Carp is one of the most popular and widely cultivated fish in the world, thanks to its high nutritional value, fast growth rate, and adaptability to various environmental conditions.
However, carp farming also faces some challenges, such as diseases, parasites, and poor feed quality.
To improve the health and productivity of carp, some farmers use feed additives, such as acidifiers, that can enhance the digestive and immune functions of the fish.
One of the well-known acidifiers is lactic acid, which is naturally produced by some beneficial bacteria in the intestines of animals.
Lactic acid can lower the pH of the intestinal environment, inhibit the growth of harmful bacteria, and stimulate the activity of digestive enzymes and immune genes.
However, the optimal dose and effects of lactic acid on carp are not well understood.
Therefore, a RUDN University biologist and colleagues from Iran conducted a study to investigate the impact of lactic acid on the growth, health, and microbiota of common carp.
Lactic acid improves carp growth and feed efficiency
The researchers divided 240 juvenile carp into four groups and fed them with four different diets for 60 days.
The control group received a basal diet without any lactic acid supplement, while the other three groups received diets with 2.5, 5, or 10 grams of lactic acid per kilogram of feed.
The researchers measured the growth performance, feed intake, and feed conversion ratio (FCR) of the fish at the end of the experiment.
They found that lactic acid significantly improved the growth and feed efficiency of carp at all doses.
The weight gain of carp increased from 78% in the control group to 94% in the group with 5 grams of lactic acid per kilogram of feed.
The FCR, which indicates how efficiently the fish convert feed into body mass, decreased from 1.38 in the control group to 1.18 in the group with 5 grams of lactic acid per kilogram of feed.
The researchers concluded that 5 grams of lactic acid per kilogram of feed was the optimal dose for enhancing carp growth and feed efficiency.
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Lactic acid modulates intestinal enzymes, genes, and bacteria
The researchers also analyzed the effects of lactic acid on the intestinal enzymes, genes, and bacteria of carp.
They collected samples from the mid-intestine of the fish and measured the activity of trypsin and chymotrypsin, two enzymes that are involved in protein digestion.
They also extracted RNA from the samples and examined the expression levels of several genes related to immunity, such as interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), lysozyme (LYZ), and immunoglobulin M (IgM).
Moreover, they used polymerase chain reaction (PCR) and sequencing techniques to identify and quantify the bacterial communities in the intestinal samples.
According to the study, lactic acid significantly increased the activity of trypsin and chymotrypsin at all doses, indicating enhanced protein digestion in carp.
Lactic acid also upregulated the expression levels of IL-1β, TNF-α, LYZ, and IgM at all doses, suggesting improved immune response in carp.
Furthermore, lactic acid altered the composition and diversity of intestinal bacteria in carp. Lactic acid increases the abundance of beneficial bacteria, such as Lactobacillus sp., which can produce more lactic acid and inhibit pathogenic bacteria.
Lactic acid also decreases the abundance of harmful bacteria, such as Aeromonas sp. and Vibrio sp., which can cause infections and diseases in fish.
The researchers explained that lactic acid may exert its positive effects on carp by creating a favorable intestinal environment that favors beneficial bacteria over harmful ones.
The beneficial bacteria may then produce more lactic acid and other metabolites that can stimulate intestinal enzymes and immune genes in carp.
The researchers suggested that lactic acid supplements may be a useful strategy to improve carp farming by enhancing fish growth, health, and quality.
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