The stakes are considerable. Atlantic salmon ranks among the ten most produced and valuable marine fish globally, with production stable at around two million metric tons since 2000. Norway dominates the market, producing over 1.5 million metric tons in 2023. But cage-based farming is increasingly challenged by climate-driven sea surface temperature increases, which are linked to higher fish mortality, welfare problems, elevated operational costs, revenue losses, and environmental spillback effects. Climate projections indicate global sea surface temperatures will rise by 1 to 3 degrees Celsius over the next century, with the greatest increases expected at higher latitudes—precisely where much of the salmon farming industry is concentrated.

Salmon lice have plagued the industry since its inception in Norway in the late 1960s. Prevention and treatment costs in Norway alone are estimated at €610 million annually. The parasite exerts the greatest economic impact of any aquaculture parasite and also damages wild fish populations, including Atlantic salmon, sea trout, Arctic char, and Atlantic cod. Warmer waters intensify the problem because lice development, larval production, and infectivity are all temperature-dependent; higher temperatures shorten the time from non-infective nauplii to infective copepodites, substantially increasing infection pressure around farms. In Norway, the traffic-light regulatory system can reduce permitted production capacity by 6 percent in areas classified as red due to high lice-related mortality risk for wild salmon smolts.

At the individual fish level, lice attachment and feeding cause epithelial damage, osmotic imbalance, stress responses, immune activation, and reduced condition—all of which suppress feed intake and divert energy away from somatic growth. Delousing treatments compound the problem, as they commonly involve fasting, crowding, pumping, and exposure to freshwater, chemicals, heat, or mechanical forces, each associated with stress, injury, reduced appetite, and short-term biomass loss. Temperature itself has a direct and non-linear effect on salmon growth: feeding, digestion, metabolism, oxygen demand, and feed conversion are all temperature-dependent. Optimal growth for post-smolts and adults in seawater is commonly reported around 13 to 14 degrees Celsius, with performance declining at both extremes.

To identify which modeling frameworks could best handle these interacting pressures, the researchers followed PRISMA guidelines and searched Web of Science and Oria using combinations of salmonid species terms and growth-model keywords. An initial focused search on Atlantic salmon growth models returned 190 papers but yielded only 12 after screening, because most literature concerned the freshwater parr life stage rather than the marine production phase. The search was therefore broadened to include trout, charr, and general salmonid terms alongside specific model names such as Thermal-unit Growth Coefficient, Ewos Growth Index, logistic growth functions, bioenergetic models, Dynamic Energy Budget, Net Energy Balance, and nutritional models. This expanded search produced 712 papers, of which 23 farmed-salmonid studies met the inclusion criteria after 689 were excluded.

Wild salmonid models were systematically excluded from the final synthesis. The authors explain that these models are generally designed for ecological or population-dynamic questions—growth, survival, migration, density dependence—rather than farm-level production forecasting. Their assumptions about food availability, mortality, and management interventions differ fundamentally from aquaculture systems, where feeding is controlled, husbandry interventions are scheduled, and the relevant outputs are production biomass, treatment timing, and harvest outcomes. One additional study was added through targeted citation searching because it directly coupled a temperature-dependent Atlantic salmon growth model with sea-lice control and economic outcomes, bringing the final synthesis to 24 temperature-dependent studies.

The retained models fell into three main classes. Index and phenomenological models—including the Thermal-unit Growth Coefficient, Ewos Growth Index, and logistic growth functions—describe growth statistically without modeling underlying physiological fluxes. They require few inputs, typically temperature or degree-days, initial and final body weight, and growth duration, all routinely available from farm production records. Bioenergetic models represent growth through energy intake, metabolic expenditure, and allocation to somatic growth, storage, or waste, incorporating feed intake, energy density, digestibility, body composition, and temperature-dependent metabolism. Nutritional models focus specifically on how feed composition, digestibility, and nutrient partitioning determine growth, body composition, feed efficiency, and waste production.

