Introduction

Vitamins are crucial for fish growth, general health, and successful reproduction like other animals (Watanabe 1985). "Vitamin E" (VE) refers to a class of fat-soluble compounds and the most active homolog of which is -tocopherol (NRC 2011). A vital part of many biological processes, VE is a structural element of cell membranes with a strong antioxidant effect that breaks chains of reactions involved in lipid oxidation. In cultured fish and shrimps, VE stimulates growth and feed utilization; promotes health status and contributes to regulate the immune system and selenium metabolism. It also enhances the reproductive performance and development of larvae and improves fillet quality and shelf life (Hamre 2011).

Animals, including fish, are not known to synthesize tocopherols or to store them in significant quantities in their bodies (El-Sayed and Izquierdo 2022). The maintenance, growth, and physiological processes of animals depend on a constant supply of dietary VE. Several studies concerning the advantages of dietary VE for growth, reproduction, antioxidant activity, feed efficiency, immunological response, and survival of various farmed fish have been reported, including tilapia (Lim et al. 2010a, b).

The dietary VE role in promoting gonadal development, reproductive processes, spawning performance, and larval growth and survival has received considerable attention during the past two decades. These studies showed that high dietary VE supplementation can improve fish fertility, egg development, and larvae quality while reducing egg malformation and abnormality. It can protect eggs against oxidation also (Erdogan and Arslan 2019; El-Sayed and Izquierdo 2022). Additionally, VE can enhance the sperm quality of turbot (S. maximus) and shield sperm cells from oxidation (Xu et al. 2015).

Tilapia is the primary focus of aquaculture in freshwater due to its excellent growth rate, high yield, high disease resistance, tolerance to a variety of environments, and acceptability of both natural and artificial feed (FAO 2016). The hybridization of Mozambique tilapia mutant (O. mossambicus) with other species of tilapia, such as Nile tilapia (O. niloticus) and, blue tilapia (O. aureus), is mainly the cause of genetic variants of red tilapia. Due to its quick growth rate, devoid of a black membrane in the cavity of body, tolerance of salinity, and adaptation to most cultural systems, red tilapia has grown in popularity (Jayaprasad et al. 2011; Pradeep et al. 2014; El-Sayed 2015).

This study was designed to evaluate the effect of vitamin E supplementation on the reproductive and growth performance, hormonal profile and, biochemical parameters of female hybrid red tilapia before spawning season (Pre-spawning).

Material and Methods

The guidelines of the Experimental Animal Care Committee were closely followed during the present study. Moreover, it was also approved by the Scientific Research Ethical Committee of the Faculty of Vet-Medicine, Suez Canal University (Approval No. 2021016).

Female Collection, Maintenance, and Tanks Preparation

Seventy-two female hybrid red tilapia (♂O. niloticus × ♀O. mossambicus) were caught from the sustainable development center and transferred to Aquatic Hatchery Production Department, Fish Farming and Technology Institute, Suez Canal University, Ismailia, Egypt. The fish were transferred in 50 L tanks with portable aerators and at a rate of 1 fish/l. The initial body weight was 272.56 ± 34.84 g and the average total length was 24.3 ± 2.5 cm. Acclimation for fish was done in laboratory conditions for about two weeks before the beginning of the experiment with artificial photoperiod (12 h light/12 h darkness) using (2500 lx) (El-Sayed 2015). The fish were anesthetize using MS-222 (Tricaine methane sulfonate, dose: 100 mg/l, Argent Lab. Inc. Philippines) after feeding stopped (Topic Popovic et al. 2012), and the fish biological measurements were determined.

Fish were kept in indoor fiberglass circular holding tanks of a maximum capacity of 3 m3 (1.7 m diameter and 1.4 m high) filled with 1.5 m3 salt water, under controlled artificial photoperiods and temperature. The used water was filtered with sandy filters and sterilized using ultraviolet units. Aeration was done continuously by an air blower through 3 diffuser stones/tank.

