Development and Optimisation of a Sustainable Feed Formulation for the New Zealand Farmed Abalone (Haliotis iris)
The expansion of aquaculture depends on the availability and sustainability of aquafeeds. The development of aquafeeds is hampered by the lack of more eco-friendly ingredients that promote animal growth and contribute to animal welfare simultaneously. The common ingredients of aquafeeds (e.g., fishmeal and plant meals) are highly nutritious due to a well-balanced amino acid profile, fatty acid, and micronutrients. However, these ingredients are considered unsustainable due to the utilisation of wild fish stocks and extensive land and energy use for their cultivation. Alternative ingredients such as insect meals and waste-by products are of interest due to their high nutritional profile and contribution to a more circular economy. Tenebrio molitor (mealworm) is one species of insect with high digestibility and high levels of polyunsaturated fatty acids. Grape marc is a waste-by product from the wine production industry which disposal is becoming problematic. Grape marc is rich in antioxidants and is a potential prebiotic source. The aim of this thesis is to evaluate the inclusion of two alternative ingredients, insect meal and grape marc, on somatic growth, nutritional profile, health, shell colour and flavour of the New Zealand farmed abalone (Haliotis iris).
Initially, the nutritional profile and metabolomic variations were assessed in a farm in Northland (Ruakaka) over a year (Chapter 3). Data collected from this chapter showed that the nutritional profile of juvenile abalone is subject to age and seasonal variations although feed remained the same. The protein levels were the most affected during the year of grow-out whereas carbohydrate, ash, and moisture did not show extreme variations. The metabolite profiles corroborated the presence of some amino acids related to flavour and tenderness, and fatty acids related to temperature regulation showing higher levels in summer compared to winter months. The study of the nutritional profile of the commercial feed allowed us to develop four experimental diets which included fishmeal at some extent and included insect meal and grape marc to reduce the nitrogen and phosphorus load in the uneaten feed while improving physical and chemical characteristics (Chapter 4). The experimental diets were encapsulated in alginate beads to promote better seawater stability. The physical and chemical properties of encapsulated feeds revealed improved seawater stability compared to commercial feed and advantages in their frozen delivery form in terms of the texture profile. Encapsulated diets with grape marc inclusion resulted in an improved resistance to abrasion, and the encapsulation with the inclusion of both, insect meal and grape marc, significantly reduced the phosphorus and nitrogen waste in uneaten feed. In addition, the inclusion of insect meal and grape marc showed growth promotion and comparable feed intake to commercial feed in 14-days.
After acceptable feed intake of the experimental diets in a 14-day feeding trial, the encapsulated diets were trialled in an abalone farm in Southland (Bluff, Invercargill) over 165 days. The nutritional profile and nutrient digestibility were assessed on the experimental diets, and growth parameters, proximate composition, amino acids, and fatty acids were assessed in juvenile abalone tissue (Chapter 5). Results showed that the inclusion of insect meal and grape marc did not affect the growth of abalone after 165 days compared to diets without the inclusion. However, the inclusion of grape marc reduced the digestibility of the diets significantly, while insect meal did not. The fatty acid profile of abalone was significantly affected mainly in the α-linolenic acid, arachidonic acid, and eicosapentaenoic acid content, while the amino acid profile was not significantly modified by the inclusion of insect meal nor grape marc.
The flavour-volatile compounds and shell coloration were also assessed after six months of feeding (Chapter 6). The results showed that the inclusion of insect meal did not significantly affect the flavour volatile profile, whereas the inclusion of grape marc significantly reduced the production of most of the volatile compounds. This reduction indicated an antioxidant effect of grape marc in the meat of abalone, suggesting a reduced oxidation of lipids. In addition, the inclusion of both insect meal and grape marc affected did not affect the lightness, redness/greenness, and yellowness/blueness coloration of the shells. The study also evaluated the effect of insect meal and grape marc inclusion on the gut health and muscle metabolome of abalone (Chapter 7). The results showed that the inclusion of insect meal and grape marc did not significantly affect the gut microbial diversity nor the intestinal morphology, indicating a capacity of abalone to adapt to those ingredients maintaining a good intestinal condition. In addition, the relative abundance of gut bacteria fluctuated with the dietary inclusion of insect meal and grape marc, suggesting a possible increase of beneficial species. This study also corroborated the relevant role of fatty acids in abalone metabolism and growth as described in Chapter 5.
In conclusion, this thesis has successfully performed a holistic evaluation of the effects of insect meal and grape marc inclusion in feeds for abalone aquaculture. The different angles of animal nutrition described in this thesis go beyond traditional growth evaluation, which has been considered as the gold standard. The insights from this thesis contribute to the development of more sustainable aquafeeds to be used in the abalone industry to promote growth and animal welfare, improve the quality of the meat, reduce environmental impact, has adequate physical properties for commercialization and represents a steppingstone for the development of a blue aquaculture in New Zealand.