Robert Konecny

Parasite fauna of farmed Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) in Uganda

An intensive parasite survey was conducted in 2008 to better understand the parasite fauna occurrence, distribution and diversity in the commercial aquaculture fish species in Uganda. A total of 265 fish collected from hatcheries and grow-out systems were examined for parasites using routine parasitological techniques. The survey yielded 17 parasite species: 11 from Oreochromis niloticus and ten from Clarias gariepinus. Four parasites—Amirthalingamia macracantha, Monobothrioides sp., Zoogonoides sp. and a member of the family Amphilinidae—were recorded for the first time in the country. The parasite diversity was similar between hosts; however, O. niloticus was dominated by free-living stage-transmitted parasites in lower numbers, whereas both trophically and free-living stage-transmitted parasites were equally represented in C. gariepinus in relatively high intensities. The patterns in parasite numbers and composition in the two hosts reflect differences in fish habitat use and diet. A shift in parasite composition from monoxenous species-dominated communities in small-sized fish to heteroxenous in large fishes was recorded in both hosts. This was linked to ontogenetic feeding changes and prolonged exposure to parasites. Polyculture systems showed no effect on parasite intensity and composition. The gills were highly parasitized, mainly by protozoans and monogeneans. Generally, the occurrence and diversity of parasites in these fish species highlight the likelihood of disease outbreak in the proposed intensive aquaculture systems. This calls for raising awareness in fish health management among potential farmers, service providers and researchers.

Dynamics and predicted decline of Anguillicola crassus infection in European eels, Anguilla anguilla, in Neusiedler See, Austria

The eel population in Neusiedler See has been maintained by regular massive stocking since 1958. After the establishment of the National Park Neusiedler See-Seewinkel in 1993, eel stocking was prohibited and the population, together with the specific parasites of eels, was predicted to decline to extinction within 10 years. This investigation was undertaken to document the decline and extinction of the Anguillicola crassus population in eels. From 1994 to 2001, 720 eels were collected from two sites in the lake. Prevalence and abundance of A. crassus were lower in spring than in summer and autumn and larger eels harboured more parasites than smaller ones. Neither year of study nor sampling site were correlated with parasite infection levels. No significant trend in the population parameters of A. crassus was detected over the 8 years of the survey. This suggested that there had been no significant decline in the eel population. This suggestion was confirmed by investigations of the fishery, which also found evidence of regular illegal stocking. The stability of the A. crassus population over the past decade seems to reflect the lack of change in eel population density. No mass mortalities of eels occurred over the period despite the many similarities between Neusiedler See and Lake Balaton in Hungary. Differences in eel size, eel diet and the lack of large-scale insecticide use are discussed as possible explanations for the absence of eel mass mortalities in Neusiedler See.

Infection dynamics of Cichlidogyrus tilapiae and C. sclerosus (Monogenea, Ancyrocephalinae) in Nile tilapia ( Oreochromis niloticus L.) from Uganda

The infection dynamics of the gill monogeneans Cichlidogyrus tilapiae and C. sclerosus on Oreochromis niloticus with respect to habitat type (reservoir, stream, ponds and cages), host sex, size and seasons was determined between January and November 2008. During the study period, 45.2% of the 650 fish examined were infected with Cichlidogyrus spp. The infected hosts harboured an average of 8.6 ± 3.4 parasites/fish. Across habitat types, the proportion of infected fish was not statistically different. In contrast, the number of parasites recorded on infected fish from different habitat types differed significantly. The highest parasite number was recorded in reservoir-dwelling fish and lowest in stream-dwelling hosts. Concerning sex, more female O. niloticus were infected and harboured a high number of parasites than male and sexually undifferentiated fish. A weak negative relationship was found between rainfall and monthly parasite infections. However, a higher number of parasites and proportion of infected hosts were found during dry than in wet seasons, except in ponds. Results of this study show that differential exposure due to changes in fish behaviour associated with habitat modification and sex may account for the infection difference across the sampled sites. Meanwhile, rainfall and the associated hydrological events are important factors regulating monogenean infections in tropical aquatic environments. The continuous presence of Cichlidogyrus spp. in fish provides evidence of possible parasite outbreaks, indicating the application of biosecurity measures as crucial for the success of intensive fish farming.

Parasites of Apollonia melanostoma (Pallas 1814) and Neogobius kessleri (Guenther 1861) (Osteichthyes, Gobiidae) from the Danube River in Austria.

Two invasive fish species, the round goby Apollonia melanostoma syn. Neogobius melanostomus (Pallas 1814) and the bighead goby Neogobius kessleri (Günther, 1861), have established a firm population in Austrian waters during the past 15 years. As there have been no records of the parasite fauna from these populations, a total of 79 specimens of A. melanostoma and 12 specimens of N. kessleri were examined for parasites between May and October 2007 from three different sampling sites from the Danube River in Austria. In total 12 parasite taxa were recovered. The protozoans Trichodina sp. and Ichthyophthirius multifiliis from the gills and skin; two crustacean species, Paraergasilus brevidigitus and Ergasilus sieboldi, from the gills; and the two monogeneans Gyrodactylus sp. and Dactylogyrus sp., from the skin and gills respectively, all occurred at low prevalence and intensities. Furthermore, cystacanths of the acanthocephalan Acanthocephalus lucii were found in the body cavity. Metacercariae of the digeneans Diplostomum sp. and Tylodelphys clavata were found in the lens of the eye and the vitreous humour, respectively. Adults of two digeneans, Nicolla skrjabini and Bunodera nodulosa, were found in the intestine. In addition, during this survey metacercariae of the Holarctic digenean Bucephalus polymorphus, encysted in the skin and fins, with prevalence up to 78%, were recorded for the first time in Austria.

