| The 1050 male yellow catfish(Pelteobagrus fulvidraco)analyzed in the present study,with a initial weight of 56.67±10.75 g and body length of 15.86±1.23 cm,were randomly cultured in 21 separated breeding boxes with 50 fish per box.The boxes were divided into 7groups: control group(T1),curcumin group(T2),chitosan group(T3),vitamin C+ vitamin B2group(T4),low-dose combination group(T5),medium-dose combination group.(T6),high-dose combination group(T7).The feeding trial lasted for 8 weeks,revealing the influence of curcumin,chitosan,(vitamin C plus vitamin B2),their collaborations and application dosage(low,medium and high)on growth performance,digestive activity,antioxidant capacity,lipid metabolism and immune response of Pelteobagrus fulvidraco,thus providing reference for the development of yellow catfish compound functional feed additives.1.Effects of different additives on the growth performance and intestinal digestive enzyme activities of yellow catfish(Pelteobagrus fulvidraco)Growth indicators and digestive enzyme activities were measured after 8 weeks of culture.The results showed that the four additives and their combinations in different dose proportion reduced the feed coefficient,and increased the rate of weight gain,specific growth rate,protein efficiency and survival rate to varying extents.The T6 group showed the largest magnitude of change,followed by T7 group;Intestinal lipase activity in each experimental group was increased to varying degrees compared with T1 group,and T6 group had the highest intestinal lipase activity(P<0.05),which was 3.4,4.2 and 4.3 times of T1 group in the foregut,midgut and hindgut,respectively(P<0.05);The highest value of intestinal protease activity appeared in T6 group(P<0.05);The highest values of amylase activity in the foregut and hindgut were found in the T6 group,and the activity was 4.58 and 5.02 times of the control group,respectively(P<0.05);The highest value of midgut amylase activity was found in the combination group T7(P<0.05),followed by T6 group(P<0.05).In summary,T6 group was the optimal additives for yellow catfish from the aspect of the growth performance and digestion.2.Effect of different additives on antioxidant capacity of yellow catfish(Pelteobagrus fulvidraco)Antioxidant related indicators were determined during the culture at 4 and 8 weeks,respectively.Taking all the antioxidant indexes of serum,hepatopancreas,spleen,heart,brain and gill into consideration,we concluded that for short-term feeding(4 weeks),high-dose combination of the four additives(T7 group)was the most effective in improving the activity of SOD,CAT,GSH,GSH-PX and reducing the content of MDA & Protein carbonyl(P<0.05).While in long-term feeding(8 weeks),the medium-dose combination of the four additives(T6group)was the most effective(P<0.05).3.Effects of different additives on the immune index and disease resistance of yellow catfish(Pelteobagrus fulvidraco)Serum and some tissues were sampled at 4 and 8 weeks of culture,respectively,to determine several immunological and biochemical indicators.In addition,after 8 weeks of culture,whole blood was taken for the detection of respiratory burst activity,and the rest fish were used in a pathogen challenge test.The results showed that,with respect to ACP activity promotion in yellow catfish,curcumin(T2 group)significantly improved the ACP activity in most tissues(P<0.05)during different periods of cultivation,while the medium dose of combined additives(T6 group)further enhanced the activity to a higher level in serum than T2.After a short-term exposure(4 weeks),high-dose combination(T7 group)improved the ACP activity in hepatopancreas more than curcumin(T2 group).The effect of middle dose combination(T6 group)on head kidney ACP was significantly better than curcumin(T2group)(P<0.05);In terms of improving AKP activity in yellow catfish,the effect of chitosan(T3 group)and vitamin C and vitamin B2(T4 group)were not significantly different,but both of them improved the AKP activity of most tissues better than curcumin(T2 group),the combinations of the four additives in various proportions(T5~T7)only improved the AKP activity in serum and spleen of yellow catfish compared with the other experimental groups(P<0.05);The combination of vitamin C and vitamin B2(T4 group)have similar effect with chitosan(T3 group)in improving MPO activity in yellow catfish,and the former had significant advantage in MPO promotion in serum and spleen(P<0.05).However,combination of vitamin C plus vitamin B2(T4 group)and single chitosan(T3 group)functions better than curcumin(T2 group)(P<0.05).In addition,the medium-dose combination