Modern aquaculture is based on a simple idea: without a precise and well-planned aquaculture nutrition There is no efficient growth, health, or profitability possible. In extensive, semi-intensive, or intensive farms, the requirements change, but the goal is the same: provide assimilable and sustainable nutrients that translate into quality biomass with minimal environmental impact.
This topic is not just academic; it involves daily decisions regarding formulation, raw material purchases, and feed handling. In fact, various research teams—such as those at the Multidisciplinary Teaching and Research Unit of the UNAM in Sisal (Yucatán)—they have been working for years to unravel which ingredients work, within what limits and How to improve digestion, efficiency, and sustainability of the production system.
What aquaculture nutrition covers and why it matters
When we talk about nutrition in aquaculture we refer to studying the effect of ingredients and diets on physiological, biochemical and nutritional responses de peces, crustaceans and molluscs of commercial interest. This includes the development of new formulations, its nutritional value by chemical composition, its behavior in water and the biodigestibility of nutrients and feed.
Aquaculture nutrition has two major areas of application: on the one hand, crops for productive purposes (for human consumption), and on the other hand, the aquaristicsIn both cases, the focus is on ensuring that each ingredient is digestible by the target species and that the diet performs its function as efficiently as possible.
The economic component is unavoidable: food is usually the highest operating cost item in semi-intensive and intensive crops. Therefore, a sound feeding regime requires a good understanding of the nutritional requirements and supply nutrients via exogenous feed and/or by enhancing the natural food, depending on the system (extensive, semi-intensive or intensive).
In intensive systems, stocking density makes natural feed weigh little or nothing; success depends on well-formulated complete diets and management that optimizes the feed conversion and growth without compromising water quality.
Fishmeal, microalgae, and new proteins: what to replace and how to do it
Fishmeal has been the historical pillar of the sector due to its Complete protein profile, useful lipid fraction, B complex and mineralsIt comes from species such as sardines and herring and, precisely because of its value, its extraction has put pressure on marine populations. Hence there is a race for reduce their inclusion without losing returns, linked to the innovation and sustainability in breeding de peces in aquaculture.
A promising line is to return to the marine primary producers: microalgaeThey offer valuable proteins, lipids, pigments, sterols, and vitamins. However, there are challenges: their cell wall limits digestion, some species contain toxins, and the cost of cultivation and processing remains critical. Therefore, their use is being investigated division (proteins, lipids, vitamins) and the modification of their components to maximize the bioavailability.
Farm experience indicates that it is unwise to switch suddenly to a complete substitution. In fact, the use of dehydrated powdered microalgae has shown suboptimal growth when replacement is overused. The technical recommendation is to identify useful species, separate and characterize their fractions, and validate inclusion with robust trials before scaling up. This transition may require 10–15 years of work coordinated if we want to alleviate the pressure on marine ecosystems.
Beyond microalgae, the market is evolving towards alternative ingredients with a good amino acid profile and a lower footprint: flours insects (Hermetia illucens, Tenebrio molitor, crickets), yeast (Saccharomyces cerevisiae) and other microbial biomasses, along with agro-industrial and fishing by-products. In insects, in addition to protein, the lipids as a source of energy and essential fatty acids, although they lack EPA/DHA at levels comparable to fish oils.
For long-chain n-3 fatty acids, certain microalgae such as schizochytrium (rich in DHA) and Nannochloropsis (EPA source) allow the design of mixtures that cover the needs of each speciesIn parallel, oil is being explored. Lipomyces starkeyi grown on waste, which could help diversify lipid sources and reduce dependency of traditional vegetable oils.
A key caveat when increasing plant-based raw materials is the mycotoxin contamination, a silent enemy: at low or moderate but sustained doses, they compromise growth and survival. Control depends on good practices throughout the chain and, where appropriate, on sequestering additives that minimize their intestinal absorption.
Proteins, amino acids and protein quality: requirements, methodology and pitfalls
Proteins are the most important macronutrient in fish and shrimp. The experimental literature places the protein requirements over a wide range (approx. 24–57% on a dry matter basis), with variations by species, life stage, temperature, and testing methodology. It is common to express needs such as % protein or as protein:energy ratio.
There are several methods to estimate requirements: from diets with increasing protein levels and observation of the growth response curve, up to the approach of maximum nitrogen retentionFor essential amino acids (EAA), gradual supplementation of crystalline amino acids and, alternatively, the quantification of the daily deposition on the corpseThe latter provides a robust and consistent reference across laboratories.
