Effect of a phytogenic feed additive on the susceptibility of Onchorhynchus mykiss to Aeromonas salmonicida

Abstract

In recent years, feed additives have increasingly been adopted by the aquaculture industry. These supplements not only offer an alternative to antibiotics but have also been linked to enhanced growth performance. However, the literature is still limited and provides contradictory information on their effectiveness. This is mainly due to the wide variety of available products and their complex mechanisms of action. Phytogenic feed additives have been shown to have antimicrobial effects and can improve growth performance. In the present study, we investigated the susceptibility of several fish pathogenic bacteria to a phytogenic essential oil product in vitro. In addition, we determined the protective effect of a commercial phytogenic feed additive containing oregano, anis and citrus oils on the resistance of rainbow trout Oncorhynchus mykiss to infection by Aeromonas salmonicida. The bacterium was administered through 3 different routes: intra-peritoneal injection, immersion in a bacterial solution and cohabitation with infected fish. Mortality rates were significantly lower in infected rainbow trout that had received the feed additive: the overall mortality rate across all routes of infection was 18% in fish fed a diet containing the additive compared to 37% in fish that received unsupplemented feed. The route of infection also significantly impacted mortality, with average mortality rates of 60, 17.5 and 5% for intraperitoneal injection, immersion and cohabitation, respectively. In general, fish were better protected against infection by immersion than infection by injection.

In vitro assessment of the antimicrobial activity of silver and zinc oxide nanoparticles against fish pathogens

“…Concurrently, there is a need to minimize use of antibiotics in farming, to combat antibiotic resistance [3, 4]. Thus, there is a growing need for alternative antimicrobial therapeutics, and metal and metal oxide nanoparticles are being widely investigated for their potential medical applications, including their use in fish medicine [22].…”

“…The EU has prohibited the use of antibiotics as growth promoters in animals since 2006 [3]. However, it is difficult to assess the quantity and identify the classes of antimicrobial agents in aquaculture [4].…”

“…Nevertheless, detailed investigations about the types and the amounts of antibiotics in fish farms are still needed [4, 6]. The problem of antibiotic resistance has become a major concern in human and veterinary medicine [2, 3, 7]. The antibiotic resistance genes could be transferred between bacteria from different environments.…”

The effect of reducing agents on challenge of rainbow trout with Aeromonas salmonicida

“…; Menanteau‐Ledouble et al . ). For instance, administration of carotenoids increased phagocytosis and lysozyme activity in rainbow trout (Amar et al .…”

Leaves from banana (Musa nana) and maize (Zea mays) have no phyto-prophylactic effects on the susceptibility of grass carp (Ctenopharyngodon idella) to Aeromonas hydrophila infection

“…Moreover, these treatments are often not available or affordable for small-scale farmers in rural areas like in Northern Vietnam. Alternatives to the application of antibiotics have therefore been investigated, including phytogenic feed supplements, several of which have been shown to improve resistance to bacterial infection [ 6 – 9 ]. In Asian grass carp-based polyculture systems, leaf material is a major feed input while in small-scale aquaculture, plant-based by-products from other farming activities are used as feeds.…”