Thermoacclimatory hematological response: Have we been using appropriate conditions and assessment methods?

Goldfish (Carassius auratus L.) were acclimated to three types of thermal regime: constant temperature (12, 28 °C), a diurnal sine-wave cycle (20 ± 8 °C), and a randomly fluctuating pattern of ±2 °C changes at 2-h intervals between 12 and 28 °C. Assessment of hematological response was based on determination of total red cell numbers and hematocrit values, and through characterization of circulating red cell populations in terms of absolute and relative abundances of juvenile, developing, mature, Trypan Blue-positive, karyorrhectic, dividing, and tailed or recently divided cells. While no significant differences in cell counts were observed, cell population composition was markedly affected by temperature regime. Variation during acclimation, particularly when this resembled that likely to be experienced under natural circumstances, was associated with significantly increased numbers of juvenile and developing cells, and thus with increased potential for reorganization of hemoglobin isomorph systems. The converse was true of mature cell abundances; these varied inversely with temperature and were significantly reduced under varying temperature conditions. It is concluded that studies involving constant acclimation temperatures are unlikely to provide valid information regarding functional hematological status, in this species at least. It is also concluded that the primary hematological indices and their derivatives (red cell numbers, hemoglobin, hematocrit, mean erythrocytic volume, and hemoglobin) commonly used to monitor hematological response to environmental change are insufficiently sensitive for the purpose.