Environmental history of one of the largest freshwater neotropical fish (Zungaro jahu) from otolith isotopic analysis

The Manguruyu Zungaro jahu, endemic to the La Plata Basin, is one of the largest neotropical fish species whose life history is virtually unknown. The objectives of this study were to determine if Z. jahu is a large-scale migratory species and to describe habitat use throughout ontogeny using the otolith Sr isotope (Sr-87/Sr-86) ratio. Surface water samples were collected in 2020 at four sites representing the main water courses of the Great Pantanal in Brazil (upper Paraguay, Cuiaba, Sao Lourenco and Vermelho rivers). Eighteen fish individuals were collected from the Parana River (Argentina). New water Sr-87/Sr-86 data were incorporated into previously established statistical models to infer the fish habitat use through the otolith Sr-87/Sr-86 ratios. The water Sr-87/Sr-86 ratio of the upper Paraguay tributaries varied (0.7209 and 0.7229) and were the highest in the La Plata Basin. The dispersal area of Z. jahu was restricted to the surroundings of the confluence of the Parana and Paraguay rivers. Fish showed chemical signatures compatible with those of the middle Parana (88%), Paraguay-Pilcomayo-Bermejo (50%) and the lower/upper Parana (66%). The discriminant analysis based on otolith core indicated natal origins from the middle Parana (37%), upper Parana (32%), and Paraguay sub-basin (32%). The dispersal area of Z. jahu migrations could be restricted to the surroundings of the confluence of Parana and Paraguay, which highlights the need to review regional fishing regulations, especially between latitudes 30 degrees-34 degrees S.

Automated summary

This study aims to determine whether Manguruyu Zungaro jahu is a large-scale migratory species and describes its habitat use throughout ontogeny using otolith Sr isotope ratio. The results showed that the dispersal area of Z. jahu is restricted to the surroundings of the confluence of the Parana and Paraguay rivers. The fish exhibited chemical signatures compatible with those of the middle Parana, Paraguay-Pilcomayo-Bermejo, and the lower/upper Parana.