Lysine in optimal amounts in the diet of tambaqui (Colossoma macropomum) improves zootechnical performance and body protein deposition
This study determined that the optimal dietary digestible lysine requirement for grow-out tambaqui (87–340 g) is 1.59% (0.53 g/Mcal digestible energy), a level that maximizes zootechnical performance and body protein deposition.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In the vast, sun-dappled waters of the Amazon, the tambaqui is a giant among fish, a species so vital to the region's economy that its farming has become a cornerstone of Brazilian aquaculture. Yet, for all its size and importance, the precise nutritional needs of this fish during its growth phase have remained somewhat of a mystery. Farmers often rely on feed formulas designed for other species, a practice that can be inefficient and costly. At the heart of this challenge lies a single, tiny molecule: lysine. This is an essential amino acid, a fundamental building block of protein that fish cannot create on their own and must obtain from their food. Without enough of it, a fish cannot build muscle effectively, no matter how much it eats. But giving too much is also wasteful, as the excess is simply excreted, polluting the water and raising costs. The question facing scientists was simple yet critical: exactly how much digestible lysine does a growing tambaqui need to thrive?
To find the answer, researchers at the Federal University of Maranhão and the State Institute of Education, Science and Technology of Maranhão set up a controlled experiment with two hundred and ten young tambaqui, each weighing roughly eighty-seven grams at the start. They placed the fish into thirty-five separate tanks within a closed water system, ensuring that every environmental factor, from water temperature to oxygen levels, remained perfect and consistent. The team then prepared a series of six different diets, each containing a slightly different amount of digestible lysine, ranging from a low level of 0.713 percent up to a high of 2.088 percent. These diets were crafted using a specific method where a high-protein reference feed was gradually mixed with a protein-free base, allowing the scientists to isolate the effect of the amino acid without changing the overall energy or other nutrients in the food. They also included a control group to verify that lysine was indeed the limiting factor in their setup.
Over the course of sixty days, the fish were fed by hand six times a day until they appeared full. The researchers watched closely to see how the different diets affected the fish's growth, how much they ate, and how efficiently they converted that food into body mass. They also examined the fish at the end of the trial, measuring the changes in their muscle, fat, and mineral content. The results painted a clear picture of how the fish responded to the varying levels of nutrition. As the amount of lysine in the diet increased, the fish grew larger and faster, reaching their peak performance when the diet contained about 1.58 percent of this amino acid. At this level, the fish gained the most weight and grew at the fastest rate. Interestingly, as the fish received more lysine, they actually ate less food overall, yet they still grew more, indicating that they were using the nutrients far more efficiently.
The study also revealed what happened inside the fish's bodies. When the diet was low in lysine, the fish stored more fat and less muscle. As the lysine levels rose to the optimal point, the fish shifted their energy toward building lean muscle tissue, depositing more protein and minerals while storing less fat. This shift is crucial because muscle is what makes the fish valuable for food. The researchers found that the point of maximum muscle building occurred at a dietary level of 1.59 percent digestible lysine. Beyond this point, adding more lysine did not help the fish grow any bigger; instead, the extra amino acids were simply broken down and wasted. The fish also became more efficient at holding onto nitrogen, a key component of protein, when the diet was balanced correctly, though this efficiency dropped slightly once the requirement was fully met and the fish began to excrete the surplus.
One of the most significant findings was that the amount of lysine needed by these larger fish was different from what is known for smaller, younger fish. While younger tambaqui require higher levels of this amino acid to support their rapid early development, these fish, weighing between eighty-seven and three hundred and forty grams, reached their peak performance at a slightly lower concentration. The study concluded that for tambaqui in this specific size range, the ideal diet should contain 1.59 percent digestible lysine, which translates to about 0.53 grams of the nutrient for every unit of energy in the food. This precise figure offers a clear target for farmers and feed manufacturers, moving away from guesswork and toward a science-based approach that maximizes growth while minimizing waste. By feeding the fish exactly what they need, the industry can produce healthier, larger fish more efficiently, ensuring that the tambaqui remains a sustainable and profitable resource for the Amazon region.
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