High-density culture brings with it chronic stress situations that affect fish welfare. In order to evaluate the effect of tryptophan (Trp) levels on the response to stress, Totoaba macdonaldi juveniles were stocked at low (13.5 kg m⁻³) and high (27.0 kg m⁻³) densities (32.5 and 56.4 kg m⁻³, respectively, at the end of the experiment) in 100-L tanks and fed for 63 days with experimental diets containing different Trp levels: control diet CD0.42 (0.42%) and three supplemented diets with 0.99, 1.55 and 2.19% (0.99Trp, 1.55Trp and 2.19Trp, respectively) (three tanks × density × diet). The high-density stocking fed with CD0.42 diets showed significantly increased blood parameters. Trp decreased catalase (CAT) activity in low- and high-density stocking, while the superoxide dismutase (SOD) activity showed no difference. Serotonin (5-hydroxytryptamine, 5-HT) content decreased, and the serotonin turnover ratio (5-HIAA:5-HT) increased in the brains of fish fed with the CD0.42 diet. Indeed, Trp-supplemented diets helped to restore homeostasis in high-density growth conditions as evaluated by the hematological and plasma parameters as well as the serotonergic activity. When the fish were provided a diet containing moderate Trp levels, plasma cortisol increased under high-density conditions. However, no differences were observed among stock densities when totoaba were fed with the 2.19Trp diet. Notably, survival was unaffected by both Trp or densities, but weight gain (WG) decreased with the dietary Trp levels in the high density culture. In sum, Trp supplementation decreased the parameter values linked to stress response on totoaba juveniles cultured at high stock densities.

高密度养殖会带来影响鱼类福利的慢性应激状况。为了评估色氨酸（Trp）水平对应激反应的影响，以低密度（13.5 kg m ^-3）和高密度（27.0 kg m ^-3）（32.5和56.4 kg m ^-3）饲养Totoaba macdonaldi少年分别在实验结束时）放入100升罐中，并用含不同Trp水平的实验饮食喂养63天：对照饮食CD0.42（0.42％）和三种补充饮食的0.99、1.55和2.19％（0.99 Trp，1.55Trp和2.19Trp）（三个罐×密度×饮食）。用CD0.42日粮喂养的高密度放养动物显示血液参数显着增加。在低密度和高密度放养中，Trp均可降低过氧化氢酶（CAT）活性，而超氧化物歧化酶（SOD）活性则无差异。饲喂CD0.42日粮的鱼的大脑中5-羟色胺（5-羟色胺，5-HT）含量降低，5-羟色胺周转率（5-HIAA：5-HT）增加。确实，通过血液和血浆参数以及血清素能活性的评估，补充有色氨酸的饮食有助于在高密度生长条件下恢复体内平衡。当给鱼提供含有适量Trp含量的饮食时，在高密度条件下血浆皮质醇会增加。但是，当用2.19Trp饲料喂养Totoaba时，种群密度没有差异。值得注意的是，存活率不受Trp或密度的影响，但是在高密度培养中，体重增加（WG）随着饮食中Trp含量的降低而降低。总而言之，补充色氨酸会降低与以高种群密度培养的totoaba幼鱼的应激反应有关的参数值。饲喂2.19Trp日粮的Totoaba，种群密度没有差异。值得注意的是，存活率不受Trp或密度的影响，但是在高密度培养中，体重增加（WG）随着饮食中Trp含量的降低而降低。总而言之，补充色氨酸会降低与以高种群密度培养的totoaba幼鱼的应激反应有关的参数值。饲喂2.19Trp日粮的Totoaba，种群密度没有差异。值得注意的是，存活率不受Trp或密度的影响，但是在高密度培养中，体重增加（WG）随着饮食中Trp含量的降低而降低。总而言之，补充色氨酸会降低与高密度饲养的totoaba幼鱼的应激反应有关的参数值。