Abstract The croaker Cilus gilberti is an important coastal food fish in Chile and Peru, and is being considered as a target marine species for diversification of Chilean aquaculture. In order to optimize culture, responses to density and potential environmental rearing conditions must be examined. Stocking density (SD) is an important factor for cultivation-related economic viability, because inappropriate SD is frequently associated with an increase of size heterogeneity, modification of social interactions and reduction of flesh quality. In addition, drastic decreases in dissolved oxygen are one of the major recurrent environmental stress factors in the area of choice for C. gilberti farming in the north of Chile, thus studies on responses to hypoxia and their associations with SD are required. Therefore, in this study, C. gilberti juveniles prior to stocking into grow-out pens were maintained for 120 days at three different stocking densities: 15 kg/m3 (LSD), 25 kg/m3 (MSD) and 35 kg/m3 (HSD), and then exposed to an acute hypoxia event. Biometric parameters, flesh quality, blood and liver biochemical parameters, and molecular markers of growth performance and stress responses were analyzed. Surprisingly, the highest body weight gain occurred in fish held at the highest density. In terms of growth-related genes, levels of growth hormone mRNA were not different between stocking densities, but liver insulin-like growth factor 1 (IGF-1) mRNA levels increased with SD and were the highest in the HSD group. There were no differences in flesh proximate composition. Similarly, glucose, lactate and HSP70 levels measured to assess chronic stress were not different among densities. There was a notable increase in lactate levels of fish in the HSD group in response to acute hypoxia, which suggests a greater reliance on anaerobic glycolysis by this group. In conclusion, results suggest that C. gilberti juveniles tolerate high stocking densities (at least 35 kg/m3) without generating chronic stress or decreasing their capacity to respond to acute hypoxia; and high SD would be preferable due to better growth. Although present results are promising, further research is needed to continue with the standardization of the SD that will allow the best productive yield of this new fish species for Chilean aquaculture.

中文翻译：

---

不同密度放养的智利黄鱼（Cilus gilberti）的生长性能、缺氧生理反应和肉质

摘要 黄花鱼是智利和秘鲁重要的沿海食用鱼，被认为是智利水产养殖多样化的目标海洋物种。为了优化养殖，必须检查对密度和潜在环境饲养条件的反应。放养密度 (SD) 是养殖相关经济可行性的重要因素，因为不适当的 SD 通常与规格异质性的增加、社会互动的改变和肉质的降低有关。此外，溶解氧的急剧减少是智利北部 C. gilberti 养殖首选地区的主要反复出现的环境压力因素之一，因此需要研究对缺氧的反应及其与 SD 的关联。因此，在本研究中，C. gilberti 幼鱼在放养到养成栏之前以三种不同的放养密度饲养 120 天：15 kg/m3 (LSD)、25 kg/m3 (MSD) 和 35 kg/m3 (HSD)，然后暴露于急性缺氧事件。分析了生物特征参数、肉质、血液和肝脏生化参数以及生长性能和应激反应的分子标记。令人惊讶的是，最高的体重增加发生在最高密度的鱼身上。在生长相关基因方面，生长激素 mRNA 水平在放养密度之间没有差异，但肝脏胰岛素样生长因子 1 (IGF-1) mRNA 水平随 SD 增加，并且在 HSD 组中最高。肉体近端成分没有差异。同样，葡萄糖，用于评估慢性压力的乳酸和 HSP70 水平在密度之间没有差异。响应于急性缺氧，HSD 组鱼的乳酸水平显着增加，这表明该组更依赖无氧糖酵解。总之，结果表明 C. gilberti 幼鱼可以耐受高放养密度（至少 35 kg/m3），而不会产生慢性压力或降低它们对急性缺氧的反应能力；由于更好的增长，高 SD 将是可取的。虽然目前的结果是有希望的，但需要进一步研究以继续标准化 SD，这将使智利水产养殖的这种新鱼种的产量最高。这表明该组更依赖于无氧糖酵解。总之，结果表明 C. gilberti 幼鱼可以耐受高放养密度（至少 35 kg/m3），而不会产生慢性压力或降低它们对急性缺氧的反应能力；由于更好的增长，高 SD 将是可取的。虽然目前的结果是有希望的，但需要进一步研究以继续标准化 SD，这将使智利水产养殖的这种新鱼种的产量最高。这表明该组更依赖于无氧糖酵解。总之，结果表明 C. gilberti 幼鱼可以耐受高放养密度（至少 35 kg/m3），而不会产生慢性压力或降低它们对急性缺氧的反应能力；由于更好的增长，高 SD 将是可取的。虽然目前的结果是有希望的，但需要进一步研究以继续标准化 SD，这将使智利水产养殖的这种新鱼种的产量最高。