Global production of animal protein from aquaculture systems is increasing in importance; however, increasing intensification of aquaculture farming systems has exposed farmed fish and shellfish to multiple stressors, including environmental variability, nutritional imbalance, and pathogens, which can disrupt the normal physiological homeostasis of animals, suppress their immune response, and lead to reduced productivity. Therefore, the industry is increasingly interested in developing sustainable alternatives to conventional chemotherapy drugs. Therapeutic plant-based products, which can include medicinal herbs, phytogenic feed additives, and botanical extracts, represent a promising ecological alternative to conventional chemotherapy agents. This review provides a comprehensive analysis of the literature regarding the use of herbs for managing stress in aquaculture with an emphasis on their immunomodulatory, antioxidant, growth-promoting, and disease-mitigating properties. In particular, the roles of these botanicals in regulating the physiological processes associated with environment, nutrition, and health of aquatic animals are emphasized. Specific bioactive phytochemicals including flavonoids, alkaloids, terpenoids, and phenolic compounds are examined for their ability to modulate redox-mediated stress pathways, cytokine networks, and metabolic efficiency under conditions of high-intensity aquaculture production. A number of representative botanicals ( Curcuma longa, Zingiber officinale, Allium sativum , and Camellia sinensis ) have demonstrated significant potential in improving the immune response of fish, their feed conversion efficiency, and their resistance to pathogens. Overall, this review demonstrates that phyto-therapeutics offer biodegradable and low-residue options for reducing dependence on antibiotics, while at the same time promoting sustainable food production. We also discuss some of the challenges that need to be addressed before phytotherapy can be translated into practical application in climate-resilient aquaculture systems.
The rapid expansion of the invasive Atlantic blue crab Callinectes sapidus in the northern Adriatic Sea has caused severe ecological and economic disruptions, particularly within the Manila clam Ruditapes philippinarum aquaculture sector in the Po Delta lagoons. In response, fishers and aquaculture cooperatives have spontaneously implemented spatial control measures, including perimeter fencing, predator-exclusion netting, and selective trapping, to mitigate predation and safeguard clam farming areas. This study documents these interventions and analyzes trends in blue crab and clam landings between 2022 and 2024 to provide a more comprehensive picture of recent dynamics. Although clam production remains far below pre-invasion levels, spatial containment and daily trapping have facilitated a partial recovery of clam farming activities. These farmer-led initiatives represent a compelling example of spatial control, whereby invasive crab densities are suppressed below damage thresholds in key productive areas. In addition, efforts to commercialize the blue crab, particularly through new export markets, have helped offset economic losses. These findings provide valuable insights into adaptive, community-driven strategies for managing aquatic invaders. Considering the substantial national government investment to subsidize fishers and support blue crab disposal, the present study demonstrates how bottom-up initiatives can complement, and even anticipate, formal management frameworks.
Cleaner fish are stocked into salmon farms to prey on salmon lice Lepeophtheirus salmonis , acting as a form of continuous parasite control. Little is known about how lice adapt to this form of biological control, although anecdotal observations suggest that lice populations in salmon cages exposed to cleaner fish are smaller, lighter, and concentrated on the head region of the host. Here, we tested whether cleaner fish selected for lice size, pigmentation level, and position on the fish. We stocked tanks with adult lice-infested Atlantic salmon Salmo salar and either ballan wrasse Labrus bergylta or lumpfish Cyclopterus lumpus . After 60-80% of lice were removed by cleaner fish, the remaining parasites were assessed for size, pigmentation, and position on the fish, and were compared to lice on salmon in tanks without cleaner fish. Remaining lice after exposure to lumpfish were 19% smaller, but pigmentation levels and position on the fish were similar to controls. After exposure to ballan wrasse, remaining lice were 11% smaller, 12% less pigmented, and their distribution had shifted toward the head. Our results demonstrate that cleaner fish select for lice traits linked to detectability, although the direction and strength of selection differ between species. The extent of selective effects will depend on the relative deployment and efficacy of each cleaner fish species under commercial conditions, and how other widely used control measures act upon these traits. Here we demonstrate that selective pressure by cleaner fish exists, with less detectable lice, including those differing in pigmentation, size, or preferred position on the fish, being more likely to survive when exposed to cleaner fish. Future studies should assess heritability through multi-generational experiments to determine whether the traits that shifted in response to selection are heritable.
