Quality control of aquafeeds is one of the most important indices to reach sustainable aquaculture. Because of high volume of diet consumption, high potent of environmental pollution and nutrient leaching, producing commercial diets of rainbow trout during the grow-out stage (500-900 g) is one of major obstacles of aquafeed industries. Physical (fine, density and food particle diameter) and biochemical quality (total volatile nitrogen) of some commercial diets (extrude and cold pellets) consumed in the rainbow trout farms of Khorasan Razavi province were studied and compared with the recommended values. Elevans samples of extrude diets and two cold pellet samples were gathered and transported to the laboratory under standard conditions. The results showed that significantly (P<0.05) highest amount of fines (0.6%) referred to the diet Be1 (cold pellet) and the significantly (P<0.05) least ones was (0.13%) for samples K1, M1 (extrude diet), respectively. Examples of cold pellet, Be1 and Be2 (0.6 and 0.3%) had significantly (P<0.05) higher fine contents than the extrude diets. The significantly (P<0.05) highest levels of total volatile nitrogen (74 mg nitrogen per 100) were referred to the sample Be2 (cold pellets) and the least one (P<0.05) belonged to the By3. Particle diameter of most diets except samples F2, F3, K2 and K3 matched with the available standards and values of the weight classes listed on the bags. It is recommended to be prepared comprehensive standards in order to monitor producing industries of aquafeed.

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