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The article deals with a study which described infestation of the Ilova River in Croatia with Postodiplostomum (P.) cuticola. It references related research on P. cuticola, a digenean trematode infecting different fish species. The study also investigated the prevalence, mean abundance and mean intensity of all hosts examined. Presented are the most prevalent metacercariae of P. cuticola, namely, the Rutilus rutilus, Pseudorasbora parva and Leuciscus leuciscus, among others. A discussion on the research findings is also given.

During the winter of 2013 and 2016, several Croatian fish farms experienced mortalities in the fry of European sea bass, Dicentrarchus labrax. Affected fish showed abnormal swimming behaviour and reduced appetite, and death ensued several days after the onset of clinical signs of disease. Necropsy revealed pale liver, empty digestive tract, distended gall bladder, and hyperaemia and congestion of the meninges. Routine bacteriological examination tested negative, and virological examination ruled out nodavirus infection. Histological examination revealed multifocal necrosis and extensive inflammation in the brain with abundant cellular debris in the ventricles. Inflammatory cells displayed intra-cytoplasmic basophilic vacuoles leading to suspicion of Piscirickettsia salmonis infection. Fluorescent in situ hybridization using an oligonucleotide probe targeting Domain Bacterium applied to tissue sections tested positive. The pathogen was identified by 16S rRNA gene sequencing of brain material, and the sequence showed 99% similarity with P. salmonis. This result enabled the design of an oligonucleotide probe specifically targeting P. salmonis. In 2016, P. salmonis was successfully isolated on CHAB from the brain of an affected specimen and identified using 16S rRNA gene sequencing and MALDI-TOF. This study describes the first outbreak of disease caused by P. salmonis in sea bass in Croatia, while new diagnostic tools will enable further research on its epidemiology and pathogenicity., (© 2021 John Wiley & Sons Ltd.)

Common carp (Cyprinus carpio) is a very important fish species for warm-water aquaculture in Croatia. All Croatian carp farms are subjected to a surveillance programme for the presence of koi herpesvirus (KHV), causing a deadly disease called koi herpesvirus disease (KHVD). However, there is no surveillance for other viral pathogens of importance like carp edema virus (CEV), a causative agent of koi sleepy disease (KSD). During regular testing within the KHVD surveillance programme, we tested samples for CEV simultaneously. The screening indicated possible outbreaks of KHVD and KSD. During 2016, KHVD broke out in an isolated area and soon thereafter a KHV eradication programme was successfully performed. However, during 2018 and 2019, two additional mortality events occurred in lakes in the southern part of Croatia during the spring. Samples from both events tested positive for CEV. An epidemiological investigation confirmed the introduction of infected carps from an infected farm to one of the lakes. To prevent the spreading of CEV into open waters, it is of utmost importance to introduce CEV testing before fish movement or to perform regular testing of all carp farms in the country to determine CEV prevalence for the purpose of implementation of control measures., (© 2020 The Authors. Journal of Fish Diseases published by John Wiley & Sons Ltd.)

The Croatian part of the Danube River extends over 188 km and comprises 58 % of the country's overall area used for commercial freshwater fishing. To date, the heavy metal contamination of fish in the Croatian part of the Danube has not been studied. The main purpose of this study was to determine heavy metal levels in muscle tissue of sampled fish species and to analyze the measured values according to feeding habits of particular groups. Lead ranged from 0.015 μg(-1) dry weight in planktivorous to 0.039 μg(-1) dry weight in herbivorous fish, cadmium from 0.013 μg(-1) dry weight in herbivorous to 0.018 μg(-1) dry weight in piscivorous fish, mercury from 0.191 μg(-1) dry weight in omnivorous to 0.441 μg(-1) dry weight in planktivorous fish and arsenic from 0.018 μg(-1) dry weight in planktivorous to 0.039 μg(-1) dry weight in omnivorous fish. Among the analyzed metals in muscle tissue of sampled fish, only mercury exceeded the maximal level (0.5 mg kg(-1)) permitted according to the national and EU regulations determining maximum levels for certain contaminants in foodstuffs, indicating a hazard for consumers of fish from the Danube River.

Aquaculture is an important segment of Croatian fishing industry with long tradition of carp and rainbow trout farming as well as marine aquaculture represented by shellfish (flat oyster and mussels), sea bass and sea bream cultivation and Atlantic bluefin tuna fattening. The fish and shellfish diseases survey is regulated by "Decree on the measures of animal health protection against infectious and parasite diseases" issued yearly by Ministry of Agriculture. This report derives from systematic clinical, parasitological, pathoanatomical, histopathological, bacteriological and virological monitoring of cultivated fish and shellfish on larger part of production during last several years. Among pathological conditions recognised on our farms, some specific viruses, bacteria and parasites represent frequently established causative nosologic agents. The overview of the main diseases with economic impact to the cultivation will be discussed in this paper.

The objective of this study was to characterise porcine circovirus type 2 (PCV2) from pigs with naturally occurring postweaning multisystemic wasting syndrome (PMWS) in Croatia, and to determine the epizootiological, clinical and pathomorphological features of the disease. During a systematic health monitoring programme conducted in the period from January 2002 to June 2003, PMWS was suspected on eight different pig-producing farms in Croatia. The diagnosis of PMWS met all three key criteria: the presence of compatible clinical signs, the presence of the characteristic microscopic lymphoid lesions, and the detection of PCV2 within the lesions by polymerase chain reaction (PCR) and by in situ hybridisation (ISH). Moreover, PCV2 DNA from swine tissues was extracted and sequenced. The phylogenetic analysis of 4 Croatian PCV2 strains showed close relationship to PCV2 strains isolated in Slovenia, France, the Netherlands, the United Kingdom, China and Hungary. PCV2 was also demonstrated by electron microscopy in the lymph node of an affected animal. This is the first demonstration of PMWS in Croatia based on all scientifically accepted diagnostic criteria.

During the spring of 1996 and autumn of 1997 unusual mortality outbreaks among rainbow trout fry and yearlings occurred at two different trout farms, resulting in mortality of 20 and 10 per cent, respectively. Generally, the affected fish, swimming at the water surface, were reluctant to eat and were dark pigmented with visible haemorrhages around and within the oral cavity. Bacterial isolates from moribund fish from both cases were identified as Yersinia ruckeri by standard biochemical tests and API 20E. The isolated strains were found to be sensitive to tetracycline, chloramphenicol, co-trimoxazole, nalidixic acid, flumequine, enrofloxacin, carbenicillin and gentamicin. Microplate agglutination assay confirmed that both isolates belonged to serotype O1. The pathogenicity of the isolated bacteria was confirmed by challenge experiment. Titres of specific antibodies were determined in the sera of survivors. The titre was highest on the 21st day postchallenge and was detectable until the 81st day.

Marteiliosis is a disease of molluscs caused by Marteilia refringens in Europe and M. sydneyi in Australia. During routine examination of cultured mussels Mytilus galloprovinciallis in the northern Adriatic, the occurrence of Marteilia sp. was recorded with a prevalence of 5%. This parasite was not detected in flat oysters reared in the same area. The affiliation of the detected parasite in M. galloprovinciallis was confirmed by in situ hybridization using a M. refringens probe, specific at the genus level. DNA of these infected mussels originating from the same area will be used to clarify the taxonomic position of this species within the genus Marteilia using a molecular approach.