Length-Weight Relationships of Sixteen Fish Species From the Upper Tietê Basin, Southeaster Brazil

This study investigated the length-weight relationship (LWR) of 16 fish species from the Upper Tietê Basin under the influence of the Atlantic Forest biome, aiming to provide updated morphometric data and contribute to the knowledge of Neotropical ichthyofauna. 2811 specimens were collected and distributed across five orders and 10 families. Standard length ranged from 0.8 to 24.5 cm, and weight from 0.01 to 34.19 g. The parameters a and b of equation W = a·L^b were estimated, revealing that most species exhibited allometric growth, with one isometric species (Astyanax lacustris), seven with negative allometry, and eight with positive allometry. The b values ranged from 2.579 (Imparfinis piperatus) to 3.651 (Phalloceros reisi), the latter being the only one outside the typical range of 2.5 < b < 3.5. The Bayesian analysis proposed by Froese indicated morphological deviations for Hyphessobrycon multifasciatus (α outside the expected range) and a lack of specific classification for Cambeva iheringi, Geophagus iporangensis, and Osteogaster aenea. An apparent scarcity of geographically delimited studies in the basin was evident, hindering broader comparisons. Only Phalloceros reisi presented compatible data, with mean, standard-length values similar to those reported in the literature. Also noteworthy is Pseudotocinclus tietensis, a threatened species that exhibited positive allometry (b = 3.2595), suggesting favorable environmental conditions for its growth in the studied basin. The results highlight the importance of regional morphometric studies as tools for monitoring and conserving ichthyofauna, especially for species whose morphometric characteristics had not yet been documented for the Upper Tietê Basin.