Effects of fermented grape pomace (Vitis sp.) inclusion on growth performance, lipid peroxidation, and hematology of juvenile Mugil liza

Efeitos da inclusão de bagaço de uva fermentado (Vitis sp.) no desempenho de crescimento, peroxidação lipídica e hematologia de juvenis de Mugil liza

ABSTRACT

This study investigated the potential use of fermented grape pomace (FerGP) as a dietary ingredient for juvenile mullet (Mugil liza). For this purpose, growth perfomance, hepatic lipid peroxidation, and hematology of juvenile mullet fed various levels of FerGP were evaluated. A total of 225 fish (0.57 ± 0.01 g) were randomly distributed into 15 tanks and fed ad libitum three times a day for 65 days with different levels of FerGP (2.5, 5, 10, and 15%). There were no significant differences (p > 0.05) in hematological parameters. Regarding the zootechnical parameters, FerGP 15% showed higher specific growth rate compared to the other treatments. Dietary inclusion of FerGP significantly reduced hepatic lipid peroxidation, as indicated by a decrease in thiobarbituric acid reactive substances (TBARS) values. The results demonstrated that the inclusion of FerGP in the diet is feasible and safe, promoting benefits to the productive performance of juvenile mullet.

Keywords
Vegetable co-products; Nutrition; Marine fish

RESUMO

Este estudo investigou o uso potencial de bagaço de uva fermentado (FerGP) como ingrediente dietético para tainhas juvenis (Mugil liza). O desempenho de crescimento, a peroxidação lipídica hepática e a hematologia de tainhas juvenis alimentadas com vários níveis de FerGP foram avaliados. O total de 225 peixes (0,57 ± 0,01 g) foi distribuído aleatoriamente em 15 tanques e alimentado ad libitum três vezes ao dia por 65 dias com diferentes níveis de FerGP (2,5, 5, 10 e 15%). Não houve diferenças significativas (p > 0,05) nos parâmetros hematológicos. Em relação aos parâmetros zootécnicos, FerGP 15% apresentou diferença significativa em comparação com os outros. A inclusão dietética de FerGP reduziu significativamente a peroxidação lipídica hepática, conforme indicado pela diminuição dos valores de substância reativa ao ácido tiobarbitúrico (TBARS), e não foram observadas diferenças significativas nos parâmetros hematológicos. Este estudo demonstrou que 15% de FerGP pode ser usado para aumentar o crescimento e reduzir a peroxidação lipídica no fígado.

Palavras-chave
Subprodutos vegetais; Nutrição; Peixes marinhos

INTRODUCTION

Viticulture is an economic activity specialized in the production of grapes, which are destined to produce juice, wine and derivatives, in addition to consumption in natura. According to data from the Food and Agriculture Organization of the United Nations (FAO), provided by FAOSTAT (2025), world production of Vitis sp. is led by China, with approximately 29 million tons in the period 2022–2023, followed by Italy with approximately 15 million tons and Spain with 10 million tons.

The grape production chain generates a significant amount of waste or co-products (Santos & Leite, 2020), which can reach 20–30% of the total processed volume (Bordiga et al., 2019; Bustamante et al., 2009). This biomass contains significant amounts of ethanol and organic acids, including tartaric acid and malic acid, as well as volatile organic compounds (VOCs) such as propionic acid, which can cause soil acidification, pollute water bodies, and consequently degrade the environment (Niculescu & Ionete, 2023; Zhang et al., 2017). Another destination for grape waste is fertilizer; however, if this waste is not previously treated, there is a possibility of environmental impact (Lopes et al., 2020). Therefore, it is important to mitigate the disposal of these materials by improving their functionalities. Given this context, the reuse of the co-products generated by winemaking makes it possible to obtain inputs with economic and sustainable potential for other sectors of the agroindustry.

The fermented grape pomace (FerGP), the main residue from winemaking, contains bioactive compounds, such as polyphenols, flavonoids, and tannins (Albuquerque et al., 2019; Beres et al., 2019; Bordiga et al., 2019; Chen et al., 2022), which have antioxidant properties and can be reused for applications in several areas, including aquaculture (Beres et al., 2019; Chen et al., 2022).

