Precision nutrition is a key practice in modern livestock production. It is the cutting-edge approach to provide the animals with the exact nutrients required for optimal growth, health, and productivity. It also leverages with the right balance of nutrients at the right time. Where are we with precision nutrition in fish farming? The challenge is the number of species, the environment fish are farmed in (freshwater, brackish water, and seawater), culture models (ponds, tanks, cages, and controlled systems) and density. There are many permutations.
A session at TARS 2024 on Finfish Aquaculture, covered a good start towards a framework on precision nutrition for fish farming as addressing this is critical towards developing species-specific feeds for improved efficiency and at all life cycle stages. Four presentations set the stage, starting with information on standardised processes for ingredient assessments. Another industry demand is reducing cost/kg fish produced which requires nutritional modulation for better feed efficiency and for health intervention to increase survival rates.
“Precision nutrition requires understanding the dietary needs of different animal sizes and essential nutrients. It is important to manage diet palatability and sensory perception in fish to enable some capacity to manage their feed intake.” Brett Glencross
It all starts with the right approach to ingredient assessment “The evolution of ingredient assessment: a feed is still only as good as its ingredients,” said Dr Brett Glencross, Research Director at IFFO and Honorary Professor at the University of Stirling, Scotland.
He discussed the evolving strategies for ingredient assessment in feed formulation, noting that modern diets focus more on nutrients than ingredients. As such, ingredient assessment also needs to increase its objectivity in line with those demands. Precision nutrition requires understanding the dietary needs of different animal sizes and essential nutrients. It is important to manage diet palatability and sensory perception in fish to enable some capacity to manage their feed intake. Diet formulation involves two information sets: understanding the animal’s needs to design the feed, and knowing the ingredients, their constraints and how to manage them.
“We focus on nutrients – not ingredients, and how to manage them effectively,” said Glencross. “With modern diets, we aim for precision nutrition, focussing on digestible energy (DE) and digestible protein (DP) rather than crude measurements. It is this digestible supply that impacts performance.”
He emphasised the importance of understanding how requirements change with fish growth stages and animal sizes. “Without this knowledge, precision approaches are impossible. We know that requirements change with fish size, so we need to accommodate this in our formulations. Furthermore, formulating based on crude nutrients alone is inadequate without understanding digestibility.”
Glencross outlined a structured four-step approach for ingredient assessment ensuring a thorough evaluation of each ingredient’s value and suitability for inclusion in animal feed. The stages are:
Characterisation: This stage involves identifying and documenting the fundamental properties and composition of the ingredient. TDS or technical data sheets are commonly used at this stage, to provide detailed information about the ingredient’s characteristics. This stage is often a desk- top based preliminary evaluation.
Digestibility and palatability: This stage is an evaluation on how well the ingredient can be digested and its appeal to animals. Digestibility measures the proportion of the ingredient’s nutrients that can be absorbed, while palatability assesses the likelihood of the animals consuming the ingredient.
Utilisation and growth: This stage investigates the effectiveness of the ingredient in supporting the growth and overall health of the animals. It includes studying the ingredient’s impact on growth rates and other performance metrics.
Omics responses, immunological responses, meat quality, and functionality: This final phase is largely the ancillary studies that may add value when added to steps 1 to 3. It aims to examine the broader biological responses to the ingredient, including omics responses such as changes in gene expression (transcriptomics), and metabolites (metabolomics), and immune system reactions, as well as the quality of the meat produced and the functionality of the ingredient within the diet.
More details are available here: The power of nutrition for the industry in Asia, Aqua Culture Asia Pacific, January/ February 2023, pages 38-41.
Glencross concluded that all ingredients have strengths and weaknesses, and the key is to find the complementarity among them. Sustainability and the environmental footprint of feed ingredients are also becoming increasingly important. In many cases these criteria are now included in the stage 1 characterisation step.
