Morphological study of the digestive tract of the cardinal tetra, Paracheirodon axelrodi (Characiformes: Characidae)

Abstract

The cardinal tetra Paracheirodon axelrodi is a species of the family Characidae of great interest as an ornamental fish. Many aspects of the biology of this species are still unknown. The present work presents a complete description of the different components of the digestive tract of P. axelrodi, analyzing its global anatomical arrangement, the adjacent glands (liver and pancreas) and the previously ignored pyloric caeca, using histological and histochemical techniques with light microscopy and scanning electron microscopy. Three levels of analysis were performed: macroscopic anatomy, histology of the gastrointestinal tract and scanning electron microscopy of mucosal surfaces. The intestinal coefficient (Ci) of P. axelrodi calculated here (0.94) is within the expected range for a carnivorous species. The anatomy of the alimentary and the resulting Ci is consistent with carnivorous diet in line with dietary studies in the wild in this species. The digestive tract, including adjacent glands (liver and pancreas), presented a relatively conserved general pattern within that described for other species of the family Characidae, especially at the histological level.

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

“…While the specific distribution of goblet cells between the anterior and posterior sections remains unclear, their presence in both areas suggests a dual function in lubrication, aiding the movement of fecal contents and providing protection against chemical substances in the intestinal lumen, including antigens, toxins, and digestive enzymes (Wilson & Castro, 2010). This distribution pattern aligns with observations in various species across different genera, where a higher abundance of goblet cells in the posterior region is often associated with the process of defecation (Cho et al., 2023; Faccioli et al., 2014; Germano et al., 2014; Matheus et al., 2021; Rincón et al., 2023). However, exceptions exist, such as in Leporinus species and farmed species, where a greater abundance of goblet cells was noted in the anterior intestine, potentially linked to neutralizing stomach acids (Albrecht et al., 2001; Bellinate et al., 2023).…”

“…Herein, the tetra fishes exhibited intestines with four main loops and pyloric caeca located in the anterior section after the pyloric stomach. Like observations in salmon species (Løkka et al, 2013) and cardinal tetra ( Rincón et al, 2023), the tetra fishes have deeply folded intestines.…”

“…Morphological traits are pivotal in understanding the trophic ecology of fish, with long intestinal length and pyloric caeca associated with herbivory, while short intestines suggest carnivorous feeding (Gerking, 1994;Karasov et al, 2011). This pattern holds for the studied species and other tetra fishes (Rincón et al, 2023). Pyloric caeca, absent in herbivores, are present in carnivores and omnivores, enhancing digestion and absorption surface area (Buddington & Diamond, 1987;Hossain & Dutta, 1996;Wilson & Castro, 2010).…”

“…However, our understanding of the diversity of teleost digestive systems remains limited due to the highly morphological and phylogenetic diversification (Albrecht et al., 2001; Dzhumaliyev, 1982; Fanta et al., 2001; Karasov et al., 2011). While histological relationships between diet and digestive tract have previously been documented, descriptive data, especially for small omnivorous Neotropical fishes, are still lacking (Alonso et al., 2015; Cardoso et al., 2015; Rincón et al., 2023). Teleosts exhibit morphological adaptations reflecting their varied diets, influencing the length of their intestines and nutrient acquisition efficiency (Ghilardi et al., 2021; Ribble & Smith, 1983; Wilson & Castro, 2010).…”