Research has highlighted the importance of including phenolic compounds and their benefits in the diet of aquatic organisms, such as improving the immune response (Morante et al., 2021; Peng et al., 2022a), growth (Arslan et al., 2018; Rosas et al., 2022), digestibility (Peña et al., 2020), antioxidant capacity (Arslan et al., 2018; Dawood et al., 2020; Mohammadi et al., 2021; Peng et al., 2022b), and antimicrobial activity (Baldissera et al., 2019). In this context, the inclusion of FerGP in the diet may represent a sustainable strategy to improve the zootechnical performance and health of farmed species.

However, it is crucial to recognize that these co-products may also contain antinutrients (Kumanda et al., 2019) that can negatively affect animal performance. Antinutrients such as tannins can interfere with the absorption of essential nutrients in the diet of animals, thereby harming their health and productivity (Vastolo et al., 2022). Therefore, understanding the balance between biocompounds and antinutrients is essential to optimize animal nutrition and ensure sustainable agricultural practices.

Among the species of interest for marine fish farming, mullet (Mugil liza) stands out for its cultivation potential, since it accepts artificial feed and occupies a lower trophic level (Cardona, 2016). This characteristic allows the use of diets with lower protein content, contributing to the reduction of feed costs (Ramos et al., 2015). In this context, the present study aimed to reuse FerGP, a co-product of the wine industry, and evaluate the effects of its inclusion in the diet on the growth performance and nutritional parameters of mullet.

MATERIAL AND METHODS

Fermented grape pomace

FerGP was donated by the Enology course of the Universidade Federal do Pampa, Dom Pedrito (RS), Brazil. The fermentation process began with grape must, defined as the juice extracted after crushing or pressing the grapes, before alcoholic fermentation, in which reducing sugars were converted into ethanol and carbon dioxide. Fermentation was carried out at 20 °C, using active dry yeast Saccharomyces cerevisiae (MAURIVIN AWRI 796), at the concentration of 20 g∙L^-1. After the fermentation was complete, the material was filtered to obtain the final co-product (FerGP) and stored at -18 °C.

Local and juvenile Mugil liza

This study was conducted at the Laboratório de Nutrição de Organismos Aquaticos, which is linked to the Estação de Aquicultura Marinha of the Instituto de Oceanografia of the Universidade Federal do Rio Grande. To carry out the experiment, 225 juvenile mullets (M. liza) were collected from Cassino Beach and kept for acclimation under controlled laboratory conditions: dissolved oxygen (6.52 mg∙L^-1 ± 0.62), alkalinity (146.90 mg∙L^-1 of CaCO₃ ± 5.07), pH (7.84 ± 0.27), temperature (27.42 °C ± 0.54), salinity (30 ppt ± 0.26), ammonia (0.08 mg∙L^-1 ± 0.04), nitrite (0.04 mg∙L^-1 ± 0.02), and photoperiod (12 h light: 12 h dark), for 30 days, in a recirculation system. Juveniles were fed ad libitum (8, 12, and 16 h) with commercial NUTRIPISCIS feed (36% crude protein) according to the recommendations of Calixto da Silva et al. (2020). This study was approved by the Animal Use Ethics Committee of the Universidade Federal do Rio Grande under protocol number 23116.005442.

Experimental design

After 30 days of acclimation, the juvenile mullets (n = 225; mean weight = 0.57 ± 0.01 g) were randomly distributed into 15 tanks (effective volume of 65 L), to start the feeding trial with five levels of FerGP inclusion, in triplicate. For 65 days, the animals were kept in a recirculating aquaculture system (RAS) with physical and biological filters and a constant water flow (1 L every 27 s). The water quality parameters were monitored daily. Temperature and dissolved oxygen were measured using a multiparameter monitor (YSI^®-550 A), salinity was assessed with a refractometer (Atago^®), and pH was measured with a digital pH meter (YSI^®-pH100). The photoperiod was maintained at 12 hours of light and 12 hours of darkness. Ammonia (UNESCO, 1983), nitrite (Strickland & Parsons, 1972), and alkalinity (APHA, 2005) levels were measured every three days. System maintenance was also performed every three days by siphoning to remove feces and feed residues.

Preparation of diets

The experimental diets consisted of a control formulation, without FerGP (0%), and formulations containing 2.5, 5, 10, and 15% of FerGP. All diets were isonitrogenic, as described by Carvalho et al. (2010). The composition of all ingredients in the feed formulation (Tables 1 and 2) was checked in the laboratory according to AOAC International methodology (2006). The diets were pelletized using a meat grinder (Metalúrgica 9000, PC-22) and dried at 60°C for 8 h in an oven (Marconi, MA035). The particle size of the pellets used was 700–850 µm, and the diets were stored in hermetically sealed plastic bags at -18°C until use. The experimental diets were tested in triplicate, and the juveniles were fed ad libitum three times a day (8, 12, and 16 h) (Calixto da Silva et al., 2020).