The science of taste
In the nutrition process, intake is the number one driver of variation in performance. Sofia Morais, Innovation AQUA Team Leader at Lucta S.A., Spain, explained how taste impacts aquaculture productivity and its application in creating effective fish feed. She highlighted, “It is important to note that food recognition in fish involves the identification of nutrients rather than specific ingredients. Fish possess many unique, special, and highly developed sensory systems.”
Three of these systems are directly involved in feed intake: smell, taste, and solitary chemosensory cells (SCCs). These systems use chemical signals to help fish locate food sources, with taste being key in the final decision to consume food.
Olfaction, or smell, and SCCs are the first to respond in the feeding behaviour process. They are the long- distance sensing systems which the fish uses to detect the food far away and to orientate itself towards it. Taste is the only sensory system that is exclusively used for feeding. It is a short-distance sensing system which finally determines consumption.
Taste modalities in vertebrates help identify food quality, guiding dietary choices. There are five taste modalities (Figure 1). Morais explained that bitter compounds often signal toxicity, sour indicates microbial degradation and spoilage and warns the fish that the source of food is no longer fresh. Umami and sweet receptors detect vital nutrients like amino acids and carbohydrates.
Morais stated that taste sensing continues after feed ingestion in fish, involving enteroendocrine cells (EECs) along the gastrointestinal tract (GIT). These receptors play a crucial role in sensing food chemostimulants as they travel through the GIT, regulating satiety, gut transit, digestion and absorption.
Stimulants that attract or make food palatable usually have low molecular weights, such as free amino acids and small peptides. These water-soluble substances disperse easily and are found in high concentrations in attractive foods (or ingredients). They leach from pellets, signalling food to animals. Mixtures of these stimulants in specific combinations are more effective than single compounds.
Taste preference varies by species. Recently, fishmeal has been reduced in diets, causing palatability issues. To achieve positive feeding cues, formulators are now using specialty ingredients like hydrolysates and krill meal, and additives, rich in stimulants.
Sensory additives can be applied to enhance the palatability of feeds with reduced fishmeal levels. The supplementation with a palatability enhancer (PE) had a significant positive impact in specific growth rate, feed intake and feed conversion, as shown in a barramundi trial in Thailand. The performance of the control diet containing only 15% fishmeal was suboptimal, despite being reinforced with krill and squid meal.
More details: Taste matters: Exploring the fish gustatory system for overcoming aquaculture challenges by Morais, S., 2025. Aqua Culture Asia Pacific, January/February 2025, pages 25-29.
These additives may become useful tools for nutritionists in developing future aquafeed formulations with emerging ingredients. For example, single cell proteins, fermentation products of various waste streams, or insect meals are often not recognised as food or are avoided by many farmed species.
“Umami and sweet receptors detect vital nutrients like amino acids and carbohydrates”
– Sofia Morais
Finally, Morais stated that using specialty ingredients and additives, boosts feed intake and efficiency, thus enhancing profitability. Reducing feed waste also supports sustainability in aquaculture.
A molecular perspective on astaxanthin in finfish aquaculture
While astaxanthin is vital for pigmentation, it also plays key roles in reproductive fitness, overall survival, and as an antioxidant, it reduces oxidative stress and lipid peroxidation in fish, according to Dr KP Chan, Regional Technical Team Lead for Vitamins & Carotenoids, Asia Pacific, BASF Animal Nutrition. Carotenoids differ by their oxygen molecules; astaxanthin’s four oxygen molecules dictate its chromophoric and antioxidant properties.
Chan described the metabolic characteristics of carotenoids. Red carps convert lutein/zeaxanthin to astaxanthin and store it, while seabream cannot convert beta-carotene and require a dietary source. Astaxanthin is used in integument for aesthetics and reproduction, and in the liver for cellular functions and antioxidation; it is also vital for ovary development, fertilisation, hatching, larval growth, and egg quality.
Focussing on stressors in fish, Chan described how astaxanthin works in stress management.
