Hematological and serum biochemical reference intervals of rainbow trout, Oncorhynchus mykiss cultured in Himalayan aquaculture: Morphology, morphometrics and quantification of peripheral blood cells

Effects of oxygen levels and temperature on growth and physiology of pikeperch juveniles cultured in a recirculating aquaculture system

This study aimed to understand how environmental factors, specifically water temperature and oxygen saturation, affect the growth performance and physiology of pikeperch (Sander lucioperca) juveniles in recirculating aquaculture systems (RASs). Given the importance of optimising growth conditions in aquaculture to maximise efficiency, it aims to assess whether different combinations of oxygen levels and temperatures can enhance growth while maintaining the physiological health and welfare of the fish. The experimental design included the culturing pikeperch juveniles (22.7 ± 7.1 g) were exposed to hypoxia (78 ± 14%), normoxia (105 ± 12%), and hyperoxia (140 ± 18%) conditions for 72 days. This was conducted at two temperatures, 20 °C and 23 °C, each in a separate but identical RAS. The level of oxygen supply was controlled with micro bubble diffusers on the bottom of each tank. The hyperoxia at 23 °C positively affected total length, BW, specific growth rate, feed intake and feed conservation rate (FCR). The slowest growth and feed intake, along with the highest FCR, were observed in hypoxia at 20 °C. Fish reared under 23 °C exhibited significantly higher visceral-somatic index (3.54 ± 0.83 at 23 °C and 2.76 ± 0.73 at 20 °C) regardless of oxygen levels. It was primarily responsible for the observed growth difference (Final BW: 58.3 ± 18.8 g at 23 °C and 53.0 ± 18.3 g at 20 °C). The water temperature also affected haematocrit, haemoglobin, leucocyte count, mean corpuscular haemoglobin, mean corpuscular volume (MCV) of the blood cells; the concentration of lymphocytes, neutrophile granulocyte bands and segments. Among biochemical markers, temperature affected cytoplasmic and mitochondrial enzymes, ammonia and triglyceride levels in blood plasma. Elevated antioxidant activity was observed in muscle, intestine and liver tissues. Oxygen levels demonstrated significant effects on growth, feed intake and conversion, the MCV of the blood cells, the concentration of the glucose, lactate and ammonia in blood plasma, and antioxidant biomarkers in the liver tissue. The analysis indicated a significant effect of oxygen on energy metabolism. The results showed hyperoxia under 23 °C create conditions for the highest growth and feed intake, high feed utilisation. There are, however, concerns about the physiological conditions and welfare of intensively cultured pikeperch juveniles, as higher feed intake led to increased visceral fat content in the body, elevated antioxidant activity in the liver, muscle and intestine tissues, morphology of blood cell, and energy metabolism.

Changes in blood serum parameters in farmed rainbow trout (Oncorhynchus mykiss) during a piscine lactococcosis outbreak

The aquaculture sector plays a vital role in global food security, yet it grapples with significant challenges posed by infectious diseases. Piscine lactococcosis is one of the significant threats in rainbow trout aquaculture due to its potential to cause severe economic losses through mortalities, reduced growth rates, and increased susceptibility to other pathogens. It poses challenges in disease management strategies, impacting the sustainability and profitability of rainbow trout farming. The current study focuses on the variations in serum blood parameters of farmed rainbow trout Oncorhynchus mykiss during a lactococcosis outbreak caused by Lactococcus garvieae. Blood samples were collected for biochemical analysis, fish were examined for parasites and bacteria, and DNA from bacterial colonies was PCR-amplified and sequenced for identification. Overall, 13 biochemical parameters, including proteins, enzymes, lipids, chemicals, and minerals, were measured in serum blood samples from both diseased and healthy fish. The results indicate significant alterations in the levels of these parameters during the outbreak, highlighting the impact of infections on the blood profile of farmed rainbow trout. Urea levels were significantly higher in diseased fish compared to controls, and creatinine, phosphorus, and magnesium also showed similar trends. Alanine aminotransferase and total protein levels were higher in control fish. Chloride levels differed significantly between groups. Iron levels were higher in controls and lower in diseased fish. No significant differences were found in other parameters. This study reveals significant changes in serum blood parameters of rainbow trout during a lactococcosis outbreak caused by L. garvieae. These changes highlight the potential of these parameters as tools for monitoring health status, stress, and aquaculture management. Continuous monitoring can provide valuable insights into disease severity and overall fish health, aiding in the development of improved management practices. The presented data contribute to understanding the pathophysiology of piscine lactococcosis and developing effective mitigation strategies for farmed rainbow trout.