Healthy fish were divided into four equal groups in triplicates which fed four different supplementation levels of VE (0, 50, 100, 200 mg/kg). The selected fish were checked for health which didn’t have tattered fins or missing scales, had bright coloration without abnormally dark spots or light coloration, didn’t seem disinterested, and swam actively with a symmetrical gait. The fish were stocked at a rate of 6 fish/tank (4 fish/m3) (Erdogan and Arslan 2019; Nascimento et al. 2014).

The Experiment Water Physico-Chemical Indicators

The water quality indicators were measured before and during the experiment as showing in Table 1. The water indicators were measured and controlled daily at the indoor holding tanks, using: Thermometer apparatus (Hai million meter, Haiyi instrument Co., LTD, China), DO meter (ExStik II D-0600, FLIR systems, Inc., USA), Digital refractometer (DRBS-300) and pH meter (Milwaukee MW-100).

Table 1 The water parameters of the experiment:
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Feeding Regime

Females were fed manually with a commercial diet (30.2% Crude protein, 6.1% Crude fat, 4.8% Fibre, 6.2% Ash, 0.0 mg VE, pellets 4 mm) 2 times/day for 8 weeks with a 3% feeding rate. The ration was purchased from Skretting Egypt Company. Vitamin E (Karma care co. for veterinary product) was added to the feed with 0 (control), 50 (T1), 100 (T2), and 200 (T3) mg VE/Kg diet. The VE levels were added to experimental diets following the procedure described by Chen et al. (2004), Ibrahim et al. (2020) and Ibrahim et al. (2021).

Biological Measurements

After 8 weeks, all starved fish of each tank were caught, counted and anesthetized in diluted MS-222 at a concentration of 100 mg/l and the final weights and total lengths were recorded. Also, 6 fish from each treatment were dissected and the viscera, liver, and gonad were weighed. Depending on the following formulas the growth parameters and biological measurements were measured:

$$\begin{aligned}\mathrm{Weight\;Gain }\left({\text{WG}}\right)&=\mathrm{Final\;body\;weight\;}\left({\text{g}}\right)\\&-\mathrm{Initial\;body\;weight }\left({\text{g}}\right)\end{aligned}$$
$$\begin{aligned}\mathrm{Length\;Gain }\left({\text{LG}}\right)&=\mathrm{Final\;total\;length }\left({\text{cm}}\right)\\&-\mathrm{Initial\;total\;length }\left({\text{cm}}\right)\end{aligned}$$

Average daily gain (g/fish/day):

$${\text{ADG}}=\frac{Weight\;gain\;\left(g\right)}{ period\;\left(days\right)}$$

Specific growth rate (%/day):

$${\text{SGR}}=\left(\frac{\left(logfinal\;body\;weight-loginitial\;body\;weight\right)}{period \left(days\right)}\right)\times 100$$
$$\mathrm{Feed\;conversion\;ratio }\left({\text{FCR}}\right)=\frac{Feed\;intake\left(g\right)}{Total\;weight\;gain\;\left(g\right)}$$

Protein efficiency ratio (PER) = \(\frac{Weight\;gain \left(g\right)}{Protein\;intake \left(g\right)}\) (Tekinay and Davies 2001; Asaikkutti et al. 2016; Ibrahim et al. 2022).

The reproductive activities and biological measurements for females were determined from the temporal Fulton’s condition factor (K), Viscerosomatic index % (VSI), Hepatosomatic index % (HSI), and gonadosomatic index (GSI) were measured depending on the following formulas:

$${\text{K}}=\frac{Body\;weight\times 100}{{Total\;length}^{3}}$$
$$\mathrm{VSI\;\%}=\frac{Viscera\;weight\;\left(g\right)}{Body\;weight \left(g\right)}\times 100$$
$$\mathrm{HSI\;\%}=\frac{Liver\;weight \left(g\right)}{Total\;Body\;weight \left(g\right)}\times 100$$
$$\mathrm{GSI\;\%}=\frac{Gonad\;weight}{Total\;Body\;weight} \times 100$$

