Investigating the roles of temperature and exercise in the development of chalkiness in Pacific halibut

The incidence of chalky muscle occurs in a small portion of commercially landed Pacific halibut affecting its marketability. Numerous studies have determined that the chalky condition is associated with increased lactic acid and subsequent lower pH in fish muscle but have yet to elucidate the biochemical processes responsible for the condition. The goal of this project was to reproduce the chalky condition in the laboratory while monitoring multiple biochemical properties of the fish. Fish were exposed to three durations of stress in a controlled experiment to simulate longline hooking to produce chalky muscle and quantify the biochemical changes in muscle and blood chemistry. Biochemical parameters determined in muscle were proximate composition, lactate, glucose, nucleotides, pH, and color. Lactate and glucose were also determined for blood samples. Based on the three-, six-, and twelve-hour stress periods, we were unable to produce the chalky condition in most of the fish. We found little or no statistical difference in the biochemical properties of experimental groups that were stressed versus controls. However, three fish that did produce chalky muscle post mortem had muscle with lower pH, higher lactate and more opacity than non-chalky muscle. Based on low initial glucose, protein and lipid levels, we concluded that the limited chalky development in this study may have been due to the condition of the fish just prior to experimentation. Future studies should address the importance of halibut condition and glucose in particular to provide a substrate for lactic acid buildup and subsequent chalky development. Also, changing the timing of capture and limiting the duration of acclimation time prior to experimentation may render more specific results.