The ghost shrimp Neotrypaea californiensis is a species of burrowing shrimp that negatively affects Pacific oysters Magallana gigas, by burying and suffocating these shellfish, and is considered a pest by shellfish aquaculture workers. The present study was undertaken to better understand the transmission and lifecycle of a larval spirurid nematode, Ascarophis sp., and determine whether this nematode could enhance biocontrol of ghost shrimp on shellfish aquaculture beds. We examined the relationship between mean larval Ascarophis sp. abundance in estuarine N. californiensis populations on the US West Coast and the feeding activity of migrating sturgeon Sinosturio spp., which feed on benthic organisms including N. californiensis and are potentially the definitive hosts of this nematode. Mean Ascarophis sp. abundance in N. californiensis populations was positively correlated with sturgeon feeding pit density, and parasite abundance was higher in larger N. californiensis (carapace length >= 12.5 mm). While nematode abundance in N. californiensis populations was positively related to sturgeon feeding activity, there was no evidence that nematode presence in the shrimp influenced this relationship. A laboratory experiment revealed that while N. californiensis size affected their burrowing speed, Ascarophis sp. infection did not. Our results do not support the idea that the presence of Ascarophis sp. enhances N. californiensis predation or would be useful for biocontrol. However, our findings improve understanding of the relationship between Ascarophis sp., their intermediate host, N. californiensis, and their potential final hosts, migrating sturgeon species.
Coastal aquaculture plays an important role in supporting food production and sustaining livelihoods in Bangladesh. However, its rapid growth in recent years has also raised questions about potential environmental impacts. This study examined differences between aquaculture site (AS) and nearby non-aquaculture site (NAS) locations across 5 coastal districts to better understand how aquaculture activities influence water quality, sediment conditions, and biodiversity. Fifty sites were surveyed between November 2024 and January 2025, and samples were analyzed for nutrient levels, heavy metals, pesticide residues, and ecological indicators. The findings showed that ASs generally had higher levels of dissolved inorganic nitrogen and phosphorus, elevated chl a concentrations, and increased amounts of heavy metals such as Cd, Pb, and Cr. In contrast, NASs supported a greater variety of species and exhibited higher Shannon diversity indices. Multivariate analyses further indicated that aquaculture practices are closely associated with nutrient loading, accumulation of contaminants, and shifts in community structure. The study highlights the importance of adopting more sustainable management strategies, including better waste handling, the promotion of integrated multi-trophic aquaculture, and stronger regulatory oversight, to help protect the health of coastal ecosystems in Bangladesh while maintaining the benefits of aquaculture.
Particulate organic waste from salmonid aquaculture represents a potential food source for benthic communities in the vicinity of fish farms. This study investigated the incorporation of farm-derived organic matter into the benthic food web at 2 deep-water fish farms in western Norway, using fatty acid (FA) and stable isotope (δ 13 C and δ 15 N) tracers. Sediments and infaunal polychaetes were collected using a grab during production and fallowing periods, while decapods and demersal fishes were collected using trawls and baited pots. Sediments and fauna collected during production generally showed stronger aquaculture-derived biochemical signatures than those collected during fallowing, although responses differed between farms and species. Tracer FAs associated with salmon feed, especially 18:2(n-6), 18:3(n-3), 20:1(n-9), and 22:1(n-11), were elevated in sediments and opportunistic polychaetes, suggesting a rapid assimilation of farm-derived organic matter at the base of the food web. Decapods and demersal fishes also showed elevated tracer FA levels, revealing both direct and indirect trophic transfer of aquaculture waste to higher trophic levels. δ 13 C was less conclusive for tracing waste inputs, but δ 15 N revealed significant shifts in trophic structure between production and fallowing periods. During production, reduced δ 15 N separation among trophic groups suggested a compressed food web supported by a common farm-derived food source. During fallowing, most FA tracers declined and δ 15 N values increased, indicating reduced reliance on aquaculture-derived material and a shift toward more natural trophic interactions. Overall, these findings show that aquaculture activities alter deep-sea benthic food webs by increasing the uptake and trophic transfer of farm-derived organic matter.
