Morphological characterization of the digestive system and health status of the invasive shortfin molly Poecilia mexicana Steindachner, 1863, in Thailand

Abstract

The shortfin molly, Poecilia mexicana Steindachner, 1863, is an ovoviviparous fish. Unfortunately, the structural characteristics related to the digestive biology of this fish are still poorly known. In the current study, detailed characterization of the digestive system was conducted for P. mexicana from natural brackish water in Thailand, based on morpho-histological observation and gut content analysis. Forty fish were collected in February 2020 from a small canal at Samut Prakan province. They were then classified into two size groups for 2.00-4.00 and 4.01-6.00 cm in total length. Results showed that the morphology of the digestive tract is similar in the two groups; it was composed of the terminal mouth, the villiform teeth in both upper and lower jaws, pharyngeal teeth, short esophagus and very long intestine. The intestine coefficients of the two groups were 1.64 ± 0.37 and 2.23 ± 0.38, respectively, suggesting that P. mexicana is an omnivorous fish. The gut contained a few prey items in both groups, in which detritus and pieces of plants dominated followed by phytoplanktons, indicating that this fish is a detritus feeder in the small canal. Importantly, many histopathological alterations were recorded, especially necrotic acinar cells and melanomacrophage centers. Although this species is generally considered to be tolerant to environmental changes, these results suggest that environmental problems had caused several lesions (gill, liver and kidney) in P. mexicana. Overall, this study provides basic knowledge about feeding ecology of this poorly studied species, warranting further research.

Keywords

• digestive histology
• gut content analysis
• histopathology
• ovoviviparous fish