Five isonitrogenous and isocaloric diets [containing 54, 30, 15, 10, and 5% fishmeal crude-protein (CP), dry matter (DM) basis] were prepared by replacing fishmeal with poultry by-product meal plus soybean meal to feed juvenile largemouth bass (LMB, with an initial mean body weight of 4.9 g) for 8 weeks. All diets contained 54% CP and 13% lipids. There were four tanks of fish per treatment group (15 fish/tank). The fish were fed twice daily with the same feed intake (g/fish) in all the dietary groups. Results indicated that the inclusion of 15% fishmeal protein in the diet is sufficient for LMB growth. However, some of the fish that were fed diets containing ≤ 15% fishmeal CP had black skin syndrome (characterized by skin darkening and retinal degeneration, as well as intestinal and liver atrophies and structural abnormalities). The concentrations of taurine, methionine, threonine and histidine in serum were reduced (P < 0.05) in fish fed the diets containing 5, 10 and 15% fishmeal CP, compared with the 30 and 54% fishmeal CP diets. Interestingly, the concentrations of tyrosine and tryptophan in serum were higher in fish fed diets with ≤ 15% fishmeal CP than those in the 54% fishmeal CP group. These results indicated that 15% fishmeal CP in the diet containing poultry by-product meal and soybean meal was sufficient for the maximum growth and feed efficiency in LMB but inadequate for their intestinal, skin, eye, and liver health. A reduction in dietary methionine and taurine content and the possible presence of antinutritional factors in the fishmeal replacements diets containing high inclusion levels of soybean meal may contribute to black skin syndrome in LMB. We recommend that the diets of juvenile LMB contain 30% fishmeal CP (DM basis).

以家禽副产品粉加豆粕代替鱼粉，制备五种等氮等热量饲料[含54%、30%、15%、10%、5%鱼粉粗蛋白（CP），以干物质（DM）计]喂养幼鱼。大口黑鲈（LMB，初始平均体重为 4.9 克）持续 8 周。所有饮食均含有 54% CP 和 13% 脂质。每个治疗组有四缸鱼（每缸 15 条鱼）。所有饮食组中的鱼每天喂食两次，饲料摄入量（克/鱼）相同。结果表明，日粮中添加 15% 的鱼粉蛋白足以促进 LMB 生长。然而，一些饲喂鱼粉CP含量≤15%的鱼会出现黑皮肤综合症（其特征是皮肤变黑和视网膜变性，以及肠道和肝脏萎缩和结构异常）。与添加30%和54%鱼粉CP饲料相比，添加5%、10%和15%鱼粉CP饲料的鱼血清中牛磺酸、蛋氨酸、苏氨酸和组氨酸浓度降低（ P < 0.05）。有趣的是，饲喂鱼粉CP≤15%的饲料中，血清中酪氨酸和色氨酸的浓度高于饲喂54%鱼粉CP组的鱼。这些结果表明，在含有家禽副产品粉和豆粕的日粮中添加 15% 鱼粉 CP 足以实现 LMB 的最大生长和饲料效率，但不足以维持其肠道、皮肤、眼睛和肝脏健康。膳食蛋氨酸和牛磺酸含量的减少以及含有高含量豆粕的鱼粉替代品中可能存在的抗营养因子可能会导致 LMB 的黑皮肤综合征。我们建议幼鱼LMB的日粮中含有30%的鱼粉CP（DM基）。