The EAAs for fish and crustaceans include, among others, lysine, methionine, threonine, tryptophan, arginine, leucine, isoleucine, valine, histidine and phenylalanine. Non-essentials remain essential at a physiological level, and some—such as cystine and tyrosine— can be formed from EAAs (methionine and phenylalanine, respectively), affecting the final dietary requirements.
A critical point: diets with a high percentage of free amino acids tend to perform worse than those based on "whole" protein, due to differences in absorption times and desynchronized plasma peaks. Although there are exceptions in certain phases (for example, in larvae of some crustaceans), the practical rule is to maximize high quality protein and use free amino acids with technological criterion (encapsulated, covered) or adjust power frequency to maintain a stable AAE profile in the tissue.
The protein quality of an ingredient depends on its AAE profile and its availability. Antinutritional factors (enzyme inhibitors in legumes), plant cell walls and certain processed foods can reduce digestibility. overheating causes Maillard reactions that trap the Lysine, decreasing its biological value. Evaluating the fraction of “available” lysine is a good indicator for monitoring these losses.
Lipids, carbohydrates, vitamins and minerals: practical ranges and priorities
Lipids provide metabolizable energy and essential fatty acids. In fattening diets, moderate values of 6–8% work well in many species, while in larval microdiets It rises to 10–20% and priority is given to phospholipids and PUFAs of interest. The choice of oil determines the steak profile and zootechnical performance.
Carbohydrates occupy a variable place: in shrimp, 5 to 25% depending on the system and species; in omnivorous fish they usually admit 30-40%, and in carnivores it moves between 10-20%. In larvae de peces, the carbohydrate fraction should not exceed, in general, the 12%, to avoid compromising digestion and growth.
Group vitamins B They are essential as metabolic cofactors; among the fat-soluble ones, the following stand out: A, E and K. In sensitive phases (e.g. larviculture) it is advisable to ensure vitamin C and E to maintain tissue integrity and protect lipids from oxidation. The stability of vitamins and their homogeneous distribution in the pellet are essential for each serving to provide the intended dose.
In minerals, many freshwater fish absorb Calcium of the water, but the match dissolved is usually insufficient and must be included in the feed (a common reference is 0,6% in the diet to cover minimums, modulating by species and phase). The formulation must assess interactions between minerals (for example, antagonisms) and balance with the rest of the nutrients, so that requirements are covered without overloading excretion.
Feed houses that work with a micronutritional approach - as described in the experiences of industrial formulation— adjust vitamins and minerals based on the species, stage, process and terms and conditions of use, avoiding clinical deficiencies and optimizing physiological robustness throughout the cycle.
Gut health, net energy, and RAS: efficiency starts in the gut
A healthy digestive system is the heart of farm performance. microbiota, intestinal morphology, immunity and absorption capacity are affected by feed quality, palatability and digestibility, and by stressors such as handling, temperature, salinity, pH, and density. The more robust the animal, tolerates stress better and the more constant its growth is.
When formulating, it is important to look not only at gross or digestible energy, but also at net energy (what remains after subtracting metabolic losses). A poor formulation can shoot these losses up to 30–40% and hinder conversion, while choosing ingredients with high digestibility coefficients and a good micronutrient profile increases actual efficiency.
The recirculating aquaculture systems (RAS) They are going further for sustainability and control: they allow reducing pressure on water bodies, recycling resources, stabilizing biosecurity and, with adequate diets, improve performance Minimizing system water contamination. Selecting RAS-compatible feeds (low fineness, good stability, high digestibility) is critical for the biofilter to function properly. do not overload.
In parallel, the preference for quality local raw materials helps to reduce the logistics footprint and —with the support of technologies such as NIR— know in real time the composition and the antinutrients (e.g. phytate) to adjust fine formulation and enzyme correctors.
Phytase and phosphorus: more digestibility, less excretion
The increase in plant raw materials brings with it more phytic acid, which binds phosphorus and reduces the availability of minerals and amino acids. Exogenous phytases release some of this bound phosphorus and provide extra-phosphoric effects (better digestibility, conversion and growth coefficients).
In rainbow trout, high doses (≈ 4000 FTU/kg) have been shown to reduce emissions to water by around 47% of phosphorus or with a 7% nitrogen, a significant environmental improvement in freshwater environments where phosphate is often the limiting nutrient eutrophicationThis translates into a lower risk of algal blooms and better water quality.
