Super Seaweed for Fish Health and Growth

October 12, 2021

Valentin (second right), Dr Asda Laining (right) and aquaculture researchers (left) on sea cages holding orange-spotted rabbitfish in Indonesia.

As part of our concerted efforts to support and encourage the next generation of Australians in study, careers and volunteering in international agricultural research, the Crawford Fund State Committees proudly support our Student Awards

These awards allow university students from around Australia to include an international component to their studies, to research and explore their chosen topic areas and gain international agricultural research experience and expertise.

One awardee from our 2019 cohort, Valentin Thépot from the University of the Sunshine Coast, has seen activities related to his project significantly delayed by the global pandemic, but he adjusted and adapted his plans for work associated with an Australian Centre for International Agricultural Research (ACIAR) project. We are excited to share the end result of his hard work and hear how he was able to go online to finish the project.

Aquaculture is facing two key challenges: replacing wild sourced ingredients in fish diets and better managing disease outbreaks. For the aquaculture industry to produce sustainable fish protein, it needs to reduce its requirements for wild-caught ingredients and minimise the impact of fish disease outbreaks which cost the aquaculture industry around US$6 billion annually.

An innovative approach underway by Valentin Thépot and his colleagues is investigating the use of low-trophic level fish (herbivores) and seaweed as functional ingredients to reduce the aquaculture industry’s reliance on wild-caught ingredients and to impact diseases. His work is associated with an ACIAR project on accelerating development of finfish mariculture.

The red seaweed Asparagopsis taxiformis.

“My research associated with Crawford Fund funding investigated the potential of seaweed dietary supplements as functional ingredient in the mottled rabbitfish Siganus fuscescens to improve their productivity and immune responses and how the fish gastrointestinal (GI) bacterial communities related to both the productivity and immune responses of the fish,” reported Valentin.

“As part of my PhD research, I have published a review highlighting the potential of seaweed dietary supplementation in farmed fish to improve their immunity and ultimately their resistance to disease.”

Research conducted at the University of the Sunshine Coast revealed that seaweeds, notably the red seaweed Asparagopsis taxiformis, can both boost the immune system and the growth rate of fish so that they are more resistant to disease and grow faster. This research was conducted using two fish species attracting significant commercial interest overseas but which have yet to realise their potential in Australia. The results highlight the promising potential of rabbitfish in aquaculture and of seaweed as a dietary supplement for fish to improve their productivity and heath.

Blood sampling from a euthanised mottled rabbitfish juvenile for the measurement of immune responses (left), and the laboratory where the fish feeding trials were performed at Bribie Island Research Centre, QLD (right).

“The marine opportunistic omnivorous rabbitfish Siganus spp. predominantly eat seaweed in the wild and thus require little to no fishmeal in their diets. In addition, rabbitfish can elongate and desaturate short-chain fatty acids to form the highly-unsaturated fatty acids that must be provided to other marine fishes by the inclusion of fish oil in diets,” explained Valentin.

The first feeding trial Valentin conducted investigated the effects of 11 seaweed species as dietary supplements on the innate immune response on S. fuscescens. From that trial he also examined the effects of the seaweed dietary supplements on the fish GI microbiome, for fish health.

Adult mottled rabbitfish in the laboratory at the Bribie Island Research Centre.

His second feeding trial investigated the best performing seaweed treatment discovered in the first trial but this time with a focus on growth. He again investigated the effect of the seaweed supplements on the GI microbiome of the fish to explore potential links between certain bacteria and growth.

At the start of his PhD, in October 2017, Valentin went to the Research Institute for Coastal Aquaculture and Fisheries Extension in Barru (South Sulawesi, Indonesia) and conducted some initial trials with Siganus guttatus broodstock and larvae.

Valentin was supposed to return to Indonesia to perform additional feeding trials but because of the COVID-19 pandemic this work was replaced by an online symposium with his ACIAR project colleagues in Australia, Indonesia and Cambodia to discuss his research on rabbitfish, seaweed supplements for fish and aquaculture research in general.

Valentin and his colleagues during the online symposium.

During the four day-symposium Valentin gave four presentations to share the results of the potential of seaweed as functional ingredient for farmed fish, and notably the potential of the red seaweed Asparagopsis taxiformis to improve the immune response and productivity of fish.

The work has received significant media interest, for example in the Sunshine Coast News, 7News Sunshine Coast and on the ABC.

“Although I was unable to travel to Indonesia, the use of online communication platforms allowed me to share the results of my research with my ACIAR colleagues. This was an enriching experience on both sides with the sharing of results and techniques used in the nutrition of rabbitfish and the use of seaweed as an ingredient in the diet of farmed fish,” said Valentin.

He noted the benefit of the research in developing collaboration with colleagues overseas and in Australia.

“I hope that my work can shed some light on rabbitfish as a promising novel and environmentally sustainable aquaculture species in Australia since we have in our coastal waters at least three Siganus species with commercial potential that are already farmed overseas.”

Challenges such as climate change, overfishing and increasing demand for seafood will only exacerbate the push towards adaptation and innovation in aquaculture. It is thanks to ACIAR and the Crawford Fund that I was able to take an innovative step towards what a more environmentally reponsible aquaculture might look like tomorrow. I also want to thank my PhD supervisors Dr Alexandra Campbell, Dr Michael Rimmer and Prof. Nicholas Paul for their guidance and mentorship during this project. Sincere thanks also go to my colleagues in Indonesia at the Research Institute for Coastal Aquaculture and Fisheries Extension Maros, South Sulawesi, and my colleagues in Cambodia at the Mariculture Research and Development Centre, Sihanoukville, Cambodia,” concluded Valentin.