Polychaetes are promising candidates for recycling organic waste from fish farming. In Norway, the polychaete Ophryotrocha craigsmithi Wiklund, Glover & Dahlgren, 2009 is currently being evaluated as an extractive species in integrated multitrophic aquaculture (IMTA), as preliminary research suggests high potential for carbon turnover. Yet knowledge gaps remain regarding dietary requirements and carbon turnover rates across their lifespan, which are crucial for estimating carbon turnover by populations. We aimed to estimate carbon turnover of O. craigsmithi feeding on different waste fractions: sludge, fish pellets, or bacteria cultivated with fish pellets. Respired carbon and carbon gained in tissues were measured for individuals, and their sum was used as a proxy for carbon turnover. No differences in respiration rates were found between diet treatments; hence, growth primarily determined the carbon turnover rates. Slow growth in polychaetes fed sludge (0.15% d-1) resulted in low carbon turnover, whereas a 6-fold higher turnover was found for individuals fed fish pellets. Allometric scaling coefficients for respiration rates were defined as log a = 0.76 and b = 0.80. Fatty acids from the bacteria-enhanced diet were assimilated by the polychaetes, though this did not improve growth or survival over the high-quality fish pellet diet. These findings provide insights into carbon turnover of fish farm waste by O. craigsmithi, and its dietary requirements alongside allometric scaling coefficients for estimating carbon turnover by populations. Our results highlight both the potential and limitations of O. craigsmithi as a waste recycling species in IMTA systems.
Cage culture has been restricted in many lakes and reservoirs due to eutrophication risks, but impacts, such as non-fed culture, vary by type and should be assessed. This study investigates the impact of non-feeding cage culture for silver and bighead carp fingerlings in Qiandao Lake, China, to better understand its ecological effects and inform environmental management. Our results showed that during the culture period of carps in cage culture systems, downstream sampling sites exhibited significantly lower concentrations of total nitrogen (TN: 1.028 +/- 0.236 mg l-1, mean +/- SD), total phosphorus (TP: 0.027 +/- 0.022 mg l-1), NH3-N (0.137 +/- 0.07 mg l-1), NO3--N (0.734 +/- 0.242 mg l-1), and chl a (4.123 +/- 2.197 mu g l-1) compared to upstream sites (TN: 1.189 +/- 0.283 mg l-1; TP: 0.035 +/- 0.016 mg l-1; NH3-N: 0.143 +/- 0.055 mg l-1; NO3--N: 0.82 +/- 0.278 mg l-1; chl a: 5.76 +/- 3.755 mu g l-1). In contrast, during non-culture periods, downstream TN, TP, and NO3--N concentrations showed no significant decline, while phytoplankton biomass and density were higher than during culture periods. These results indicate that non-fed cage culture of these filter-feeding fish species did not cause significant adverse impacts on water quality. Furthermore, Mantel test analysis revealed highly significant correlations (p < 0.01) between phytoplankton community dynamics and T, CODMn, TN, and NO2--N during cultivation, whereas significant correlations with TN and TP were observed in non-cultivation periods. Collectively, non-fed cages likely altered N and P limitation patterns via (1) fish grazing on algae, modifying nutrient availability; and (2) cage flow obstruction, enhancing particle sedimentation.
Mussel aquaculture is generally considered sustainable, but benthic impacts from biodeposition remain a concern. Mussel culture in The Netherlands is in transition from wild seed harvesting to spat mussel collectors (SMCs) for seed production. While the environmental impacts of conventional mussel culture systems have been widely studied, those of SMCs remain largely unknown. The use of SMCs differs from conventional submerged culture because they are deployed during different periods and in more high-energy environments. We assessed sediment characteristics at 3 high-energy Dutch Wadden Sea sites before (May) and after (September) SMC deployment, comparing areas inside and outside SMC zones. No significant differences in grain size, organic carbon, nitrogen, or stable isotopes (delta C-13, delta N-15) were detected between positions. Effect sizes for SMC proximity were small (Cohen's d = 0.47-0.54), contrasting with the large effects (d > 1.6) that are reported from conventional submerged culture in sheltered waters. Stable isotope analysis revealed strong system-wide seasonal changes (delta N-15 declined 3-9 parts per thousand; d = 0.95-2.18) that overwhelmed any potential localized SMC signals. Natural environmental gradients (depth, wave exposure, tidal currents) dominated spatial variability in all parameters. Strong tidal currents (0.8-1.4 m s(-1)) probably promoted continuous sediment redistribution, preventing biodeposit accumulation despite substantial operations (2.0-4.4 million kg harvest per site annually). High-energy environments effectively disperse biodeposits, supporting SMC deployment as a low-impact seed source when properly sited.
