Effect of Sacha inchi seed on growth performance, immune responses, and expression of genes related to immunity in Nile tilapia

Abstract

This present study was conducted to determine the effects of substituting fishmeal with sacha inchi seed on growth performance, the whole-body composition, apparent coefficient digestibility, hematological parameters, histological characteristics, and expression of genes related to immunity in Nile tilapia (Oreochromis niloticus). Two control diets including control diet 1 (fish oil-based diet) and control diet 2 (soybean oil-based diet) and other six experimental diets were formulated to replace fishmeal protein source with different inclusion protein levels of sacha inchi seed from 8%, 15%, 25%, 50%, 75%, and 100%. The experiment was divided into eight treatments and each treatment had 4 replicates. Moreover, Nile tilapia fingerlings with an initial mean weight approximate 11 g were selected and transferred to 32 fiber tanks at a density of 15 fish per fiber tank. Fish were fed up to apparent satiation with the experimental diets twice daily at 9:00 am and 16:00 pm for 10 weeks. After 10 weeks trial, the results indicated that Nile tilapia fed SIS25 diet had the highest value in term of average body weight (ABW), specific growth rate (SGR), feed intake (FI), feed conversion ratio (FCR), productive protein value (PPV), and apparent digestibility coefficient of dry matter and protein. Depending on the growth parameters, Nile tilapia fed SIS15 diet had the highest weight gain, followed by fish fed SIS25 diet which did not show significant differences with control diets. The whole-body fish composition showed significant differences (p < 0.05) after substituting FM with SIS in diets with exception to moisture content. Nile tilapia receiving SIS25 diet had the highest value of the whole-protein content. No significant difference was detected in terms of the whole-fat content of fish fed SIS25 diet compared to control diet 1, but significantly higher compared to control diet 2. However, its values of both whole-protein and -fat content showed significant decreases after fish fed SIS between 50%-100% in diets. Fish fed SIS25 diet had the highest value in terms of the apparent digestibility coefficient of dry matter and protein which did not show significant differences with control diets. These values were significantly decreased when fish fed SIS between 50%-100% in diets. Additionally, significant differences (p<0.05) were observed in terms of blood biochemistry parameters in fish fed the experimental diets. Fish fed with SIS up to 25% had higher values of hemoglobin concentration, hematocrit, RBCs, and WBCs compared to fish fed SIS substituted between 50%-100%. The highest intestinal villus height was observed in fish fed SIS25 diet and it started decreasing after receiving SIS between 50%-100%. The staining liver cells sections showed that nuclei of all treatment fish were damaged. Furthermore, the liver tissues of Nile tilapia receiving SIS between 75%-100% protein levels showed intra cytoplasmic round circumscribed fat vacuoles. There were no significant differences in expression levels of target genes (TNF-α, IL-1β, and TGF-β gene) when SIS were used to replace fishmeal. However, the expression levels of TNF-α, IL-1β, and TGF-β gene tend to increase when substituting FM with SIS up to 25%. The increased levels of target genes were the same trend with the WBCs value. According to economic analyses of experimental diets showed that the SIS25 diet offers the best economic viability, taking into consideration the cost of feed fed over the trial period. These responses suggest that substituting FM with inclusion levels up to 25% of SIS can be a consequence of improved immune response and showed the best growth performance.

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