Performance varied considerably across model classes. Empirical models often showed strong fit within controlled experiments or region-specific datasets—Thyholdt’s regional logistic growth functions for Norwegian farmed salmon achieved R² values above 0.95—but their transferability depends heavily on local calibration. Notably, temperature effects differed by region: warmer conditions increased growth in Northern and Central Norway but reduced it in Southern Norway, where fish are already closer to upper thermal limits. Mechanistic bioenergetic and nutritional models required substantially more parameters and higher-resolution data but could predict a broader range of outputs, including feed conversion, nutrient deposition, waste production, harvest timing, product quality, and economic consequences. Dynamic Energy Budget models were applied to simulate growth under environmental forcing in several studies, including site-selection analysis in the Yellow Sea and harvest-timing estimation across European systems.

The most striking finding was how rarely biotic stressors are explicitly integrated into growth models. Most retained studies did not represent parasites, bacteria, or viruses as dynamic drivers of growth, feed intake, mortality, or treatment timing. One framework linked deterministic growth models with stochastic host–pathogen dynamics, mortality, and economic loss, but its salmon case concerned viral disease rather than salmon lice. The closest salmon-lice example came from a 2014 study that coupled a Thermal-unit Growth Coefficient-based salmon growth model with empirical lice and treatment profiles, linking treatment events to direct costs, growth delay, added mortality, production loss, and profit in Norwegian farming. However, even this framework used an empirical lice profile rather than a mechanistic lice population model.

The review concludes that no single model class is optimal for all purposes, but for scenario-oriented assessment of warming and salmon lice in Atlantic salmon aquaculture, the most practical near-term framework is a validated, temperature-driven farmed-salmon growth model—locally calibrated with production and environmental data—coupled modularly to a lice-dynamics or infestation-pressure component. Such a framework would require an explicit lice module representing temperature-dependent development, larval production, infection pressure, attachment, and treatment thresholds, together with a stress-effect function translating lice burden and delousing events into reduced growth, appetite suppression, mortality, or delayed harvest. More complex bioenergetic or nutritional components should be added only when feed intake, waste output, nutrient retention, oxygen demand, or product-quality endpoints are central to the research question. As sea temperatures continue to climb and lice pressure intensifies, this modular approach offers the industry a realistic pathway toward quantitative climate adaptation planning.

Subject of Research: Growth modeling for farmed Atlantic salmon aquaculture under ocean warming and salmon-lice pressure

Article Title: Growth models for farmed post-smolt to adult salmonids: a systematic review for Atlantic salmon aquaculture under warming and salmon-lice pressure

Article References: Kleiven, S. K., Abdel-Fattah, D., & Bøhn, T. (2026). Growth models for farmed post-smolt to adult salmonids: a systematic review for Atlantic salmon aquaculture under warming and salmon-lice pressure. Frontiers in Aquaculture, 5, Article 1835152. https://doi.org/10.3389/faquc.2026.1835152

Image Credits: AI Generated

DOI: 10.3389/faquc.2026.1835152

Keywords: Atlantic salmon, aquaculture, salmon lice, growth models, sea surface temperature, climate change, bioenergetic models, Dynamic Energy Budget, Thermal-unit Growth Coefficient, systematic review, fish welfare, Norway

Salmon lice are ectoparasites that feed on the skin, mucus, and blood of fish. Their feeding activity creates open wounds that can become infected, reducing the market value of farmed fish and increasing the likelihood of secondary infections. Beyond the direct damage to individual animals, infestations impose enormous costs on the aquaculture sector. Sea lice infestations in Atlantic salmon farming cost the industry more than one billion dollars a year through mortality, lost production, and the implementation of control measures. Understanding the biology of the parasite at a molecular level is therefore considered a critical step in developing new, safe, and effective strategies for its control.

The central innovation of the new study lies in its sampling approach. Previous methods for extracting SEPs from salmon lice involved pooling together large numbers of individuals before analysis. While such pooled samples could yield enough material for detection, they averaged out the natural differences between individual lice. Those differences, the researchers argue, can provide vital insight for developing targeted treatments or vaccines, because they reveal how variable the parasite’s secretory arsenal is across a population. By contrast, the new method allows the collection of high-quality samples from a single louse per test, with substantial yields of secretory proteins per individual, while also reducing the potential for contamination of the samples with louse faecal material.

The collection procedure itself is elegantly simple in concept. Researchers place a small drop of solution over the mouthparts of an individual louse and allow the animal to release its secretory proteins into that droplet. The protein-laden solution is then examined using liquid chromatography tandem mass spectrometry, a state-of-the-art analytical technique that separates the components of a sample, breaks them into fragments, and analyses those fragments to reveal the exact protein composition of each sample. Applied to single-louse samples, this approach produces a detailed proteomic fingerprint of what each individual parasite is secreting at the moment of collection.

