Aims: To identify bacterial pathogens of diseased NiIe tilapia Oreochromis niloticus and determine their virulence. Methods and Results: Sixteen bacterial isolates were recovered from diseased Nile tilapias (O. niloticus) reared in floating cages in Adolfo Lopez Mateos (ALM), Sanalona and Dique IV dams in Sinaloa, Mexico, from February to May 2009. The bacterial isolates were identified by phenotypic and molecular (rep-PCR and 16S rRNA sequencing) methods and were mostly isolated from the kidneys and the brain of tilapias. Bacterial cells and extracellular products (ECPs) of strains were characterized and used in experimental infections with sole Solea vulgaris and Mozambican tilapia Oreochromis mossambicus. The fish challenged with Aeromonas dhakensis sp. nov. comb nov, Pseudomonas mosselii and Microbacterium paraoxydans (3Á1 9 10 6 CFU g À 1) exhibited mortality between 40 and 100% starting at 6 h postinoculation. The ECPs displayed gelatinase, haemolytic and cytotoxic activity, causing the total destruction of the HeLa cell lines. Conclusions: Aeromonas dhakensis and Ps. mosselii were virulent to O. mossambicus, whereas Mic. paraoxydans displayed virulence to S. vulgaris. Significance and Impact of the Study: This the first time that Aeromonas dhakensis and Ps. mosselii are reported as pathogens to tilapia and Mic. paraoxydans was isolated from fish; then, these fish pathogens could be a threat to farmed Nile tilapia in Mexico. IntroductionSeveral species of tilapia are cultured commercially, but Nile tilapia (Oreochromis niloticus) is the predominant cultured species worldwide (FAO 2012). Strains of Aeromonas hydrophila, Edwarsiella tarda, Pseudomonas fluorescens and Streptococcus sp. have been reported to be virulent to farmed tilapia around the world (Al-Harbi and Uddin 2005; El-Sayed 2006). The heterogeneity of Aeromonas populations has also been observed in wild and farmed freshwater fish (Burr et al. 2012). Aeromonas species, although they have been misidentified many times, are well-known agents of fish disease, and two major groups are recognized. Aeromonas salmonicida sensu stricto causes fish furunculosis, particularly in salmonids, and mesophilic species (Aer. hydrophila and Aer. veronii) cause a similar assortment of diseases in fish, including motile aeromonas septicaemia (MAS), red-sore disease and ulcerative infections in carp, tilapia, perch, catfish, salmon, cod and goby (Joseph and Carnahan 1994).Moreover, the genus Pseudomonas includes metabolically versatile organisms utilizing a wide range of organic compounds. The bacteria belonging to the genus Pseudomonas are present in most natural waters and infect a Journal of Applied Microbiology 115, 654--662

No abstract

We estimated the impact on economic risk associated with the prevalence of white spot disease in shrimp farms in the State of Sinaloa, Mexico. Farms located in the jurisdiction of Local Aquaculture Health Boards (LAHBs) were used for preparing estimates during 2008–2010. Probability distributions of economic losses were calculated by comparing net revenues obtained under normal operations and operations affected by the disease, using Monte Carlo simulation, to estimate the impact of prevalence on losses in absolute and relative terms, probability of losing and loss per unit risk at USD$484.27/ha, 28.9%, 72.9% and 0.20. Regression analysis allowed estimating that, by an increases of 1% in prevalence, there were increases in the estimators of risk of USD$11.49/ha, 0.96%, 0.47% and 0.005. Correlation analysis showed that there were significant differences in prevalence among LAHBs districts and years. The higher prevalence coincided with the districts and years that exhibited higher risk. The source of water and use of nursery systems were the main differences in operating conditions among the districts, possibly determining to a large extent the differences in economic risk calculated for the districts. Sensitivity analysis indicated that prevalence was the main factor determining risk. A significant inverse relationship was found between shrimp prices and prevalence, as a consequence of speculative market conditions. The possibility of using this relationship for syndromic surveillance is considered. We propose the use of the estimators employed in this study for assessment of economic risk associated with white spot disease (and possibly others) and standardization of results for future research.

Tilapia is the most cultivated fish around the world. The fish’s environment can harbor bacteria, especially coliforms, which are not normal biota of fish. These microorganisms are contamination indicator groups (IGs) reflecting the possible presence of pathogens, which can compromise the safety of fishery products. The IGs prevalence was estimated in tilapia and water from 29 aquaculture farms. Total and fecal coliforms (TC, FC), mesophilic aerobic bacteria (MAB), S. aureus, E. coli, Salmonella sp., and Streptococcus sp., were investigated. In tilapia, TC and FC were detected in 64% and 48% of the samples, ranging from 4.0 x 101 to 9.8 x 105, and from 1.0 x 101 to 6.4 x 103 CFU/g, respectively; MAB were detected in 90% of the samples. In water, TC and FC were detected in 57% and 35% of the samples, oscillating from 1.0 x 101 to 2.28 x104, and from 1.0 x 101 to 1.2 x 103 CFU/mL, respectively. MAB were detected in 89% of the water samples. Mostly E. coli and Enterobacter agglomerans were detected. Generally, IGs concentrations meet the Mexican regulations; however, the tilapia’s microbiological quality must be continuously monitored.

White spot disease is one of the most serious problems in the shrimp‐farming industry in Mexico. An assessment of risk of an outbreak of the disease could be useful for farmers making decisions concerning early harvest to minimize economic losses. A group of researchers identified the most important risk factors, classified in four broad categories: management variables at the regional level, environmental variables at the regional level, management variables at the farm and population variables at the farm. For each variable, categories were defined and a risk score assigned. To validate these scores, a survey was carried out with 65 stakeholders. A semi‐quantitative risk assessment model was proposed and implemented as a questionnaire containing 21 risk variables with weighted scores. The most important risk factors were the period of fallowing within farm's region and health quality of larvae. Also important were estimated level of viral load and virus detection in wild hosts in the surrounding area, pond water temperature, length of fallowing period of pond, vector control at water intake and stocking density. The overall estimated risk was calculated as the sum of all scores with a further adjustment, according to maximum and minimum total scores. Three risk levels for white spot disease outbreak at ponds are based on estimated risk: low (≤0.2), moderate (0.2–0.4) and high (≥0.4).