GROWTH PERFORMANCE AND INTESTINAL HEALTH OF RAINBOW TROUT Oncorhynchus mykiss PREVIOUSLY SUBJECTED TO INFLAMMATION WITH DEXTRAN SODIUM SULPHATE (DSS)

Aquaculture production has undergone remarkable growth during the past few decades, and it will continue to rise in the coming years to meet higher demand for safe, healthy and convenient seafood products. A lower usage of finite marine-harvested resources has been a major trend in the aquafeed industry. Grain and oilseed by-products are promising sources of protein and energy for aquaculture feeds. However, high dietary inclusion levels of plant proteins have often been associated to detrimental effects on growth, feed efficiency, intestinal dysbiosis and immune response, threatening the profitability of major aquaculture species.

 Feed solutions that enhance digestive and metabolic processes have shown to be crucial to make these new feed formulation scenarios work, while reduce the environmental impact of aquaculture and promoting fish welfare.  In the scope of this sustainable approach, Mixscience  (France)  developed a specific  Phytogenics based  solution that helps to reduce the negative impact of challenging feeds .

The aim of this study is to examine the effect of graded levels of feed additive (PHY) on the zootechnical performance, nutrient digestibility and intestinal mucosal health in rainbow trout (Oncorhynchus mykiss), previously subjected to a standardized inflammatory event with dextran sodium sulphate (DSS).

The Trout trial includes 5 treatments.

• A positive control (PC) = optimal diet for the targeted fish
• A negative control (NC) with lower levels of digestible protein and digestible energy due to fish meal replacement by challenging ingredients derived from defatted soybean meal and sunflower meal, which tend to reduce digestibility and negatively affect intestinal integrity.
• 3 additional diets, based on the NC formula, supplemented with the tested product (PHY) at a dose of 50 (PHY50), 100 (PHY100) or 200 (PHY200) g/Tonne of feed.

The trial comprised 3 experimental phases:

• Phase I: A chemically induced intestinal inflammation using a diet with 1% dextran sodium sulphate (DSS) on the overall fish population for 10 days
• Phase II: An experimental feeding of the 6 experimental feeds over 86 days, to assess their effect on the growth performance and restoration of intestinal health criteria
• Phase III: a measurement of apparent digestibility of nutrients

The results indicate very clearly that in trout, compared to an optimal feed (PC), a challenge feed (NC) in which part of the fish meal has been replaced by plant ingredients and stress inducers, induces negative metabolic reactions: increase in systemic inflammatory status, expressed at blood and fecal level, a decrease in nutrient digestibility (Figure1). This outcomes in lower feed efficiency, and performance of fish (Table 1). The negative impact of a challenging feed can be compensated by specific phytogenics that activate key metabolic activities to save energy and maintain overall resistance that limits dysbiosis and intestinal disorders under stressful

conditions and helps maintain a healthy optimal feeding efficiency and an overall fitness of the host. The results consolidate the results obtained in 2023 with Seabream. The optimal dose demonstrated for seabream of 200 g/T of feed is confirmed for trout. A positive effect is observed at a lower dose of 100 g/T of feed. A dose of 50 g/T is not sufficient to have a positive effect.