Blood Sampling and Analysis

At the experiment end, three females from each replicate were taken and anesthetized in diluted MS-222 at a concentration of (100 mg/l) for collecting two blood samples that were quickly withdrawn from heart puncture into clean and dry screw-copped Eppendorf tubes. One sample was left to clot and centrifuged for 5 min at 5000 rpm for separating serum which was stored at (-25 °C) to determine different hormonal profiles (FSH, LH, Estradiol E2, Progesterone) and, biochemical parameters (aspartate aminotransferase ‘AST’, alanine transaminase ‘ALT’, total protein ‘TP’, albumin ‘ALB’, globulin ‘GLO’, triglyceride ‘TG’, and alkaline phosphatase ‘ALP’). The second sample was taken with an anticoagulant (heparine 20 IU/ ml, Amoun Pharmaceutical Co.) and used directly for the determination of haematological Parameters. It ought to be mentioned that blood sampling of fish was executed in the morning around 8:00 a.m. before providing food (Rinchard et al. 1993).

Haematological Parameters

Under the light microscope, total erythrocytic count (RBCs), total leucocytic count (WBCs) and platelets count were determined using a neubauer hemocytometer after blood dilution with phosphate-buffered saline (pH, 7.2) (Shalaby et al. 2019 and Abdel-Tawwab et al. 2020). Hct (hematocrit) was immediately determined according to (Rehulka 2000) after sampling by placing fresh blood in glass capillary tubes, centrifuged in a micro-hematocrit centrifuge (Centurion Scientific, United Kingdom), and measuring the packed cell volume. Hgb (Hemoglobin concentration) was determined according to (Jain 1993) colorimetrically. According to Haney et al. (1992) MCV, MCH, and MCHC were calculated as follows:

$$\mathrm{MCV }\left(\mathrm{Mean\;cell\;volume}\right) \left({\text{fl}}\right)=\frac{Hct\%\;{\text{x}}\;1000 }{\mathrm{RBCs }\left({\text{mill}}/{mm}^{3}\right)}$$
$$\mathrm{MCH }\left(\mathrm{mean\;cell\;hemoglobin}\right) \left({\text{pg}}\right)=\frac{Hgb \left(\frac{g}{dl}\right) {\text{x}} 10 }{\mathrm{RBCs }\left({\text{mill}}/{mm}^{3}\right)}$$
$$\mathrm{MCHC }\left(\mathrm{mean\;cell\;hemoglobin\;concentration}\right) \left({\text{g}}/{\text{dl}}\right)=\frac{Hgb \left(\frac{g}{dl}\right)\mathrm{ x }100}{{\text{Hct}}}$$

Biochemical Parameters

Serum samples were collected to determine protein profiles, (total protein TP and, albumin ALB) contents (Henry 1964 and Doumas et al. 1997). Globulin (GLO) levels were also determined by subtraction of ALB from TP values. Blood triglycerides (TG) and Alkaline phosphatase (ALP) levels were measured colorimetrically using commercially purchased specific kits (all laboratory procedures were accomplished depending on the manufacturer's protocol) and according to Reitman and Frankel (1957), transaminases (AST & ALT) were determined.

Determination of Hormonal Profile

FSH, LH, E2 (Estradiol), and Progesterone levels were determined using commercial assay ELISA kits as manufactories instructions.

Statistical Analysis

Collected data were presented as mean ± stander error (SE) between all groups. Statistically significant differences between groups were calculated using one-way ANOVA at 5% level of probability followed by post hoc multiple comparison tests (Duncan's 1955). SPSS Program version 20. (SPSS, Richmond, USA) was used in the current study's statistical analysis as described by (Dytham 2011).

Results

The Impact of Different Doses of Vitamin E on the Growth Performance of Female Hybrid Red Tilapia

Female hybrid red tilapia weight gain and length gain were significantly affected (P ≤ 0.05) by dietary vitamin E (VE) (Table 2). The treated groups produced significantly (P ≤ 0.05) better growth performance than the control group. The highest values of weight gain and length gain were detected in T1 (87.09 g) and (3.68 cm) respectively.

