ALTERATIONS IN LIVER COMPOSITION OF CHANNEL CATFISH (ICTALURUS-PUNCTATUS) DURING SEASONAL ACCLIMATIZATION

Compositional alterations in liver and heart in channel catfish during seasonal acclimatization were compared with patterns observed during temperature acclimation. Hepatosomatic index (HSI) was minimal in the summer (> 25-degrees-C), highest in the spring and fall (12-degrees - 18-degrees-C), and intermediate in winter (4-degrees-9 - degrees-C). Alterations in heart (ventricle) mass were in the order winter > fall > summer and correlated with the pattern observed during acclimation. Liver protein content was relatively constant except in summer, when total liver protein was approximately half that of other seasons. Dietary insufficiency was indicated in summer animals by elevated tissue water content. Liver DNA, like HSI, showed maxima in fall and spring and minima in summer and winter. Liver RNA levels were lowest in the summer and biggest in the spring. Protein/DNA and RNA/DNA ratios increased from fall through winter to a maximum in the spring as a prelude to spawning but declined precipitously in the summer. Liver glycogen content, which was biggest in the fall, was reduced during summer to values 13-fold lower than in the fall. Total lipid was biggest in the spring and lowest in summer, primarily reflecting alterations in neutral lipid. Phospholipid showed little seasonal variation except in summer, when it was half that at other seasons, and this may reflect significant alterations in either subcellular organelles or hepatocyte numbers. Although temperature plays a major role in the observed alterations in tissue composition and often reflects a pattern similar to that observed for laboratory acclimation, other factors, particularly dietary deficiencies at seasonal temperature extremes, likely modify compositional patterns.