Research shows that red-bellied pacu fish grow best when fed diets containing 260 to 290 grams of carbohydrates per kilogram of food, with optimal growth performance and feed conversion at these levels. According to Gram Research analysis, exceeding 350 grams of carbohydrates per kilogram reduced growth and caused blood cell changes, indicating that too many carbs can harm fish health and performance.
Scientists studied how different amounts of carbohydrates in fish food affect how well red-bellied pacu grow and stay healthy. According to Gram Research analysis, fish fed moderate carbohydrate levels (between 260 and 290 grams per kilogram of food) grew the best and converted their food into body mass most efficiently. The research also showed that too many carbohydrates can change how fish process energy and may affect their overall health. This finding helps fish farmers create better diets that support healthy growth without wasting resources or harming the fish.
Key Statistics
A 2026 controlled trial of juvenile red-bellied pacu found that diets containing 260 to 290 grams of carbohydrates per kilogram produced optimal growth performance and feed conversion efficiency over 45 days.
Research on red-bellied pacu showed that fish fed the highest carbohydrate diet (350 grams per kilogram) exhibited reduced red blood cell counts but increased hemoglobin concentration, suggesting metabolic stress from excess carbohydrates.
A 2026 study of 45 juvenile red-bellied pacu demonstrated that moderate carbohydrate levels (260 to 320 grams per kilogram) increased intestinal enzyme activity for carbohydrate and fat digestion while reducing protein-digesting enzyme activity.
Research found that fish fed high-carbohydrate diets showed increased liver size and higher triglyceride levels in the blood, reflecting increased carbohydrate processing and storage in the body.
The Quick Take
- What they studied: How different levels of carbohydrates in fish food affect growth, body composition, digestion, and how fish bodies process energy
- Who participated: Young red-bellied pacu fish weighing about 70 grams at the start, divided into 15 tanks with three groups receiving different carbohydrate levels, studied over 45 days
- Key finding: Fish grew best when their food contained 260 to 290 grams of carbohydrates per kilogram of food, with better feed conversion and nutrient storage at these levels
- What it means for you: If you raise fish commercially, feeding the right amount of carbohydrates saves money and produces healthier fish. Too many carbs can reduce growth and affect fish welfare, so precise diet planning matters
The Research Details
Researchers fed young red-bellied pacu fish five different diets over 45 days. Each diet had the same amount of protein and energy but different carbohydrate levels: 230, 260, 290, 320, or 350 grams per kilogram of food. The fish were kept in 15 tanks and fed three times daily until they stopped eating naturally. Scientists measured how much the fish grew, how efficiently they converted food to body mass, and tested their blood and organ tissues to understand how their bodies processed the different diets.
This experimental design is called a controlled trial because researchers changed only one thing (carbohydrate level) while keeping everything else the same. This approach helps prove that carbohydrate changes, not other factors, caused the differences in fish performance. The researchers replicated each treatment three times to ensure their results were reliable and not due to chance.
Understanding how fish use different nutrients helps aquaculture farmers produce food more sustainably and efficiently. Since fish farming feeds billions of people worldwide, improving diet formulations reduces waste, lowers costs, and ensures fish stay healthy. This research also reveals how fish bodies process carbohydrates at the molecular level, which applies to understanding fish nutrition broadly
The study used a controlled experimental design with replicated treatments, which strengthens confidence in the findings. Researchers measured multiple outcomes (growth, blood markers, enzyme activity, organ size) rather than just one, providing a complete picture. The 45-day study period was long enough to see meaningful changes in fish growth and metabolism. However, the study focused on one fish species, so results may not apply equally to all fish types
What the Results Show
Fish fed diets with 260 to 290 grams of carbohydrates per kilogram of food showed the best growth and most efficient feed conversion. These fish also stored nutrients in their bodies most effectively. When carbohydrate levels went above 290 grams per kilogram, growth performance declined, suggesting too many carbs became counterproductive.
The liver (the organ that processes nutrients) grew larger in fish fed high-carbohydrate diets, and these fish stored more sugar in their muscles and liver. However, fish fed the highest carbohydrate level (350 grams per kilogram) had fewer red blood cells, which could indicate stress or reduced oxygen-carrying capacity.
Enzymes that help digest carbohydrates and fats increased at moderate carbohydrate levels, but enzymes that break down proteins decreased. This suggests the fish’s digestive system adapted to process more carbohydrates and fewer proteins when carbs were higher in the diet.
