Mugil liza is one of the most important fishery resources in west margin of Southwestern Atlantic. Its northern population (northward of 23°40’S) is distributed along the Brazilian coast and, including the Guanabara Bay (GB, 22°50’S, 43°10’W). This study aimed to evaluate the ring formation in the sagitta to estimate the fish age and growth. Based on monthly samplings (2011–2013), 815 individuals were caught (285–815 mm TL), and a subsample of 299 otoliths were analyzed. The otoliths were embedded, cross-sectioned and read in terms of “annual” rings (macrostructural analysis). Then, they were analyzed in terms of daily rings (microstructural analysis) and the deposition of calcium carbonate (ultrastructural analysis). The comparison among the three methods revealed that five macro rings are formed in the first year. Ulterior to this diagnosis, back-calculation and growth models were simulated and tested to describe the growth in the first year and the general growth pattern. The ages varied from 0.63- up to 5 years-old, with a high variability of total lengths by ages. The von Bertalanffy growth model based on back-calculated lengths of Dahl-Lea best described the growth pattern. Mugil liza at GB presented sexual dimorphism in terms of growth, females being longer and older, and it was revealed a fast growth pattern. These findings reinforce the identity of a probable stock of M. liza at GB and change drastically the current knowledge their age and growth. The regulatory marks for the species must be reviewed, at least for GB. The current results evidence the need of current assessment and monitoring of fisheries resources, identifying the patterns of population groups.

穆吉尔丽莎是西南大西洋西缘最重要的渔业资源之一。其北部人口（23°40'S 以北）分布在巴西海岸，包括瓜纳巴拉湾（GB，22°50'S，43°10'W）。本研究旨在评估箭矢环的形成，以估计鱼的年龄和生长。根据月度采样（2011-2013），捕获了 815 个人（285-815 毫米 TL），并分析了 299 个耳石的子样本。耳石被嵌入，横截面并根据“年轮”（宏观结构分析）读取。然后，根据日轮（显微结构分析）和碳酸钙的沉积（超结构分析）对它们进行分析。三种方法的比较表明，第一年形成了五个宏环。除了这个诊断，模拟和测试了反算和增长模型，以描述第一年的增长和总体增长模式。年龄从 0.63 岁到 5 岁不等，总长度随年龄变化很大。基于反向计算的 Dahl-Lea 长度的 von Bertalanffy 生长模型最好地描述了生长模式。GB 的Mugil Liza在生长方面表现出性别二态性，雌性更长更老，并且显示出快速生长模式。这些发现加强了对英国可能存在的M. liza种群的身份，并彻底改变了目前对其年龄和生长的了解。必须审查该物种的监管标志，至少对于 GB。目前的结果证明需要对渔业资源进行当前评估和监测，确定种群模式。