What makes feed more appealing for farm-raised shrimp?

Krill meal and scents additives can boost feed intake of farm-raised shrimp and may improve growth, find US researchers. 

A team of researchers based at Georgia State University and Integrated Aquaculture International are exploring ways to improve the attractiveness and palatability of the aquafeed used in shrimp production.

Initial experiments in the project were published in the journal Aquaculture ​and examined what shrimp found attractive in feed and what could be used to improve feed intake in pellets made with limited amounts of marine animal protein, said lead researcher Charles Derby regents’ professor of neuroscience and biology at Georgia State University.

“There’s very little out there that looks at behavior of the animals,”​ he told FeedNavigator. 

The group started with a look at the attractiveness of krill meal and response its use in pelleted feed, he said. A follow-up series of experiments tested blends of scents that could be added to feed.

“I would have thought that the [krill] additives would make animals eat faster, but it didn’t do that,” ​he said. “They were eating at the same rate, but eating more because they ate longer.”​

Why krill and alternatives​

Aquafeeds often rely on fishmeal, said researchers in the experiment report. “For example, they utilized 63% of global fish meal supply in 2009, with crustacean feeds accounting for 26% of fish meal used for aquafeed production (Tacon and Metian, 2008 and Chamberlain, 2010),”​ they added. 

Farm-raised shrimp is increasingly fed a diet made of soybean meal or plant-based products, they said. However, those feeds can be less attractive and palatable than ones that include animal meal.

Interest is developing in the use of feed attractants or chemostimulents that can be added to a plant-based diet to improve food intake and reduce waste, they said.

“The efficacy of krill meal, other animal meals, or other chemicals as chemostimulatory additives is often evaluated using growth rate as a measure (e.g. Harpaz, 1997, Felix and Sudharsan, 2004, Smith et al., 2005, Nunes et al., 2011 and Suresh et al., 2011),” ​they said. “However, this metric does not allow parsing out the underlying mechanisms, such as enhancement of consumption or direct nutritional effects due to the quality of ingested protein or other nutrients, which is important in designing better additives.”​

The initial study was designed to explore the mechanisms, like food handling or consumption rate, that are triggered by inclusion of the krill meal in the feed pellets, they said.

However, the end goal of a larger research project is to move past use of a product like krill meal and find artificial or non-animal additives that can be used to make shrimp feed more attractive and palatable, said Derby. Few people are looking at the process from the perspective of what chemicals are attractive to shrimp.

Experiment details​

In the initial experiment, a group of Pacific white shrimp were raised to small juveniles and then used in a series of behavior experiments, said the researchers.

Testing started by assessing shrimp reactions to the release of an aqueous extract of the feed ingredient and then of an aqueous solution of the feed pellet, said the researchers. The aqueous pellets were tested with inclusions of 0%, 1%, 3% and 6% of a commercial krill meal.

The pellets included soybean meal, poultry protein concentrate, wheat flour and other ingredients, they said. The work examined the mechanism underlying why the krill-pellets were more attractive.

A later stage of the experiment offered a series of pellets made from the four test diets to the shrimp and the number completely consumed was recorded, said the researchers. “For each animal, the time to eat each pellet, feeding rate (mg/min) for each pellet, total number of pellets eaten, total mass of pellets eaten, and total time spent eating were calculated,”​ they added.    

Initial results​

Work with aqueous krill meal demonstrated that it is attractive to the animals, said the researchers.

When present in the water, shrimp became more “alert, move toward, probe, and grab an airstone releasing it in a concentration-dependent manner and at concentrations as low as 13.3 μg/ml,” ​they said.  

In the later set of experiments, researchers found that including 6% krill meal meant shrimp ate more of the pellets during a 60-minute test, they said. The lower amounts of krill meal had results close to the control.

In a three-hour test, results were still highest for the 6% krill pellet, they said.

The krill pellets were more attractive in the longer, 60-minute feeding trials but not in the short simulated tests, they said. They also found that the inclusion of the krill did not make shrimp eat faster, but that they ate more of the feed.

“Taken together, our results support the idea that krill meal is a chemostimulant whose major effect when added to feed pellets is to increase the pellets' palatability by prolonging the feeding bout and thus the amount eaten, but not affecting how quickly a shrimp eats each pellet,”​ they said.

The team also found that there is a relationship between how attractive the shrimp find the pellets and how many they will eat, said Derby.

Next step research ​

Based on the information gathered, the research team designed a set of four separate diets for a follow-up study, said Derby. These include a control, one that includes 5% krill meal, and ones that include 1% or 5% of a blend of non-animal additives.

The blends were created based on both their ability to be palatable for shrimp and for being inexpensive, he said. The ingredients used also should not have the same availability challenges as popular products like fishmeal.

“It turned out that the lower concentration with the premix was more effective than the higher concentration,” ​he said. “[And, the] 1% was better than 5% krill. The 1% mixture is probably as cheap, or cheaper, than 5% krill.”​

Additionally, the group is now running a scaled-up grow-out experiment looking at use of the test products during an eight-week period, said Derby. In it 150 animals are being fed one of the four diets.

Shrimp getting the diet with 1% of the mixed additive are trending to have the largest growth, but it is very close to what is shown by shrimp getting the 5% krill meal, he said.

“Adding 1% mixture plus premix or 5% krill meal is enhancing the grow-out,” ​he said. “Their growth rate is faster in each of the first six weeks. So it sounds promising.”​

When the project is concluded a future step will be to scale up and run pond-sized tests, he said. “If this works we could adjust this for different species or life stages of these animals,”​ he added.