RESUMEN
Symbiotic bacteria within the gut microbiome of various organisms, including fish, provide the host with several functions that improve the immune system. Although the spleen plays an important role in the modulation of immune responses, the role of spleen microbiota in shaping the immune system is unclear. Our study aimed at understanding the relationship between fish health and microbiota composition in the intestine and spleen. Our model organism was the hybrid tilapia (Oreochromis aureus × Oreochromis niloticus). We sampled intestine and spleen from healthy and diseased adult tilapia and determined their microbiota composition by sequencing the 16S rRNA gene. Significant differences were found between the intestine and the spleen microbiota composition of healthy compared to diseased fish as well as between intestines and spleens of fish with the same health condition. The microbiota diversity of healthy fish compared to diseased fish was significantly different as well. In the intestine of healthy fish, Cetobacterium was the most abundant genus while Mycoplasma was the most abundant genus in the spleen. Vibrio was the most abundant genus in the intestine and spleen of diseased fish. Moreover, it seems that there is a co-infection interaction between Vibrio and Aeromonas, which was reflected in the spleen of diseased fish. While Vibrio, Aeromonas and Streptococcus were the probable pathogens in the diseased fish, the role of Mycoplasma as a pathogen of cultured hybrid tilapia remains uncertain. We conclude that the intestine and spleen microbiota composition is strongly related to the health condition of the fish.
RESUMEN
Intensive freshwater aquaculture in the Spring Valley, Israel, is implemented mainly in earthen fishponds and reservoirs that are stocked with a variety of edible fish species. Here we sampled six different healthy fish species from these intensive aquacultures. The fish were hybrid striped bass, European bass, red drum (all carnivores), hybrid tilapia, flathead grey mullet (both herbivores), and common carp (an omnivore). Significant differences were found among the intestinal microbiota of the six studied fish species. The microbiota composition diversity was strongly related to the trophic level of the fish, such that there was a significant difference between the carnivore and the herbivore species, while the omnivore species was not significantly different from either group. The most abundant genus in the majority of the fishes' intestinal microbiota was Cetobacterium. Furthermore, we found that beside Cetobacterium, a unique combination of taxa with relative abundance >10% characterized the intestine microbiota of each fish species: unclassified Mycoplasmataceae, Aeromonas, and Vibrio (hybrid striped bass); Turicibacter and Clostridiaceae 1 (European bass); Vibrio (red drum); ZOR0006-Firmicutes (hybrid tilapia); unclassified Mycoplasmataceae and unclassified Vibrionaceae (flathead grey mullet); and Aeromonas (common carp). We conclude that each fish species has a specific bacterial genera combination that characterizes it. Moreover, diet and the trophic level of the fish have a major influence on the gut microbiota of healthy fish that grow in intensive freshwater aquaculture.