Controlled tests under different temperatures have found that with 2500 FTU/kg Higher and better final weights are achieved feed conversion, even without added inorganic phosphorus when the plant matrix is high. In warm water fish such as catfish (Ictalurus punctatus and the hybrid with I. furcatus), “on top” supplementation at 2500 FTU/kg improved weight already in the first month, lowered the FCR and elevated minerals in blood and liver.
En tilapia, a factorial design with two levels of available phosphorus (0,40% and 0,65%) and phytase (0 and 2000 FTU/kg) showed, as the main effect of the enzyme, better phosphorus digestibility, greater weight gain, better FCR and more phosphorus deposition in boneIn summary, phytase with high substrate affinity and rapid activity is a tool to reduce phosphate use, cut costs and limit the excretion of nutrients.
To maximize returns, it is essential to know the real level of phytic phosphorus in the diet (NIR helps), the culture temperature (which modulates enzyme kinetics), the transit time and the ingredient profile, adjusting doses and, if appropriate, combining with other enzymes to destroy antinutritional factors.
Species and cases: penaeids, Octopus maya, sea bass, grouper and octopus
In shrimp, the absence of certain lipids and sterols takes its toll: deficiency of omega-3 affects gonadal development and, if there is no cholesterol sufficient in the diet, the synthesis of the molting hormone is affected, complicating growth due to failures in the ecdysis. In addition, penaeids are sensitive to protease inhibitors (such as trypsins) present in some plant proteins, which requires processing and/or additives to neutralize this problem.
When replacing fish meal with lower protein vegetable pastes (35–45% vs. 50–70% for fish meal), it is common to see worst growth, not only by the protein percentage but also by amino acid profiles incomplete and the presence of antinutrients. The solution is to combine protein blends well balanced in EAA, process them to increase their digestibility, use enzymes when appropriate and close the formulation with adequate lipids and micronutrients.
Among fish, notable work has been done with local species such as the white sea bass’s most emblematic landmarks, the Caribbean red grouper and the octopus, with an emphasis on nutrition from the juvenile phases and pilot tests close to commercial conditions. A unique case is Octopus maya (Caribbean red octopus): Understanding its digestive system, its habits and the way it uses food has allowed us to define strategies for more balanced diets to their physiology.
In production, the criteria that decide whether a formulation “works” are the survival and growth (length and weight). The producer looks at the final biomass (survivors × weight per unit area), so any feed that does not offer the best growth It will be difficult for it to prosper in the market, even if it is cheap.
In parallel, there are warning signs in some local fisheries (e.g. grouper and octopus in Yucatan), which is driving interest in reproduce in captivity and close cycles. Nutrition is a key piece of the puzzle to achieve this without compromising the Economic performance.
Proteins: structure, classification and non-protein compounds
It is worth remembering that proteins are not all the same: there are fibrous (collagen, elastin, keratin), globular (enzymes, hormones, albumins, globulins, histones) and conjugated (phosphoproteins, glycoproteins, lipoproteins, chromoproteins, nucleoproteins). These nuances determine their solubility and digestibility, and therefore its use in feed.
Nitrogenous compounds are also derived from amino acids. non-protein crucial: purines and pyrimidines (DNA/RNA), creatine (energy reserve), bile salts, thyroid hormones and catecholamines, histamine, serotonin, porphyrins (hemoglobin) or niacin, among others. The diet helps the animal synthesize or receive These elements in the right quantity and time.
We must not lose sight of the antagonisms between amino acids (e.g. leucine/isoleucine) and the possible toxicity of certain amino acids derived from indicted (such as lysinoalanine in alkali-treated soybeans) or present in some legumes (mimosine in Leucaena, L-DOPA in Vicia faba). The selection and processing of raw materials is therefore decisive.
To evaluate the protein quality and performance of a feed, beyond the specific growth rate, indicators such as the conversion factor, feed efficiency, protein efficiency ratio and net protein utilization. Under controlled conditions (clear water or intensive systems), these parameters provide reliable comparisons between formulations.
Aquaculture nutrition is today an applied and dynamic field: from replacing marine flours and oils without losing performance, to maximizing digestibility with enzymes and biotechnology, through intestinal health care and adaptation to RAS. With real-time ingredient information, formulation by net energy, and antinutrient monitoring, it is possible to design complete diets that take care of the animal, the pocket and the environment.
