发酵鱼溶浆替代鱼粉对大菱鲆幼鱼生长、抗氧化能力、蛋白质代谢及相关基因表达的影响

The Effect of Replacing Fish Meal with Fermented Stickwater on Growth, Antioxidant Capacity, Protein Metabolism and Related Gene Expression of Juvenile Turbot(Scophthalmus maximus L.)

为研究发酵鱼溶浆(FSW)替代鱼粉对大菱鲆(Scophthalmus maximus)幼鱼生长、抗氧化能力、蛋白质代谢及相关基因表达的影响,实验设正对照组(50%鱼粉),负对照组(30%鱼粉),在负对照组基础上分别以2%、4%、6%、8%的FSW替代鱼粉,分别命名为FSW2、FSW4、FSW6和FSW8组,饲喂初始体重为(30.00±0.03)g的大菱鲆幼鱼8周。结果显示,各组间幼鱼成活率均无显著差异(P>0.05),FSW2~FSW8组幼鱼增重率、蛋白质效率与正对照组无显著差异(P>0.05),但均显著高于负对照组(P<0.05)。FSW2~FSW8组全鱼和背肌粗蛋白含量与正对照组无显著差异,但显著高于负对照组(P<0.05);负对照组全鱼和背肌粗脂肪含量显著高于其他组(P<0.05)。负对照组血清谷丙转氨酶(ALT)、谷草转氨酶(AST)和甘油三脂(TG)均显著高于正对照组(P<0.05),负对照组、FSW2~FSW8组血清中总胆固醇(T-CHO)、ALT和AST呈先降低后升高的趋势,肝脏中ALT和AST含量则呈相反趋势。负对照组血清中高密度脂蛋白胆固醇(HDL-C)含量显著低于正对照组(P<0.05)。负对照组肝脏中蛋白激酶A(PKA)、蛋白激酶C(PKC)和乳酸脱氢酶(LDH)活性均显著低于正对照组(P<0.05)。与正对照组相比,负对照组肠道中氨基酸转运载体b0at1和小肽转运载体pept1表达量上调,氨基酸转运载体cat1、pat1表达量差异不显著,FSW2~FSW8组b0at1、cat1、pat1和pept1表达量均显著高于正对照组和负对照组(P<0.05)。综上所述,饲料中添加FSW显著改善了实验鱼对饲料蛋白质的利用率,缓解了植物蛋白造成的生长性能下降。以增重率为评价指标,添加FSW可使饲料中鱼粉的使用量降低至22%,且鱼体在生长和体组成上与50%鱼粉组无显著差异。

With the rapid development of the aquaculture industry and the shortage of global fishery resources, the contradiction between supply and demand of fish meal has become increasingly significant. Therefore, finding new substitutes for fish meals and reasonably reducing the amount of fish meal in formula feed has become an important research topic in aquatic feed. Stickwater is a byproduct of fishmeal processing. It contains many water-soluble molecules, such as small molecular peptides, biogenic amines, taurine, and high unsaturated fatty acids. These components are regarded as particular nutrients or bioactive substances in the fish meal. Studies have shown that stickwater can replace part of fish meal in recent years and achieve good results in fish and other aquatic animals.The fermented feed has excellent advantages for fish meal replacement. Studies have shown that after fermentation, the contents of anti-nutritional factors in plant raw materials are decreased.In contrast, the contents of small peptides and free amino acids are increased, the nutrient composition is changed, and the intermediate metabolites of microorganisms are obtained, which can further improve the replacement level of fish meal. There are few studies on the fermentation of feed materials, such as fish meal and stickwater, which do not contain anti-nutritional factors. Our laboratory’s preliminary study found that stickwater combined with other animal and plant proteins could replace 40% of fish meal in the feed. This experiment fermented stickwater first, then replace fish meal in high plant protein formula feed with fermented stickwater(FSW), aims to further increase the amount of fish meal replacement, reduce the negative effect of the plant protein source on the turbot, for FSW application in feeds for turbot provide a theoretical reference.The stickwater in the experiment was a brown viscous liquid, with a water content of 48.73%,dry matter crude protein content of 64.08%, and crude fat content of 8.91%. The strains used were Bacillus subtilis and Lactobacillus. The fermentation conditions were as follows: Temperature of 37℃, the addition of 1% sugar as auxiliary material, Bacillus subtilis and Lactobacillus(1:1) added to 1% of the total mass of the stickwater, and the fermentation period was five days. After fermentation,the content of acid-soluble protein decreased significantly. Still, the crude protein, crude fat, and free amino acids showed no significant changes. It was then used for turbot culture.Healthy juvenile turbot with an average bodyweight of(30.00±0.03) g were randomly divided into six groups with three replicates and 30 fish per replicate. The trial lasted for eight weeks. Six diets consisted of a positive control diet with 50% fish meal(positive control group), a harmful control diet with 30% fish meal(negative control group), and experimental diets formulated by FSW were used to replace 2%, 4%, 6%, and 8% of the fish meal with the harmful control diet, respectively(FSW2, FSW4, FSW6, and FSW8). The results showed: There were no significant differences in the survival rate of juvenile turbot among all groups(P>0.05). There were no significant differences in juvenile turbot’s weight gain rate and protein efficiency ratio in the FSW2~FSW8 group compared with that of the positive control group. Still, they were all higher than those in the negative control group. The crude protein content of whole fish and dorsal muscle in the FSW2~FSW8 group was not significantly different from that in the positive control group. Still, it was significantly higher than that in the negative control group. The highest crude lipid content of whole fish and dorsal muscle was found in the negative control group(P<0.05). Serum ALT, AST, and TG levels in the negative control group were significantly higher than those in the positive control group;the negative control group and FSW2~FSW8 group showed first decreasing and subsequent increasing serum ALT, AST, and T-CHO levels. At the same time, the ALT and AST levels in the liver showed an opposite trend. The serum HDL-C content in the negative control group was significantly lower than that in the positive control group. The activities of PKA, KPC, and LDH in the liver were significantly lower in the negative control group than in the positive control group(P<0.05). Compared with the positive control group, the expression of b0at1 and pept1 in the intestine was upregulated in the negative control group. In contrast, the expression of cat1 and pat1 was not significantly different. The expression levels of boat1, cat1, pat1, and pept1 in the FSW2~FSW8 group were significantly higher than those in the positive control and negative control groups(P<0.05). The results showed that FSW was an excellent substitute for fish meals, and the added amount could be up to 8% in the feed. In the feed with high plant protein, the fish meal can be replaced by FSW to reduce the amount of fish meal further, reduce the metabolic abnormality caused by plant proteins, and improve juvenile turbot’s antioxidant capacity. Under these experimental conditions, the group supplemented with FSW achieved the same growth effect as the positive control group. In conclusion, the fish meal content of juvenile turbot feed can be reduced to 22% by adding FSW without adverse effects on the growth of juvenile turbot. This provides a theoretical reference for the fermentation process of SW and subsequent application of FSW in seawater fish.