The Interactive Effect of Temperature and Salinity in the Nile Tilapia (Oreochromis niloticus)

Frequent measures that aim to identify the tolerance of an organism to various environmental conditions rely on the mortality of said organism. However, the effects of sub-lethal stress can be just as important to consider as they may give rise to how an organism may live in such an environment (growth, reproduction, etc.). Coping with changes in environmental conditions can have a high energy cost. Even starting a cellular stress response alone has proven to be costly. It is therefore reasonable that organisms in stressful situations will dedicate energy sources to survival mechanisms, and downregulate non-necessary activities like growth, and reproduction. As a tropical freshwater species, Nile Tilapia are subject to both Winter Stress Syndrome and saltwater intrusion as global climate change progresses, making them an ideal model organism. In order to test the physiological limits of this species, we exposed Nile Tilapia to a variety of treatments (two temperatures: 21°C & 14°C, three salinities: 0ppt, 16ppt, 34ppt) for one hour. By manipulating both temperature and salinity simultaneously the author hopes to shed light on the future of this species as global climate change progresses. Cell cycle arrest can occur at cellular checkpoints such as the ones located at G1 or G2/M. Monitoring the DNA replication process is crucial to cellular activities, and disruptions such a cell size issues or DNA damage can cause this process to stop indicating the presence of sub-lethal stress. There were no significant changes in the proportions of cells in G1, S, or G2 due to an increase of salinity in warm water. In cold water, there was a steady decrease of the percentage of cells in G1 as salinity increased suggesting cell cycle arrest is occurring at a different checkpoint. A significant increase in the number of cells in G2 in response to cold temperature was found, however, this effect was not made greater by the addition of salinity. Increasing number of cells in G2/M suggests that there is cell cycle arrest occurring at the G2/M checkpoint. The concentrations of three proteins involved in the regulation and arrest of the cell cycle were measured in gill tissue by dot blotting. Western blotting was performed to ensure the specificity of the protein antibodies. Three proteins of interest were chosen due to their roles in regulating cell cycle proliferation (Proliferating Cell Nuclear Antigen), growth arrest (Growth Arrest and DNA Damage-45) and programmed cell death (p53). Proliferating Cell Nuclear Antigen (PCNA), Gadd45, p53 all showed significant decreases in concentration in gill tissue exposed to saltwater (34 ppt) in the warm temperature treatment. There was no significant effect of salinity within the cold temperature treatment for any of the proteins tested. The CCAAT/Enhancer-binding proteins (C/EBP) are a class of transcription factors that act upon cellular proliferation and differentiation. C/EBP-�� is the specific protein that is activated in response to stress stimuli. There were no significant differences observed in C/EBP-�� concentrations in gill tissue.