Table 1
Proximal composition of fermented grape pomace (Vitis sp.).

Composition	%
Crude protein	17.55
Moisture	3.46
Fiber	25.78
Lipid	8.57
Mineral matter	5.96
Non-fibre carbohydrates	38.69

Table 2
Composition of the experimental diets and proximate analysis of diets containing different levels of fermented grape pomace meal (Vitis sp.) fed to mullet juveniles.

Ingredients	Fermented grape pomace (%)
	0	2.5	5	10	15
Fishmeala	41.0	41.0	41.0	41.0	41.0
Soybean mealb	15.0	14.5	14.0	13.0	12.0
Wheat branc	15.0	14.0	13.0	11.0	9.0
FerGP meal	0.0	2.5	5.0	10.0	15.0
Fish oild	4.0	3.8	3.6	3.2	2.8
Gelatine	2.0	2.0	2.0	2.0	2.0
Starchf	20.0	19.2	18.4	16.8	15.2
Premix (mineral + vitamin) g	1.0	1.0	1.0	1.0	1.0
Celluloseh	2.0	2.0	2.0	2.0	2.0
Total	100.0	100.0	100.0	100.0	100.0
Proximate analysis (%)
Crude protein	35.27	35.24	35.21	35.15	35.1
Moisture	4.68	6.77	5.59	7.01	6.11
Fiber	3.65	4.17	4.7	5.75	6.79
Lipid	7.87	7.87	7.87	7.88	7.89
Mineral matter	15.29	16.23	15.42	15.54	15.67
Non-fibre carbohydratesi	33.24	29.72	31.21	28.66	28.44

• ^a
  Leal Santos, Rio Grande, RS, Brazil. FM composition: crude protein 55.60, lipids 8.80, ash 33, moisture 5.57, fiber 7.46;
• ^b
  Sulino, RS, Brazil;
• ^c
  Sulino, RS, Brazil;
• ^d
  Campestre, São Paulo, SP, Brazil;
• ^e
  gelatin powder, Exodus scientific;
• ^f
  Maizena, Brazil;
• ^g
  Premix M, Cassab, São Paulo, SP, Brazil [Vitamin A (500,000 U∙kg^-1), vitamin D3 (250,000 U∙kg^-1), vitamin E (5,000 mg∙kg^-1), vitamin K3 (500 mg∙kg^-1), vitamin B1 (1,000 mg∙kg^-1), vitamin B2 (1,000 mg∙kg^-1), vitamin B6 (1,000 mg∙kg^-1), vitamin B12 (2,000 mg∙kg^-1), niacin (2,500 mg∙kg^-1), calcium pantothenate (4,000 mg∙kg^-1), folic acid (500 mg∙kg^-1), biotin (10 mg∙kg^-1), vitamin C (10,000 mg∙kg^-1), choline (100,000 mg∙kg^-1), inositol (1,000 mg∙kg^-1). Trace elements: selenium (30 mg∙kg^-1), iron (5,000 mg∙kg^-1), copper (1,000 mg∙kg^-1), manganese (5,000 mg∙kg^-1), zinc (9,000 mg∙kg^-1), cobalt (50 mg∙kg^-1), iodine (200 mg∙kg^-1)]; ^{h i}
• ^h
  microcrystalline cellulose PA, Synth;
• ⁱ
  determined by difference.

Zootechnical performance variables

Weight was measured at the beginning and end of the experiment. Animals were anesthetized with 50 ppm benzocaine (da Silva Braz et al., 2017) in an aquarium (3 L). Subsequently, the weight was measured using a digital scale (BIOPRECISA, model JH2102, precision 0.1 g). Food supplied and mortality were also registered. Data were used to calculate the weight gain (WG), survival, specific growth rate (SGR), and feed conversion (FCR). Equations 1, 2, 3, and 4 was used:

(1) $\mathrm{WG}\left(\mathrm{g}\right)=\mathrm{Final}\mathrm{weight}\left(\mathrm{g}\right)-\mathrm{Initial}\mathrm{weight}\left(\mathrm{g}\right)$