“Its molecular structure allows it to intercalate into the lipid bilayer very effectively and sequester the reactive oxygen species (ROS). A study by Qiang et al. (2022) demonstrated that fish fed with 150mg/kg feed astaxanthin exhibited considerable enhancements in terms of growth, feed utilisation, as well as viscerosomatic and hepatosomatic indices.”
In terms of dosage, as shown with the tilapia, an inclusion rate of 150mg/kg feed produced optimal performance for the tilapia. “Beyond this level, we see that the performance equals that of the negative control meaning that the astaxanthin functions as a pro-oxidant i.e. it induces oxidative stress. It becomes a metabolic load for the fish and affects the performance of the fish. For shrimp pigmentation, dosage depends on farming conditions, stress, growth and feed. There is no fixed rule but typically around 50-100ppm.”
Why micro-encapsulate astaxanthin?
The compound has a large molecular weight close to 600mg and in the native form, is crystalline. “Nothing is going to happen if fed as crystalline astaxanthin since it is not soluble in water and in itself, is very susceptible to oxidation. We need to convert this from a crystalline into an amorphous form, breaking them into smaller particles and microencapsulate.”
“Overall, the choice of astaxanthin formulation can determine its effectiveness in enhancing pigmentation, growth, and reproductive performance in aquaculture species”.
– KP Chan
Micro-encapsulation of astaxanthin improves its stability, bioavailability, and ease of handling, making it more effective in aquafeeds. It improves bioavailability, ease of handling and allows for rapid dispersibility in cold water which is ideal for post-pelleting liquid applications (PPLA).
Two technologies stabilise astaxanthin through microencapsulation. Beadlet technology traps finely dispersed astaxanthin in a solid matrix like silica, making the beadlets stable and dust-free for extreme processing. Granulation technology creates cold water dispersible granules, suitable for post-pelleting liquid applications and quick dispersal in water. Both methods aim to improve the stability, bioavailability, and handling of astaxanthin in aquafeeds.
Chan noted that synthetic astaxanthin deposits more in fish muscle than natural astaxanthin, suggesting that it is more effective for enhancing pigmentation. Although effective, natural astaxanthin shows lower deposition levels when used at the same dosage.
Overall, the choice of astaxanthin formulation can determine its effectiveness in enhancing pigmentation, growth, and reproductive performance in aquaculture species.
Feed additives to reduce mortality in tilapia farming
“Indonesia’s farmed tilapia faces challenges from stress and diseases. High stocking densities over 200 fish/m² increase stress and disease susceptibility, impacting productivity and profitability,” said Abung Simanjuntak, Technical Expert Manager – Aqua Region Greater APAC, dsm-firmenich. Stress also arises from handling, transportation, disease treatment, and feeding regime.
To mitigate these challenges, it is crucial to focus on controllable aspects such as genetics, feed, and farming methods while adopting sustainable practices and innovative solutions. The targets are higher survival rates (current averages are 60-70%), fast growth and feed efficiency, considering, the uncontrollable aspects, diseases, and the environment. In feeds, use of more plant meals brings in another dimension as these meals have 10-45% indigestible fractions.
Abung discussed how essential oils at different dosages and combinations of organic acids reduce mortality. “When the feed is enhanced with organic acid, there are added benefits such as increases in feed efficacy. Exogenous enzymes increase nutrient utilisation and improve the digestibility of the raw material. Phytase reduces the phosphorus in the environment as well as in the feed formulation. The overall effects are lower nitrogen in the water environment, less eutrophication and harmful algal bloom (HAB). Ultimately, in high density tilapia farming, we reduce the pathogen load.”
“The use of more plant meals brings in another dimension as these meals have 10-45% indigestible fractions”. – Abung Simanjuntak
However, Abung cautioned that it is important to understand the challenges within the whole farm ecosystem. “Our feedback from tilapia farms show benefits from feeds supplemented with feed additives go hand in hand with farm practices. For example, we need to find the best dosage of additives in the different farming systems (cages or flow through systems) to see any benefits.”
