Intensive systems require more efficient and fast‐acting alkalizing agents. This study evaluated the effects of different concentrations of calcium hydroxide (Ca(OH) 2 ) on water quality, growth performance, skin coloration, and gill histology of Nile tilapia ( Oreochromis niloticus ) juveniles raised in a recirculating aquaculture system (RAS). Two hundred juveniles were randomly distributed into five treatments with four replicates and exposed to 0.00, 0.01, 0.02, 0.03, and 0.04 g/L of Ca(OH) 2 for 60 days. The 0.02 g/L dose was the most efficient, promoting a significant increase in survival, final biomass, and biomass gain ( p < 0.05), in addition to maintaining stable water quality parameters. In contrast, doses of 0.03 and 0.04 g/L caused total mortality before the end of the experiment due to sharp increases in pH in the first 24 h after application, highlighting the toxic potential of excessive alkalinization. Histological analyses showed that fish exposed to 0.02 g/L presented preserved gill morphology, while the control group exhibited hyperplasia and aneurysms, and fish subjected to 0.01 g/L showed epithelial detachment and alterations in mucous cells. Juveniles cultivated in 0.02 g/L showed greater skin color saturation, indicating better physiological condition and well‐being. The beneficial effects observed at this dose are associated with increased buffering capacity and stabilization of the culture environment, reducing physiological stress and promoting better metabolic performance. These results demonstrate that Ca (OH) 2 can be used as an effective alkalizing agent in RAS systems, with 0.02 g/L being the safest and most efficient dose for juvenile Nile tilapia, while higher concentrations should be avoided due to their toxic potential.
This study investigated the effects of 84‐day biculture rearing of Danube salmon ( Hucho hucho ) and rainbow trout ( Oncorhynchus mykiss ) on their growth performance, feed efficiency (FE), survival rate (SR), organosomatic indices, and plasma biochemical parameters in a recirculating aquaculture system (RAS). Fish were reared in Danube salmon monoculture (HU100), rainbow trout monoculture (HU0), and biculture (HU50). Rainbow trout exhibited significantly improved growth performance, FE, and condition factor under biculture, whereas Danube salmon achieved higher weight gain (WG) and specific growth rate (SGR) in monoculture. Organosomatic indices were largely unaffected by treatment, while plasma biochemical responses differed between species. The results suggest that rainbow trout gained a competitive advantage under bicultural conditions, whereas Danube salmon exhibited reduced growth performance under the tested stocking ratio and feeding regime. These results suggest that rainbow trout gained a competitive advantage under bicultural conditions, whereas Danube salmon exhibited reduced growth performance. The study is also helpful in the practical implementation of the effective and profitable intensive aquaculture of these salmonid species, especially regarding the balance between the culture of Danube salmon and rainbow trout under a bicultural system.
This study evaluates the effectiveness of Lemna minor as a biofilter in a recirculating aquaculture system (RAS) for the cultivation of Sumatran barb ( Puntius tetrazona ). The experiment was conducted over 40 days using four treatments based on the surface area coverage of L. minor : 0% (control/T0), 20% (T1), 40% (T2), and 60% (T3), with five replications. The results demonstrated that integrating L. minor significantly influenced water quality and physiological responses. The phosphate concentration was significantly lower in T2 (1.44 ± 0.59 mg/L) than in T0 ( p < 0.05). The highest specific growth rate (SGR) was found at T2 (0.60% ± 0.09%/day) and was numerically higher than T0, though the difference was not statistically significant ( p > 0.05). The survival rate (SR) was highest in T1 (96.86% ± 3.72%) and T0, but was significantly lower in T3 (92.82% ± 4.55%), suggesting a negative impact of excessive plant coverage ( p < 0.05). Physiologically, fish in T2 exhibited the lowest stress levels, indicated by significantly lower blood glucose levels (57.28 mg/dL) and oxygen consumption rates (0.40 mg O 2 /g/h) compared to other groups. Based on water quality maintenance, growth efficiency, and physiological stress indicators, a 40% surface coverage of L. minor is recommended as the optimal biofilter density for Sumatran barb culture in RAS.
