Due to their pathogenic potential, identifying Vibrio species from recirculating aquaculture systems (RAS) for Pacific white shrimp (Litopenaeus vannamei) is of great importance to determine the risk for animal's as well as for the consumer's health. The present study compared identification results for a total of 93 Vibrio isolates, including type strains and isolates from shrimp aquaculture. Results from biochemical identifications, 16S rRNA sequencing, sequencing of the uridylate kinase encoding gene pyrH and analysis of the protein spectra assessed by MALDI‐TOF MS were compared. The results achieved by these different methods were highly divergent for many of the analysed isolates and for several Vibrio spp difficulties in reliably identifying occurred. These difficulties mainly resulted from missing entries in digital databases, a low number of comparable isolates analysed so far, and high interspecific similarities of biochemical traits and nucleotide sequences between the closely related Vibrio species. Due to the presented data, it can be concluded that for identifying Vibrio spp. from samples in routine diagnostics, it is recommended to use MALDI‐TOF MS analysis for a quick and reliable identification of pathogenic Vibrio sp. Nevertheless, editing the database, containing the main spectra of Vibrio is recommended to achieve reliable identification results.

Natural swimming pools (NSP) have become more popular in the past 20 years, both for private and public use, but their hygienic status remains a matter of discussion. Elimination rates in NSP are well defined for Escherichia coli, enterococci and Pseudomonas but a lack of knowledge exists regarding elimination rates in NSP concerning the parasitic protozoans Giardia and Cryptosporidium. First studies indicate that in-situ zooplankton filtration proved to reduce these protozoans efficiently: the in-situ elimination of Cryptosporidium is dependent on the population of zooplankton. In the 50% percentile the elimination rate is four times faster than in the chlorinated pool. The ex-situ elimination of Cryptosporidium in an NSP is approximately 10% faster than in a chlorinated pool. In ex-situ treatment of NSP the elimination rate reached 2 log-steps versus 1 log-step in chlorinated pools. For the further development of NSP for the best possible hygiene and health status some elementary questions, stated in this paper, will have to be solved in the next years or decades. This work describes the in-situ (water treatment inside the pool) and ex-situ water treatment (water treatment via external water treatment plants) of NSP, and the influence of zooplankton in existing NSP on the elimination rate of Cryptosporidium and Giardia.

Pacific white shrimp (Litopenaeus vannamei) are one of the most frequently cultivated shrimp species worldwide (Ezquerra Brauer, Salazar Leyva, Bringas Alvarado, & Rouzaud Sández, 2003). Their native habitat is the eastern Pacific coast of South America with an average water temperature of above 20°C and a salinity of 34-37‰. In aquaculture, these shrimps are produced in extensive pond culture at water temperatures between 26-32°C in large quantities, mostly in South America and Asia (Bundesverband Aquakultur Garnele, 2018; FAO). By developing land-based recirculating aquaculture systems (RAS), the production of L. vannamei has become

When tropical shrimps are kept in recirculating aquaculture systems (RAS), one of the limiting factors is the maintenance of a sufficient water quality, and therefore, often disinfectants like peracetic acid (PAA) are added to the water either as prophylactic or treatment measure. In this study, PAA in concentrations of 0.1 mg/L, 1 mg/L and 10 mg/L was applied continuously for 56 days to small‐scale seawater RAS stocked with Litopenaeus vannamei. Treatment with 0.1 mg/L did not result in a reduction in the total bacterial amount and therefore was not effective. A concentration of 10 mg/L led to significant changes in the chemical water parameters already after 2 days and was therefore not recommendable. A concentration of 1 mg/L led to increased levels of ammonia and nitrite within 2 days and to a significant increase in the bacterial amount in the water, most probably due to an enhanced growth of heterotrophic bacteria. The microflora showed significant fluctuations, and there were indications that the welfare of the shrimps was affected. Using 1 mg PAA/L for prophylactic use is therefore also not recommendable but might be an alternative option for short‐term treatment in cases of disease outbreaks.

By keeping Pacific white shrimp (Litopenaeus vannamei) independent from natural sea water on inland farms in recirculating aquaculture systems (RAS), the production of these animals has become possible in northern European countries. A reduced consumption of water, a low environmental impact and the possibility of high stocking densities and therefore high productivity are the primary advantages of keeping shrimp in RAS. Challenging are the maintenance of high water temperatures and appropriate salinities. Nevertheless, the costs for artificial sea salt can be reduced, as Pacific white shrimp are very tolerant against low and moderate salinity levels and RAS can be operated under brackish water conditions at 10-13‰ salin