Atlantic salmon Salmo salar are exposed to parasitic sea lice as they enter the marine environment, particularly in areas with high densities of open net-pen salmon farming, where infestations can reach harmful levels. Given the correlation between infestations on farmed and wild fish, the highly specialized salmon louse Lepeophtheirus salmonis, which often causes disease outbreaks in salmon farms, is considered the main cause for sea lice infestations in wild populations. However, this has not been validated, as sessile life stages of L. salmonis cannot easily be distinguished from other caligid sea lice species. Through diagnostic PCR analysis of sessile sea lice (n = 1243) collected from wild Atlantic salmon post-smolts in central and western Norway, we document a large disparity in the occurrence of L. salmonis (98%) compared to Caligus elongatus (2%), the other sea lice species found on salmonids in Norway. The occurrence of L. salmonis was substantially greater among sessile sea lice in all fjords (n = 6) and sampling events (n = 9), and the contribution of C. elongatus only exceeded 8% in the 2 sampling events with the markedly lowest prevalence and mean intensity of sea lice. These findings demonstrate that L. salmonis is the dominant caligid sea louse on wild Atlantic salmon post-smolts migrating through fjords in central and western Norway.
Phytoplankton dynamics plays an essential role in the functioning and sustainability of integrated multi-trophic aquaculture (IMTA) systems. We investigated seasonal and spatial variations of phytoplankton communities in oyster Crassostrea angulata, kelp Saccharina japonica and non-cultivation zones of a subtropical marine ranch in southeastern China. High-throughput sequencing of 18S rDNA across 4 seasons and 2 water depths identified 402 operational taxonomic units (OTUs) (239 phytoplankton species), with Dinophyta as the most abundant group (average relative sequence abundance >36%). Contrary to previous studies of aquacultural impacts on phytoplankton communities, alpha diversity and community composition did not differ significantly among cultivation types (Shannon-Wiener indices: 2.620 ± 0.483, 2.606 ± 0.298 and 2.747 ± 0.200 for oyster, kelp, and non-cultivation areas, respectively). Instead, seasonal variation explained the majority of community turnover (R2 = 0.62, p < 0.001), with diatoms peaking in summer (average relative sequence abundance 23.2%) and dinoflagellates in winter (average 41.5%). Water temperature, dissolved inorganic nitrogen and chlorophyll a were the strongest environmental drivers. Null model analyses indicated that stochastic processes dominated community assembly (76% of β-nearest taxonomic unit index values between -2 and +2). These results demonstrate that natural seasonal succession, rather than aquaculture, governs phytoplankton dynamics in this system. The findings highlight the resilience of phytoplankton assemblages to moderate cultivation pressures and underscore the need for seasonally adaptive management in subtropical mariculture.
Understanding organic carbon dynamics in coastal bivalve aquaculture zones is essential for sustainable management, yet comprehensive studies on seasonal variations and aquaculture impacts remain limited. This study investigates the organic matter (OM) distribution and resuspension effects in Dinghai Bay, China, through field surveys in winter, summer, and autumn combined with controlled incubation experiments. Using the IsoSource approach with particulate organic carbon isotope (POC-δ13C) and amino acid (Asp/Glu) indices, we quantitatively assessed the contributions of resuspension, bacteria, phytoplankton, and terrestrial plants to particulate organic matter (POM). Results revealed significant seasonal resuspension patterns, with maximum intensity in winter driven by winds and minimal activity in summer during peak phytoplankton growth. Incubation experiments demonstrated that resuspension releases labile dissolved organic matter (DOM) from porewater, with microbial degradation being the dominant removal pathway in turbid waters. Additionally, clam-feeding experiments quantified their impact on water column chemistry, showing alterations in DOM composition (freshness) and decreased nutrient N/P ratios close to the Redfield ratio. Extrapolating the incubation results indicated that feeding activities reduced total suspended matter by 29% in the aquaculture area, but by less than 1% across the entire Dinghai Bay. Our results provide a new understanding of seasonal OM dynamics, resuspension impacts, and bivalve-aquaculture interactions, offering critical insights for sustainable coastal ecosystem management.
