Epsilon Archive for Student Projects

Abstract

Aquaculture production has significantly advanced, contributing significantly to the global protein supply. However, its intensification raises sustainability concerns, especially with climate change exacerbating stress and disease susceptibility in farmed fish like rainbow trout. Natural nutraceuticals, derived from plants, algae, and microbes, offer a sustainable solution by enhancing fish health, immunity, and resilience against thermal stress and pathogens without harming the environment. This thesis aimed to evaluate the efficacy of a nutraceutical formulation in enhancing the robustness of rainbow trout under stress conditions. Specifically, the study investigated the formulation's impact on the survival of trout exposed to acute and chronic stress in controlled laboratory experiments, assessed its antibacterial properties against key salmonid pathogens (Vibrio campbellii, Yersinia ruckeri, and Moritella viscosa), and validated its anti-stress effects in a pilot field trial under Swedish aquaculture conditions. The study evaluated the effects of a plant-based nutraceutical formulation (NUTR) on the health and thermal tolerance of rainbow trout fry through three experiments. Laboratory trials tested the antibacterial effects of the formulation against pathogens, optimized its dosage for improving thermal stress tolerance in laboratory conditions, and validated its impact under real-world farm conditions. Against Vibrio, NUTR showed no inhibition in disk diffusion assays but exhibited dose-dependent effects over time in a broth medium, with higher concentrations (20 μl/ml) reducing growth. For Yersinia, NUTR significantly inhibited growth at all the tested doses (p<0.005), though its efficacy was less pronounced compared to antibiotics, with 4 μl/ml supporting the most consistent growth over 24 h. Similarly, Moritella growth was inhibited at 20 μl/ml, while lower doses promoted bacterial proliferation. In rainbow trout fry, NUTR enhanced thermal stress tolerance, with 250 ppm demonstrating optimal effects, reducing mortality significantly to 15% compared to 60% in controls. Higher doses (500–1000 ppm) showed diminishing benefits, highlighting the importance of dose optimization for host tolerance outcomes. The study demonstrated that the nutraceutical formulation exhibited antibacterial and anti-stress effects in both laboratory and pilot field settings, with effective doses varying across bacterial species and stress intensity. While the research focused on survival and growth parameters, the formulation effectively inhibited pathogen growth and enhanced thermal stress tolerance in trout fry. Future studies should explore additional doses, exposure durations, and the formulation's mode of action to optimize its application in real farm environments.