Optimising Juvenile Lumpfish (Cyclopterus lumpus) Diet Through a Comparative Study of Wild and Farmed Populations of the Faroe Islands

Abstract

Lumpfish welfare has become a concern as the use of cleaner fish in salmon farms continues to grow. High mortality rates at the deployment phase have raised ethical concerns, highlighting the need to ensure optimal welfare for lumpfish (Cyclopterus lumpus). Challenges in addressing lumpfish welfare include infectious diseases, lack of established nutritional requirements, and standardised operational welfare indicators (OWI) for this species. The aim of this PhD was to investigate the nutritional status, health and welfare of farmed lumpfish compared to the wild counterparts in order to optimise feed formulations and enhance welfare and robustness in farming environments. Chapter 1 provided an overview of lumpfish biology in the wild, its role in aquaculture, and key welfare and nutritional considerations. Chapter 2 detailed the general methodology for fish sampling, welfare scoring, and laboratory analyses. Chapters 3 and 4 compared the nutritional and biochemical differences between farmed and wild lumpfish in the Faroe Islands. Chapter 3 focused on body composition, amino acid, and fatty acid profiles, revealing significant differences in lipid content being higher in farmed fish. This difference reflect the impact of high-energy diets, feeding regimes and controlled environments in farming conditions. The fatty acid profile of wild fish reflects the fatty acid composition of their natural prey, while the farmed fish is influenced by the aquafeed composition, mainly the use of vegetable ingredients, and the availability of seasonal preys in the sea cages. The amino acid profile is also influenced by diet and environmental conditions. Even though the amino acids had similar levels in both farmed and wild lumpfish, some differences were found in methionine and cysteine levels. Chapter 4 investigated liver colour and nutritional composition, showing differences in lipid content, lipid classes, fatty acid, and carotenoid levels. The high fat storage of farmed fish, both in whole fish and liver, from land-based hatcheries suggest they have good energy storage and appear ready for deployment. However, the high mortality rates observed post-deployment indicate that the hatchery diet may not adequately prepare lumpfish for the challenges of the sea cage environment. Chapter 5 assessed the impact of farming practices on OWI and liver health of lumpfish compared to wild populations, finding higher levels of physical damage and compromised liver health in farmed lumpfish. Chapter 6 examined the effects of varying levels of EPA and DHA on the growth, health, chemical composition, and stress response of lumpfish. Results showed that diets with higher EPA and DHA levels (2-3% of diet) led to better growth performance, higher survival rates, and lower stress responses. Chapter 7 discussed findings and implications for feed formulation and best practices in husbandry, proposing future research directions. This research highlights the importance of tailored nutritional strategies in promoting lumpfish welfare in aquaculture, providing insights that enhance sustainability and ethical use of lumpfish as cleaner fish.