Linking anatomical and histological traits of the digestive tract to resource consumption and assimilation of omnivorous tetra fishes

This study explores the interplay between digestive tract traits, food intake, and assimilation in omnivorous tetra fishes (Psalidodon bifasciatus, P. aff. gymnodontus, and Bryconamericus ikaa) from the Iguaçu River basin, an ecologically significant region known for high endemism. We hypothesize that variations in digestive tracts across species would associate with differences in diet, isotopic composition in fish tissues, and overall diet assimilation. To test this, we employed stereoscopic and light microscopy to characterize the gross anatomy, histomorphology, and histochemistry of fish digestive tracts. Additionally, the study used stomach content and stable isotope analyses to trace fish diets. While these tetra fishes shared histological structures, disparities were noted in anatomical digestive traits and diet preferences. The smallest species, B. ikaa, with a shorter intestine, had fewer pyloric caeca and primarily consumed animal-based diets. Conversely, P. bifasciatus and P...., Model species and sampling
We studied three sympatric omnivorous tetra fish from two headwater streams in the lower Iguacu River basin: Psalidodon bifasciatus (Garavello & Sampaio 2010), Psalidodon aff. gymnodontus Eigenmann 1911, and Bryconamericus ikaa Casciotta, Almirón & Azpelicueta 2004. We sampled the fishes in July and December 2017 using electrofishing with three passes of 40 minutes. First, we anesthetized the specimens in eugenol and measured the standard length and weight. We then visually inspected the presence of mature gonads of all sampled fishes and selected adult specimens of each species for further analysis. For the histological analysis, during each sampling period, we selected five individuals of each species from each stream. We dissected their digestive tracts with a longitudinal incision along the ventral region. Then, we fixed the digestive tract in ALFAC (alcohol 80%, 85 mL; formaldehyde PA, 10 mL; and acetic acid PA, 5 mL; Caputo et al., 2011) and cons..., , # Linking anatomical and histological traits of the digestive tract to resource consumption and assimilation of omnivorous tetra fishes

[https://doi.org/10.5061/dryad.x95x69ps2](https://doi.org/10.5061/dryad.x95x69ps2)

We have submitted our raw data (**Gross_anatomy_data.exe; Histological_data.exe; Stable_isotopes_data.exe; and Stomach_content_data.exe**) and R script (**Neves_statistical_analysis.R**).

## Description of the data and file structure

The data is organized in the following spreadsheets:

**Gross_anatomy.xlsx**: contains the standardized size (mm) of the species, intestinal length (mm), intestinal coefficient and number of pyloric caeca.

* *ID*: specimen identification number
* *Species*: code for species name (Bik: *Bryconamericus ikaa*;  Pbi: *Psalidodon bifasciatus*; Pgy: *Psalidodon aff.* gymnodontus)
* *Stream*: stream where the individual was collected (S1 or S2)
* *Standart_length*: standard length of the individual (mm)
* *Intestine_length*: intestine length of...