Chinook salmon must deal with many stressors such as high water temperatures, changes in water salinity, toxins, hypoxia, and disease (Nover 1991, Volker et al. 1992, Forsyth et al. 1997, DuBeau et al. 1998, Iwama et al. 1998). In response to stressors that cause denaturation of proteins, heat shock proteins (hsps) are produced. Hsps are also called stress proteins because they are produced in response to stressors other than heat (Iwama et al. 1998). Overall, there are three groups of hsps: hsp90, hsp70, and low molecular weight hsp (Basu et al. 2002). Hsp90 is involved with the cytoskeleton and steroid hormone receptors (Csermely et al. 1998, Pearl and Prodromou 2000, Young et al. 2001 from Basu et al. 2002), and hsp70 with maintenance of proteins by repairing denatured proteins or translocating permantly damaged proteins to lysosomes and proteosomes (Kiang and Tsokos 1998, Lund et al. 2002). Low molecular weight hsps are involved in many different functions and are species-specific.

Concentrations of hsp70 in fish tissues can be good measure of stress, or protection against stress (Parsell and Lindquist 1993, Iwama et al. 1999, Podrabsky et al. 2004). However, in a cellular stress response, each type of hsp only responds to certain stressors, and is produced at different levels in different tissues. There is a link between an organism’s temperature tolerance and the temperature limit of hsp70 (White et al. 1994, Norris et al. 1995, Hightower et al. 1999). Furthermore, some hsps produced in response to one stressor, such as increased water temperature, can exhibit protection against other stressors, such as increased water salinity (DuBeau et al. 1998). This phenomenon is termed cross protection.

The half life of hsp70 is at least 4 days in some organisms (Lindquist 1986; Sanders 1990 from Lund et al. 2002). Hsps can be detected in chinook salmon immediately after subjection to a stressor, and these increased levels of hsps can still be detected 24 hours later (Palmisano et al. 2000, Pan et al. 2000). Also, older individuals tend to have lower levels of hsps and this may be a cause for senescence (Fangue et al. 2006).