Weathered polyethylene microplastics induced immunomodulation in zebrafish

Microplastics are pollutants of emerging concern and the aquatic biota consumes microplastics (MPs), which has a range of toxicological and environmental effects on aquatic organisms that are not the intended targets. The current study looked into how weathered polyethylene (wPE) MPs affected Danio albolineatus immunological and haematological markers. In this experiment, fish of both sexes were placed in control and exposure groups, and they were exposed for 40 d at the sublethal level (1 μg L-1) of fragmented wPE, which contained 1074 ± 52 MPs per litre. Similarly, fish exposed to wPE MPs showed significant modifications in lysozyme, antimicrobial, and antiprotease activity, as well as differential counts. Results of the present study show that the male fish were more susceptible than female fish after 40 d of chronic exposure. Further studies are needed to ascertain how the innate and humoral immune systems of the fish respond to MPs exposure.

Comparative analysis of blood protein fractions in two mediterranean farmed fish: Dicentrarchus labrax and Sparus aurata

Total protein levels in fish are widely used in health and welfare studies, providing a simple and accessible measure. However, the multifaceted role of blood proteins makes it sometimes challenging to link total protein content to specific health issues, while specific protein fractions may offer more precise insights into fish biology and health, particularly in farmed fish species where such data is often lacking. Data were gathered from two experiments involving Dicentrarchus labrax and Sparus aurata, key species in European marine aquaculture. The aim was (1) to assess how different globulin fractions contribute to total protein content in blood and (2) how these contributions vary across different sampling times in healthy animals. In D. labrax, the beta1 globulin fraction emerged as the major contributor (34.16%), followed by albumin and alpha2 globulins (18.24% and 16.41%, respectively). In contrast, pre-albumins and alpha1 fractions had the least contribution (5.49% and 7.71%). S. aurata exhibited albumin as the primary contributor (23.39%), followed by beta1 and alpha2 globulins (19.71% and 19.15%, respectively), with gamma and alpha1 fractions contributing the least (5.34% and 8.63%). Notably, the study revealed relatively stable contributions of globulin fractions to total proteins within both species, albeit with minor variations over time, potentially linked to environmental and individual factors. Furthermore, larger fish displayed higher total protein levels. This research underscores the need for further investigation into the diverse factors influencing globulin contributions to total proteins, ultimately enhancing health and welfare monitoring for farmed fish species.

Effects of dietary nanoliposome-coated astaxanthin on haematological parameters, immune responses and the antioxidant status of rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Astaxanthin is the most prevalent carotenoid in the marine environment and is widely used as an additive in formulated aquafeeds.

OBJECTIVES

A 60-day feeding trial was conducted to consider the effect of dietary nanoliposome-coated astaxanthin (NA) on haematological parameters, serum antioxidant activities and immune responses of rainbow trout, Oncorhynchus mykiss.

METHODS

A total of 450 healthy fish weighing 31.00 ± 2.09 g were randomly assigned in triplicate (30 fish per replicate) to 5 dietary treatments: 0 (control), 25.00, 50.00, 75.00, and 100.00 mg kg-1 NA.

RESULTS

Fish fed the diet supplemented with 50.00 mg kg-1 NA exhibited the highest values of red blood cells, white blood cells, haemoglobin and haematocrit of 1.64 ± 0.01 × 106 mm-3, 5.54 ± 0.21 × 103 mm-3, 8.73 ± 0.24 g dL-1 and 46.67% ± 0.88%, respectively, which were significantly higher than those fed the basal diet (p < 0.05). The lowest and highest percentages of lymphocytes (67.67% ± 0.33%) and neutrophils (27.33% ± 1.20%) were also obtained in fish fed 50.00 mg kg-1 NA compared to those fed the basal diet (p < 0.05). Fish receiving diet supplemented with 50.00 mg kg-1 NA revealed the highest serum activity in superoxide dismutase, catalase, glutathione peroxidase, lysozyme and alternative complement and the lowest level of total cholesterol, cortisol, aspartate aminotransferase and alanine aminotransferase than fish receiving the basal diet (p < 0.05). Serum immunoglobulin (Ig) and ACH50 contents significantly increased with increasing dietary NA supplementation to the highest values of 43.17 ± 1.46 and 293.33 ± 2.03 U mL-1, respectively, in fish fed diet supplemented with 50 mg kg-1 NA (p < 0.05).