More on palatability
Dr Romi Novriadi from Jakarta Technical University of Fisheries moderated the panel and Q&A. Piet Vertstraete, Managing Director of 4SEA Consulting in Thailand, emphasised the significance of palatability in marine fish feed formulations. He discussed stabilising feed composition during raw material changes and using palatants to improve feed intake under stress or to enhance performance.
Vertstraete explained that one example is the initial feeding after transferring fish from the hatchery to grow- out cages. Palatants are frequently used during stressful conditions or when there is a need to produce larger fish to meet market demands.
Palatability enhancer and disease mitigation
Morais explained that it is hard to simulate experimentally
the role of palatability enhancers during disease outbreaks. “When fish face mortality and pathogens, they often stop feeding as their metabolism prioritises survival. Diseases exploit stress, and prolonged or repeated stress can cause immunodepression in fish. At this critical stage, improving feed and energy intake levels is essential for coping with stress.”
She noted that farmers are aware of the conditions that lead to the development of pathogens and often use functional feeds or add their own functional ingredients to feed. These functional compounds, such as phytogenics, may be bitter and unfamiliar to the fish. This situation can result in reduced appetite and an adverse response to the feeds. While it is possible to enhance palatability at this critical point, proving its effectiveness might be challenging.
Vertstraete gave an example of marine fish farming in the Mediterranean with an overwintering cycle. When temperatures drop, digestion, the immune system and membrane fluidity are affected, and fish eat less. At the same time, opportunistic bacteria get a chance to challenge the fish. “Using functional ingredients and palatants can encourage fish to eat and stay healthy, even if they don’t grow much,” he said.
Measuring palatability
Several methods exist, such as adding palatants to feeds and evaluating performance on lab scale. Verstraete noted that the real test is feeding under farm conditions and evaluate feed intake. A robust software system can track various cages under different conditions and formulations based on lab trials. This is efficiently implemented in large fish farming companies. Powerful information systems can connect feed formulations and ingredient choice to farm performance.
For Abung, it is important to test in both controlled and uncontrolled environments. “After testing, we focus on environmental factors and actions. It is essential to understand both factors. We should know the differences between uncontrollable environmental factors and controllable aspects. The decision based on these tests will be made accordingly.” Many factors influence palatability, sinking rate, and pellet quality. Chan said, “I prefer to evaluate feed performance (FCR) and growth under each condition to see what works best for the farm.”
Morais highlighted the difficulty in gathering data to support perceptions, especially on farms. “Creating experimental models is nearly impossible, even in labs. Evaluating fish feeding behaviour is complex compared to shrimp, which feeds slowly. Few consider attractability when feeding fish. Fish typically eat quickly, focussing mainly on total feed intake is a rough measure of palatability.”
She added that underwater cameras and AI aid precision feeding by detecting fish hunger. This is effective in clear waters but difficult in low visibility conditions, such as in tilapia or pangasius farming.
Glencross explained that measuring palatability involves making nutrition adjustments, which can introduce inaccuracies. The goal is to find the least disruptive path, typically involving nutrition adjustments.
“On methodology, I would combine palatability and digestibility. For digestibility assessment, there is an acclimation period and feed intake is measured each day to assess the response of the animal. There are two key drivers controlling appetite – the hedonic response (seconds, minutes, hours) and the homeostatic response (days). When doing the digestibility study, acclimating for 2 weeks, we pick up hedonic responses which is relevant in terms of palatability.”
Digestible protein
Formulating diets based on digestible protein (DP) rather than crude protein (CP) means that the CP value is higher. According to Glencross, “Formulating on DP basis is crucial as DP is what really matters, not CP. While CP can vary within a range, there is a specific DP:DE ratio that must be maintained for optimal growth. In formulations, DP can derive from various sources.”
Vertstraete added that formulation is on DP and digestible amino acids which the animal needs for optimal growth. However, labels on bags still require CP values as per registered specifications. “But by selecting the most digestible ingredients, you narrow that gap between digestible and crude protein,” said Verstraete.
