Background. Guanabara Bay is a species-rich estuary in the South-western Atlantic and its shores are among the most densely populated urban areas in the world. The biology of clupeiform fishes from Guanabara Bay is currently poorly known. The most extensively exploited species is a small pelagic Atlantic anchoveta or toothless anchovy, Cetengraulis edentulus (Cuvier, 1829). The significant knowledge gap concerning the local fish biodiversity hinders the development of the fisheries management tools for this significantly impacted body of water. Materials and methods. The population biology of Cetengraulis edentulus was analyzed based on samples taken from Guanabara Bay twice a month by an otter-trawl. Five sites were selected, representing the upper, middle, and lower estuary. They were sampled between 2005 and 2007, and a second phase was conducted between 2013 and 2015 at two of the original sites to evaluate the middle and lower estuary.  Furthermore, the relative abundance, spatial distribution, and the length–weight relation of the local Clupeiformes were also assessed. Results. A total of 6053 fish individuals collected represented 15 species and three families: Anchoa januaria; Anchoa lyolepis; Anchoa marinii; Anchoa tricolor; Brevoortia aurea; Cetengraulis edentulus; Chirocentrodon bleekerianus; Engraulis anchoita; Harengula clupeola; Odontognathus mucronatus; Opisthonema oglinum; Pellona harroweri; Sardinella brasiliensis. The most abundant was the family Engraulidae (7), followed by Clupeidae (4), and Pristigasteridae (3). While Cetengraulis edentulus was predominant during the first phase, a higher presence of Brevoortia aurea (Spix et Agassiz, 1829) characterized the second phase. Furthermore, C. edentulus was mainly restricted to the upper estuary, with no seasonal pattern. Estimated values for this species comprised growth (L∞ = 19.3 cm, k = 0.54 yr–1), mortality (Z = 1.62 yr–1, M = 1.32 yr–1 (T = 26.6°C), F = 0.3 yr–1, E = 0.19 yr–1), longevity (5.6 yr), survival (19.8% yr–1) and capture probability (L25 = 9.95 cm, L50 = 10.87 cm, L75 = 11.79 cm). Conclusion. The exploitation rates of Cetengraulis edentulus indicate that this species is underfished, although these results may be due to the fishing gear used herein, which may have underestimated fishing mortality rates. A high Clupeiformes richness was verified, corroborating other bay ichthyofauna components. In addition, the occurrence of monospecific peaks identified for other trophic groups was also observed for C. edentulus.

toothless anchovy, Atlantic anchoveta, Guanabara Bay, growth, mortality, exploitation