A linear relationship between water activity (a,) in moist salted fish products and NaCl molality was found: (a,) SF = 1.002-0.042 rn ; where rn is the NaCl molality considering it to be in true solution in the total water content of the product.The linear approximation was analyzed with reference to the a, values of pure NaCl solutions and to a thermodynamic approach for a, prediction; it was found consistent and appropriate for a, estimation in moist salted fish products, with errors within the accepted range for intermediate moisture foods (IMF).

Adsorption and desorption isotherms of raw hake (Merlucius hubbsi) muscle were determined at 5 , 20 and 30°C. From the temperature dependence of the isotherms, isosteric heats of sorption were evaluated by means of the Clausius-Clapeyron equation. Monolayer moisture contents are calculated by means of the B.E.T. analysis. The magnitude of the hysteresis between desorption and adsorption isotherms was quantified. Results are compared with those reported in the literature for other fish species.