Using this assay, the team identified 148 secretory proteins in total, 64 of which were detected across each of the tested conditions. The consistency of that core set of proteins across individuals and conditions makes it particularly interesting from an applied perspective, because proteins that are reliably present in the parasite’s secretions could represent potential targets for vaccine development. A vaccine that prompts fish to mount an immune response against molecules the louse depends on for feeding or immune evasion could, in principle, reduce the parasite’s ability to establish itself on its host.

One of the most striking findings of the study was the degree of variation observed between individual lice. The secretory protein profiles of single animals showed wide variation in both the number and the diversity of proteins detected, a pattern the researchers note is consistent with what has been seen in other ectoparasites such as ticks and mosquitoes. This individual-level variability would have been invisible in pooled samples, and it underscores why the ability to study lice one at a time matters. If different lice deploy different combinations of secreted molecules, control strategies may need to account for that diversity in order to be effective across a whole parasite population.

The researchers emphasise that the methodology has value well beyond cataloguing proteins. Because the protocol allows reproducible, reliable, and efficient extraction of high concentrations of salmon louse secretions while minimising faecal contamination, it can serve as a platform for future experiments. Mr Dindial noted that the protocol could be used to investigate how drug or therapeutic treatments might alter louse secretory activity, which would allow scientists to test whether candidate interventions disrupt the parasite’s ability to feed or evade immunity. In this way, the assay functions both as a discovery tool and as a screening tool for evaluating new control measures.

The study also builds directly on a first-of-its-kind investigation led by Mr Dindial and published the previous year, which uncovered major differences in the secretions the parasite uses to feed and evade the immune system at different stages of its life cycle. Taken together, the two studies sketch a picture of a parasite whose chemical toolkit changes as it develops, and whose secretions vary from one individual to the next. That level of biological detail is exactly the kind of information needed to design interventions that are precise enough to work against the parasite while avoiding some of the drawbacks of existing treatments.

The need for better tools is pressing. Various treatments have been developed to tackle sea lice infestations in Atlantic salmon aquaculture, but some of these can be expensive, unreliable, environmentally damaging, or harmful to animal welfare. Chemical treatments can lose effectiveness as the parasite develops resistance, and mechanical or biological control approaches each carry their own limitations and costs. A strategy grounded in the parasite’s own secretory biology, whether through vaccination, targeted therapeutics, or the breeding of more resistant fish, offers the prospect of control measures that are both more effective and more sustainable than those currently available.

The research was funded by EastBio as part of Mr Dindial’s PhD studentship, with a funding contribution from the Moredun Research Institute. It was conducted in collaboration with the project Towards lice-resistant salmon: functional genetics and genome editing to enhance disease resistance in aquaculture, funded by the UK Biotechnology and Biological Sciences Research Council, the Sustainable Aquaculture Innovation Centre, and Benchmark Genetics Limited, and involving partners from the Roslin Institute at the University of Edinburgh, the Centre for Environment Fisheries and Aquaculture Science, the Atlantic Veterinary College at the University of Prince Edward Island, and Kames Fish Farming Ltd. The study, titled Investigation of a novel assay for the proteomic screening of the secretory and excretory products of individual salmon lice Lepeophtheirus salmonis, was published in Veterinary Parasitology on 1 May 2026. As the aquaculture industry continues to search for durable solutions to its costliest parasite problem, the ability to read the chemical language of individual lice may prove to be a decisive step forward.

Subject of Research: Proteomic analysis of secretory and excretory products of individual salmon lice for parasite control in aquaculture

Article Title: A University of Stirling study could pave the way for the more efficient study of the secretions that salmon lice use to avoid fish defences, potentially enabling the development of new strategies to protect salmon from infestations. Research led by PhD

Article References: A University of Stirling study could pave the way for the more efficient study of the secretions that salmon lice use to avoid fish defences, potentially enabling the development of new strategies to protect salmon from infestations. Research led by PhD. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: salmon lice, aquaculture, proteomics, mass spectrometry, secretory proteins, Lepeophtheirus salmonis, vaccine development, parasite control, Atlantic salmon, University of Stirling, Veterinary Parasitology, immune evasion