November 10, 2020
Nofima researcher explores tunicate meal's inclusion in fish feed
In the search for new, sustainable fish feed ingredients, researchers are working to see if the ingredients can be used in feed technically, Norwegian research institute Nofima said.
Tor Andreas Samuelsen and his colleagues at Nofima in Bergen, Norway, have a number of advanced techniques in store. Samuelsen said it is underestimated how important it is that new ingredients being introduced to fish feed actually have the correct technical quality.
Some ingredients require too much water while others require too high a temperature. Others disrupt the structural properties of the pellet.
"If you cannot produce feed with high physical quality, it will crush into pieces before it reaches the fish and the fish will not be able to eat it," said Samuelsen.
As part of the EU projects AQUABIOPRO-FIT (funded by BBI JU Horizon 2020) and FutureEUAqua (Horizon 2020) as well as the Swedish VINNOVA-funded project Marine Feed, the researchers have found that tunicate meal meets the nutritional requirements for ingredients that can replace some of the fishmeal and soybean meal commonly used in feed.
Tunicate meal is rich in the essential amino acids that fish need to build protein, but there's still a work to be done to reduce its salt content. Samuelsen tested the technical quality of tunicate meal and determined how much can be used in the feed.
Trial feeds were produced at a feed technology centre in Bergen. First, feed mixtures with different levels of tunicate meal were fed into an extruder, where the mixtures were cooked, kneaded, expanded and dried into pellets with a porous structure. The pores were then filled with rapeseed oil and then subjected to an oil leakage test.
Samuelsen then used a CT scanner to examine the microstructure inside the pellet. A CT scanner is an advanced X-ray device which makes it possible to see the 3D structure without slicing the pellet.
"By studying the pellet's inner structure, we gain a detailed understanding for example on how various ingredients affect the pore structure," said Samuelsen.
The scan showed that feed pellets with a large percentage of tunicate meal had large pores. The pellet with the largest pores adsorbed the highest amount of oil, but also resulted in highest oil leakage.
By running a mixture design experiment in the statistics programme, Samuelsen set some quality requirements for the pellet as he added tunicate meal to the feed.
He explained: "I want as much tunicate meal as possible in the feed mixture, but the pellet still needs to be of high physical quality and as porous as possible to make it adsorb the necessary quantities of oil. It also needs to have a high water stability."
Samuelse found that 50% of the fish meal could be replaced by tunicate meal without compromising the physical quality of the feed.
The work on tunicate meal is a good example of how important it is to have advanced tools for studying ingredients and feed, said Samuelsen.
He added: "We need to understand why ingredients differ from each other to be able to model the production process and physical properties of the feed before we start."