SUMMARY—Studies were conducted on the nutritive value of fish protein concentrate (FPC) preparations produced by extracting cod fillet with 1, 2‐dichloroethane (DCE). These were fed to immature rats at either a 20 dietary protein level or at a 10 protein level in conjunction with 10 casein protein. Findings were compared to those from immature rats fed diets containing 10 or 20 casein protein. Nutritive value of the FPC preparations was dependent on the temperature and length of time at which extraction occurred. Rats fed diets containing 10 or 20 casein protein. Nutritive value of the FPC preparations was dependent on the temperature and length of time at which extraction occurred. Rats fed diets containing FPC extracted at 65°± 2°C or 40°± 2°C for 24 hr or at a temperature of 83°C for 6 hr or 3 hr and vacuum dried without steaming were normal in appearance and exhibited increments in body weight and feed efficiency comparable to those of rats fed similar diets containing 20 casein protein. FPC prepared under similar conditions except that it was extracted for 24 hr at 83°C without replacing evaporated solvent during the last 6 hr of extraction was toxic. Subjecting the latter to vacuum steaming for 45 min at 10 in. of vacuum eliminated its toxic properties as determined in a 7‐day feeding test, although some impairment of its nutritional value was still manifest. Cod fillet prepared by the same procedure as the toxic material except that evaporated solvent was replaced at 2‐3 hr intevals throughout the entire 24‐hr period of extraction was non‐toxic in a 7‐day feeding test and differed only slightly from case
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