Effects of Diets with Varying Astaxanthin from <i>Yarrowia lipolytica</i> Levels on the Growth, Feed Utilization, Metabolic Enzymes Activities, Antioxidative Status and Serum Biochemical Parameters of <i>Litopenaeus vannamei</i>

<i>Litopenaeus vannamei</i> was divided into seven groups (defined as diets A0–A6) and fed with diets respectively containing 0, 0.5, 1, 2, 4 and 8 g/kg <i>Yarrowia lipolytica</i> (astaxanthin content: 1.5%) and 3 g/kg <i>Haematococcus pluvialis</i> (astaxanthin content: 2%). After an eight-week feeding trial, the results reflected that different levels of <i>Y. lipolytica</i> and <i>H. pluvialis</i> could significantly increase the weight gain rate of <i>L. vannamei</i> (<i>p</i> < 0.05). The condition factor and weight gain rate of group A4 were significantly higher than those of the other groups (<i>p</i> < 0.05); the HSI significantly decreased with the increase of <i>Y. lipolytica</i> (<i>p</i> < 0.05). The addition of <i>Y. lipolytica</i> to the diet had significant effects on total protein (TP), albumin (ALB), glutathione peroxidase (GSH-Px), malonaldehyde (MDA) and total antioxidant capacity (T-AOC) (<i>p</i> < 0.05). The total protein and albumin of the A5 and A6 groups were significantly higher than those of the other groups (<i>p</i> < 0.05). The GSH-Px activity of the A5 group was the highest and the T-AOC of the A0 group was the lowest. Inducible nitric oxide synthase (I-NOS) increased with the addition of <i>Y. lipolytica</i> (<i>p</i> < 0.05). <i>Y. lipolytica</i> inclusion had no negative effect on physiological and biochemical parameters and some serum immune and antioxidant indexes (<i>p</i> > 0.05). Astaxanthin in <i>Y. lipolytica</i> had an obvious effect on body color. After cooking, the body color of the shrimp deepened with increasing <i>Y. lipolytica</i> content. The red body color of <i>L. vannamei</i> was significantly improved by adding yeasts hydrolysate 2~8 g/kg to the diet. According to the regression analysis between the level of <i>Y. lipolytica</i> added to the diets and the weight gain rates, the optimal level of <i>Y. lipolytica</i> is 4.64 g/kg.