CONCLUSIONS

Supplementation of NA in rainbow trout diet at 50 mg kg-1 exhibited a positive effect on haematological parameters, antioxidant capacity and immune responses. Administration of such dosage can enhance rainbow trout immune responses against unfavourable or stressful conditions, for example disease outbreaks, hypoxic condition, thermal stress and sudden osmotic fluctuations, which usually happen in an intensive culture system.

Mitigating Aflatoxin B1-Induced Growth Impairment and Hepatic Stress in Nile Tilapia (Oreochromis niloticus): Comparative Efficacy of Saccharomyces cerevisiae and Silicate-Based Detoxifiers

The objective of this study was to detect the effects of acute aflatoxin B1 (AFB1) exposure in Nile tilapia (Oreochromis niloticus) and the effectiveness of Saccharomyces cerevisiae and silicate in reducing these effects. Two hundred and forty Nile tilapia fingerlings (16 ± 0.5 g) were randomly assigned to four experimental groups, each with 60 fish and three replicates. Control basal diet (Diet 1) and three test diets were formulated, where Diet 2 was supplemented with 200 ppb AFB1. Diets 3 and 4 were intoxicated with AFB1 (200 ppb) and supplemented with 0.5% S. cerevisiae or 0.5%, respectively. After 60 days, Diet 1 had considerably greater growth characteristics than the other groups (p < 0.05). Diet 2 revealed a reduced (p < 0.05) survival rate after 1 month of exposure. In addition, Diet 1 showed higher (p < 0.05) total protein and albumin levels than Diets 3 and 4. AFB1 residues were detected in the liver in fish-fed Diet 2, Diet 4, and Diet 3. Alanine aminotransferase, aspartate aminotransferase, creatinine, and urea levels increased (p < 0.05) in fish-fed Diet 2. The glutathione peroxidase, lysozyme, and catalase activity were decreased (p < 0.05) in the fish-fed Diet 2. The malondialdehyde level was significantly higher in fish given Diet 2 (p < 0.05) than in fish-fed Diets 3 and 4. Histopathological investigation of fish-fed Diet 2 revealed impaired liver and spleen; however, both treatments (Diets 3 and 4) successfully lowered inflammation and preserved liver and spleen integrities. In conclusion, AFB1 impaired growth performance and posed a severe health risk to Nile tilapia. Furthermore, S. cerevisiae alleviated the contamination of AFB1 effects more efficiently than silicate employed for toxin adsorption.

The haematology of clinically healthy, farmed juvenile Asian seabass (Lates calcarifer Bloch)-reference intervals, and indicators of subclinical disease

This study establishes the blood reference intervals (RIs) for clinically healthy and farmed juvenile Asian seabass (Lates calcarifer), within 4-6 weeks after stocking into flow-through, marine aquaculture systems. The 90% percentile RIs (n = 156, mean bodyweight 41.8 g) are as follows: glucose (GLU) 2.4-11.3 mmol/L, haematocrit (Hct) 18.9%-39.2%, haemoglobin concentration (Hb) 56.0-85.0 g/L, total plasma protein (TPP) 56.0-77.0 g/L, total red blood cell (RBC) count 4.1-11.2 × 1012 /L, total white blood cell (WBC) count 5.3-69.9 × 109 /L, total lymphocytes 4.7-51.4 × 109 /L, monocytes 0.3-16.2 × 109 /L and heterophils count 0.6-8.4 × 109 /L. Pearson's method analysis showed weak but significantly positive correlations between fish bodyweight and Hct, Hb, TPP and total RBC count (p < 0.05). Histopathology of 42 of the 156 clinically healthy fish used to derive the RIs, with blood values within the 90% percentile range, did not exhibit any abnormal pathology. In contrast, histopathology from a different group of clinically healthy L. calcarifer (n = 72, mean bodyweight 31.3 g) with blood values falling outside of these established 90% percentile RIs showed that 25% of these fish had severe, chronic granulomatous enteritis, and 13% had severely depleted lipid stores in their liver. Point biserial correlation analysis of blood values from this second group of 72 fish showed that elevated total WBC, monocyte and heterophil counts and reduced Hct levels are significantly associated (p < 0.05) with the occurrence of severe, chronic granulomatous enteritis and depleted lipid stores in their liver. Reduced blood GLU and TPP levels in the second group of fish were significantly associated with fish that had depleted lipid stores in liver (p < 0.05), corroborating a period of malnutrition. This study is among the first to establish blood RIs for clinically healthy, farmed juvenile L. calcarifer and detection of subclinical diseases in fish to support early intervention.