Geosmin is a volatile sesquiterpenoid with an ‘earthy’ odour that negatively affects the flavour of aquaculture fish. While bioconcentration models for this compound in fish exist, there is an absence of studies that account for physiological kinetics across different organs and stress‐related biochemical variables. A deeper understanding of geosmin kinetics is crucial for refining models of its absorption, elimination and metabolic transformation in fish to improve predictions of its impact on flavour quality and clarify its effect on fish stress response and welfare. This study examines the waterborne absorption and distribution of geosmin in rainbow trout ( Oncorhynchus mykiss ) in blood, liver and fillet, as well as in aquaculture water, and assesses stress responses via biochemical markers. Trout were exposed to a single dose of 0.4 ng/mL geosmin ( n = 28; plus no exposure, n = 28, as a control) under static water conditions. The concentrations of geosmin in water and fish tissues were measured at five intervals over 144 h (all fish in one exposure and one control tank for each interval) using gas chromatography‐mass spectrometry (GC‐MS) analysis. Concomitant evaluations of eight biochemical stress indicators were undertaken. No significant stress response to geosmin exposure was observed, but biological tissues exhibited varying concentrations of geosmin, characterised by an initial increase followed by a decline. Strong effects of tissue‐specific properties and exposure duration on distribution kinetics and concentrations were observed. Second‐order polynomial regressions effectively captured the concentration dynamics of geosmin across all fish tissues and water. Cumulatively, over 88% of the geosmin dose remained unaccounted for, with only minor proportions of geosmin detected in water and animal biomass. This suggests primarily hepatic metabolic biotransformation in the fish, with a possible contribution from unsampled biomass and minor analytical/compartmental losses. These results advance the understanding of geosmin distribution dynamics in fish, with implications for aquaculture practices.
Oysters have recently been recognized globally as a preferred species, not only for their high‐quality meat and sustainable aquaculture practices but also for their environmental value including carbon sequestration and nitrogen removal in aquaculture ecosystems. However, ongoing and predicted climate change stressors in coastal oyster farming areas are already threatening traditionally selected oysters and the overall industry output. The use of genomics to breed plants and animals that can handle climate change has become a popular research area, yet the oyster farming industry is only just starting to use genomic tools to identify oyster strains that have important traits like disease resistance, better meat quality, and climate change adaptation. Genomic resources, including molecular markers, genetic linkage maps, transcriptomes, and annotated draft genomes, are increasingly being used to enhance important commercial traits in oysters. Modern genomic resources use a broad array of applications, including population structure demarcation, visualization of migration patterns, pedigree analysis, detection of quantitative trait loci associated with specific traits, marker‐associated breeding, and genome‐wide association studies (GWAS). This article reviews the relevant literature in the field and discusses the application of genomics resources for fast‐forwarding genomic breeding platform development in the oyster industry. The current challenges and future directions for enhancing, optimizing, and leveraging genomic resources in oyster aquaculture are also discussed.
Intensive aquaculture often exposes fish to crowding stress, impairing growth performance and overall physiological stability. This study evaluated the effects of dietary Dormival (D) and lemon oil (LO) supplementation on the growth performance, antioxidant status, and immune response of Nile tilapia ( Oreochromis niloticus ) juveniles reared under high‐density conditions for 42 days. Six diets were tested, including control, 0.5% LO, 0.2%–0.4% D, and their combinations. Fish receiving D, either alone or with LO, showed significantly higher weight gain (WG), specific growth rate (SGR), and feed efficiency ( p < 0.05) compared with the control. Moderate D inclusion (0.2%–0.4%) enhanced survival, antioxidant defense (superoxide dismutase [SOD], glutathione [GSH], total antioxidant capacity [TAC]), and immune activity (lysozyme, immunoglobulin M [IgM]). However, excessive supplementation (0.4% D + 0.5% LO) increased aspartate aminotransferase (AST) and malondialdehyde (MDA), suggesting mild metabolic stress. Proximate composition indicated higher lipid and ash with elevated D levels. Overall, 0.2% D, alone or combined with 0.5% LO, effectively mitigated crowding stress and promoted superior growth and physiological resilience in Nile tilapia.
