In a statement, the University of Coimbra (UC) explained that this new diet for aquaculture fish uses glycerol, a by-product of biodiesel, as an alternative ingredient, which "can help solve one of the great challenges of this business area".

Currently, the rations marketed "are too expensive and often unsustainable, as they are produced based on ingredients of animal origin".

The team, made up of Portuguese and French researchers, is led by Ivan Viegas, from the Center for Functional Ecology of the Faculty of Science and Technology of the University of Coimbra (FCTUC), who stressed that it is urgent to find "alternative ingredients whose nutritional and energy content, but also their ecological footprint, ensure a more profitable, safe, sustainable production and resulting in a nutritious final product".

"In this context, the development of aquaculture feed should focus on the use of by-products from other industries, based on the reuse, recovery and reuse of nutrients as postulated in the principle of the circular economy", he explained.

The project, which, in addition to the University of Coimbra, includes researchers from the Interdisciplinary Center for Marine and Environmental Research (CIIMAR) and the National Institute of Agriculture, Food and Environment of France (INRAE), bet on glycerol, "a byproduct of the biodiesel industry whose increase in global production has led glycerol to become an abundant ingredient, available and attest to how safe,  european food safety authorities, for use in animal feed".

"With the fuel crisis coming, biodiesel production will even be expected to increase. It is therefore urgent to find uses for its by-products," said the study leader.

According to Ivan Viegas, glycerol "is a molecule that is structural to humans, present, for example, in triglycerides."

"It has been successfully used as an alternative ingredient for swine and aviculture, however, its potential as an ingredient in aquaculture fish feed has remained unexplored," he said.

To evaluate the reliability, performance and limitations in the use of diets supplemented with glycerol, as well as its consequences, "two important species of farmed fish in Portugal were tested: rainbow trout and sea bass".

The experimental diets prepared by the scientists, "supplemented with 2.5% and 5% glycerol, were efficiently digested by both species," he found.

The various analyses allowed us to conclude that "the performance in [fish] growth may be affected in the highest percentage, however, intermediate supplementation up to 2.5% does not substantially alter the performance and efficacy in metabolic use and nutritional profile of the fillet".

According to the UC researcher, this means that "there is scope for the incorporation of glycerol into the diet of these species."

"We looked at the liver of the tested species, the main regulatory body of all 'metabolic machinery', and with the help of our INRAE partners in France, we found that there were no changes in the enzymatic regulation of the liver metabolism of these fish by glycerol," he said.

The study, developed in the last four years, was funded by the Foundation for Science and Technology (FCT) and gave rise to several scientific publications.

Source: SAPO