(2) $\mathrm{Survival}(\%)=(\mathrm{Final}\mathrm{number}\mathrm{of}\mathrm{fish}/\mathrm{Initial}\mathrm{number}\mathrm{of}\mathrm{fish})\mathrm{x}100$

(3) $$\begin{array}{c}\mathrm{SGR}(\%\mathrm{day}-1)=\left[\right(\ln \mathrm{final}\mathrm{weight}\left(\mathrm{g}\right)–\ln \mathrm{initial}\\ \mathrm{weight}\left(\mathrm{g}\right))/\mathrm{experimental}\mathrm{period}(\mathrm{days}\left)\right]\mathrm{x}100\end{array}$$

(4) $\mathrm{FCR}=\mathrm{feed}\mathrm{provided}\left(\mathrm{g}\right)/\mathrm{weight}\mathrm{gain}\left(\mathrm{g}\right)$

Carcass proximal composition

The proximal composition of the fish was determined in triplicate at Laboratório de Nutrição de Organismos Aquáticos following the methods described by AOAC (2006). The fish carcasses were dried in an oven at 105 °C to obtain dry matter. Crude protein was determined by the Kjeldahl method using a nitrogen distiller, and crude fat content was evaluated using a Soxhlet extractor and a solvent (petroleum ether). The mineral matter content was determined by gravimetry after the calcification of the samples at 600 °C in a muffle furnace, and the crude fiber content was determined using the method described by Silva and Queiroz (2009).

Hematological analysis

For blood collection, at the end of experimental period three fish from each experimental unit were randomly selected and anesthetized (Silva & Queiroz, 2009). Collection was performed by puncturing the caudal vein using heparinized syringes. After collection, the blood extensions were prepared on glass slides, dried, and stained (eosin, methylene blue and azure B) using the Romanowsky principle (Laborclin, Pinhais, PR, Brazil). Blood extension was evaluated using an optical microscope (Olympus, model CX21FS1; Tokyo, Japan) with an immersion objective (1,000 × magnification). Counts were performed to establish the differential profiles of blood leukocytes (monocytes, lymphocytes, erythrocytes, and total granulocytes).

Biochemical analysis of the liver

To analyze lipid peroxidation levels, the thiobarbituric acid reactive substances (TBARS) method was used as described by Oakes and Van Der Kraak (2003). Three fish per tank were euthanized with a megadose of benzocaine (500 ppm), and liver samples (50 μL) were combined with 20 μL of BHT solution (67 μM), 150 μL of 20% acetic acid, 150 μL of 0.8% thiobarbituric acid (TBA), 50 μL of Milli-Q water, and 20 μL of 8.1% sodium dodecyl sulfate (SDS). After heating at 95°C for 30 min, the samples were centrifuged (3,000 × g for 10 min at 15°C), and 100 μL of Milli-Q H₂O and 500 μL of n-butanol were added to the final solution. The resulting supernatant was used to measure the fluorescence (excitation at 520 nm and emission at 580 nm) using a BioTek microplate reader (Synergy HT). The results were expressed in nanomoles of tetramethoxypropane (TMP, supplied by ACROS Organics) per gram of wet tissue, using TMP (1,1,3,3-tetramethoxypropane) as the standard for calibration.

Statistical analysis

Data are expressed as the mean and standard deviation. Data normality and homogeneity were assessed using the Shapiro-Wilk’s and Levene’s tests, respectively. After checking the assumptions, the respective data were subjected to analysis of variance (one-way ANOVA), and when necessary, Tukey’s post-hoc test was performed to compare the means. Linear and quadratic regressions were performed for all the variables. All analyses were performed with a significance level of 5%.

RESULTS

Water quality parameters remained stable throughout the 65-day experimental period, presenting average values of dissolved oxygen (DO) of 6.36 ± 0.46 mg∙L^-1; temperature of 27.46 ± 0.77 °C; total ammonia (N–NAT) of 0.08 ± 0.05 mg∙L^-1; nitrite (N–NO₂) of 0.06 ± 0.07 mg∙L^-1; alkalinity of 144.84 ± 9.69 mg∙L^-1 CaCO₃; salinity of 30.48 ± 1.10 ppt; and pH of 7.73 ± 0.27.