The organoleptic quality of aquaculture products is often diminished by off‐flavours described as ‘earthy’ or ‘mouldy’, typically associated with the odour compound geosmin. While compartmental bioconcentration models for geosmin exist, a physiologically based toxicokinetic (PBTK) multi‐compartment model that maps its organ‐specific distribution has not been established to date. This study proposes a PBTK model for waterborne geosmin uptake in liver, blood, fillet and residual biomass of rainbow trout ( Oncorhynchus mykiss ) using a hybrid machine learning approach. To address initial data limitation, polynomial regression coefficients from sparse experimental data (Part I) were used to generate interpolating synthetic time‐series data via Monte Carlo sampling. Empirical and synthetic datasets were combined to train three machine learning models, whereby random forest (RF) regression showed the best predictive performance and was selected to validate the expanded dataset. A PBTK ordinary differential equations (ODEs) model was formulated, incorporating literature‐derived physiological parameters for blood, liver, fillet and unsampled residual biomass. The RF regression model provided data to solve the ODEs, and rate constants for uptake, excretion and metabolic biotransformation of geosmin, interpreted as intrinsic tissue‐based kinetic parameters, were optimised through R‐based DEoptim and Optim algorithms. The numerically solved model refined kinetic parameters from prior compartmental models, highlighted the central role of liver in geosmin metabolism and allowed a detailed characterisation of organ‐specific geosmin distribution in fish. The hybrid approach improved descriptive accuracy and enhanced the understanding of geosmin bioconcentration dynamics, with implications for aquaculture practices and geosmin mitigation strategies.
Mark-recapture studies using fluorochrome dyes are a valuable approach for validating the age determination of fish, yet the optimal chemical marker and its dosage for adult European flounder (Platichthys flesus Linnaeus, 1758) remain unclear. We assessed the effectiveness of tetracycline hydrochloride and calcein at different concentrations for marking otoliths and the survival rates. A total of 117 adult European flounder were injected intraperitoneally either with one of the chemical markers or with a saline solution as a control. They were held in stationary net pens in the western Baltic Sea over a 69-day period. Fish were monitored for survival, growth, and body condition, and otoliths were examined for fluorescence mark quality. Survival was highest in the tetracycline groups: 90% at 25 and 50 mg/kg, and 82% at 100 mg/kg, whereas calcein treatments were associated with intermediate survival: 55% at 0.5 mg/kg and 50% at 5 mg/kg. A total of 76% of otoliths in the tetracycline hydrochloride-treated fish showed usable fluorescence marks (good: 12%, poor: 64%), while marks of calcein-treated fish were only observed in 10% of the otoliths. The differences in survival outcome between the three tetracycline dosages were not significant, supporting the use of the lowest tested tetracycline dose (25 mg/kg) for effective marking. These results indicate that tetracycline hydrochloride is a suitable and well-tolerated chemical marker for adult European flounder, whereas calcein was unsuitable due to the recorded mortality and low marking success. The findings provide a methodological basis for mark-recapture studies of European flounder in the Baltic Sea and may inform similar applications in other areas and in related flatfish species.
Selective breeding has improved the performance of Pacific white shrimp (Penaeus vannamei), yet routine selection still relies mainly on late-stage phenotypes that are costly to measure and sensitive to fluctuating pond environments. Here, we tested whether early-life hepatopancreas metabolomes can capture line-associated physiological differences relevant to production. Postlarvae at day 40 (PL40) from four breeding lines (designated as TK1-TK4) were profiled using an UHPLC-HRMS-based untargeted metabolomics workflow in positive-ion mode. Metabolomic signatures were related to a matched 60-day grow-out evaluation, in which TK3 achieved the highest final weight (15.80 +/- 1.20 g) and the lowest observed feed conversion ratio (FCR) (1.50 +/- 0.07), whereas survival varied substantially across lines (54.1%-89.5%), with TK3 and TK4 showing higher survival than TK1 and TK2. Principal component analysis (PCA) revealed line-dependent clustering, and pairwise orthogonal partial least squares-discriminant analysis (OPLS-DA) models supported exploratory discrimination of TK3 from each comparator line. Differential metabolite and pathway analyses implicated coordinated variation in amino acid and nitrogen handling, nucleotide turnover, and lipid utilization, with recurring enrichment of histidine metabolism, lysine degradation, purine metabolism, and glutathione-related processes. Receiver operating characteristic (ROC)-based prioritization further highlighted a subset of candidate metabolites for follow-up targeted validation. Given the limited metabolomics cohort size, these findings should be interpreted as exploratory discovery-stage signatures rather than validated biomarkers. By leveraging known grow-out divergence among breeding lines, this study adopted a performance-anchored retrospective design to nominate PL40 metabolic pathways and candidate metabolites that may support future pre-growout screening in shrimp improvement programs after independent validation.