Indexing hematological and serum biochemical reference intervals of Himalayan snow trout, Schizothorax esocinus to instrument in health assessment

Schizothorax esocinus, commonly known as snow trout, is one of the main contributors of food and livelihood in the colder zone of Himalayan region. The comprehensive information on its hematological and serum biochemical reference intervals is not reported yet. In the present study an attempt has been made to elucidate the hematological and serum biochemical reference intervals of S. esocinus from River Jhelum using protocols of the American Society of Veterinary Clinical Pathology (ASVCP). Wild fish were sampled over a period of 2 years from the pollution free sites of river Jhelum. Fish blood was harvested through caudal venipuncture and hemato-biochemical analysis performed thereof. Data values from a total of healthy 432 adult fish specimens (216 male, 216 female) were systematically recorded. The reference intervals for hematological and serum biochemical parameters of S. esocinus were established using Reference Value Advisor software v 2.1. RIs for hematological and serum analytes ranged as: hemoglobin (Hb) 78.38-116.35 (g/L); white blood cells (WBC) 10-20 (×10⁹/L); red blood cells (RBC) 1.30-2.15 (×10¹²/L); packed cell volume 27.00-39.45 (%); total protein 39.21-61.62 (g/L); albumin 8.20-22.02 (g/L); globulin 27.58-49.55 (g/L); glucose 3.25-7.18 (mmol/L); urea 0.96-2.38 (mmol/L); cholesterol 3.80-6.90 (mmol/L). The study also depicted that certain blood measurands were influenced with respect to sex. Significantly (p < 0.05) higher values of Hb, red blood cells count and serum glucose were noted in male as compared to female which, on the other hand, registered higher white blood cells count and serum cholesterol level (Mann Whitney U test, p < 0.05). The work, therefore, provides baseline information on hematological and serum biochemical analytes of this species which holds high commercial importance. RIs reported here can help monitor the health status of fish by improving the use of non-lethal diagnostic methods in piscine medicine.

Parámetros hemocitarios y química de la hemolinfa en reproductores de la concha prieta Anadara tuberculosa (Arcoida: Arcidae)

Con motivo de conocer el estado de salud de poblaciones silvestres de la concha prieta Anadara tuberculosa se estudiaron los parámetros hemocitarios (viabilidad, conteo total y diferencial, estabilidad lisosomal, fragilidad osmótica) y la química sanguínea (hemoglobina-Hb, proteínas, triglicéridos, glucosa, lactato deshidrogenasa-LDH y catalasa-CAT). Se extrajo hemolinfa en reproductores salvajes aparentemente sanos colectados en la isla Corazón, río Chone, Ecuador. La viabilidad celular fue elevada, con presencia de 5 morfotipos: eritrocitos (74%), granulocitos traslucidos (6%), amebocitos (3%), hialinocitos (12%), blastocitos (5%). Los hemocitos presentaron membranas lisosomales estables al rojo neutro durante 240 min y una fragilidad osmótica media (FO50) de 4.8‰. Las concentraciones de Hb, proteínas, lípidos y glucosa denotan la función respiratoria y reservas energéticas durante los cambios de marea. La actividad de LDH está vinculada al metabolismo anaeróbico y CAT a la capacidad de mantener el equilibrio redox del sistema inmunitario. Los parámetros hemocitarios y química de la hemolinfa pueden servir como índices fisiológicos normales de referencia en reproductores de A. tuberculosa.

Effect of Supplementation of Vitamin A on Growth, Haemato-Biochemical Composition, and Antioxidant Ability in Cyprinus carpio var. communis