The zootechnical parameters of juvenile mullet are presented in Table 3, with no significant effect observed from the different dietary levels of FerGP (p > 0.05), except for the specific growth rate. As illustrated in Fig. 1, the specific growth rate showed a quadratic response as a function of FerGP inclusion levels, with the best performance observed at the 15% inclusion level. Statistically significant differences (p < 0.05) were observed among treatments for fish body content of ether extract (EE%) and mineral matter (MM%). EE% levels were significantly higher in treatments with higher FerGP inclusion compared to the control (p < 0.05). For mineral matter, FerGP 0% and FerGP 2.5% were different than the other treatment (p < 0.05) (Table 4).

Table 3
Zootechnical parameters of mullet (Mugil liza) fed diets containing different levels of fermented grape pomace<tfn href="* Values expressed as mean ± standard deviation, n = 3, p > 0.05 (no significant difference).tfn12">*</tfn>.

Parameters	Treatments (%)					p-value	Regression
	0.0	2.5	5.0	10.0	15.0		linear	quadratic
Initial weight (g)	0.57 ± 0.13a	0.56 ± 0.15a	0.57 ± 0.12a	0.57 ± 0.12a	0.56 ± 0.14a	> 0.05	p > 0.71 r2 = 0.003	p > 0.51 r2 = 0.107
Final weight (g)	9.55 ± 0.24 a	8.90 ± 0.15a	8.97 ± 0.86a	8.75 ± 0.66a	9.57 ± 1.62a	> 0.05	p > 0.81 r2 = 0.001	p > 0.34 r2 = 0.166
Weight gain (g)	8.99 ± 0.24 a	8.34 ± 0.14a	8.40 ± 0.86a	8.18 ± 0.64a	9.00 ± 1.63a	> 0.05	p > 0.90 r2 = 0.001	p > 0.33 r2 = 0.168
Survival (%)	100.00 ± 0.00 a	95.67 ± 7.50a	88.67 ± 14.01a	100.00 ± 0.00a	86.67 ± 23.09a	> 0.05	p > 0.10 r2 = 0.063	p > 0.67 r2 = 0.063
Food conversion	2.47 ± 0.11 a	2.69 ± 0.31a	2.79 ± 0.29a	2.70 ± 0.25a	2.97 ± 0.35a	> 0.05	p > 0.06 r2 = 0.246	p > 0.18 r2 = 0.248
Specific growth rate (% day-1)	4.35 ± 0.04 a	4.24 ± 0.01a	4.24 ± 0.17a	4.20 ± 0.07a	4.84 ± 0.27b	< 0.05	p < 0.02 r2 = 0.349	p < 0.0003 r2 = 0.744

• ^*
  Values expressed as mean ± standard deviation, n = 3, p > 0.05 (no significant difference).

Table 4
Analysis of the proximal composition of the mullet carcass (Mugil liza) fed with diets containing different levels of fermented grape pomace<tfn href="tfn11">*</tfn>.

Proximal composition (%)	Treatments (%)					p-value	Regression
	0.0	2.5	5.0	10.0	15.0		linear	quadratic
Moisture	65.60 ± 0.50a	65.55 ± 0.19a	66.23 ± 0.36bc	65.83 ± 0.76ab	66.65 ± 0.32c	< 0.05	p < 0.05 r2 =0.305	p < 0.05 r2 = 0.31
Crude protein	17.10 ± 0.41a	17.07 ± 0.58a	16.76 ± 0.91a	17.39 ± 0.56a	16.78 ± 0.83a	> 0.05	p > 0.70 r2 =0.003	p > 0.79 r2 = 0.011
Ether extract	6.20 ± 0.45a	11.41 ± 0.81c	10.40 ± 0.64c	8.15 ± 1.12b	11.19 ± 1.86c	< 0.05	p < 0.01 r2 =0.138	p < 0.02 r2 = 0.164
Mineral matter	1.89 ± 0.17b	1.69 ± 0.11b	1.37 ± 0.12a	1.34 ± 0.23a	1.26 ± 0.13a	< 0.05	p < 0.05 r2 = 0.561	p < 0.05 r2 = 0.678

• ^*
  Values expressed as mean ± standard deviation, n = 9, p < 0.05 (significant difference). Different letters indicate differences between treatments (p < 0.05).

Figure 1
Relationship between the inclusion of grape pomace in the diet and the specific growth rate (SGR, % of live weight per day).

Table 5 shows the values for the erythrocytes, lymphocytes, granulocytes, and monocytes. There were no significant hematological variations (p > 0.05) with the inclusion of the FerGP.

Hematological analysis of mullet (Mugil liza) fed with diets containing different levels of fermented grape pomace<tfn href="tfn12">*</tfn>.

