Abstract
The aim of the study was to investigate the composition of intestinal microflora of freshwater fish in Latvia. A total amount of 28 fish were collected from fishermen (n=20) and retail outlets (n=8), including roach Rutilus rutilus, n=15, crucian carp Carassius carassius, n=5, perch Perca fluvialitis, n=5, bream Blicca bjoerkna, n=3. Microbiological testing consisted of the detection of total viable count (TPC), Enterobacteriaceae and coliforms with subsequent identification with MALDI-TOF Biotyper. TPC, coliforms and Enterobacteriaceae counts ranged from 2.7±0.4 to 5.4±0.3, 2.4±1.5 to 3.7±0.7 and 2.00±1.2 to 3.7±2.5 log cfu/g in gut of wild crucian carp and retailed roach, wild perch and retailed roach, and crucian carp and bream, accordingly. The TPC, coliforms and Enterobacteriaceae counts were significantly higher in retailed fish than in wild fish gut samples (P≤0.05). Gut microbiota were represented by Proteobacteria (93.0%), Firmicutes (3.9%) and Ascomycota (3.1%). The most abundant families were Enterobacteriacea (50.8%) and Pseudomonadaceae (36.7%). Rahnella aquatilis, Serratia fonticola and Pantoe aagglomerans were the most abundant among Enterobacteriaceae while Pseudomonas extremorientalis and P. fragi among the Pseudomonadaceae. Results of the present study show that the gut of freshwater fish were mostly represented by Enterobacteriaceae and Pseudomonadaceae and the presence of fish bacterial pathogens must be considered.
Highlights
The digestive tract of fish is a habitat of heterogeneous microflora and is colonized by a high variety and number of microorganisms (Burr et al, 2005)
The total plate count (TPC), coliforms and Enterobacteriaceae counts were significantly higher in retailed fish gut than in wild fish gut samples (P≤0.05), while the significant differences between the bacterial counts of retailed fish were not identified (P≥0.05)
Enterobacteriaceae family was predominated in the gut of wild roach and crucian carp, while there were no differences between the abundance of Enterobacteriaceae and Pseudomonas in the gut of retailed roach, bream and perch
Summary
The digestive tract of fish is a habitat of heterogeneous microflora and is colonized by a high variety and number of microorganisms (Burr et al, 2005). The gut microbiota is important for digestion of food, protection of fish against the bacterial pathogens and development of immunological response. Composition of fish gut microbiota depends on various influencing factors, including fish species, age, nutritional, genetic factors and environmental conditions of habitat (Gómez and Balcázar, 2008; Floris et al, 2013). The normal indigenous microbiota act competitively and prevent the colonization of gut by pathogens, the different other groups of pathogenic microorganisms of fish, animal and human health significance can be found in gut (Austin, 2006). The identification and analysis of fish gut microbiota helps recognize the composition of fish microflora in different environments, and to tackle potentially pathogenic microorganisms affecting the fish health. Fish is an important food source and the studies on fish gut microbiota are important for an assessment of fish health and safety of fish for consumption as well (Holben et al, 2002)
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