The spatial and seasonal dynamics of shallow water fish assemblages and their relationship with physical-chemical variables were investigated on Guanabara Bay, one of the largest coastal bays in Brazil, southwestern Atlantic. Fishes were collected monthly between June 2016 and May 2018, in the shallow waters of six beaches distributed in four sectors along the major axis of the bay (adjacent and entrance - one site each, middle and inner - two sites each), using a beach seine net. A total of 79 fish species was recorded, mostly juveniles. Marine estuarine dependent, marine estuarine opportunist, solely estuarine and marine straggler were the most representative ecological guilds in the bay during the sampling period. Following the index of relative importance (IRI) categories, top dominant species (IRI ≥ 10%) within sector beaches were: the solely estuarine Atherinella brasiliensis from the inner to the entrance; marine estuarine dependent Eucinostomus argenteus in the middle; marine estuarine dependent Harengula clupeola and marine straggler Diplodus argenteus at the entrance, and marine stragglers Umbrina coroides, D. argenteus, and marine estuarine dependent Dactylopterus volitans in the adjacent sector beach. All analyses identified distinct fish assemblages that were distributed in two main areas: adjacent/entrance and middle/inner. Transparency and chlorophyll a were responsible for most of the spatial variability and played an important role in structuring fish assemblages. Water temperature was responsible for seasonal fluctuations indicating the distinct habitat use from different life cycle stages of fish species. This investigation suggests the importance of all sector beaches as nursery and growth areas due to the high representation of juvenile individuals.

在大西洋西南部巴西最大的沿海海湾之一瓜纳巴拉湾调查了浅水鱼类组合的空间和季节动态及其与物理化学变量的关系。2016 年 6 月至 2018 年 5 月期间，每月在沿着海湾主轴分布在四个部分的六个海滩的浅水区（相邻和入口 - 各一个，中部和内部 - 各两个），使用一个海滩围网。共记录了 79 种鱼类，主要是幼鱼。依赖海洋河口、海洋河口机会主义者、单独河口和海洋落后者是采样期间海湾最具代表性的生态行会。根据相对重要性指数 (IRI) 类别，部门海滩内的顶级优势物种 (IRI ≥ 10%) 是：Atherinella brasiliensis从内到入口；海洋河口依赖Eucinostomus argenteus在中间；入口处有依赖海洋河口的Harengula clupeola和海洋掉队者Diplodus argenteus，以及邻近扇区海滩的海洋掉队者Umbrina coroides、D. argenteus和依赖海洋河口的Dactylopterus volitans。所有分析都确定了分布在两个主要区域的不同鱼类组合：相邻/入口和中间/内部。透明度和叶绿素a负责大部分空间变异，并在构建鱼类组合中发挥重要作用。水温是季节性波动的原因，表明鱼类物种不同生命周期阶段的不同栖息地利用。这项调查表明，由于青少年个体的高代表性，所有部门的海滩作为育苗区和生长区的重要性。