Cell type	Treatments (%)					p-value	Regression
	0.0	2.5	5.0	10.0	15.0		linear	quadratic
Erythrocytes	1,480.6 ± 738.6a	1,131.20 ± 263.0a	1,066.4 ± 347.9a	1,192.3 ± 354.1a	1,130.4 ± 388.6a	> 0.05	p > 0.30 r2 = 0.025	p > 0.06 r2 = 0.059
Monocytes	35.2 ± 23.3a	40.8 ± 53.3a	18.2 ± 6.8a	49.4 ± 49.9a	25.7 ± 16.2a	> 0.05	p > 0.82 r2 = 0.001	p > 0.90 r2 = 0.005
Lymphocytes	45.3 ± 35.8a	24.2 ± 24.2a	21.3 ± 12.4a	32.40± 26.5a	34.9 ± 23.9a	> 0.05	p > 0.90 r2 = 0.0004	p > 0.26 r2 = 0.061
Granulocytes	36.0 ± 19.7a	19.6 ± 11.8a	17.4 ± 6.9a	32.13 ± 14.9a	20.2 ± 13.7a	> 0.05	p > 0.95 r2 = 0.00007	p > 0.38 r2 = 0.046

• ^*
  Values expressed as mean ± standard deviation, n = 9, p > 0.05 (no significant difference).

Regarding the TBARS values in the liver, ANOVA showed no statistically significant differences (p > 0.05) among treatments. However, a statistically significant, albeit weak, linear relationship was observed between increased dietary FerGP levels and reduced hepatic lipid peroxidation (R² = 0.15; Fig. 2).

Figure 2
Content of thiobarbiturate-reactive substances in µmol TMP/g per tissue in the liver of Mugil liza fed with differences in fermented grape pomace inclusion. Values are expressed as mean and standard deviation (n = 9).

DISCUSSION

In the present study, the average final weight, feed conversion, and survival did not show significant differences, except for SGR, which showed improvement with an increase in the inclusion of FerGP at the level of 15%, indicating a promising response in terms of its inclusion in diets for juvenile mullet. The same was observed for juveniles of the common carp (Cyprinus carpio), which showed better zootechnical performance with the highest level of grape pomace inclusion evaluated (15%) (Mahmoodi et al., 2023).

Furthermore, studies have reported that the inclusion of grape pomace in fish diets influences the fatty acid composition (Mahmoodi et al., 2023) and reduces lipid oxidation in fish muscle (Barbacariu et al., 2024). Research on rainbow trout fry has indicated that diets containing grape pomace led to an increase in several polyunsaturated fatty acids, which are beneficial to human health (Peña et al., 2020). In our study, there was greater lipid deposition in mullet carcasses of the FerGP-treated groups. In contrast, Mahmoodi et al. (2023) found that the inclusion of grape pomace at high concentrations reduced lipid levels in common carp muscle with increasing feeding levels. These differences can be explained not only by the bioavailability of the bioactive compounds present in the ingredients used, but also by species-specific metabolic responses, considering that the present study evaluated a marine species (M. liza), while Mahmoodi et al. (2023) investigated a freshwater species (C. carpio). Understanding the interactions that regulate feeding behavior in fish still represents a significant challenge, especially in aquaculture species, in which physiological and metabolic responses to food intake can exhibit high variability (Plagnes-Juan et al., 2025). Marine and freshwater fish exhibit differences in lipid metabolism, osmotic physiology, and micro and macronutrient requirements, especially regarding the synthesis and utilization of long-chain polyunsaturated fatty acids (LC-PUFAs) such as arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) (Baldisserotto, 2025), which may contribute to the divergent effects observed.

Furthermore, the inclusion of grape pomace can significantly alter the carbohydrate, fiber, lipid, and protein content in the diet of organisms (Taladrid et al., 2023). The fibers present in grape pomace can improve the overall digestibility and promote intestinal health, whereas the composition of lipids and proteins can directly influence the growth and nutritional quality of fish (Peña et al., 2020; Silva et al., 2022). However, an excessive amount of carbohydrates can reduce the digestibility of other nutrients owing to their lower absorption efficiency (Costa et al., 2019). This highlights the importance of considering the specificities of cultured organisms and the feeding context when evaluating the nutritional effects of grape pomace, as well as understanding how different levels of inclusion and processing can affect the efficiency of nutrient absorption and overall fish health, contributing to the development of more balanced and beneficial diets (Antonić et al., 2020; Peña et al., 2020).