Table 2 The impact of different doses of vitamin E on body weight gain (WG), and length gain (LG) of female hybrid red tilapia
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SGR, ADG, FCR, and PER values of female hybrid red tilapia supplemented with VE were impacted significantly (P ≤ 0.05) than the control. SGR increased significantly in T1 (50 mg VE) versus the control and other treated groups. Regarding ADG and FCR, all supplemented groups exhibited better significant values than the control. PER in T1 demonstrates a higher significant value than control and other treatments. PER recorded the lower values in control regardless to others (1.27 ± 0.055) (Table 3).

Table 3 The impact of different doses of vitamin E on specific growth rate (SGR), average daily gain (ADG), feed conversion rate (FCR) and protein efficiency ratio (PER) of female hybrid red tilapia
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The Impact of Different Doses of Vitamin E on Viscera Somatic Index, Gonadosomatic Index, Hepatosomatic Index and Condition Factors of Female Hybrid Red Tilapia

T1 exhibited higher significant values in VSI, GSI and HSI of female hybrid red tilapia when compared to control and other supplemented groups (T2, T3). The highest value of the K factor of female fish specimens was calculated in 50 mg vitamin E treatment (T1) (Table 4).

Table 4 The impact of different doses of vitamin E on viscera somatic index (VSI), gonadosomatic index (GSI), hepatosomatic index (HSI) and condition factors (K) of female hybrid red tilapia
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The Impact of Different Doses of Vitamin E on Haematological Parameters of Female Hybrid Red Tilapia

For Hemoglobin (Hgb) and RBCs, the greatest significant value (P ≤ 0.05) of Hgb and RBCs were recorded in T1. Regarding, Hct and platelets values, no significant variation was observed between the control and treatments. MCV was significantly (P ≤ 0.05) increased in T3 (180.33 fl) than the other treatment. The highest significant values of MCH, and MCHC have been observed in T1 53.67 pg and 33.33% respectively. WBCS were significantly (P ≤ 0.05) increased in T1 and, T2 versus control in (Table 5).

Table 5 The impact of different doses of vitamin E on haematological analyses of female hybrid red tilapia
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The Impact of Different Doses of Vitamin E on Biochemical Parameters of Female Hybrid Red Tilapia

TP and TG were significantly (P ≤ 0.05) increased in T1 and, T2 than in control and T3. There was no significant variation in ALB and AST values between all treated groups. While GLO showed the greatest significant value in T2 3.55 g/dl. A higher significant level of ALT (12.65 u/l) was recorded in T2 versus control and other treated group (T1 and T3). ALP levels were significantly (P ≤ 0.05) enhanced with increasing VE levels recorded in T2 and, T3 (Table 6).

Table 6 The impact of different doses of vitamin E on biochemical parameters (total protein TP, albumin ALB, globulin GLO, transaminases (AST & ALT), alkaline phosphatase ALP and triglyceride TG) of female hybrid red tilapia
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The Impact of Different Doses of Vitamin E on Hormonal Profile of Female Hybrid Red Tilapia

FSH and LH levels were significantly increased at T1 (50 mg/Kg) and decreased afterward. Regarding the impacts of VE on E2, the highest level was recorded in T1 and, T2 when compared to control and T3. The peak level of progesterone was noticed in T1 (0.12 ng/ml) (Table 7).

Table 7 The impact of different doses of vitamin E on hormonal profile (FSH, LH, E2, Progesterone) of female hybrid red tilapia
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Discussion

Finding out the impact of Vitamin E on fish performance, antioxidation, quality, immunity, and, metabolic processes and other biological events has taken up a significant portion of the research in recent years (Hamre 2011; El-Sayed and Izquierdo 2022). In our study, we demonstrate the optimum dose of VE administration and the impacts of this vitamin on reproductive and growth performance, blood analyses, and the hormonal profile of female hybrid red tilapia before the spawning season (pre-spawning).

