Recently, yeast has become a new ingredient in aquaculture diets due to its strong performance as an immunostimulant and important nutritional enhancer for many farmed fish species. Researchers from King Abdulaziz University and the University of Rajshah (Indonesia), published a scientific review discussing different aspects of the use of yeasts in nutrition and immunostimulation in aquaculture.
Yeast based formulations and nutritional properties
Yeast is defined as a unicellular eukaryote containing membrane-bound organelles such as the mitochondria, nucleus and endomembrane system. Different types of yeasts such as: Saccharomyces cerevisiae, Kluyveromyces, Torulaspora, Saccharomyce
and torulopsis are used as protein sources in aquafeeds for shrimp and marine fish larvae farming.
The chemical composition of the whole yeast cell depends on the strain, culture medium and growth conditions, and subsequent processing after fermentation and development of cellular biomass.
Several studies have reported that S. cerevisiae contains about 32 to 62 percent protein.
Use of yeast in fish food
The use of yeasts as food in fish farming is not a new idea, since the 1980s a series of experiments have been conducted to verify their efficacy. Yeasts are a protein-rich, single-celled organism with a low toxicity potential and can be grown on a wide variety of substrates.
In addition to vital amino acids such as lysine and sulfur-containing amino acids, yeast provides several important vitamins such as vitamin B and folic acid.
Furthermore, researchers report that: S. cerevisiae is an effective natural source of protein when supplemented with fishmeal in tilapia food. Some yeasts are used as a feed supplement in aquaculture because they improve growth efficiency, disease resistance in fish, water quality and diversity of microbial communities.
Studies on the effects of partial and complete replacement of fishmeal with brewer’s yeast on the growth, body composition, feed intake and digestibility of juvenile tilapia are ongoing.
Yeasts as main protein component in aquafeeds
Ingredients of unicellular organisms are a relatively large class of materials that in some cases contain products extracted from bacteria, fungi (yeasts), microalgae or a combination thereof.
According to the researchers, the yeast of the candida species can effectively replace nearly 40 percent of fishmeal without affecting production or efficiency. Similarly, research also shows that using 100 percent yeast protein in rainbow trout diets leads to dangerous levels of uric acid in the kidneys and anemia.
On the other hand, the yeast S. cerevisiae contains several immunostimulating compounds indicating the potential use of all yeasts as natural immunostimulants in the diet of fish such as sea bream (Sparus aurata).
Yeasts as probiotics
The most commonly used probiotics in aquaculture include the use of yeasts containing bacteria from the Bacillus sex. Studies have shown that fungal polysaccharides are components of prebiotics that are recognized as a nutritional ingredient for the control of health and growing conditions in aquaculture.
Other studies have reported that Indian shrimp Fenneropenaeus indicus shows substantial improvement in immune response and growth when fed marine yeast beta-glucans.
Some yeasts such as: Debaryomyces hansenii, Rhodotorula sp, Metschnikowia zobeliiand Trichosporon cutaneumcommonly found in the gut of fish, is known to accelerate the development of the digestive system in fish.
Likewise, bioactive compounds with potential application in mariculture can be produced by marine yeasts in combination with nutritional supplements such as probiotics.
Use of yeasts in live food
Yeasts and microalgae are food sources that can be used in live food cultures (Artemia, Rotifera, Copepods). Significant impact on the production of gnotobiotics, according to the researchers Artemia has been reported when brewer’s yeast has been provided as the staple food.
On the other hand, a study of the optimal feeding speed and feeding frequency of Brachionus plicatilis determined that the adequate feeding rate for rotifers is an average of 0.3 grams of baker’s yeast for one million rotifers.
Finally, the researchers report studies showing that yeasts increase the density of copepods Thisbe furcata in culture and may be a potential candidate in the future to supplement the diets of these organisms.
“As discussed in this review article, yeast applications in aquaculture have become very important and feasible for inclusion as an alternative protein source in the fish feed industry,” they say.
Likewise, yeasts can be used as a promising food for breeding live foods (Artemia, rotifers, copepods); and as a probiotic to provide better immunity to pathogens, as well as to improve water quality in aquaculture crops. However, the researchers do not recommend completely replacing yeast with other types of proteins in aquafeeds, despite the potential benefits. They want complete replacement to negatively affect the kidney function of some fish species.