HYDROLYSATE-ENRICHED FISHMEAL SUPPORTS PERFORMANCE IN ATLANTIC SALMON Salmo salar L. FOLLOWING THERMAL LICE TREATMENT

Introduction

Acute delousing stress in Atlantic salmon (Salmo salar L.) significantly reduces post-treatment feed intake, impairing growth, health and welfare (Bowers et al., 2000; Grave et al., 2004; Hamre et al., 2009; Igboeli et al., 2014). Identifying factors, including dietary ingredients and bioactive components, that can mitigate these stress effects and help fish resume feeding sooner is therefore essential. The side-stream biomass from fish catch, in the form of abundant and nutrient-rich fish protein concentrate (FPC), represents an underutilized resource with potential for valorization, enhancing sustainability by reducing future aquaculture's dependency on fish meal. However, not all feed factories are equipped to utilize wet silage products, hence enriching fishmeal (FM) with added hydrolysate makes it a more suitable ingredient.

Materials and Methods

This study evaluated the effectiveness of dietary FPC and two enriched FMs, either with FPC (FPCM), or with fish protein hydrolysate (FPHM), compared to a commercial FM, in mitigating stress from exposure to repeated simulated delousing treatments in salmon (428 to 894 g body weight). Five diets were tested: low fishmeal (LFM; 7.5% FM); medium fishmeal (MFM; 15% FM); FPC (7.5% FPC + 7.5% FM) and two hydrolysate-enriched fishmeal diets (7.5% FPCM + 7.5% FM and FPHM + 7.5% FM). Salmon performance was evaluated under optimal rearing conditions for 3 months, interrupted by three acute heat (32 °C; 30 sec) and crowding (15 min) stress treatments mimicking a commercial acute high temperature delousing (AHTD) treatment (Grøntvedt et al., 2015; Noble et al., 2018) with three weeks between each treatment.

Results and discussion

By the end of the trial, fish fed the diets containing FPC or the enriched FMs showed similar feed intake and growth compared to the MFM treatment, while the FPC had higher feed intake compared to LFM and FPHM, and FPC and FPCM treatments resulted in higher growth compared to LFM. Fish plasma cortisol, glucose, and lactate levels were elevated after repeated AHTD treatments, confirming a sustained stress response. Dietary effects on plasma metabolites and qPCR analyses for genes involved in the gut-brain axis control of appetite and energy utilization in salmon will be presented. In conclusion, diets with low-impact and circular ingredients, such as fish protein concentrate (FPC) and a fish meal product enriched with fish protein concentrate (FPCM), can support similar feed intake and performance as high-quality fishmeal during periods of repeated acute stress. FPC contributed to sustained high feed intake, while FPCM gave higher efficiency, following repeated occurrences of acute heat stress treatments simulating commercial heat treatments against lice.

Figure 1. Feed intake (%BW/day) (left), SGR (mid) and feed conversión rate (FCR) (right) in fish fed LFM, MFM, FPC and hydrolysate-enriched fishmeals FPCM & FPHM during repeated episodes of acute heat lice treatment stress (N=3). One-way, ANOVA P < 0.05.

Acknowledgment

This work was funded by the Reseach Council of Norway [grant numbers 268987, 329104, 245883], BioMar AS, Pelagia AS, and Aker Qrill Company AS.

References

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