Effects of organic plant oils and role of oxidation on nutrient utilization in juvenile rainbow trout (Oncorhynchus mykiss)

The study compared the effect of four either fresh or force oxidized organic plant oils in diets for juvenile rainbow trout (Oncorhynchus mykiss) in which 47% of conventional LT fish meal protein was substituted by a mixture of 3 organic plant protein concentrates. Fish oil was completely substituted with either organic linseed oil; rape seed oil; sunflower oil or grape seed oil and evaluated based on feed intake, feed utilization, growth and digestibility. None of the plant oils affected feed intake and growth parameters. Organic plant oils had all a positive effect on lipid digestibility as compared with the fish oil based control diet, despite the very different FA profiles. The organic vegetable oils did not undergo autoxidation, as opposed to the fish oil control for which lipid digestibility was significantly negative influenced

Lipid oxidation of fish meal stored under different storage conditions

Changes of chemical quality and physical properties of fish meal due to lipid oxidation under different storage conditions were studied using a 3-factor factorial design (2x2x4). Premium grade fish meal (72%protein) was divided into two portions, with and without ethoxyquin, each portion was then stored at either ambient temperature or 4oC for 0, 1.5, 3 and 4.5 months. The results showed no interaction between 3factors (supplemented with or without ethoxyquin, at 27-32oC and 4o and storage time) on protein, lipid and ash of fish meal. Peroxide value (PV) and anisidine value (AnV) increased with storage time with the highestvalue in the non-ethoxyquin sample stored at ambient temperature for 4.5 months. An increase of TBARS was found in non-ethoxyquin fish meal stored at both ambient temperature and 4oC with the highest valuein the sample stored at 4oC for 4.5 months. Storage conditions without ventilation/air circulation caused an accumulation of malonaldehyde in the fish meal storage at 4oC for a long period. FFA content was highestin the ethoxyquin treated fish meal stored at ambient temperature for 3 months. At 4.5 months, the nonethoxyquin fish meal stored at ambient temperature showed higher FFA content than other samples. Levels of TVN of samples stored at ambient temperature decreased with time but those stored at 4oC changed inan opposite direction, which could be explained by the similar phenomenon as the changes of TBARS value. Parameters tested by feed microscopic and simple chemical techniques did not show any difference among fish meal under studied conditions

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