Marine sea-cage aquaculture continues to expand, increasing the need for monitoring tools capable of distinguishing farm-related nutrient enrichment from natural coastal variability. This study evaluated the trophic status of 18 sea-cage aquaculture farms along the southern Black Sea coast using the Trophic Index (TRIX), which integrates chlorophyl-a, oxygen saturation deviation, dissolved inorganic nitrogen, and total phosphorus. A nested hierarchical sampling design was used to compare cage and reference site types across three depth strata (surface, midwater, and bottom). A total of 131 TRIX observations were analyzed using linear mixed-effects models, with farm identity included as a random intercept to distinguish cage-proximity effects from farm-level background conditions. TRIX values fell predominantly within the good (4-<5) to moderate (5-<6) trophic classes, with the highest mean values observed in Zone 3 during spring. Model-adjusted means were similar between site types (reference: 4.98; cage: 4.89), indicating no systematic evidence of water-column enrichment associated with cage proximity at the examined spatial scales. In contrast, trophic conditions exhibited significant vertical structuring. Variance partitioning showed that fixed effects explained 29.6% of TRIX variability (R(2)m = 0.296), whereas the full model explained 66.1% (R(2)c = 0.661), with substantial among-farm heterogeneity (ICC = 0.518). Multivariate ordination further indicated a strong overlap between the cage and reference samples, with the first two PCA axes explaining 60.0% of the total variance. In sum, these findings suggest that the pelagic trophic variability in this region is governed primarily by bathymetry and local hydrographic context, supporting the spatial planning strategies that prioritize deeper, well-flushed sites.
For aquaculture, animal welfare constitutes a fundamental dimension of sustainability because it directly influences health, productivity, resource efficiency, and the ethical standards of production systems. Spotted seatrout (Cynoscion nebulosus) is a marine fish recognized as an emerging candidate for aquaculture in the Gulf of Mexico and, like other developing species, is continually subjected to experimental research to support the advancement of its culture technologies. In this context, identifying effective anesthesia conditions is essential for minimizing stress during operational procedures and improving the consistency of experimental outcomes. The aim of this study was to comparatively evaluate anesthetic effectiveness in juvenile spotted seatrout using behavioral responses and blood biochemical stress indicators. The anesthetic effectiveness of MS-222, eugenol, and Cymbopogon flexuosus essential oil (CFEO) was evaluated in juvenile spotted seatrout (mean +/- SD: 28.2 +/- 3.5 g wet weight and 14.7 +/- 0.7 cm total length). MS-222 at 200, 250, and 300 mg L-1, eugenol at 25, 30, 35, and 40 mg L-1, and CFEO at 100 and 125 & micro;L-1 induced deep anesthesia within 15 min, followed by complete recovery within 5 min. However, only MS-222 at 300 mg L-1 and eugenol at 40 mg L-1 achieved deep anesthesia within 3 min, 110.0 and 149.5 s, respectively. Despite this, MS-222 at 300 mg L-1 produced the highest plasma lactate levels, whereas eugenol at 40 mg L-1 elevated both plasma lactate and glucose relative to the control group. In contrast, eugenol at 35 mg L-1 resulted in the lowest plasma lactate and glucose levels. These findings indicate that eugenol at 35 mg L-1 represents a balanced anesthetic option for juvenile spotted seatrout. Moreover, rapid anesthetic induction does not necessarily imply reduced physiological stress in this species.
This study evaluated the physiological and molecular mechanisms underlying cold stress tolerance in golden pompano (Trachinotus ovatus) after a 56-day feeding trial with high-lipid diets (18%) supplemented with varying methionine (Met) levels (1.04%, 1.14%, 1.24%, 1.34%, 1.44%, 1.54%, and 1.64%). After the feeding period, fish fed 1.24% Met (HLM3) exhibited the highest thermal growth coefficient (TGC) and relative growth rate (RGR), together with the lowest feed conversion ratio (FCR) among all treatments (p < 0.05). Survival remained 100% across all dietary groups throughout the feeding period. Afterwards, 10 fish from each cage selected randomly were subjected to a 96-h cold stress from 19.30 +/- 0.06 degrees C to 14.38 +/- 0.01 degrees C to assess survival, lipid metabolism, antioxidant capacity, immune function, ferroptosis, inflammation, and apoptosis. T. ovatus in the HLM3 group exhibited significantly reduced serum levels of total cholesterol, triglycerides, LDL-C, AST, ALT, and NEFAs, accompanied by elevated antioxidant enzyme activities (SOD, CAT, T-AOC, and GSH-Px) and lower MDA and ROS levels (p < 0.05). Immune parameters (IgM, LZM, ACP, and AKP) were also markedly enhanced in HLM3. Moreover, hepatic Met and cysteine levels were higher in HLM3, while hepatic lipid deposition was suppressed. Lipolytic (cpt1a, atgl, lpl, and ppar alpha) and antioxidant genes (nrf2, ho-1, gxp4, and MnSOD) were upregulated, along with increased NADP(+)/NADPH ratio and downregulation of keap1. S lc7a11, bcl2, and bcl-xl genes were elevated, while ferroptosis and apoptosis markers were alleviated. Overall, dietary inclusion of 1.24% Met in an 18% high-lipid diet enhanced the nrf2-mediated antioxidant defense, lipid catabolism, and antiferroptotic pathways, thereby improving cold stress resilience in T. ovatus.