The current findings showed that the addition of 50, 100, 200 mg/kg of VE significantly improved the growth performance of female red tilapia (weight gain and length gain). Similarly, VE treatments have been demonstrated to considerably modulate the growth performance in female Nile tilapia (O. niloticus). The final weight and length of female Nile tilapia were increased significantly with VE concentrations ranging from 40 to 160 mg/kg feeds (Zhang et al. 2021). Adding 140 mg/kg of VE to the carp feed and 50—100 mg/kg to the catfish (I. punctatus) feed could accelerate weight gain and length gain (Abdel-Hameid et al. 2012; He et al. 2017).

The levels of VE 43.2–45.8 mg/kg (Jiang et al. 2020) and 50—100 mg/kg (Lim et al. 2009) with 6% lipid feeds were required to modulate the performance (final weight gain) and health status of tilapia which consistent with the percentage of lipid in fish feed in current study. The dietary VE supplement could improve WG and WG % significantly of the Nile tilapia (Rohani et al. 2022; Ahmed et al. 2021).

The present results of SGR, ADG, FCR, PER were enhanced significantly by supplementation with 50, 100, 200 mg/kg of VE and, the best values were recorded with the addition of 50 mg/kg of VE treatment. These results agreed with the previous studies of Rohani et al. (2022) who recorded that dietary 50 mg/kg of VE supplement significantly enhance SGR, FCR, and, PER of the Nile tilapia and Saheli et al. (2021) who noted that dietary 35.4 and 78.8 mg/kg of VE supplement significantly improve SGR and PER and decreased FCR of the Caspian trout but fish fed diet unsupplemented with VE had the lower WGR, SGR and PER. The study of Zhang et al. (2021) have shown that 120 and, 160 mg/kg of VE could significantly decrease the FCR in female tilapia, which is constant with previous research.

The current findings showed that supplementing with VE in the right proportions can enhance fish performance, feed assimilation, and absorption with lower the cost and period of hybrid red tilapia pre-spawning preparation which may be due to the VE role as a cofactor of many enzymes that may promote the secretion and activity of digestive enzymes and enhances digestion and nutrient absorption (Swain et al. 2019). Fish species, life stage, feeding regimen, rearing environment, diet composition, and even the sample analysis method may all have an impact on the amount of VE needed which is a vital dietary component for fish (Lee et al. 2015; Lu et al. 2016). Although it had been claimed that vitamin E was necessary for fish to thrive, other research found that excessive amounts of VE in feed which might serve as prooxidants were hazardous to fish and could stunt fish growth (Paul et al. 2004; Li et al. 2013).

The present results regarding biological measurements and reproductive performance including VSI, GSI, and HSI have been improved significantly by supplementation with 50 mg/kg of VE without significant variations in the K factor. similar observations were achieved by Pamungkas et al. (2014) who reported that the peak of female GSI of Nile tilapia was found in broodstock fed with 75 and 375 mg/kg VE. The gonad development index of M. albus was significantly affected by the addition of VE (200 mg/kg) to the feed (Zhang et al. 2007). The best GSI level of female tilapia was achieved at 120 mg/kg of VE (Zhang et al. 2021). While Gammanpila et al. (2010) noticed that the final females’ GSI of Nile tilapia were not influenced by supplementation of the VE. The increase of GSI with 50 mg/kg and, 200 mg /kg of VE may be due to the responsibility of VE in the gonad development process and its impacts on the progress of the vitellogenesis process. Vitamin E with the right amount acts as an antioxidant against fat, preventing the oxidation of fat that happens when vitellogenin is present and will accelerate the vitellogenesis process. As a result, more vitellogenin is present when the oocyte develops, and the gonad weight increases, reflecting an increasing the GSI percentage (Arfah and Setiawat 2013; Tarigan et al. 2021; Ashari et al. 2021).

