PhD on microalgae as feed for salmon
Yangyang Gong will dispute Friday, December 7th for his PhD degree at Nord University with the dissertation: «Microalgae as feed ingredients for Atlantic salmon».
Fishmeal and fish oil are limited resources and have, to a large extent, been replaced by plant products in commercial feed for salmon. Plant products cannot fulfil all the nutritional requirements for salmon, and plant oils also contribute to a modified fatty acid composition in the salmon.
This has led to discussions about salmon as the source of long-chain polyunsaturated omega-3 fatty acids, and if the content is large enough of the desired fatty acids. There is a great desire to find new sustainable protein and oil sources with a balanced nutritional composition that can be produced in scalable volumes with increasing demand.
Microalgae can be an alternative
Photosynthetic microalgae can provide a sustainable alternative to fishmeal and fish oil or plant-based raw materials in fish feed. Nutrient content such as protein and fat as well as fatty acid composition varies between different microalgae, indicating that their potential as a feed ingredient for carnivorous fish may vary between different sources.
The overall aim of this doctoral dissertation is to investigate the potential for microalgae as feedstocks for Atlantic salmon. The utilisation of micro-layer-based diets was evaluated by measuring apparent digestibility, growth, feed utilisation, the chemical composition of the fish and fish intestinal health.
The specific objectives are as follows:
- To estimate apparent digestibility of nutrients to various microalgae feed for Atlantic salmon.
- Investigate the effect of different levels of interference in fishmeal-based or plant-based diets on digestibility, growth performance, feed utilisation, chemical composition and fish intestinal health.
Evaluate the use of a thermo-mechanical treatment (extrusion) as well as two different feed additives to increase nutrient utilisation of microalgal feed.
Likes the feed with microalgae
The fish showed a healthy appetite on the feeds containing microalgae. The microalgae Nannochloropsis Oceania is more digestible than Desmodesmus sp. Mixing of microalgae up to 10% in either fishmeal or plant protein-based salmon feed shows no adverse effect on growth, feed utilisation, condition indices, health parameters and chemical composition of Atlantic salmon.
The results also show that extrusion can be used as a cost-effective method for improving digestion of nutrients from microalgae. Use of additives does not improve feed utilisation. Increased PUFA content is observed in the whole body composition of Atlantic salmon fed with Nannochloropsis oceanica combined with one of the additives than fish fed with Scenedesmus sp. Increased content of PUFA is beneficial and makes salmon healthier as human food.
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