Effects of temperature and body size on immunological development and responsiveness in juvenile shortnose sturgeon (Acipenser brevirostrum)

Sturgeon are an important evolutionary taxa of which little is known regarding their responses to environmental factors. Water temperature strongly influences growth in fish; however, its effect on sturgeon immune responses is unknown. The objective of this study was to assess how 2 different temperatures affect immune responses in shortnose sturgeon (Acipenser brevirostrum) relevant immune organs such as the meningeal myeloid tissue, spleen, thymus and skin. These responses were studied in 2 different sizes of same age juvenile sturgeon kept at either 11 °C or 20 °C (4 treatment groups), before and after exposure to an ectoparasitic copepod (Dichelesthium oblongum). Based on a differential cell count, temperature was found to strongly influence immune cell production in the meningeal myeloid tissue, regardless of the fish sizes considered. Morphometric analysis of splenic white pulp showed a transient response to temperature. There were no differences between the groups in the morphometric analysis of thymus size. Splenic IRF-1 and IRF-2 had similar expression profiles, significantly higher in fish kept at 20 °C for the first 6 weeks of the study but not by 14 weeks. In the skin, IRF-1 was significantly higher in the fish kept at 11 °C over the first 6 weeks of the study. IRF-2 had a similar profile but there were no differences between the groups by the end of the trial. In conclusion, higher water temperatures (up to 20 °C) may have beneficial effects in maximizing growth and improving immunological capacity, regardless of the fish sizes considered in this study.