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Metacercariae of various species within the genus Holostephanus Szidat, 1936 (Trematoda: Digenea: Cyathocotylidae) occur in muscles of both farmed and wild fish, including common carp (Cyprinus carpio Linnaeus, 1758). The life cycle includes a snail as first intermediate host, fish as second intermediate host and birds or mammals as final hosts. We studied the zoonotic potential and the viability of Holostephanus metacercariae from common carp following exposure to various physical and chemical treatments. Muscle tissue samples of common carp specimens from a fish farm in the north-eastern part of Hungary were examined and metacercariae recovered. The zoonotic potential was evaluated experimentally by using small mammals as models (albino mice, n = 2; and Syrian hamsters, n = 4) infected per os with Holostephanus cysts. Parallelly, Metagonimus metacercariae were used as positive controls. We could not confirm the zoonotic potential of Holostephanus metacercariae as they did not survive in the mammalian intestine whereas Metagonimus metacercariae developed to the adult stage. We assessed the viability of metacercariae isolated from common carp specimens during exposure to different physical treatments (temperatures of -18°C, +20°C, +40°C and +60°C) and chemical agents (5% and 10% acetic acid and 10% sodium chloride (NaCl)). Metacercariae lost viability by freezing at -18°C (2 h), heating at 60°C (20 min), incubation in 5% and 10% acetic acid (5 min) and 10% NaCl (2 h). These methods served as models to investigate the effectiveness of food preparation techniques (such as cold and hot smoking, freezing, salting and pickling) on the survival of metacercariae.

Our relationship with common carp has a long history and tradition. Carp was considered luxury food in the middle and late Roman period. Later, fish ponds were constructed and maintained by Christian monasteries. Controlled semi-natural pond breeding and fry rearing of carp in Europe started in the 19th century. Today, common carp amounts to 4% of European aquaculture, and it is the favourite Christmas dish in Czech Republic, Slovakia and Poland, as well as in some regions of Austria, Germany and Hungary

There is an extensive range of helminthic parasites of fish, but only a moderate number of species are capable of producing foodborne diseases in humans. These diseases are either caused by an infection following ingestion of viable parasites, or by an allergic reaction against parasite antigens which occurs, so far, due to nematodes of the family Anisakidae. Anisakis simplex is the species most frequently associated with human disease, followed by Pseudoterranova decipiens (Adams, Murrell et al. 1997) and Contracaecum osculatum (Strom, Haarder et al. 2015). In fact, A. simplex is the second most predominant biological hazard, constituting 33% of the reported hazards in 2009 (Kleter, Prandini et al. 2009). Other fish helminths of zoonotic concern are cestodes and trematodes (especially Diphyllobothriids and episthorchioidea,respectively). They have received less attention despite of the reported human cases in Europe caused by these freshwater fish-bornezoonotic parasites Thus far, the available epidemiological data for farmed freshwater fishare scarce and necessary. For these main reasons in 2010, EFSA recommended studies to evaluate the effects of different farming practices on the prevalence of parasites in aquaculture (EFSA 2010). As a matter of fact, one of the conclusions of this report suggests that Atlantic salmon (AS), reared in floating cages and fed compound foodstuffs, are unlikely to contain live zoonotic parasites and therefore the risk of infection is negligible. However, a later survey detected anisakid and raphidascarid larvae (A. simplex and Hysterothylacium aduncum respectively) in AS runts (Mo, Gahr et al. 2014) which contrasts with a number of previous studies that confirmed no anisakids larvae in sea-farmed salmonids (Inoue, Oshima et al. 2000; Skov, Kania et al. 2009; EFSA 2010; Wootten, Yoon et al. 2010). These discrepancies were solved in a very recent study were 4,184 farmed AS, including runts, were sampled and examined in 2014/15. The fis

Oligochaetes living in the Mijares River close to the Sitjar reservoir, and polychaetes from the brackish and marine waters of a channel flowing into the Mediterranean Sea, both in the province of Castellón (Spain), were examined for the presence of actinosporea. An aurantiactinomyxon was isolated from 60 specimens of the oligochaete Branchiura sowerbyi collected from the river, but no actinospores were isolated from 160 polychaetes collected from the sea channel. The aurantiactinospores were detected by the cell-well plate method. The detected species are not identical with any of the aurantiactinomyxon forms hitherto described in the literature. This is the first report on the occurrence of an actinosporea in Spanish waters.