1 Aquaculture Laboratory, National Institute of Marine Sciences and Technologies; 28, Rue 2 mars 1934 Salammbo 2025, Tunis, Tunisia.
Animal. 2013 Nov;7(11):1865-74. doi: 10.1017/S1751731113001493. Epub 2013 Aug 6.
The growth dispersion of farmed fish is a subject of increasing interest and one of the most important factors in stocking density. On a duration of 60 days, the effect of stocking density on the growth, coefficient of variation and inter-individual variation of feed intake (CVFI) of juvenile Nile tilapia Oreochromis niloticus L. (14.9 ± 1.2 g) were studied in an experimental tank-based flow-through system. Groups of fish were stocked at four stocking densities: 200, 400, 600 and 800 fish/m3, corresponding to a density of ∼3, 6, 9 and 12 kg/m3 and referred to as D1, D2, D3 and D4, respectively. Each treatment was applied to triplicate groups in a completely randomized design. No treatment-related mortality was observed. The fish densities increased throughout the experiment from 3 to 23.5, 6 to 43.6, 9 to 56.6 and 12 to 69 kg/m3. Results show that mass gain and specific growth rate (SGR, %M/day) were negatively correlated with increased stocking density. Groups of the D1 treatment reached a mean final body mass (FBM) of 119.3 g v. 88.9 g for the D4 groups. Feed conversion ratios (FCRs) were 1.38, 1.54, 1.62 and 1.91 at D1, D2, D3 and D4 treatments, respectively. Growth heterogeneity, expressed by the inter-individual variations of fish mass (CVM), was significantly affected by time (P < 0.001), stocking density (P < 0.001) and their interaction (P < 0.05). The difference in CVM was particularly conspicuous towards the end of the experiment and was positively correlated with stocking density. Similarly, radiographic study shows that CVFI was also found to be significantly greater for groups reared at high stocking densities (D3 and D4) than the other treatments (D1 and D2). These differences in both CVM and CVFI related to the stocking density need to be taken into account by husbandry practices to assure the production of more homogeneous fish size. A simple economic analysis indicates a parabolic relationship between profit and density with optimal final density at the peak of the curve. Given reasonable assumptions about production costs, the optimal final density (D opt) is 73.7 kg/m3. A sensitivity analysis shows that changes in the fixed cost have no effects on the optimal final density. However, small change in variable costs, such as feed and juvenile costs, may have substantial effect on the optimal density.
养殖鱼类的生长离散度是一个日益受到关注的课题，也是放养密度最重要的因素之一。在一个为期 60 天的实验中，研究了放养密度对幼尼罗罗非鱼（Oreochromis niloticus L.）（14.9±1.2g）生长、变异系数（CV）和个体间饲料摄入量变异系数（CVFI）的影响。在一个基于实验水箱的流动系统中，将鱼分组放养在四个放养密度下：200、400、600 和 800 尾/立方米，分别对应于约 3、6、9 和 12kg/m3，分别称为 D1、D2、D3 和 D4。每个处理应用于完全随机设计的三组重复。未观察到与处理相关的死亡率。在整个实验过程中，鱼的密度从 3 增加到 23.5、6 增加到 43.6、9 增加到 56.6 和 12 增加到 69kg/m3。结果表明，体重增加和特定生长率（SGR，%M/天）与放养密度的增加呈负相关。D1 处理组的平均最终体重（FBM）达到 119.3g，而 D4 组为 88.9g。饲料转化率（FCR）分别为 1.38、1.54、1.62 和 1.91 在 D1、D2、D3 和 D4 处理中。生长异质性，用鱼体质量的个体间变异（CVM）表示，受时间（P<0.001）、放养密度（P<0.001）及其相互作用（P<0.05）的显著影响。CVM 的差异在实验结束时尤为明显，与放养密度呈正相关。同样，射线照相研究表明，在高放养密度（D3 和 D4）下饲养的鱼的 CVFI 也明显大于其他处理（D1 和 D2）。CVM 和 CVFI 与放养密度的这种差异需要在养殖实践中加以考虑，以确保生产出更均匀的鱼体大小。简单的经济分析表明，利润与密度之间存在抛物线关系，曲线峰值处的最终密度最佳。考虑到生产成本的合理假设，最佳最终密度（Dopt）为 73.7kg/m3。敏感性分析表明，固定成本的变化对最佳最终密度没有影响。然而，饲料和幼鱼成本等可变成本的微小变化可能对最佳密度有重大影响。