VSI and, HSI of females in our study were increased with the addition of 50 mg/kg VE. The increase in HSI may be due to fat and VE cumulation in the liver (Amlashi et al. 2011). Hepatosomatic index values are adversely correlated with fecundity and VE content in diet (Nascimento et al. 2014) which explain the decrease in HSI at 200 mg/kg of VE. HSI was increased with dietary VE supplement 35.4 and, 78.8 mg/kg in the study of (Saheli et al. 2021) from 8.9 to 156.9 mg/kg in the study of (Lu et al. 2016). In studies conducted on Nile tilapia by Satoh et al. (1987), HSI dramatically decreased most likely resulting from tissue degradation with an absence of VE treatment and by Lim et al. (2009), supplementation of 50 mg/ kg of VE to diets (6 to 14% lipid) was sufficient to prevent degeneration and/or fat infiltration of liver tissue.

The current results declared that the VE-treated fish cause an increase in their Hgb and RBCs, especially by 50 and 100 mg/kg but without changes in Hct % compared with other treatments. At the same time, 200 mg/kg VE declines Hgb, and RBCs. These results are in agreement with Ispir et al. (2011) who reported that RBCs and Hgb of Nile tilapia were increased by 80 and, 160 mg/kg of VE and decreased by a higher dose (240 mg/kg) of VE. Adding 50 mg/kg of VE improves Hgb and RBCs of Nile tilapia and there are no changes in Hct % when compared to 0 mg/kg of VE and other treatments (Ibrahim 2014). Hct, Hgb and RBCs can be an indicator of oxidative status because erythrocytes are the main sources of free radicals and some of them can cause sutured fatty acids in their membrane phospholipids to peroxide, changing the quality (integrity, size), quantity, and composition of the erythrocytes (Kiron et al. 2004). The obtained value of MCV in the current study represented a significant raising with the VE level of 200 mg/kg followed by 100 mg/kg and decreased at the VE level of 50 mg/kg. However, the peak calculated values of MCH and, MCHC were obtained at the VE level of 50 mg/kg followed by 100 mg/kg. These results are in agreement with Ispir et al. (2011) who reported that 240 mg/kg of VE raised MCV while 80 and, 160 mg/kg of VE raised MCH and, MCHC. The main impact of VE was highly significant at the 28days period for MCV, MCH, and MCHC (Ibrahim 2014).

The total counts of WBC showed that 50 and, 100 mg/kg of VE increased the WBCs significantly, without significant impacts of VE on platelets. Similar results were obtained in a study conducted on Nile tilapia by Ispir et al. (2011) when using 80 and, 160 mg/kg of VE could enhance the WBCs. VE’s main effect was significant for WBC and 50 mg/kg of VE could increase WBCs compared to 0 mg/kg of VE and other treatments (Ibrahim 2014). VE act as a potential antioxidant that protects the leucocyte function, it was discovered that WBC is a vitamin efficiency indicator and a defense mechanism indicator in fish (Sahoo and Mukherjee 2002). VE contributed to the hypothalamic-sympathetic- chromaffin cell axis and interferes in stress responses, where they protect the WBC functions (Ortuño et al. 2003). Supplementation of dietary VE improved haematological parameters (Ibrahim 2014).

In our study, enhanced total protein and globulin values were recorded in fish fed with 50 and 100 mg/kg of VE while they were decreased with supplementation of 200 mg/kg of VE without change in albumin levels. Our results agree with the findings of Saber et al. (2019) who found a significant rise in total protein was recorded in VE-supplemented fish when compared with other groups. Adding 50 mg/kg of VE could enhance the TP, ALB, and, GLO of Nile tilapia compared to 0 mg/kg of VE and other treatments (Ibrahim 2014). Contrary to our results, Lim et al. (2009) and Lim et al. (2010a) noticed that Rising levels of VE from 50 to 100, 200 or 500 mg/kg feed had no impact on serum total protein Nile tilapia. Vitamin E may activate protein phosphatase 2A, diacylglycerol phosphatase, and protein tyrosine phosphatase and inhibit protein kinase A2, phospholipase A2, cyclooxygenase, and lipoxygenases, according to later studies of (Hamre 2011; Zingg 2007, 2019).