Waterborne probiotic administration has emerged as a practical approach for modulating microbial populations during the early development stages of fish. However, limited information is available regarding the influence of probiotic dosage and timing of exposure on culturable bacterial dynamics in rainbow trout (Oncorhynchus mykiss). Therefore, this study evaluated the dose and stage-dependent waterborne administration of Lactobacillus rhamnosus PTCC 1637 on culturable bacterial populations from 1 to 60 days postfertilization (dpf). Three treatments (control, 10(6), and 10(7) CFU/mL) were applied during the eyed egg stage (1-7 dpf). During the alevin stage (8-20 dpf), five treatments were evaluated, including two additional groups in which probiotic exposure was initiated at hatching. Seven treatments were assessed during the juvenile stage (20-60 dpf), with probiotic application every other day until 20 dpf and every 4 days thereafter. All treatments were conducted in triplicate. Water and fish samples were collected before and 24 h after probiotic application and cultured on nutrient agar (NA) for total culturable bacterial counts and on Man, Rogosa and Sharpe (MRS) agar for culturable lactic acid bacteria (LAB). Probiotic supplementation significantly increased total culturable bacterial counts and culturable LAB counts in water and fish-associated samples compared with the control groups (p < 0.05). The highest values were generally observed in the 10(7) CFU/mL treatment, particularly when exposure began during earlier developmental stages. In the juvenile stage, culturable intestinal bacterial counts reached 7.96 log CFU/g, while culturable LAB counts reached 5.98 log CFU/g by Day 60. Earlier probiotic exposure resulted in consistently higher culturable LAB counts throughout development. These findings indicate that both probiotic dose and timing of administration influence culturable bacterial dynamics in rainbow trout and provide practical guidance for stage-specific waterborne probiotic application in hatchery systems.
Fish oil (FO) is widely used in aquaculture feed due to its high levels of long-chain omega-3 fatty acids. But increasing cost, limited supply, and sustainability concerns have led to the search for alternative omega-3 sources. Bioengineered (BE) oilseeds, such as docosahexaenoic acid (DHA) canola (Brassica napus, OECD Unique Identifier: NS-B5 & Oslash;& Oslash;27-4, branded Aquaterra), offer a scalable, land-based source of DHA and other long-chain omega-3 fatty acids. This study evaluated the efficacy of DHA canola oil (DCO, Aquaterra), as a replacement for FO in the diet of Pacific white shrimp (Penaeus vannamei). Five isonitrogenous, isolipidic, and isocaloric diets were formulated by replacing FO with graded levels of DCO (0%, 25%, 50%, 75%, and 100%). Postlarval shrimp (initial weight 0.7-0.8 g) were stocked in a recirculating saltwater system (30 ppt) comprised of 40 aquaria (eight tanks for each diet), and shrimp were fed four times daily for 11 weeks. Results showed no significant differences in growth performance or survival across different dietary groups. Feed intake was reduced at 100% FO replacement, but feed conversion ratio (FCR) and energy retention improved. Whole-body protein and energy remained stable across all dietary groups, while lipid retention increased with DCO-fed groups. Whole-body amino acid and fatty acid compositions were influenced by DCO inclusion, with the 50% replacement group exhibiting comparable composition to that of the 100% FO group, especially in terms of the high content of total omega-3 fatty acids. For growth, DCO can replace up to 100% FO in shrimp diets; however, 75% DCO replacement is recommended when considering the whole-body fatty acid profile and n-3/n-6 ratio. Based on the present findings, 50%-75% FO replacement with DCO in shrimp diets can be considered optimal, supporting its use as a robust and viable lipid source for commercial shrimp aquaculture.
