PhD students

PhD students and projects at DTU Aqua within the research area Aquaculture.

Alexandre Nguyen-tiêt

Title of the PhD project
Characterization of H2S producers in recirculating aquaculture systems (RAS)

Supervisors
Sanni-Leea Hellevi Aalto and Lars-Flemming Pedersen, DTU Aqua & Stefan Bertilsson, Swedish University of Agricultural Sciences

Background of the project
Hydrogen sulfide (H₂S) is an extremely toxic compound for organisms, preventing aerobic respiration. In marine land-based recirculating aquaculture systems (RAS), H₂S production is a major challenge, leading to fish mortality and thus important economic consequences. Because of the high sulfate (SO₄^2-) and organic matter concentration present in marine RAS, H2S production has been associated with the sulfate-reducing bacteria (SRB). However, there are also other pathways for producing H₂S that could play a significant role but are currently neglected, e.g. some bacteria have the capacity to degrade the cysteine to produce pyruvate, ammonia and H₂S. In both marine and freshwater RAS, cysteine is present, originating from the uneaten feed and feces of fish, suggesting that cysteine degradation could be an important H₂S source in aquaculture environment.

About the project
The main goal of this PhD project is to gain knowledge on the bacterial communities responsible of H₂S production in RAS and especially the cysteine degrading bacteria. To do so, I will first enrich and cultivate H₂S producing bacteria from samples collected at several locations in RAS. After that, I will use metagenomic/metatranscriptomic analysis to identify the bacteria as well as the metabolic pathways responsible of H₂S production and develop primers to examine H₂S production dynamics and microbiology in aquaculture biofilms.

Perspectives
The results obtained through this project will give a better understanding of the microbial community responsible of H₂S production in land-based aquaculture. With this new knowledge, I can develop ways to quantify and monitor both the traditional (SRB) and cysteine-degradation H₂S producers in RAS to avoid production losses related to H₂S exposure and to promote safe and stable fish production in the future.

Matthew Mainieri

Title of PhD Project
Microalgae in fish feeds

Supervisors
Ivar Lund & Anne Johanne Tang Dalsgaard, DTU Aqua

Background of the project
The global population is on the rise and with this increase comes multiple climatic as well as food security issues. Anthropogenic activity has caused a widespread increase of greenhouse gases including rising CO₂ levels. Microalgae play a crucial role in mitigating rising CO₂ levels through sequestration while also serving as a valuable resource in aquaculture. Their biochemical composition can be altered by environmental stressors such as CO₂ levels and photoperiod, impacting their nutritional value. In marine fish larviculture, microalgae enhance live feeds like rotifers and Artemia, improving larval growth, survival, and microbiome development. The "green water technique" further supports larval health by enriching the rearing environment. Optimizing microalgae nutrient profiles for both live feeds and water quality can significantly improve fish larval growth, survival, and long-term robustness.

About the project
The project will encompass all aspects of teleost larval rearing. I will begin by applying various abiotic stressors to the microalgae culture of multiple species to manipulate the omega-3 polyunsaturated fatty acids (DHA, EPA) profile which are essential in early larval development. I will follow the microalgal culture trials by culturing and enriching live feeds (rotifers and Artemia) with the cultured microalgae and analyzing their nutrient retention efficiency. Lastly, I will culture finfish larvae while utilizing the results from the live feeds trial and condition the water with the cultured microalgae in an attempt to enhance larval growth, development, and survival.

Perspectives
The potential gained perspectives of the PhD project are to 1) address how microalgae species respond to various stressors in terms of growth, nutrient profile, and physio-chemical interactions, 2) promote growth and survival of finfish larvae through live feed nutrition and water conditioning and to better understand the mechanisms and interactions behind the growth and survival, 3) discover the short and the long-term effects on larval growth, development, and robustness from initial early nutrition and environmental exposure.

Hien La Nguyen The

Title of PhD Project
Amino acid optimization of fish feed

Supervisors
Anne Johanne Tang Dalsgaard & Kylian Manon Eggink, DTU Aqua

Background of the project
Nitrogen waste is a major concern in the aquaculture industry, as it can create toxic environments for fish and may lead to eutrophication in receiving water bodies. In aquaculture systems, dissolved nitrogen waste primarily originates from fish excretion, particularly in the form of ammonia. The amount of ammonia produced by fish largely depends on the amino acid composition of the feed. Both excesses and deficiencies of amino acids can negatively affect growth performance and nitrogen metabolism in fish. Therefore, optimizing diets to achieve balanced compositions of both essential amino acids (EAAs) and non-essential amino acids (NEAAs) is considered as a key to regulating not only protein retention for growth but also to mitigating the environmental impact of nitrogen‐rich effluents. Commercial aquafeeds are designed to meet the dietary requirements for essential amino acids; however, the composition of non-essential amino acids is generally not considered.

About the project
The project aims to investigate and develop nitrogen-optimized feed to reduce nitrogen excretion, improve protein retention and feed utilization in rainbow trout (Onchorynchus mykiss). At the beginning of the project, digestibility trials will be conducted to determine the apparent digestibility (ADC) of amino acids, protein, ash, fat, moisture and phosphorus. Based on the digestibility data of raw materials, R&D feed will be formulated with different amino acids profiles (focus on NEAAs) and tested in the mass balance trials for 6-8 weeks in recirculating aquaculture system (RAS) to estimate the optimized diets for rainbow trout. Beside optimized amino acid profiles, the project also aims to investigate the bioavailability of amino acid isomers (DL-amino acids) as well as the role of mammalian target of rapamycin complex 1(mTORC1) in protein synthesis and the normal growth development in rainbow trout.

Perspectives
The project is expected to provide new insights into the role of nitrogen-optimized feed for reducing nitrogen excretion and enhancing fish welfare. These findings may later be translated into industrial applications to reduce the environmental footprint of feed and contribute to more sustainable production practices.