Fish meal quality evaluated by chemical analysis and feed microscopy techniques

Quality of 20 fishmeal samples from the Southern Provinces produced by different raw materials and processing method were evaluated using both chemical and feed microscopy methods. Samples were collected from fishmeal plants, shrimp feed mills and local feedstuff store. One sample using sardine as a raw material was produced in the laboratory by lyophilization as a control fishmeal. Five samples having protein contents over 65% were grouped into shrimp grade including the control fishmeal which had the maximum protein content of 74.09%. Eight samples were grouped into Grade 1 including the imported fishmeal from Chile. The rest of the samples which were mostly produced from trash fish fell into Grade 2 with low protein and high ash content. Chemical analyses of salt content, total volatile base nitrogen (TVN), ammonia nitrogen, histamine content, free fatty acid (FFA), thiobarbituric acid number (TBA) and peroxide value showed the fishmeal from feedstuff store was the most deteriorated sample. This high level of deterioration might be due to low quality raw materials and a long storage time. Among the shrimp grade samples, the most denatured protein was found in Pattani 1 with high level of TVN, ammonia nitrogen and histamine. Moreover, the high levels of TVN were detected in Phangnga 1 (grade 1) and Trang 2 (grade 2). Lipid damage was associated with high fat contents in fish meal which was detected in every group of the samples. The results from feed microscopic examination were in line with those of the chemical analyses. The most deteriorated sample from feedstuff store showed the highest decomposition level and was the only sample that non protein nitrogen was detected. For feather meal adulteration test, seven samples were positive with the highest level in unidentified sample and trace amount in other samples including 2 shrimp grade samples. To confirm feather meal adulteration, protein digestibility test should be performed for these samples