Abstract
The reliance of the aquafeed industry on marine resources has to be reduced by innovative approaches in fish nutrition. Thus, a three-factorial approach (fish oil reduced diet, phytochemical genistein, and temperature reduction) was chosen to investigate the interaction of effects on growth performance and tissue omega-3 long chain polyunsaturated fatty acid (LC-PUFA) levels in juvenile sea bream (Sparus aurata, 12.5 ± 2.2 g). Genistein is a phytoestrogen with estrogen-like activity and thus LC-PUFA increasing potential. A decrease in the rearing temperature was chosen based on the positive effects of low temperature on fish lipid quality. The experimental diets were reduced in marine ingredients and had a fish oil content of either 6% dry matter (DM; F6: positive control) or 2% DM (F2: negative control) and were administered in the plain variant or with inclusion of 0.15% DM genistein (F6 + G and F2 + G). The feeding trial was performed simultaneously at 23°C and 19°C. The results indicated that solely temperature had a significant effect on growth performance and whole body nutrient composition of sea bream. Nevertheless, the interaction of all three factors significantly affected the fatty acid compositions of liver and fillet tissue. Most importantly, they led to a significant increase by 4.3% of fillet LC-PUFA content in sea bream fed with the diet F6 + G in comparison to control fish fed diet F6, when both groups were held at 19°C. It is hypothesized that genistein can act via estrogen-like as well as other mechanisms and that the dietary LC-PUFA content may impact its mode of action. Temperature most likely exhibited its effects indirectly via altered growth rates and metabolism. Although effects of all three factors and of genistein in particular were only marginal, they highlight a possibility to utilize the genetic capacity of sea bream to improve tissue lipid quality.
Highlights
In order to reduce the reliance on marine resources from capture fisheries, namely fish meal and fish oil, the aquafeed industry has turned to plant products
Fish farmed on diets low in fish meal and fish oil can be subject to reduced lipid quality in terms of low amounts of omega-3 (n-3) long chain polyunsaturated fatty acids (LC-PUFAs) like eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) [3,4]
Growth performance and whole body nutrient composition are mainly affected by holding temperature
Summary
In order to reduce the reliance on marine resources from capture fisheries, namely fish meal and fish oil, the aquafeed industry has turned to plant products. Besides potential effects of the reduced n-3 LC-PUFAs on the fish’s health status, physiological functions, and development [5,6], the nutritional benefits of fish for human nutrition might be decreased Such reduced lipid quality is especially distinctive in carnivorous marine fish that depend on their diet as a source for n-3 LC-PUFAs. The in vivo hepatic fatty acid synthesis converting the precursor fatty acid α-linolenic acid (ALA; 18:3n-3) to EPA and DHA is disrupted in marine fish [6]. The genetic capacity is present, the functionality of certain enzymes is impaired [7,8,9,10] For these reasons, suitable fish oil replacements like novel EPA and DHA rich sources [11,12,13], oils rich in functional fatty acids like stearidonic acid [14], or strategies improving the efficiency of fish oil utilization need to be investigated. Another alternative might be the use of functional and bioactive food supplements that interact with the lipid metabolism of fish, protect fatty acids from oxidation, or stimulate the in vivo synthesis of EPA and DHA from ALA [18,19,20,21,22]
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