A novel krill meal ingredient enhances feed intake following high-temperature lice treatment stress in Atlantic salmon

Managing sea lice infestations in Atlantic salmon (Salmo salar L.) aquaculture often involves mechanical treatments that can cause acute stress, reducing feed intake and compromising growth. This study, led by Hanne Jorun Sixten, investigated the efficacy of a novel krill meal ingredient, QRILL Stick Water (QSW), in enhancing feed intake and growth performance in Atlantic salmon following repeated simulated high-temperature lice treatment stress. The study compares QSW to traditional krill meal (QRILL Aqua, QA) and fishmeal-based diets under both optimal and stress conditions.

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Experimental Design 

The trial was conducted with Atlantic salmon (initial weight: 431±11g) over a period that included adaptation and stress phases. The fish were divided into groups and fed four different diets: 

  1. Low Fishmeal (LFM, 7.5%) 

  2. Medium Fishmeal (MFM, 15%) 

  3. Krill Meal QA (7.5%)  

  4. Krill Meal QSW (7.5%) 

The fish were reared in indoor tanks with a temperature of 14°C and salinity of 34 ppm until they reached an average weight of 960±38g. Stress treatments mimicking commercial lice treatment (Thermolicer) involved crowding for 30 minutes followed by immersion in a 32°C heat bath for 30 seconds. These treatments were repeated three times with three weeks in between each event. 

Measurements 

Performance metrics, including cumulative feed intake, growth rate, and condition factor, were evaluated during both the adaptation period and the stress period. Plasma cortisol, glucose, and lactate levels were measured to assess stress responses. 

Results 

Feed Intake and Growth 

Under optimal conditions, fish fed QSW and QA diets showed comparable growth, and higher feed intake for QSW. During the stress period, both QSW and QA diets maintained higher feed intake compared to LFM and MFM diets (Figure 1). Specifically, fish fed QSW exhibited higher feed intake both in optimal and stressing conditions but also a higher Feed Conversion atio (FCR), sustaining similar growth rates to those fed QA. 

Stress Biomarkers 

Plasma analysis revealed elevated cortisol, glucose, and lactate levels in fish subjected to acute heat stress, indicating significant stress responses. However, fish fed QSW and QA diets demonstrated better resilience to stress, maintaining higher feed intake and growth compared to those on LFM and MFM diets. 

Fillet Quality and Condition Factor 

Fish fed QSW showed a lower dress-out percentage but a higher condition factor compared to those on LFM and MFM diets. This suggests that QSW contributes to better overall fish health and quality under stress conditions. 

Figure 1: Cumulated feed intake (kg/tank) in fish fed QA and QSW during optimal conditions, and in fish fed LFM, MFM, QA & QSW during acute heat lice treatment stress, with ”Thermolicer” treatments marked in grey bars (N=3).

The study highlights the potential of QSW as a sustainable and effective dietary ingredient for Atlantic salmon, particularly under stress conditions. The ability of QSW to maintain high feed intake and growth during repeated acute heat stress treatments underscores its value in commercial aquaculture. Utilizing marine side-stream products like krill stick water not only enhances sustainability but also provides a nutritional advantage, supporting fish welfare and economic revenue for producers. 

QRILL Stick Water (QSW) is sustainable alternative to traditional krill meal (QA) for use in Atlantic salmon diets. It supports high feed intake and growth performance during both optimal and stress conditions, making it a valuable ingredient for improving resilience to handling and treatment stress. The use of QSW can contribute to more sustainable aquaculture practices by utilizing underutilized marine resources and reducing the environmental footprint of feed production.