Creatine Kinase Activity as an Indicator of Energetic Impairment and Tissue Damage in Fish: A Review

Creatine kinase (CK) is an enzyme that produces and uses phosphocreatine to transfer energy to maintain tissue and cellular energy homeostasis, being considered the main controller of cellular energy homeostasis. Its activity in plasma/serum has been commonly used to evaluate tissue damage, since CK is released into the bloodstream during damage. This review summarizes the current knowledge regarding the use of CK activity in fish, focusing on its potential as an indicator of the impairment of energetic homeostasis and tissue damage during stressful situations, such as exposure to contaminants (metals, pesticides, microplastic), hypoxia, thermal stress, and diseases (fungal, parasitic, and bacterial). Based on the data, we can conclude that tissue CK activity can be used as a suitable indicator of the impairment of energetic homeostasis in fish exposed to different aquaculture challenge conditions, while serum/plasma CK activity can be used as the first evidence of possible tissue damage, due to its release into the bloodstream.