Vitamin A requirement in fingerling common carp, Cyprinus carpio var. communis (1.64 ± 0.02 g; ABW ± SD), was evaluated by conducting a 10 week growth experiment. Casein-gelatin-based test diets representing six graded levels of vitamin A (0, 0.03, 0.07, 0.11, 0.15, and 0.19 g/kg, dry diet) were designed and fed to the triplicate group of fish at 08:00 and 16:00 hrs at the rate of 4% body weight per day. Growth parameters like live weight gain (LWG %), feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR), and body protein deposition (BPD) improved significantly (P < 0.05) with each elevated dietary vitamin A level and found maximum growth rate along with the best- FCR at 0.11 g/kg diet. Dietary vitamin A levels also significantly (P < 0.05) affected haematological parameters of the fish. Highest haemoglobin (Hb), erythrocyte count (RBC), haematocrit content (Hct %), and lowest leucocyte count (WBC) were observed at 0.11 g/kg vitamin A fed diet compared to all the diets. Highest protein and lowest fat content were observed in the group of fingerlings fed with 0.11 g/kg vitamin A containing diet. Blood and serum profile also showed some significant (P < 0.05) differences with elevating concentration of dietary vitamin A levels. Serum parameters like aspartate aminotransferase (AST), alanine aminotransferase (ALT), and cholesterol values decreased significantly (P < 0.05) at 0.11 g/kg vitamin A fed diet compared to control diet. However, except albumin the other electrolytes improved significantly (P < 0.05) and maximal values of these parameters were also evident at 0.11 g/kg of vitamin A fed diet. Better value of TBARS was found in the group that fed 0.11 g/kg vitamin A diet. Hepatosomatic index and condition factor improved significantly (P < 0.05) with fish fed at optimal dose 0.11 g/kg of vitamin A diet. Based on quadratic regression analysis of LWG%, FCR, BPD, Hb, and calcium values of C. carpio var. communis against the varying levels of dietary vitamin A, an optimum growth, best FCR, higher BPD, Hb, and Ca values lie in the range of 0.10 to 0.12 g/kg diet, respectively. The data generated during this study would be important in developing vitamin A balanced feed for successful intensive culture of C. carpio var. communis.

Temporal variations in hematological, immunological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss) acclimated to high-saline water in the Northern Aegean Sea

The present study evaluated the health status of rainbow trout (30.24±5.34 g) acclimated to high-saline water (28‰). Among adaptation procedures, gradually-acclimated (for 48 h) fish showed best performance, which were then introduced to the offshore cage-farm for further monitoring of fish health in marine environment over a long-term period of 100 days, until harvest weight of 319.9±48.51 g. Fish health and welfare was evaluated by means of biochemical parameters (viscerasomatic index, hepatosomatic index, mesenteric fat index, and spleen somatic index), hematological parameters (serum glucose, triglyceride, cholesterol, total protein, albumin, globulin), and immune parameters (lysozyme, myeloperoxidase, respiratory burst and potential killing values). Gradual acclimation to high-saline water did not show any adverse effects on health parameters. No significant differences were found in biometric measures (P>0.05). However, a time-dependent increase was recorded in hematology markers (P<0.05) after seawater transfer, and the health status improved over long-term from March 7 to June 14, 2018. All serum biochemical markers, except the total protein showed significant alterations (P<0.05) in long-term but without detrimental influence by day-100. Therefore, it seems possible to expand trout farms from brackish water sites to higher saline environments up to 28‰ salinity, with no detrimental impacts on fish health, that in turns may significantly contribute to the extension of potential aquaculture sites to wider areas.

The role of sex, season and reproduction status on blood parameters in snow trout (Schizothorax labiatus) from River Jhelum, Kashmir, India

The current investigation was carried out with an aim to evaluate disparity in haematological and serum biochemical parameters of healthy male and female Schizothorax labiatus with respect to its four reproductive phases, i.e. preparatory (autumn), pre-spawning (winter), spawning (spring) and spent (summer). The study indicated that significant (p < 0.05) alterations were seen in gonadosomatic index (GSI) of S. labiatus with maximum value for both sexes noted in spring while minimum value in autumn. Contrary to this, the highest value of hepatosomatic index (HSI) for both sexes was noted in the autumn season and the lowest value in spring. The haemoglobin (Hb) content, red blood corpuscle (RBC) and white blood corpuscle (WBC) counts and haematocrit amount of S. labiatus also revealed significant (p < 0.05) variations with peak values noted in summer while least values were recorded during winter. It was also observed that male fishes comprised significantly (p < 0.05) maximum level of all these parameters amongst all seasons of the year, except WBC count. Erythrocyte indices specifically mean corpuscular haemoglobin (MCH), MCH concentration (MCHC) and mean corpuscular volume (MCV) exhibited insignificant (p > 0.05) alterations between the sexes. The lowest levels (p < 0.05) of serum glucose, cholesterol and urea were recorded in the pre-spawning period, i.e. winter, while as the highest values (p < 0.05) were seen in the summer because of the cessation of reproductive activities and greater availability of food. Similar trend was also noted in the amount of total protein, albumin and globulin of the fish, although insignificant (p > 0.05) variation was observed between sexes.

