Rzgar M. Jaafar

Effects of adjuvant Montanide™ ISA 763 A VG in rainbow trout injection vaccinated against Yersinia ruckeri

Enteric redmouth disease (ERM) caused by the fish pathogen Yersinia ruckeri is a major threat to freshwater production of rainbow trout (Oncorhynchus mykiss) throughout all life stages. Injection vaccination of rainbow trout against Y. ruckeri infection has been shown to confer better protection compared to the traditionally applied immersion vaccination. It may be hypothesized, based on experience from other vaccines, that adjuvants may increase the protective level of ERM injection vaccines even more. Controlled comparative vaccination studies have been performed to investigate effects of the oil adjuvant Montanide™ ISA 763 A VG (Seppic) when added to an experimental Y. ruckeri bacterin (containing both biotype 1 and 2 of serotype O1). A total of 1000 fish with mean weight 19 g was divided into five different groups (in duplicated tanks 2 × 100 fish per group) 1) non-vaccinated control fish (NonVac), 2) fish injected with a commercial vaccine (AquaVac(®) Relera™) (ComVac), 3) fish injected with an experimental vaccine (ExpVac), 4) fish injected with an experimental vaccine + adjuvant (ExpVacAdj) and 5) fish injected with adjuvant alone (Adj). Injection of the experimental vaccine (both adjuvanted and non-adjuvanted) induced a significantly higher antibody (IgM) level, increased occurrence of IgM(+) cells in spleen tissue and significant up-regulation of several immune genes. Additional experiments using a higher challenge dosage suggested an immune enhancing effect of the adjuvant as the challenge produced 100% mortality in the NonVac group, 60% mortality in both of ComVac and Adj groups and only 13 and 2.5% mortalities in the ExpVac and the ExpVacAdj groups, respectively.

Comparative evaluation of infection methods and environmental factors on challenge success: Aeromonas salmonicida infection in vaccinated rainbow trout

When testing vaccine-induced protection an effective and reliable challenge method is a basic requirement and we here present a comparative study on different challenge methods used for infection of rainbow trout Oncorhynchus mykiss with Aeromonas salmonicida, a bacterial pathogen eliciting furunculosis. Fish were vaccinated with three different adjuvanted trivalent vaccines containing formalin killed A. salmonicida, Vibrio anguillarum O1 and O2a. These were 1) the commercial vaccine Alpha Ject 3000, 2) an experimental vaccine with water in paraffin oil adjuvant, 3) an experimental vaccine with water in paraffin oil in water adjuvant. Fish were then exposed to A. salmonicida challenge using i.p. injection, cohabitation in freshwater, cohabitation in saltwater (15 ppt) or combined fresh/saltwater cohabitation. Cohabitation reflects a more natural infection mode and was shown to give better differentiation of vaccine types compared to i.p. injection of live bacteria. The latter infection mode is less successful probably due to the intra-abdominal inflammatory reactions (characterized in this study according to the Speilberg scale) induced by i.p. vaccination whereby injected live bacteria more effectively become inactivated at the site of injection. Compared to cohabitation in freshwater, cohabitation in saltwater was less efficient probably due to reduced survivability of A. salmonicida in saltwater, which was also experimentally verified in vitro.

Toltrazuril (Baycox vet.) in feed can reduce Ichthyophthirius multifiliis invasion of rainbow trout (Salmonidae)

Various compounds have been applied for control of Ichthyophthirius multifiliis (commonly known as Ich) which is the parasitic pathogen, responsible for the white spot disease, in freshwater aquaculture worldwide. Available methods are based on disinfection of fish tank water, targeting infective free-swimming theronts and escaped tomonts. No legal drug is available and licensed for treatment or prevention of the disease. The presently reported study was performed to test the potential of toltrazuril (Baycox® vet.)—a drug licensed for treatment of coccidial infections in other animal species—to reduce Ich infections when administered orally. Commercial pelleted feed containing 5.0 or 2.5 mg toltrazuril per 1 g of feed was offered to rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (Actinopterygii: Salmoniformes: Salmonidae), during a three day feeding regime (1% of biomass offered per day). Two trials were performed: one with feeding before exposure to parasites and one where already infected fish were treated. Before the treatment it was tested if fish would eat feed containing different drug concentrations and it was found that feed with the high drug concentration was not eaten by the fish whereas all feed containing 2.5 mg per 1 g feed was eaten. Following the exposure to infective I. multifiliis theronts it was found that the fish treated with toltrazuril before challenge obtained a significantly lower parasite burden (number of trophonts in the skin) compared to untreated control. On the other hand, toltrazuril proved to be ineffective when administered to the fish which were already infected before the treatment.

Comparative Efficacies of Sodium Percarbonate, Peracetic Acid, and Formaldehyde for Control of Ichthyobodo Necator—An Ectoparasitic Flagellate from Rainbow Trout

The ectoparasitic flagellate Ichthyobodo necator is known to induce ichthyobodosis in both wildand cultured host populations and notably young fish are vulnerable. The parasite infects gills, skin, and fins and causes severe epizootics in aquaria, hatcheries, and rearing ponds worldwide (Urawa and Kusakari 1990, Urawa 1992, Urawa 1993). Rainbow trout (Oncorhynchus mykiss) farming in Denmark is currently suffering from I. necator infections and trout farmers apply formaldehyde bath treatments for control. A series of antiparasitic compounds were tested by Tojo et al. (1994) and Tojo and Santamarina (1998) elucidating efficacies of 11 drugs used for bath treatment and further 32 drugs administered orally against I. necator infection of rainbow trout. It was shown that oral treatments using metronidazole (40 g · kg–1 feed, 10 days), secnidazole (20 g · kg–1 feed, 2 days), and triclabendazole (40 g · kg–1 feed, 5 days) were effective and did show elimination of the flagellates. The first two nitroimidazoles are banned for use in fish production within the EU. In addition, although oral medical treatments may have a potential role in future control it is worth investigating auxiliary water bath treatments based on environmentallyfriendly compounds. Recently Farmer et al. (2013) tested copper sulphate, potassium permanganate, and peracetic acid against I. necator infection of channel catfish but the only substance which significantly reduced the parasite burden and improved the survival of I. necator-infected channel catfish was copper sulphate applied at a rate of 2.1 mg · L–1 (once daily at 24-h intervals for 3 days). ACTA ICHTHYOLOGICA ET PISCATORIA (2013) 43 (2): 139–143 DOI: 10.3750/AIP2013.43.2.06