European centre of excellence
for sustainable water technology

Investigating the diet of worms

Published: 7 april 2017
Investigating the diet of worms

Anyone who enjoys a good seafood dinner will appreciate what Bob Laarhoven, a PhD student at Wageningen University, has been working on with his colleagues at Wetsus: analyzing the diet of the worm Lumbriculus variegatus, which is eaten by many carnivorous fish such as salmon and trout.

Based on his research results, Laarhoven is also spearheading a start-up company called Dutch Blackworms with the goal of developing a large-scale worm biomass production system for the fish industry—and ultimately, a more sustainable way to grow some of the most popular edible fish.

An important requirement in the aquaculture industry is to use fish feed that is not contaminated with heavy metals, micropollutants, or pathogens. One way to ensure this, is to grow the worms on a diet of organic material produced by waste streams from the food industries.

In a paper published in a recent issue of PLOS ONE, Laarhoven and his colleagues have reported on the development of a standardized agar sediment test that can determine which waste streams make good “worm food” based on their concentrations of protein and other nutrients that L. variegatus needs to thrive. Laarhoven’s test evaluates the worm growth performance of different waste streams and identifies which streams produce the greatest amount of worm biomass.

“The standardized agar sediment test makes it possible to control the growth conditions independently of the quality of the food,” Laarhoven said. “This could never be done without the addition of agar gel. Worms in these test setups have outstanding growth rates in comparison with other available test setups.”


                                   Aquatic worm reactor for controlled worm production.

This ability to raise fast-growing worms also has potential applications in research areas beyond the development of worm biomass production systems.

“I am hoping that this method will be noticed and accepted by scientists working in the field of eco-toxicology, because worms are excellent bio-indicators but test designs used nowadays never induce much growth,” Laarhoven said.

In another recent study, published in the Journal of Insects as Food and Feed, Laarhoven and his coauthors have shown that L. variegatus will grow and reproduce on organic waste streams produced by wheat processing byproducts from the food industry.

“Our work shows that worms are able to grow on a diet that only contains vegetable proteins—something which was never clear before,” Laarhoven said. “Also it reveals that sugars are not that important. It’s all about protein and fat level.”

Although the worms’ growth and reproduction rates were not as high as on a control diet containing a commercial fish feed, the use of wheat byproducts suggests a promising path toward developing a future worm biomass production system.

To bring these research results to the greater benefit of society, Laarhoven founded Dutch Blackworms on July 1, 2016.

“Dutch Blackworms is a start-up established by me and Hellen Elissen (former Wetsus employee and worm specialist),” Laarhoven said. “We believe that the mass production of aquatic worms using waste streams from the food industry makes good business, as there is a strong need for high-quality proteins for aquaculture feeds.”

At this moment, the company is increasing its worm stock to an amount needed for the first commercial production. The plan is to first sell the worms to wholesalers dealing with live feeds for ornamental fish owners, and then to commercial fish feed producers.

The inspiration for Dutch Blackworms, along with all of the research that makes it possible, is the type of multidisciplinary project that flourishes in an environment like that of Wetsus, Laarhoven explained.

“Wetsus is an amazing institute with a lot of resources that allow PhD students to design their research in ways that are normally more restricted,” he said. “This means that the results at Wetsus are often very impressive. The multi-disciplinary character and experts around allow you to get support from all kind of fields. For me this was really important as I combined wastewater technology, aquaculture and aquatic biology in one project. It changed my way of thinking, and I am more creative than ever before—not afraid anymore to combine different fields of expertise.”

While continuing his research and advancing Dutch Blackworms, Laarhoven also plans to complete his PhD later this year. In addition, he currently works on wastewater research and also has his hands full with two young children.

“Besides being and staying a happy dad, I am trying to spend most of my time extending the company,” he said. “I started a new job at the University of Groningen, working on the detection of cellulose in wastewater and the re-use of cellulose recovered from our own municipal wastewaters. The job is coming to an end, which allows me to spend more time on finalizing my PhD research and establishing Dutch Blackworms even more.”


The proposed sustainable solution for fish farming begins with waste streams from the food industries and ends with high-quality fish (farmed eels eating a block of frozen blackworms). Credit: Bob Laarhoven


Laarhoven B, Elissen HJH, Temmink H, Buisman CJN (2016) “Agar Sediment Test for Assessing the Suitability of Organic Waste Streams for Recovering Nutrients by the Aquatic Worm Lumbriculus variegatus.” PLoS ONE 11(3): e0149165.

B. Laarhoven, H.J.H. Elissen, C.J.N. Buisman, H. Temmink. “The carbon to nitrogen ratio in isoenergetic wheat based diets controls the growth rate of the aquatic worm Lumbriculus variegatus.” Journal of Insects as Food and Feed: 2 (4) - Pages: 225 – 231.

combining scientific excellence with commercial relevance