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Faktory ovlivňující výživovou hodnotu ryb
KHALILI TILAMI, Sarvenaz
When considering fish as food, first of all the n-3 LC-PUFA, particularly EPA and DHA are in focus. Furthermore, it gets obvious that the proteins and peptides in fish have not only a high nutritional value but also impact on human health issues. In addition, fish can be considered as a good source of several minerals, vitamins and micronutrients. The overall aim of the thesis was to highlight different factors which influence nutritional quality of fish and to focus on the nutritional value of some commercially important river fish species from the Czech Republic. Moreover, to examine different sustainable alternatives to replace FO and FM in the feed of carnivorous. According to our results, there were some variation of FA composition in the selected seven freshwater fish species from the Czech Republic, depending on the natural habitat and differences in feed and its availability. Simultaneously, we observed a very favourable FA composition with good proportions of n-3 PUFA, including EPA and DHA in all analyzed species which reflects the composition of the natural diet. Consequently, the values of both index of atherogenicity (IA) and index of thrombogenicity (IT) were low and close to the values of the so-called Eskimo diet, which is related to very low incidences of the coronary heart disease. According to our findings we concluded that the chosen species have a standard protein content, minimum carbohydrates and relatively low contents of fat, which can, however, vary to some degree in various localities, most probably related to the availability and composition of the feed. Due to the combination of the drastic increase in the need for aquaculture feed as well as decline in the sources of FM and FO, utilization of alternative sources received more attention. Based on our result, it is possible to replace VO by yeast oil produced from lingocellulose in the feed of Arctic char (Salvelinus alpinus). There were no significant differences in the study, regarding weight gain, feed conversation ratio, condition factor and hepatosomatic index between the control and the yeast oil fed group. According to the results of another study, partial (25% of pellet replaced live house cricket, 25% of pellet replaced by superworm, combination of 12.5% crude energy of each group) or total replacement (50% of each) of house cricket and superworm for FM in the commercial diet of rainbow trout indicated no negative effects on growth, survival, FCR and gross energy utilization. Inclusion of insect was connected with lower content of nutritionally valuable n-3 FAs (EPA and DHA). In our study total replacement showed the mixture of insects, caused the better growth performance compared to the commercial feed of similar energy value as insects are good live food for salmonids. With increase in the proportion of insect's inclusion in the feed of fish, changes in the sensory properties, texture and colour of fish flesh was in a way that showed less acceptability and preference by consumers. Replacement of 25% FM by a mixture of insect meal including house cricket- (Acheta domesticus) and superworm- (Zophobas morio) meal (with an amino acid adjustment) in the diet of perch, on survival, growth, feed conversion with special emphasis on lipid changes and composition showed FA composition of the fish fillet was only affected to a minor extent. However, the lower growth performance in the fish group fed by insect indicated lower nutritional value and digestibility of the feed along with the taste of the feed. Interestingly, the significant increase of 18:2 n-6 in the group fed by insect was due to the higher content of this FA in both insects and subsequently in the experimental diet which from the nutritional point of view this change was neglectable.
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