One issue is to discern the difference between a chronic and an acute thermal change and the rate of change or the ramping rate is an important consideration. One protocol listed temperature acclimations using adjustments of 1 °C/h with a maximum of 7 °C/day [47]. A second listed acclimation changes of 3 °C every 48 h over a maximum range of 15 °C [27]. Others presented a 6 °C change in temperature using an acclimation program of 1 °C/day, which is likely to be a more gentle acclimation procedure [36]. Given that the latter study reported only six gene expression differences this may indicate a markedly less impactful acclimation process. A study in sea bass looked at seasonal variation of humoral immune parameters and found little variation [48]. It is interesting to consider the rates of change here are natural, varying on a seasonal basis and that as a consequence the immune functions were not impacted. A study on gene expression in the erythrocytes of rainbow trout (Onchorynchus mykiss) that were exposed to a transient rise in temperature from 13 °C to 25 °C, with a ramp of 3 °C/h, showed an increase in the expression of a number of genes including; apolipoprotein and Ig light chain [49].
Some studies look at multiple stressor interactions. One investigated the interaction between temperature and salinity in turbot noted that expression of both Hsp70 and IgM were positively correlated to both temperature and salinity and that temperature was the dominant factor [27]. Another study on cod found little variation in natural antibody levels when animals were reared at different salinities and temperatures [50].
Conclusion
While there are trends in the information available, there are still contrasting or contradictory results. Many papers indicate a bias towards innate immune function at lower temperatures. Many also indicate an up-regulation of antibody related functions at increasing temperature. But the development of clear response patterns to temperature changes across all teleosts is not apparent and probably shouldn't be expected given the number of species involved.
Another facet that may bear consideration is that these changes in immune response are associated with operation within permissive temperatures and that exceeding these temperatures, 16 °C in the case of cod, 23 °C for carp, 25 °C for turbot and 28 °C for tilapia, can often put these animals into an environment where they have exceeded their optimum range for effective immune function [16], [51], [52] and [53].