of four additives(T6 group)was the most effective in improving the activity of MPO in hepatopancreas and head kidney(P<0.05),while their high dose combination(T7 group)was the most efficient in improving the activity of MPO in spleen and kidney(P<0.05);After a short-term feeding(4 weeks),combined vitamin C and vitamin B2(T4 group)significantly increased the serum levels of GM-CSF,Ig M,IL-2 and other immune factors(P<0.05),followed by chitosan(T3 group)and low-dose combination of four additives(T5group)and medium-dose combination(T6 group).Curcumin(T2 group)and the high-dose combination(T7 group)only significantly promoted a few immune factors(P<0.05).In long-term feeding(8 weeks),curcumin(T2 group)and medium-dose combination(T6 group)both significantly increased the content of most immune factors in serum(P<0.05),and curcumin(T2 group)had improved efficiency;In addition,chitosan(T3 group),combined vitamin C plus vitamin B2(T4 group)and the high-dose combination of the four additives(T7 group)significantly(P<0.05)stimulated part of the immune indicators detected,but the low-dose combination of the four additives(T5 group)only enhanced serum LZM(P<0.05);However,considering the effects of different additives on the respiratory burst activity in blood cells and disease resistance of yellow catfish,moderate-level of combined additives(T6group)was the best for long-term feeding(8 weeks).4.Effects of different additives on liver function and lipid metabolism related index of yellow catfish(Pelteobagrus fulvidraco)Serum and hepatopancreas were sampled and analyzed for liver function and lipid metabolism related index after 8 weeks of culture.The results showed that the GOT activity in hepatopancreas reached a maximum level in T6 group,which was increased by 149.21%,while GPT activity in hepatopancreas was significantly decreased in T7 group(P<0.05)when compared with T1 group;Compared with the T1 group,the serum GPT activity in the T3 group,T5~T7 group was significantly decreased(P<0.05)by 57.98%,71.60%,80.16%,and74.71%,respectively;the LDH activity in serum reached the lowest value in the T6 group(P<0.05),while the TBIL content reached the lowest value in the T4 group and decreased by53.55% compared with the T1 group;the serum LDL-C content in the compatibility group(T5,T6,T7)was significantly lower than that in the T1 group(P<0.05),and the T7 group had the maximum reduction as 53.25%;the TG content in hepatopancreas reached the lowest value in the T6 group,which was 56.94% lower than that in the T1 group,while the lowest TG content in the serum appeared in the T7 group,which was 57.87% lower than that in the T1 group;the content of T-CHO in hepatopancreas decreased significantly in T2 group(P<0.05),while the content of T-CHO in serum reached the lowest value in T7 group,which was 63.76% lower than that in T1 group;the LPL activity in the hepatopancreas of T5 group and T6 group was3.32 times and 9.44 times that of T1 group,respectively;the HL activity of hepatic pancreas was the highest in T6 group,which was 2.58 times of T1 group;compared with T1 group,TL activity in T5 group and T6 group in hepatopancreas was significantly increased(P<0.05).In conclusion,the combinations of the four additives,especially in moderate dose,functioned better than single additive in promotion of liver function and lipid metabolism of Pelteobagrus fulvidracot.5.Effect of additives on metabolic regulation of yellow catfish(Pelteobagrus fulvidraco)based on transcription levelAfter a 8 weeks feeding trial,the hepatopancreas of the control group(T1 group)and the medium-dose combination of the four additives(T6 group)were collected for extraction of total RNA.A high-throughput sequencing was performed subsequently using the Hi Seq X-ten platform.The results showed that 100,895 Unigenes were obtained after sequencing by transcriptome,and 538 differentially expressed genes were obtained after screening for differentially expressed genes,including 188 up-regulated genes and 350 down-regulated genes.Some immune and lipid metabolism related genes and their enriched pathways were screened out.It was concluded that the combination of four additives may stimulate the immunity of yellow catfish through up-regulation the expression of RPB8 in the cytoplasmic DNA sensing pathway and CANX plus COLEC12 in the Phagosome pathway.In the other hand,the medium-dose combination of the four additive presumably promoted the lipids metabolism by up-regulating the expression of CPT1 A,PGAR and Gy K in the PPAR signaling pathway,thereby maintaining the normal level of lipid. |
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