Shin Jaehyeong, Kim Suhyeok, Lee Yeonji, Lee Yein, Kim Wonhoon, Song Sanghyun, Kim Sua, Lee Kyeong-Jun
Department of Marine Life Science, Jeju National University, Jeju, 63243, South Korea.
Marine Life Research Institute, Jeju National University, Jeju, 63333, South Korea.
Fish Physiol Biochem. 2025 Sep 27;51(5):169. doi: 10.1007/s10695-025-01584-x.
The olive flounder (Paralichthys olivaceus) is an economically important species in South Korea. However, the specific dietary requirement for tryptophan (Trp) has not been determined for this species at any growth stage. Thus, this study aimed to determine the dietary Trp requirement for juvenile olive flounder under low water temperature conditions. Two consecutive feeding trials were conducted, each using diets with different concentrations of dietary Trp: Exp-Ⅰ (0.39-14.46 g kg) and Exp-Ⅱ (0.93-6.96 g kg). The initial mean body weights of the olive flounder were 4.38 ± 0.03 g (Exp-Ⅰ) and 18.4 ± 0.1 g (Exp-Ⅱ). In Exp-Ⅰ and Exp-Ⅱ, fish were randomly distributed into 18 tanks (120 L), corresponding to six dietary groups with three replicates per group (30 fish per tank). Fish were fed the experimental diets for 13 weeks (Exp-Ⅰ) and 8 weeks (Exp-Ⅱ). The water temperatures during the trials were 18.2 ± 2.4 ℃ in Exp-Ⅰ and 17.5 ± 2.8 ℃ in Exp-Ⅱ, representing suboptimal thermal conditions. The results indicate dietary Trp concentration significantly affected the growth and survival of the fish. In particular, the lowest growth and survival were observed in fish fed the diet with the lowest concentration of Trp in both feeding trials. Additionally, the fish fed the Trp-deficient diet (0.39 g kg) exhibited lower levels of hematological parameters, immunity, antioxidant capacity and whole-body crude protein compared to Trp supplemented groups (2.33-14.46 g kg). In fish fed a Trp-deficient diet (0.39 g kg), expression of tight junction proteins was down-regulated, abnormal development of mucosal folds was observed, and intestinal inflammatory cytokines were upregulated compared to Trp supplemented groups (2.33-14.46 g kg). Fish fed Trp-supplemented diets showed significantly higher plasma levels of Trp, serotonin, melatonin and cortisol compared to those fed the Trp-deficient diet. The dietary Trp concentration required for fish growth was estimated to be 3.08 g kg (6.06 g kg of protein) in the juvenile stage (Exp-Ⅰ) and 2.17 g kg (4.27 g kg of protein) in the post-juvenile stage (Exp-Ⅱ), respectively, as determined by broken-line regression based on final body weight.
牙鲆（Paralichthys olivaceus）是韩国一种具有重要经济价值的鱼类。然而，在牙鲆的任何生长阶段，其对色氨酸（Trp）的具体膳食需求尚未确定。因此，本研究旨在确定低温条件下牙鲆幼鱼对膳食色氨酸的需求量。进行了两项连续的饲养试验，每项试验使用不同色氨酸浓度的饲料：试验一（0.39 - 14.46 g/kg）和试验二（0.93 - 6.96 g/kg）。牙鲆的初始平均体重分别为4.38 ± 0.03 g（试验一）和18.4 ± 0.1 g（试验二）。在试验一和试验二中，鱼被随机分配到18个水箱（120升）中，对应六个饲料组，每组三个重复（每个水箱30条鱼）。鱼分别喂食试验饲料13周（试验一）和8周（试验二）。试验期间的水温试验一为18.2 ± 2.4℃，试验二为17.5 ± 2.8℃，代表次优温度条件。结果表明，饲料色氨酸浓度显著影响鱼的生长和存活。特别是，在两项饲养试验中，喂食色氨酸浓度最低饲料的鱼生长和存活最差。此外，与补充色氨酸组（2.33 - 14.46 g/kg）相比，喂食色氨酸缺乏饲料（0.39 g/kg）的鱼血液学参数、免疫力、抗氧化能力和全身粗蛋白水平较低。在喂食色氨酸缺乏饲料（0.39 g/kg）的鱼中，与补充色氨酸组（2.33 - 14.46 g/kg）相比，紧密连接蛋白的表达下调，观察到黏膜褶皱发育异常，肠道炎性细胞因子上调。与喂食色氨酸缺乏饲料的鱼相比，喂食补充色氨酸饲料的鱼血浆中色氨酸、血清素、褪黑素和皮质醇水平显著更高。根据最终体重通过折线回归确定，幼鱼阶段（试验一）鱼生长所需的饲料色氨酸浓度估计为3.08 g/kg（蛋白质6.06 g/kg），幼鱼后期阶段（试验二）为2.17 g/kg（蛋白质4.27 g/kg）。
