Multiple lysine forms support growth, production of catfish, Nile tilapia

Channel catfish and Nile tilapia diets provide platform for comparing forms of lysine used in feed, say researchers. 

A team of researchers in the School of Fisheries at Auburn University compared results​​ from diets for channel catfish and Nile tilapia created with either crystalline lysine or intact lysine, said Allen Davis, alumni professor of aquaculture and aquatic sciences. One project goal was to provide data on the effectiveness of crystalline amino acid use.

“There’s two sides to this fence – you have nutritionists who believe in crystalline amino acids or nutritionists [who] can’t put a true economic value on turning crystalline amino acids into protein,” ​he told FeedNavigator.

The team found that fish had similar results with either form of lysine when it was added to their diet, said Davis.

The group concluded that given the growth, feed conversion ratio and net protein retention data generated, an intact lysine from a high lysine corn protein concentrate is similar to using crystalline lysine as a supplement in catfish and Nile tilapia diets. “Thus, the high lysine corn protein concentrate is a feasible ingredient for aquaculture feeds, which can be used to balance the amino acid composition of the diet without addition of crystalline lysine,”​ they said.

Fishmeal costs

As fishmeal has become more expensive and aquaculture diets have turned to more plant-based protein sources, greater emphasis has been placed on meeting dietary amino acid requirements, including lysine, said the researchers. However, there has been a lot of debate generated on the use of crystalline amino acids in feed.

Although most comparisons find that crystalline sources work, sometimes nutritionists find them to be less efficient.

Historically, crystalline lysine has been used commercially to improve the amino acid balance and consequently the nutritional profile of the diets. However, the use of crystalline lysine has been observed to cause reduced growth and feed efficiency of fish in some studies related to palatability, pH change, leaching and rapid uptake (Zarate and Lovell, 1997 and Zarate et al., 1999).

In recent years, the researchers said the adaptation of new manufacturing technology has allowed the introduction of high lysine corn protein concentrate with intact lysine sources (Cargill's Lysto) to substitute crystalline lysine in the diets of farmed fish. 

The new product, said the authors, contains a high concentration of methionine, lysine, and other essential amino acids.

The study was one way to compare both uses, said Davis.

The group tested the lysine sources in channel catfish and tilapia because they are easy species to feed and evaluate, he said.

“Those are two of the primary species that we work with, and they both have acidic stomachs,” ​continued Davis. “A catfish has a shorter digestive system, and tilapia has a much longer intestine, so though they both have an acidic stomach, they have digestive tract differences.”​

Study details​

In the catfish feeding trials a series of nine diets with increasing levels of lysine from either a crystalline lysine additive or a high lysine corn protein concentrate were made, said the researchers. The crystalline diets were 1.21%, 1.34%, 1.45%, 1.56% and 1.72% and the high lysine corn protein were 1.40%, 1.57%, 1.77% and 1.91%.

Diets for the tilapia trial with levels of crystalline lysine were 0.92%, 1.11%, 1.23%, 1.34%, 1.54% and 1.65% and those made with high lysine corn protein included 1.13%, 1.38%, 1.61%, 181% and 2.02%, they said.

Diets were pelletized and samples were taken for analysis, they said. Each feed was given to a tank of nine fish with multiple replications.

Fish were weighed every two weeks for a 10-week period and weight gain, survival and feed conversion ratio were calculated at the conclusion, said the researchers.

Findings ​

Higher lysine amounts in the diet led to improved growth performance for both species, said the researchers. Groups getting the larger amounts of supplemental lysine had better final weight, weight gain, thermal-unit growth coefficient and a lower feed conversion ratio.

No combined effect of lysine source and supplement levels was found for channel catfish, they said. However, those getting the crystalline lysine had slightly improved protein retention.

In tilapia no differences were found for fish getting higher levels of lysine regardless of source, they said.

“High lysine corn protein concentrate was utilized as efficiently in meeting the essential amino acid requirements of channel catfish and tilapia as those of crystalline form,” ​said the researchers. “The corn protein concentrate with dried l-lysine fermentation product is a feasible ingredient for aquaculture feeds, which can be used to replace fishmeal and balance the amino acid composition of the diet along with other plant-based protein without addition of crystalline lysine.”​

“If this [inefficiency with crystalline amino acids] is real we thought we would see the difference – but we didn’t.”​