclimation temperatures, indicating that adaptation to increased temperatures in H. brachysoma is primarily characterised by quantitative changes in isozyme expression.