Effects Of Dietary Selenomethionine Levels On Intestinal Health And Antioxidant Function Of Zebrafish Pre-fed Oxidized Fish Oil

In this study,Danio rerio fed with oxidized fish oil was used to study the effects of different levels of selenomethionine on the intestinal health and immune functions.The study was divided into 2 parts.The first part was a preliminary test to determine the amount of the pre-fed oxidized fish oil in the zebrafish(Danio rerio).A one-factor design was adopted,and 480 one-month-old zebrafish with a healthy body weight of 0.054 ± 0.003 g were selected and randomly divided into 8 groups,with 4 replicates in each group,and 15 fish per replicate.Fish in the treatments FF,OF1,OF2,OF3 were fed different amount of oxidized fish oil(containing 0,2%,4%,6%,respectively).The results were as follows: 1)At the end of the14 d feeding trial: a.compared to the FF group,with the increase in the amount of feed oxidized fish oil,the remaining groups in FBW,WG and SGR,had significantly decreased(P<0.05),and FCR showed a downward trend.There was no significant difference in rates.b.compared to the FF group,with the increase in the amount of feed oxidized fish oil,the T-SOD activity decreased significantly.GSH-Px,CAT activity increased significantly,and the MDA content increased significantly(P<0.05).c.compared to the FF group,with the increase in the amount of feed oxidized fish oil,the intestinal morphological damage score showed an upward trend,except for OF1 group,OF2 and OF3 group had significantly increased(P<0.05).2)At the end of the 28 d test period: a.compared to the FF group,with the increase in the amount of feed oxidized fish oil,the activities of FBW,WG,SGR and FCR of the remaining groups had all decreased significantly(P<0.05).In addition,the survival rate decreased significantly(P<0.05).b.The trend of intestinal antioxidant function was the same as 14 d.c.compared to the FF group,with the increase in the amount of feed oxidized fish oil,the intestinal morphological damage score had increased significantly(P<0.05).In summary,adding 4% oxidized fish oil to the feed for 14 days could induce irreversible damage to the intestinal tissue structure of zebrafish,the antioxidant energy was also weakened,and the growth performance was reduced.The second part was designed two different pre-feeding methods,choosing 720 healthy one-month-old zebrafish with a weight of 0.076 ± 0.003 g,randomly divided into 12 groups,each group of 4 repetitions,each repetition of 15 fish.Group C(C1,C2,C3,C4,and C5)fed with basic feed for 14 d while Group T(T0,T1,T2,T3,T4,and T5)fed with basic feed containing 4% oxidized fish oil for 14 d.After the 14 d pre-fed feeding trial,both groups were fed different levels of selenomethionine basic feed(containing0,0.1,0.2,0.3,0.4,0.5 mg/kg Se-Met)for 28 d.At the end of the experiment,the intestinal health and growth-related indicators of the test fish were measured.The results were as follows: 1)With the level of Se-Met addition increased,in group C: compared to the CK group,the remaining groups activities of FBW,WG,WG,SR were significantly increased and showed an upward trend and then a downward trend(P<0.05),with the highest fish in the C3 group,while FCR were decreased significantly and showed an upward trend(P<0.05).The activities of T-SOD,GSH-Px,CAT,LZM,ACP in intestine and liver were increased first and then decreased,with the highest in group C3 while the lowest in group CK,the MDA content first decreased and then increased,the lowest in group C3,the highest in CK group,the significant differences were observed between C3 and CK(P<0.05);compared to CK group,microvilli were well organized arranged in C3 group,while intestinal cavity ruptured cells were rare.There was no significant difference in Chao and ACE between CK group and C3group(P>0.05).However,there were significant differences in Shannon and Simpson(P<0.05).The relative abundance of the potential intestinal pathogens Flavobacterium and Neochlamydia were decreased in group C3,while the relative abundance of beneficial bacteria Akkerman and Cetaceae were increased.2)Compared to the T0 group,with the increase in the amount of feed Se-Met added in the T group,the activities of WG,SGR and FBW of each group were increased significantly and showed an upward trend and then a downward trend(P<0.05),with the highest in the T4 group.The FCR was decreased significantly and showed a downward trend and then an upward trend(P<0.05),with the lowest in the T4 group.The activities of T-SOD,CAT,GSH-Px,LZM and ACP intestinal and liver were significantly increased(P<0.05),while the highest in the T4 group.The MDA content was significant decreased with the lowest in the T4 group;compared to the T0 group,there was no significant difference in Chao1,ACE,Shannon and Simpson index(P>0.05),the relative abundance of Flavobacterium and Neochlamydia in the T4 group was significantly reduced,and the relative abundance of Akkermansia and Cetaceae increased.Compared to the T0 group,the intestinal villi in the T4 group were well organized arranged,and the intestinal cavity was rarely broken.In summary,under the conditions of this experiment,the addition of0.3 mg/kg Se-Met to the feed can promote the development of zebrafish intestinal tissue,optimize the composition of intestinal microflora,improve the antioxidant and growth performance of zebrafish.The addition of 0.4 mg/kg Se-Met to the feed can effectively alleviate the fish intestinal tissue damage which caused by 4% oxidized fish oil,weakened antioxidant function,decreased growth performance and increased intestinal pathogenic flora abundance.