It is interesting to note that despite presenting greater carcass lipid deposition in mullets fed with FerGP, a negative linear relationship was observed between the concentration of TMP equivalents and the increase in FerGP inclusion in liver tissue, suggesting that the greater the inclusion, the lower the lipid peroxidation. This finding indicates that the antioxidant compounds present in FerGP, especially the phenolic compounds, can act as free radical scavengers, including the hydroxyl radical—one of the main initiators of lipid peroxidation due to its high reactivity and ability to attack membrane lipids, forming lipid hydroperoxides. Neutralizing these radicals can interrupt oxidative chain reactions, contributing to the reduction of lipid peroxidation and oxidative stress (Aziz et al., 2019; Peixoto et al., 2018; Shahab et al., 2023; Vuolo et al., 2019). Chien et al. (2023) investigated the impact of dry grape extract on the diet of white shrimp Litopenaeus vannamei, focusing on establishing the ideal dietary level. The results indicated that increasing the dietary level of dry grape extract to 500 ppm resulted in an increase in superoxide dismutase (SOD) activity and a reduction in the levels of reactive substances such as TBARS in the shrimp hepatopancreas. In a study conducted by Rosas et al. (2022), lower lipid peroxidation and greater antioxidant capacity in the hepatopancreas of juvenile white shrimp (L. vannamei) was recorded when FerGP was included in the diet.

Studies on the effects of grape pomace in fish diets on hematological parameters are scarce, although there are studies on vegetable co-products. For example, a significant improvement in hematological parameters was observed in carp fed a pomegranate peel (Punica granatum) supplement (Sayed-Lafi et al., 2023). In the present study, the increasing inclusion of FerGP in the diet did not promote significant changes in the hematological parameters of juvenile mullet. Considering that hematological parameters are widely used as sensitive indicators of health, stress, and metabolic response in fish (Ahmed et al., 2020; Witeska et al., 2022), the observed balance suggests that the inclusion of FerGP, at the levels evaluated, is safe from a hematological point of view. However, given the relevance of these variables for the assessment of health in aquaculture species, further studies are recommended to deepen the understanding of the hematological responses of M. liza to the prolonged inclusion of agro-industrial by-products in the diet.

Barbacariu et al. (2024) observed changes in carp fed diets containing grape pomace, highlighting an increase in the number of monocytes, in addition to lymphopenia at moderate inclusion doses. These changes were attributed to the modulation of the intestinal microbiota and the activation of innate immune mechanisms, especially associated with the presence of phenolic compounds. In another study, dietary supplementation with a plant-derived prebiotic in juvenile pacu (Piaractus mesopotamicus) resulted in an increase in the number of leukocytes and thrombocytes, indicating an improvement in the overall health of the fish (Deon et al., 2021). These findings highlight the importance of expanding studies on the different levels and forms of processing of plant co-products, especially considering the relevance of hematological parameters as indicators of health and immune response, in addition to their application in functional diets for marine species.

This study demonstrated that the inclusion of grape pomace, a byproduct of the wine industry, did not compromise the growth performance of juvenile mullet (M. liza), indicating its viability as an ingredient in diets for this species. The absence of significant differences between dietary treatments for most of the parameters evaluated reinforces the potential of grape pomace as an alternative and environmentally sustainable ingredient in aquaculture feed formulations. In this context, the use of this byproduct represents an opportunity for the valorization of agro-industrial waste, contributing to more sustainable practices in aquaculture. Future studies are needed to evaluate its long-term effects, as well as different levels and forms of winemaking byproducts.

CONCLUSION

This study demonstrated that FerGP can be included in the diet of mullet at levels up to 15 g per 100 g of feed, without negative effects on growth, thus establishing itself as an alternative and environmentally sustainable ingredient for aquaculture.

ACKNOWLEDGMENTS

Not applicable.

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  Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
  Financial code 001
  Conselho Nacional de Desenvolvimento Científico e Tecnológico
  Grant No.: 305112/2023-6
  Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul
  Grant No.: 19/2551-0001874-6

DATA AVAILABILITY STATEMENT

The data will be available upon request.

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Edited by

• Section editor:
  Leonardo Tachibana https://orcid.org/0000-0002-5847-8723

Publication Dates

• Publication in this collection
  25 May 2026
• Date of issue
  2026

History

• Received
  16 May 2025
• Accepted
  24 Mar 2026