Effect of blood removal protocol and superchilling on quality parameters of prerigor filleted farmed Atlantic cod (Gadus morhua).

UNLABELLED: A total of 40 farmed Atlantic cod (Gadus morhua) were in 2 groups either fillet directly after stunning and spray washed or produced into fillets according to traditional slaughter methods including exsanguination for 30 min, gutting and washing. Both groups were either stored superchilled or traditionally on ice. After 7 d postmortem color (CIE L*, a*, b*) and fillet shrinkage was measured by computer imaging along with drip loss and texture hardness. Results show that superchilled fillets had significant lower core temperature than fillets stored on ice during the entire 7 d storage period. This resulted in reduced fillet shrinkage from 14.7% to 6.9% and less drip loss dropping from 9.45% to 3.99% in average. Processing the fish directly into fillets resulted in satisfactory blood drainage, where all groups were in particularly well exsanguinated with a* values below zero. No color difference was observed between filleting groups or chilling methods. Spray washing of the fillets resulted in water uptake and higher drip loss in interaction with chilling method. We conclude that filleting farmed fish in one step is feasible. PRACTICAL APPLICATION: Traditionally farmed fish are slaughtered and processed over several steps, which often include live chilling, stunning, exsanguination, chilling, gutting, rinsing, decapitation, filleting before the fillets are packed into polystyrene boxes and shipped with ice. These processes are often time, laboring, space, and energy consuming. A novel processing line for filleting of farmed fish is gutting and filleting the fish directly after decapitation and replacing exsanguination with spray washing the fillets. In addition, all the cooling steps are replaced by superchilling the fillets. This novel process line gives fillets with comparable if not superior quality compared to the traditional process.

Detection of nodavirus in seawater from rearing facilities for Atlantic halibut Hippoglossus hippoglossus larvae.

We used (1) ultracentrifugation followed by RT-PCR and (2) real-time RT-PCR to detect and quantify nodaviruses in seawater in which Atlantic halibut Hippoglossus hippoglossus larvae/fry had been held at rearing facilities. Evaluated against in vitro propagated viruses, the viral concentration corresponded to 1.6 x 10(4) TCID50 (50% tissue culture infectious dose) ml(-1). Evaluated against in vitro transcribed RNA, the concentration was estimated at 2 x 10(7) virus particles ml(-1) seawater.

Detection of infectious salmon anaemia virus by real-time nucleic acid sequence based amplification.

We have developed a real-time nucleic acid sequence based amplification (NASBA) procedure for detection of infectious salmon anaemia virus (ISAV). Primers were designed to target a 124 nucleotide region of ISAV genome segment 8. Amplification products were detected in real-time with a molecular beacon (carboxyfluorescin [FAM]-labelled and methyl-red quenched) that recognised an internal region of the target amplicon. Amplification and detection were performed at 41 degrees C for 90 min in a Corbett Research Rotorgene. The real-time NASBA assay was compared to a conventional RT-PCR for ISAV detection. From a panel of 45 clinical samples, both assays detected ISAV in the same 19 samples. Based on the detection of a synthetic RNA target, the real-time NASBA procedure was approximately 100x more sensitive than conventional RT-PCR. These results suggest that real-time NASBA may represent a useful diagnostic procedure for ISAV.

Protection against Atlantic halibut nodavirus in turbot is induced by recombinant capsid protein vaccination but not following DNA vaccination.

Fish nodaviruses (betanodaviruses) are small, non-enveloped icosahedral single-stranded positive-sense RNA viruses that can cause viral encephalopathy and retinopathy (VER) in a number of cultured marine teleost species, including Atlantic halibut (Hippoglossus hippoglossus). A recombinant protein vaccine and a DNA vaccine were produced, based on the same capsid-encoding region of the Atlantic halibut nodavirus (AHNV) genome, and tested for protection in juvenile turbot (Scophthalmus maximus). Vaccine efficacy was demonstrated in the fish vaccinated with recombinant capsid protein but not in the DNA-vaccinated fish, despite the fact that in vivo expression of the DNA vaccine-encoded antigen was confirmed by RNA in situ hybridisation and immunohistochemistry. Combined DNA and recombinant vaccine administration did not improve the effect of the latter. Surprisingly, fish vaccinated with 50 microg recombinant protein demonstrated a threefold lower survival rate than the two groups that received 10 microg recombinant protein. Neither the recombinant protein vaccine nor the DNA vaccine induced anti-viral antibodies 9 weeks after immunisation, while antibodies reactive with the recombinant protein were detectable mainly in fish vaccinated with 50 microg recombinant protein. The study also demonstrates evidence of viral replication inside the myocytes of intramuscularly challenged fish.

A DNA vaccine directed against a rainbow trout rhabdovirus induces early protection against a nodavirus challenge in turbot.

A DNA vaccine encoding the envelope glycoprotein from a fish rhabdovirus, viral hemorrhagic septicemia virus (VHSV), has previously been shown to induce both early and long time protection against the virus in rainbow trout. Challenge experiments have revealed that the immunity established shortly after vaccination is cross-protective against heterologous fish rhabdoviruses. In this study, we show that the DNA vaccine encoding the VHSV glycoprotein also induces early protection against a non-enveloped, positive-sense RNA virus belonging to the Nodavirus family, the Atlantic halibut nodavirus (AHNV). In a vaccine efficacy test using juvenile turbot as model fish, the fish injected with the VHSV vaccine were completely protected against a nodavirus challenge performed 8 days post vaccination, while the cumulative mortality in the control group reached 54%. A DNA vaccine carrying the gene encoding the capsid protein of AHNV revealed no protective properties against the nodavirus challenge. Histological examination of muscle tissue sections from the vaccine injection site showed that the DNA vaccine against VHSV triggered a pronounced inflammatory response in turbot similar to what has earlier been observed in rainbow trout.