In the current study, no significant impacts of different doses of VE supplement were found on AST but 100 mg/kg of VE could increase the ALT value. ALP levels were increased significantly by the increase of VE levels. The blood concentration of hepatic enzymes including ALP, AST, and, ALT is known to be correlated with the functional role of VE (Abdulazeez et al. 2019). The Liver is the primary organ participatory in xenobiotics metabolism (Ibrahim 2014). Activities levels of AST and, ALT could also give evidence about the liver condition (Ghodrati et al. 2021), while ALP is the most important hepatobiliary damage biomarker that catalyze the hydrolysis of organic phosphate esters (Aulbach and Amuzie 2017). The 50 mg/kg addition of VE increases the AST level and decreases the ALP level of Nile tilapia non-significantly after 28 days of treatment but the same dose of VE could decrease the ALP level significantly (Ibrahim 2014). Our findings may be confirmed that VE did not have any adverse impacts on the liver function when used within the suggested dose and these findings could be referred to the following issues, a) VE encourages the synthesis of cytokine, which consider a crucial component of the inflammatory response that protected liver cells., b) the activity of VE as an antioxidant and, anti-inflammatory vitamins agents that keep the hepatic fibrosis and dysfunction that aid making liver act within the normal function (Eddowes et al. 2019).

Supplementation with 50 and 100 mg/kg of VE could increase the TG levels, but 200 mg/kg of VE decreased TG significantly. Similarly, in red seabream raising dietary VE level correlated with reduced TG concentration. The reduction of TG value by VE supplement (200 mg/kg) could be related to TG decrease in chylomicrons (Gao et al. 2012). TG is measured to track metabolism of lipids. High levels of TG can cause nephritic syndrome, glycogen storage disease, and liver failure (Osman et al. 2010). In the study of Taalab et al. (2022), the total lipid profile, was shown to be lower in Nile tilapia-fed diets containing high-level VC, VE, or β-carotene. These conclusions may be due to the role of VE in improving the profiles of lipids in the blood, HDL-C (high-density lipoprotein cholesterol), inhibiting the oxidation of lipids and lowering the risk of atherosclerosis of LDL-C (low-density lipoprotein cholesterol) (Ashor et al. 2016).

In our study, 50 mg/kg of VE could improve the reproductive hormonal levels including (FSH, LH, E2, and Progesterone) significantly. Our findings may be due to the fact of the provision of VE through pituitary cells in vitro triggers the FSH and, LH expression in the fish pituitary (Huang et al. 2019). The increase of E2 and, progesterone in our study may be due to Low-level of VE may stimulate female tilapia to secrete large quantities of steroid hormones (Zhang et al. 2021). Both pituitary FSH LH, and, E2 have major responsibilities in controlling all aspects of the gonadal development and, function across vertebrates (including fish) ( Swanson et al. 2003; Xu et al. 2008; Levavi-Sivan et al. 2010). Progesterone can adjust gonadotropin production and play a role in reproduction (Sun et al. 2020). Similar outcomes were noted in the study of (Zhang et al. 2021) who reported that the FSH of female tilapia was the largest in the group supplemented with 40 mg/kg of VE followed by 80 mg/kg of VE, but the various levels of VE had no impact on E2 and the peak level was recorded in the group supplemented with 120 mg/kg of VE. A level of 120 mg/kg followed by 40 mg/kg of VE could enhance the level of progesterone and demonstrate that these vitamin levels can promote the reproductive performance of female tilapia. In the study of turbot, the mRNA expressions of FSH and, LH in the cells were both increased in vitamin E treated groups when compared to the control group which confirmed that VE promoted the GTHs expression at a molecular level (Huang et al. 2019). Quite a little information has been previously reported about the act of VE in regulating fish FSH, LH, E2, and progesterone. So, the impacts of VE on the hormonal profile of female hybrid red tilapia need additional follow-up investigation.

Conclusion

It was concluded that, the addition of vitamin E in a dose of 50 mg/kg diet has a beneficial impact on the growth and reproductive performing, hormonal profile, and biochemical parameters of female hybrid red tilapia. So, it is advisable that adding 50 mg/kg to the fish diet support the benefits of VE and are recommended for enhancing the health, growth and, reproductive performance of fish before spawning season (pre-spawning).