Helminth communities of the barbel Barbus barbus from large river systems in Austria

The composition and diversity of the total and intestinal component endohelminth communities were determined in the cyprinid barbel from three study areas in two large river systems in Austria. Two sample sites in the Danube and one site in the River Drau are the only free flowing stretches of these rivers in Austria. Nine helminth species were identified, with the acanthocephalan Pomphorhynchus laevis being dominant in the Danube, with up to 100% prevalence. In the Drau, where the dominant species was the cestode Bathybothrium rectangulum, species diversity was higher than in the Danube.

Infection patterns of Nile tilapia (Oreochromis niloticus L.) by two helminth species with contrasting life styles

The larval stages of Bolbophorus sp. (digenean) and Amirthalingamia macracantha (cestode) are frequently reported in Oreochromis niloticus in Uganda. Little, however, is known about their infection patterns. This study examined the influence of habitat type, host size, and sex and weather patterns on the parasite populations in Uganda. A total of 650 fish were collected between January and November 2008 from a reservoir, cages, fishponds and a stream. The prevalence and intensity of A. macracantha and the prevalence of Bolbophorus sp. differed across the water bodies reflecting the effect of habitat characteristics on parasite transmission. Host sex did not significantly influence the infection patterns, although female fish were slightly more parasitized than male and sexually undifferentiated individuals. The fish size was positively correlated with helminth infections demonstrating accumulation and prolonged exposure of larger (older) fish to the parasites. The metacercariae population did not vary significantly across months, while monthly A. macracantha infection fluctuated markedly. With regard to rain seasons, higher prevalence and intensity of A. macracantha were recorded in wet season. For Bolbophorus sp., only the prevalence varied with seasons, with higher prevalence recorded in the dry season than in wet season. Generally, Bolbophorus sp. responded weakly to changes in water body, host sex and size and weather patterns. Rainfall appears to be an essential cue for coracidia hatching.

Bucephalus polymorphus Baer, 1827 – a new fish parasite in Austria?

ZusammenfassungIm Rahmen parasitologischer Untersuchungen an der jüngst nach Österreich eingewanderten Fischart Schwarzmundgrundel Apollonia melanostoma (Pallas, 1814) von 3 Standorten an der Donau im Jahr 2007 wurde der digene Trematode Bucephalus polymorphus Baer, 1827 zum ersten Mal in Österreich nachgewiesen. Enzystierte Metazerkarien des Wurmes wurden auf den Flossen, der Haut und den Kiemen der Fische gefunden. Das Vorkommen des Parasiten ist an das der Dreikantmuschel Dreissena polymorpha (Pallas, 1771) gebunden, da sie als ausschließlicher erster Zwischenwirt fungiert. Sie ist ebenfalls in Österreich neu eingewandert, jedoch schon ca. 1870. Ob der Parasit erst mit den Grundeln oder schon zuvor nach Österreich gekommen ist, wird sich wohl nicht mehr mit Sicherheit klären lassen, doch sollten die Fragen ob eine stabile Etablierung des Parasiten in Österreich möglich sein wird, und welche Auswirkungen diese neuen Parasitenart auf die einheimische Fischfauna haben wird, Gegenstand von zukünftigen Untersuchungen sein.SummaryDuring parasitological studies of the invasive round goby fish species Apollonia melanostoma (Pallas, 1814) from the Danube River in 2007 the digenean Bucephalus polymorphus Baer, 1827 was detected for the first time in Austria. Encysted metacercariae of the parasite were found on the fins, skin and gills of the fish. The occurrence of the parasite is strictly dependant on the zebra mussel Dreissena polymorpha (Pallas, 1771), which acts as the obligatory first intermediate host in its life cycle. The mussel has also invaded Austrian waters, but has appeared in 1870 already. It will not be possible to establish whether the parasite was introduced to Austria with the gobies, or has arrived earlier, but it should be the subject of future investigations to ascertain whether the parasite will be able to establish a firm population in Austria, and whether this introduction puts additional pressure on the native fish populations.

The occurrence of Caryophyllaeus laticeps in the nase Chondrostoma nasus from Austrian rivers: possible anthropogenic factors.

Between April 2003 and November 2006 a total of 198 nase Chondrostoma nasus (L.) were examined for parasites from seven river sites in Austria. The selected sites showed different levels of anthropogenic alterations in river morphology ranging from pristine areas, with minor anthropogenic alterations, to strongly physically altered rivers. A variety of parasites were recovered from the skin, gills, swimbladder and eyes, with Caryophyllaeus laticeps (Pallas) being identified as the only cestode species occurring in the intestine. This is the first record of this species in nase in Austria. Caryophyllaeus laticeps was confined to the first 20% of the intestine, even in heavily infected hosts. The occurrence of C. laticeps within the fish population seems to be correlated with the degree of anthropogenic changes of the nases habitat. In rivers with a high degree of ecological integrity or in rivers that are only partially dammed, C. laticeps is either absent in C. nasus or occurs with low prevalence (5.6-20%) and low mean intensity values (1.0-4.0). Where anthropogenic factors have changed the entire river into a reservoir, and fish cannot escape, the prevalence of infection with C. laticeps increases from 46.2 to 78.2% and the mean intensity from 8.8 to 17.2.