Peptidoglycan recognition proteins (PGRPs) could serve as key pattern recognition receptors (PRRs) in the innate immune systems of invertebrates. In this study, a short PGRP, designated as ApPGRP, was identified and functionally characterized from the mollusk Atrina pectinata to investigate its roles in immunity. The ApPGRP gene was cloned and found to encode a protein of 314 amino acids. ApPGRP shares 55.6-76.1% sequence identity with other PGRPs and is phylogenetically most closely related to the PGRP from Mimachlamys nobilis. In healthy A. pectinata, ApPGRP mRNA was constitutively expressed in all examined tissues, with the highest level in hepatopancreas. Its expression was significantly up-regulated following bacterial challenge. Recombinant ApPGRP (rApPGRP) exhibited binding ability to peptidoglycan (PGN), chitin, glucan, and zymosan, but not LPS. In vitro, rApPGRP demonstrated potent agglutination capabilities against E. coli and M. luteus. rApPGRP demonstrated Zn2+-dependent amidase activity, enabling the catalytic cleavage of PGN. Additionally, rApPGRP displayed direct antibacterial activity against E. coli and V. anguillarum and was capable of inhibiting E. coli biofilm formation in the presence of Zn2+. These findings suggest that ApPGRP contributes to the innate immune response of A. pectinata through pathogen recognition, agglutination, and bacterial clearance.
As global aquaculture expands, sustainable alternative feed ingredients are needed to reduce reliance on fishmeal (FM) and conventional plant proteins. Herein, this study evaluated defatted black soldier fly (BSF; Hermetia illucens) larvae meal as a replacement mainly for soybean meal (SBM) and soy protein concentrate (SPC) in juvenile mirror carp diets. Fish (initial weight: 7.28 +/- 0.09 g) were reared in a recirculating aquaculture system and fed for 8 weeks on either a control diet or diets containing 20% (BSF20) or 40% (BSF40) BSF meal. After the trial, growth performance was significantly improved in BSF-fed groups, with higher final weight, weight gain, specific growth rate and a better feed conversion ratio compared with the control. Orthogonal polynomial contrasts indicated predominantly linear responses in growth and feed utilisation parameters. Histological analysis showed significantly enhanced intestinal morphology in BSF-fed groups, including increased mucosal fold length (MFL), microvilli length (MVL) and intraepithelial lymphocyte (IEL) density. At the molecular level, il10 and slc6a18 expression were significantly upregulated in the anterior intestine (AI) and posterior intestine (PI), respectively, of BSF-fed fish. The PI microbiota profiling via 16S rRNA gene metabarcoding showed that BSF inclusion promoted several beneficial microbial shifts. While the dominant phyla were Proteobacteria, Fusobacteria and Firmicutes, fish fed the BSF40 diet exhibited a higher relative abundance of Firmicutes and a reduced relative abundance of several potentially pathogenic phyla. The relative abundance of beneficial genera, including Bacillus and Enterococcus, increased significantly, whereas the relative abundance of potentially pathogenic genera such as Mycobacterium, Staphylococcus and Enterobacter were reduced by BSF meal. Overall, BSF meal represents a nutritionally viable and functional protein source that improves growth performance and intestinal health, and supports sustainable aquafeed development in juvenile mirror carp.
Vibriosis, caused by Vibrio spp ., poses a significant challenge in marine aquaculture, leading to severe economic losses. Vaccination has emerged as a safer and more effective alternative to antibiotics for disease control, with oral vaccination offering advantages such as ease of administration and scalability for large‐scale aquaculture operations. This study evaluated the efficacy of an oral inactivated Vibrio harveyi vaccine in a field environment with cage‐cultured Asian seabass ( Lates calcarifer ) at Pulau Ketam, Klang, Selangor, Malaysia. Fish were divided into two groups: (1) a vaccinated group fed a commercial diet supplemented with formalin‐killed V. harveyi (10 8 CFU/mL) and palm oil as an adjuvant and (2) a placebo control group fed a commercial diet supplemented with phosphate‐buffered saline (PBS) and palm oil adjuvant. The vaccine was administered orally at weeks 0, 2, and 6 for three consecutive days at a dosage of 4% of the fish’s body weight. Immune‐related gene expression, including dendritic cells (DCs), complement factor 3 (C3), chemokine ligand 4 (CCL4), tumor necrosis factor‐α (TNF‐α), and immunoglobulin‐T (IgT), was significantly upregulated ( p < 0.05) in vaccinated fish compared to controls, with peak expression observed following booster doses. At week 10, a laboratory challenge trial with V. harveyi (1 × 10 8 CFU/mL) demonstrated an 80% relative percentage survival (RPS) in the vaccinated group, whereas the unvaccinated group exhibited 100% mortality. In addition, vaccinated fish displayed reduced clinical signs following infection. These findings highlight the potential of oral inactivated V. harveyi vaccines to induce robust immune responses and confer effective protection against vibriosis in Asian seabass. This approach provides a practical and scalable solution for disease management in marine aquaculture, improving health outcomes and productivity for fish farmers.