While aquaculture is increasing worldwide, there are concerns on the east coast of Canada about the influence of finfish aquaculture sites on crustacean distribution patterns. This study evaluated the abundance and movement of American lobsters Homarus americanus and rock crabs Cancer irroratus in the vicinity of 2 salmonid aquaculture leases in Liverpool Bay and Port Mouton, Nova Scotia. The study was done over a full 3 yr production cycle in Liverpool Bay. In Port Mouton, the study was done over 4 mo in 2019, 4 yr after salmonid production had ceased. Each year, around 50 lobsters and 50 crabs were tagged with acoustic transmitters and released at an existing fish farm or at 1 of 2 reference sites. Tagged lobsters travelled throughout Liverpool Bay and showed little affinity to the farm, as most lobsters caught and released adjacent to or below the farm did not stay in the area over time, and their home ranges did not exhibit much overlap with the farm. Very similar patterns were observed for lobsters released in the reference areas and in Port Mouton sites. In contrast, rock crabs moved more slowly than lobsters and seemed to be associated with the farm in Liverpool Bay, as their home ranges had a high overlap with the farm for crabs tagged directly under it. Overall, both rock crab and lobster associated with the Liverpool Bay aquaculture site, although the degree of association varied by species with rock crabs being much more attracted to the area under the farm.
The mortality of Pacific oysters Crassostrea gigas remains a persistent challenge for aquaculture, driven by complex interactions between environmental conditions, pathogen dynamics, and host factors. We monitored 96 sentinel oyster cohorts across 8 French sites over 4 yr (2014-2018) to assess age-specific mortality risks and environmental influences. Survival analyses and Cox hazard models confirmed that spat exhibit the highest mortality, while juveniles and adults demonstrate increased survival, reflecting age-related physiological resilience. Seawater temperature emerged as the strongest predictor of mortality, with risks increasing significantly between 16 and 24°C, highlighting a critical temperature threshold. Wind speed and relative humidity also modulated survival, likely influencing pathogen dispersal and physiological stress. Importantly, the impact of these factors was neither constant nor always significant over time, emphasizing the need for non-proportional risk functions to accurately capture mortality dynamics. Over the monitoring period, no significant increase in spat survival was observed, suggesting that resistance to infectious agents in farmed oysters has not markedly improved under natural environmental conditions. In response, oyster farming practices have evolved to integrate mortality risks, notably by increasing spat input and adjusting rearing conditions. This study underscores the necessity of incorporating environmental and life-history parameters into predictive models for improved risk assessment. By providing long-term insights into mortality patterns, our findings support the development of sustainable management strategies to enhance oyster resilience in the face of climate change and evolving pathogen threats.
Exposure of fish pens to strong currents in the open ocean facilitates the dispersion of farm-derived organic-rich solid wastes (faeces, uneaten feed) and thus lessens the effect of waste deposition on the seafloor ecosystem. Quantifying this effect requires tools that can detect deviations in seafloor ecosystem functioning, including trends that, if left unattended, accumulate to cause adverse effects. Here, we demonstrate a spatial gradient in the seafloor O2 demand, maintained by local deposition of farm-derived organic waste, that could be used as such a tool. To detect this gradient, we measured the in situ sediment-seawater O2 flux with 2 seafloor landers, a benthic chamber lander and an aquatic eddy covariance lander, deployed at 19 sites along a 3000 m transect heading towards a salmon farm in the D’Entrecasteaux Channel, Tasmania, Australia. We found that the seafloor O2 demand gradually increased within approximately 500 m of the farm from a background level of 220-560 to 1922 µmol m-2 h-1. The observed gradient was consistent with a gradient in the biological structure of the seafloor, demonstrated by traditional analyses of benthic macrofaunal assemblages. We discuss how regular monitoring of the seafloor O2 demand with autonomous benthic landers can support proactive ecosystem-based management of open-ocean fish farms.