Reference Intervals for Blood Biomarkers in Farmed Atlantic Salmon, Coho Salmon and Rainbow Trout in Chile: Promoting a Preventive Approach in Aquamedicine

Simple Summary

We report the integrated reference intervals (RIs) of 44 blood biomarkers for presmolts, smolts, postsmolts and adults of intensively farmed Atlantic salmon, coho salmon and rainbow trout species in Chile. Overall, RIs were obtained from 3.059 healthy salmon and trout from 78 different culture centers. Our results indicate that the variability of most blood biomarkers depends on the salmonid species, age range and/or interaction between them, but they are often biologically related to each other. Finally, we provide a standardized pre-analytical protocol to improve preventive vision in aquamedicine. RIs for blood biomarkers specific to salmonid species and age ranges are essential to help improve clinical, zootechnical and nutritional management for the health and welfare of farmed fish.

Abstract

The mission of veterinary clinical pathology is to support the diagnostic process by using tests to measure different blood biomarkers to support decision making about farmed fish health and welfare. The objective of this study is to provide reference intervals (RIs) for 44 key hematological, blood biochemistry, blood gasometry and hormones biomarkers for the three most economically important farmed salmonid species in Chile (Atlantic salmon, coho salmon and rainbow trout) during the freshwater (presmolt and smolt age range) and seawater stages (post-smolt and adult age range). Our results confirmed that the concentration or activity of most blood biomarkers depend on the salmonid species, age range and/or the interaction between them, and they are often biologically related to each other. Erythogram and leukogram profiles revealed a similar distribution in rainbow trout and coho salmon, but those in Atlantic salmon were significantly different. While the activity of the most clinically important plasma enzymes demonstrated a similar profile in Atlantic salmon and rainbow trout, coho salmon demonstrated a significantly different distribution. Plasma electrolyte and mineral profiles showed significant differences between salmonid species, especially for rainbow trout, while Atlantic salmon and coho salmon demonstrated a high degree of similarity. Furthermore, electrolytes, minerals and blood gasometry biomarkers were significantly different between age ranges, suggesting a considerably different distribution between freshwater and seawater-farmed fish. The RIs of clinically healthy fish described in this study take into account the high biological variation of farmed fish in Chile, as the 3.059 individuals came from 78 different fish farms, both freshwater and seawater, and blood samples were collected using the same pre-analytical protocol. Likewise, our study provides the Chilean salmon farming industry with standardized protocols that can be used routinely and provides valuable information to improve the preventive vision of aquamedicine through the application of blood biomarkers to support and optimize health, welfare and husbandry management in the salmon farming industry.

Changes in Serum Blood Parameters in Farmed Rainbow Trout (Oncorhynchus mykiss) Fed with Diets Supplemented with Waste Derived from Supercritical Fluid Extraction of Sweet Basil (Ocimum basilicum)

The antimicrobial and immunostimulant proprieties of aromatic plant extracts have been widely described, but their effects on serum blood biochemistry in fish have not. For this study, we assessed the changes in serum blood biochemical parameters in rainbow trout fed with a fish diet supplemented with a basil supercritical extract (F1-BEO). Our hypothesis was that treatment and time would be associated with changes in 10 serum blood biochemical parameters. F1-BEO was added to a commercial feed (0.5, 1, 2, 3% w/w). The fish were fed for 30 days, and the blood samples were collected at 2 time points (15 and 30 days). A two-way ANOVA showed a significant effect of treatment, time, and interaction treatment × time on creatinine, urea, total protein, albumin, magnesium, and phosphorus (p < 0.05), a significant effect of both time and interaction treatment × time on cholesterol (CHOL), glutamic oxaloacetic transaminase (GOT), and glutamic pyruvic transaminase (GPT) levels, and a significant effect of time on triglycerides (p < 0.05). While changes in several of the parameters were observed, the levels remained within the normal range for rainbow trout. Notably, after 30 days there was a significant decrease in CHOL in fish treated with 0.5% and 1% w/w F1-BEO (p < 0.05). The statistically non-significant increase in GOT and GPT in the fish fed with F1-BEO up to 3% w/w indicated a positive effect of basil on liver health. Our findings suggest a potential use for basil extracts (for example., F1-BEO) in fish feed to reduce antibiotic use and improve fish welfare.