Aquaculture faces significant challenges, including water pollution and low productivity in traditional systems. Biofloc technology (BFT) offers a sustainable alternative by recycling nutrients and improving water quality. The present study assessed the efficacy of bioflocs enriched with the freshwater microalgae such as Chlorella sorokiniana and Scenedesmus sp. in Nile tilapia ( Oreochromis niloticus ) culture. Four treatments were tested; the biofloc systems were inoculated with i) control group without microalgae inoculation, ii) C. sorokiniana in an initial density of 1 × 10 6 cells/mL, iii) Scenedesmus sp. (1 × 10 6 cells/mL), and iv) mixed culture (1 × 10 6 cells/mL for each species). Growth performance, proximal composition of bioflocs, hematological parameters, and water quality were analyzed. Results demonstrated that treatment with C. sorokiniana achieved the highest biomass (6.9 × 10 6 cells/mL) compared to the treatment with Scenedesmus sp., (2.8 × 10 6 cells/mL) as well as better nutritional composition in C. sorokiniana treatment. Tilapia reared in the C. sorokiniana biofloc system showed significantly higher final body weight (63.51 g), weight gain (WG; 55.77 g), specific growth rate (SGR; 3.01% day −1 ), and improved feed utilization ( p < 0.05) compared to the control and other treatments. This treatment also optimized water quality, reducing nitrite levels to 2.68 mg/L, compared to 4.27 mg/L in the control group. Hematological parameters did not differ significantly among treatments, indicating no adverse physiological effects. The mixed algae biofloc treatment yielded no synergistic benefits, likely due to interspecies competition. Overall, the incorporation of C. sorokiniana ‐enriched bioflocs significantly enhances tilapia performance and water quality, demonstrating their potential for sustainable aquaculture.
Aquaculture is a key to global food and nutrition security, but intensification has increased disease pressure, antibiotic use, antimicrobial resistance (AMR), and wider One Health concerns. Functional microbial products (FMPs), including probiotics, prebiotics, synbiotics, postbiotics, and paraprobiotics, are widely promoted as sustainable alternatives to antibiotics. However, their growing use has not resulted in sustained replacement of antibiotics in commercial aquaculture practice. This review examined why this gap persists and what conditions are required for these products to contribute credibly to antibiotic reduction. A PRISMA‐guided systematic review was conducted across major scientific databases, yielding 654 records, of which 97 studies were retained for qualitative synthesis. The evidence shows that FMPs can improve growth, feed efficiency, immune response, disease resistance, survival, and, in some systems, water quality. Beyond these performance outcomes, the review identifies host immune modulation as a central biological pathway linking FMPs to disease resilience, particularly through mucosal barrier reinforcement, innate immune priming, activation of humoral and cellular defenses, cytokine and inflammatory regulation, antioxidant protection, and stabilization of the host–microbiome axis. Probiotics had the strongest overall evidence base, synbiotics showed the most consistent combined gains across growth, immunity, and survival, while postbiotics emerged as promising options because of their stability and biosafety advantages. However, direct evidence of sustained farm‐level reductions in antibiotic use remains limited. Multiple interlinked constraints explain this gap including biophysical stress in production systems, inconsistent product quality, misaligned application practices, mechanistic uncertainty, biosafety risk, and weak diagnostic, advisory, and regulatory systems. Overall, FMPs are best understood as preventive and resilience‐building tools rather than direct therapeutic substitutes for antibiotics. Meaningful antibiotic reduction will depend less on product substitution alone and more on integrating these products into stronger health‐management systems supported by quality control (QC), clear deployment protocols, diagnostics, advisory services, and enabling regulation.