Considering the environmental pollution of land-based and marine nearshore aquaculture, deep-sea cage culture has gradually become a more popular model for mariculture. Fish, an important biological group in marine ecosystems, are one of the main biological indicators of the quality of the ecological environment. West Island, in Sanya Bay, South China Sea, China, is situated in a national coral reef nature reserve, and its surrounding water is the location of the deep-sea cage culture. In this study, α and β species diversity in deep-sea cage and non-cage culture areas surrounding West Island in the South China Sea were studied based on environmental DNA (eDNA) metabarcoding to analyze the impacts of deep-sea cages on the fish community. According to the results, cage culture did not cause a change in fish species richness, but the Shannon-Wiener index and Simpson’s index of fish decreased. The major fish farming species Trachinotus ovatus had absolute dominance in the cage culture area (eDNA abundance exceeded 60%) and might be the main reason for the low level of species diversity in this area. In addition, the results of fish β-diversity indicated that there were significant differences in the composition of the fish community between deep-sea cage and non-cage culture areas; the dominant species in the cage area were omnivorous, while the dominant species in the non-cage area were carnivorous. Therefore, we speculated that cage culture may have caused changes in the feeding structure of the fish community.
Mathematical models play a crucial role in bivalve aquaculture research and management, facilitating the optimization of coastal aquaculture. These models vary in complexity and can be applied at different spatial and temporal scales and resolutions, which have implications for the research question and the required computational power. This study examined the performance of fjord- and farm-scale models in simulating bivalve growth and farm productivity, focusing on the effects of spatial and temporal resolution under a range of environmental conditions in the Hardangerfjord, Norway. We relied on 2 previously published models: a fjord-scale model (NORWECOM.E2E), which has been recently coupled to a dynamic energy budget (DEB) model to simulate mussel bioenergetics, and a farm-scale model that simulates the effect of the suspended canopy, defined as the floating infrastructure and crop, on local hydrodynamics to predict mussel growth using DEB. A series of numerical experiments revealed that the characterization of water currents in relation to the orientation of the farm is challenging and can lead to uncertainty in farm-scale models. Further, the discrepancies between modelling approaches were strongly dependent on the stocking biomass, with low biomass scenarios minimizing these discrepancies. Based on the results of these experiments, the NORWECOM.E2E-DEB fjord-scale model can be used to explore site selection and aquaculture-environment interactions without impacting the estimations of farm production to a critical level. The study underscores the potential of combining both modelling approaches for holistic coastal and farm management, providing valuable insights for future aquaculture development.
Capture-based aquaculture can reduce production times for slow-growing species and provide ecological benefits when overabundant populations are harvested. Globally, some barren-forming species of sea urchin are a target for capture-based aquaculture because of the valuable roe they can produce, but knowledge gaps remain about the viability of commercial-scale urchin culture. Here, we tested whether stocking density and level of isolation between conspecifics affect roe enhancement of the purple sea urchin Heliocidaris erythrogramma. Urchins were housed at 2 different densities (60 and 120 urchins m-2) and in partial or total isolation from conspecifics during a 12 wk roe-enhancement period. Urchins produced a high proportion of marketable roe (90 to 97% grades 'A' + 'B') with substantial gonad growth in all treatments (16.1 +/- 0.2%, mean +/- SE). In addition to gonad growth, urchins also increased in test size. Somatic growth rate over the 12 wk was affected by density, with urchins cultured in low-density treatments growing 44% faster. Density or isolation level did not influence gonad growth, or the proportions of A and B grade produced. These findings show that while H. erythrogramma roe enhancement is robust against the stresses of high-density production, tank design and level of isolation may influence how urchins utilise energy resources, in terms of investing in somatic or gonadal growth, interaction with conspecifics, and the quality of roe produced.
