Important disease conditions of newly cultured species in intensive freshwater farms in Greece: first incidence of nodavirus infection in Acipenser sp.

Abstract

We describe here the main pathological conditions of freshwater fish recently introduced for intensive rearing (open ponds and recirculating freshwater systems) in Greece. Sturgeon were susceptible to skeletal abnormalities of the spine (scoliosis and lordosis) of unknown aetiology. Horizontal transmission of nodavirus from infected sea bass to sturgeon was detected for the first time. This caused serious pathology and clinical signs, such as lethargy and imbalance, leading to secondary infections with Aeromonas hydrophila and Trichodina sp. and chronic, but steady, mortality. Sea bass were very susceptible to nodavirus infection, monogenean infections and gas bubble disease. Mullet reared under recirculated and open-flow conditions were very sensitive to Chilodonella sp. infection, whereas catfish were susceptible to infection with Ichthyophthirius sp. leading to secondary infections with A. hydrophila, Saprolegnia sp. and Myxobacteria spp. Tilapia were very susceptible to gas bubble disease and A. hydrophila. This bacterium was associated with management manipulations for all species and fully responsive to corrective hygiene methods. KEY WORDS: Freshwater aquaculture · Acipenser sp. · Mugil sp. · Recirculating systems · Nodavirus Resale or republication not permitted without written consent of the publisherDis Aquat Org 60: [247][248][249][250][251][252] 2004 MATERIALS AND METHODS Fish. Sea bass Dicentrarchus labrax weighing approximately 50 to 80 g, reared in both recirculating and open freshwater production facilities situated in western Greece, showed nervous signs during an outbreak of clinical disease in late summer 2000 (during the present project period) when water temperatures were 25 to 28°C. The fish from both facilities were originally obtained from the same marine hatchery and transported to freshwater conditions when they weighed 1.5 g. They were subsequently reared in well freshwater in both recirculating and open-flow system facilities at a salinity of 0 ‰ and pH of 7.8. Sea bass were fed on commercial pellets specific to this species and their size.Mullet Mugil cephalus was also reared in both recirculating and open freshwater production facilities. The fish from both facilities were originally obtained from the same marine hatchery and transported to freshwater conditions when they weighed 1.5 g. After transfer to the farm, all fish were reared in freshwater until the end of their production cycle. Mullet were fed on commercial pellets containing approx. 40 to 45% protein and 12 to 18% lipids, depending on fish size. Stocking densities for sea bass and mullet in the recirculating system was 45 kg m -3 and the temperature ranged from 18 to 21°C. In the open-flow system densities were 15 and 20 kg m -3 for sea bass and mullet, respectively. Water temperature ranged from 16 to 18°C in winter and 19 to 21°C in the summer (Table 1).The other species examined in the present study were reared in freshwater in a commercial hatchery and transported to the farm when they weighed 2 to 5 g. ...

Betanodavirus of Marine and Freshwater Fish: Distribution, Genomic Organization, Diagnosis and Control Measures

“…Larval or juvenile stages are more prone to this viral infection, but significant mortality can also occur in older fish up to production-size as in European seabass, sevenband grouper, humpback grouper Cromileptes altivelis and Atlantic halibut Hippoglossus hippoglossus [4,37,71,83,86,125]. Infections are also reported in freshwater fish, such as Chinese catfish (P. asotus); Australia catfish (Tandanus tandanus); Barramundi (L. calcarifer); Medaka (Oryzias latipes); guppy (Poicelia reticulata) and zebrafish (Danio rerio) [5,22,52,53,62,63,76]. Several experimental infection studies have demonstrated that both marine and fresh water finfish are susceptible to betanodavirus infection [23,38,39,52,53,63].…”

Isolation, characterization and sequence determination of Noda virus from sea bass (Dicentrarchus labraxL.) reared in freshwater and marine facilities in Greece

“…Οι Athanassopoulou et al (2003Athanassopoulou et al ( ,2004 ανί χνευσαν για πρώτη φορά τον ιό στην Ελλάδα σε ασθε νή λαβράκια που εκτρέφονταν σε γλυκό νερό, καθώς και σε οξΰρρυγχους με PCR, ενώ ο Jalil J., (2004, προ σωπική επικοινωνία) έχει αναφέρει συμπτώματα σε κέφαλο (Liza-auratus).…”

“…από δυο διαφορετικά εντατικά συστήματα εκτροφής σε γλυκό νερό (Athanassopoulou et al, 2003) και σε εντα τικά εκτρεφόμενους οξΰρρυγχους (Athanassopoulou et al, 2004).…”

“…These researchers confirmed the presence of a Noda virus strain belonging to the RGNNV group, with antigenic similarity to marine Noda virus isolates. Noda virus identification via PCR did also succeed in diseased sea bass originating from two different intensive culturing freshwater systems (Athanassopoulou et al, 2003) and in intensively cultured sturgeons (Athanassopoulou et al, 2004).…”

“…There are only few reports indicating its presence and survival in fresh water fish. Athanassopoulou et al (2003Athanassopoulou et al ( , 2004 reported the presence of the virus in cultured sea bass and sturgeon in freshwater for the first time using PCR, and Jalil J. (2004, personal communication) reported clinical signs in mullet (Liza auratus).…”