Fish fed moderate carbohydrate levels had higher triglyceride levels (a type of fat in the blood), which is normal when bodies process more carbohydrates. The intestines and liver showed changes in enzyme activity that reflected how the fish were processing different nutrients. Fish fed the highest carbohydrate diet had lower enzyme activity for breaking down amino acids, suggesting their bodies shifted away from protein metabolism when carbohydrates were abundant
Previous research on fish nutrition suggested that fish could use carbohydrates less efficiently than land animals, but this study shows that moderate carbohydrate levels actually support good growth in pacu. The finding that 260 to 290 grams per kilogram is optimal aligns with modern aquaculture practices that use plant-based ingredients (which contain carbohydrates) to reduce costs while maintaining fish health
The study examined only one fish species, so results may not apply to other types of fish with different digestive systems. The 45-day study period captures short-term effects but does not show whether these diets affect fish health over their entire lifespan. The research did not test whether these optimal carbohydrate levels work equally well for fish of different ages or sizes. Environmental factors like water temperature and quality were not varied, so results apply specifically to the conditions tested
The Bottom Line
Fish farmers should formulate diets containing 260 to 290 grams of carbohydrates per kilogram of food for juvenile red-bellied pacu. This range is supported by strong evidence from controlled experiments showing improved growth and feed efficiency. Exceeding 290 grams per kilogram is not recommended, as performance declines and fish welfare may be compromised. These recommendations apply specifically to juvenile pacu and may need adjustment for other fish species or life stages
Commercial fish farmers raising red-bellied pacu should apply these findings to optimize their feed formulations and reduce costs. Fish nutritionists and aquaculture researchers can use this data to develop better diets. Home aquarium keepers raising pacu may benefit from understanding that moderate carbohydrate levels support health, though commercial feed formulations typically already account for this. Fish species other than pacu may have different optimal carbohydrate levels
Fish showed measurable improvements in growth within the 45-day study period, suggesting benefits appear relatively quickly when diet is optimized. Farmers could expect to see improved feed conversion and reduced feed costs within weeks of switching to the recommended carbohydrate levels. Long-term health benefits over months or years remain unknown based on this study
Frequently Asked Questions
What is the best amount of carbohydrates to feed fish for growth?
Fish grow best with 260 to 290 grams of carbohydrates per kilogram of food. This range optimizes growth performance and feed conversion efficiency. Exceeding 290 grams reduces benefits and may harm fish health
Can fish digest carbohydrates as well as protein?
Fish can digest and use carbohydrates effectively when levels are moderate, but they process them differently than protein. At optimal carbohydrate levels, fish show increased enzyme activity for carbohydrate digestion while protein-digesting enzymes decrease
What happens if you feed fish too many carbohydrates?
Excessive carbohydrates (above 290 grams per kilogram) reduce growth performance, increase liver size, and may cause blood cell changes. Fish welfare can be compromised, making precise diet formulation important for health
How quickly do fish show growth improvements from better diet?
Fish showed measurable improvements in growth and feed conversion within 45 days of eating optimized diets. Farmers could expect to see benefits within weeks of switching to the recommended carbohydrate levels
Does this carbohydrate recommendation apply to all fish species?
This study examined only red-bellied pacu, so results may not apply equally to other fish species. Different fish have different digestive systems and nutrient needs, so optimal carbohydrate levels likely vary by species
Want to Apply This Research?
- Track weekly fish weight gain and feed consumption to calculate feed conversion ratio (amount of food needed to gain one unit of body weight). Compare your results to the optimal range of 260 to 290 grams carbohydrates per kilogram of diet
- Adjust your fish feed formulation to match the recommended carbohydrate range, or switch to a commercial feed labeled with carbohydrate content in this range. Monitor fish behavior and appearance weekly for signs of health changes
- Maintain a feeding log that tracks feed type, carbohydrate content, fish weight, and growth rate over 6 to 8 weeks. Compare growth performance before and after diet adjustment to confirm the change is working for your specific fish population and conditions
This research applies specifically to juvenile red-bellied pacu under controlled laboratory conditions. Results may not apply to other fish species, different life stages, or varying environmental conditions. Fish farmers should consult with aquaculture nutritionists before making major diet changes, as individual farm conditions, water quality, and fish genetics may affect optimal carbohydrate levels. This information is for educational purposes and should not replace professional nutritional advice for commercial aquaculture operations. Always monitor fish health and performance when implementing dietary changes
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.