Introduction

Striped catfish (Pangasianodon hypophthalmus), widely known as Asian catfish, is a freshwater species of considerable economic significance, especially in Southeast Asian countries1,2,3. Owing to its rapid growth, resilience to intensive aquaculture conditions, high consumer preference for boneless fillets, and high export value, this species has become an important candidate species in global aquaculture4,5. Despite its economic importance in aquaculture, it faces quality challenges such as inconsistent texture, high-fat deposition in the muscle and visceral region, suboptimal nutrients, and poor sensory attributes, hindering its export potential6,7,8. Optimised feed formulation caters to industry demands by boosting growth performance, enhancing nutrient utilisation, ensuring good flesh quality to meet consumer expectations, and promoting eco-friendly aquaculture practices9,10. Often, feed formulations are mainly focused on growth and production performance11. However, for this species, fillet quality is a major attribute affecting market demand and price, thereby impacting farmers’income. Consumers now prioritise high-quality, safe, and nutritious food, demanding better sensory characteristics and nutritional profiles12.

Protein and lipid are essential macronutrients in aquafeeds and play pivotal roles in supporting fish growth, body composition, and overall physiological health11,13. Proteins act as fundamental building blocks for muscle development, while lipids serve as a concentrated energy source and provide essential fatty acids critical for various metabolic processes14,15. Optimisation of these nutrients is vital for achieving maximum growth performance and better product quality. Recent studies have focused on the effects of varying dietary protein levels on the growth performance of fry-striped catfish. For example Bano et al.16, demonstrated that a 40% protein diet, formulated using locally sourced ingredients, also improved and significantly enhanced muscle quality in fry-striped catfish. Similarly Lubis et al. 17, demonstrated that different protein levels significantly affected protein and lipid retention in striped catfish. A study by Van Nguyen et al.18 found that incorporating specific oils into the diet of striped catfish juveniles improved growth performance, body composition, and fatty acid profils. Excess dietary protein can increase costs and lead to inefficient utilisation, producing higher nitrogenous waste11,19,20,21. These findings underscore the importance of balancing protein and lipid levels in aquafeeds to achieve desired production outcomes and flesh quality.

The flesh quality is primarily determined by its nutrient composition, including proteins, lipids, and carbohydrates16,17. Studies have highlighted that dietary protein and fat content play a pivotal role in influencing flesh quality22,23. Flesh quality, encompassing factors such as texture, flavor, and nutritional composition, plays a crucial role in determining the market value of fish beyond simple growth metrics24. Sensory attributes such as taste and texture significantly influence consumer acceptance, while biochemical factors such as lipid oxidation and protein content impact both shelf life and nutritional value25. Despite the existing nutritional requirements, there is a need for comprehensive studies that concurrently assess the combined effects of dietary protein and lipid levels on the growth performance, nutrient retention, and flesh quality of growing striped catfish. Such investigations are essential for developing optimised feed and feeding strategies that enhance production efficiency and product quality.

Despite the importance of optimising feed formulations for striped catfish, limited studies have explored the combined effects of protein and lipid on the flesh quality of grow-out pangasius. To address this knowledge gap, a 3 × 3 factorial experiment was designed to investigate the impacts of varying dietary protein and lipid levels on the growth performance and flesh quality of striped catfish (Pangasianodon hypophthalmus). The present study integrated sensory and biochemical assessments to offer a holistic view about the influence of dietary nutrients (protein and lipid). The results can guide the development of optimised feed formulations that align with industry standards and consumer preferences, thereby supporting the sustainable growth of striped catfish.

Materials and methods

This study was conducted and reported in accordance with the ARRIVE guidelines (https://arriveguidelines.org) for the care and use of animals in research. All methods were performed in accordance with the relevant guidelines and regulations.

Experimental diets and design

This study used a 3 × 3 factorial design to investigate the effects of dietary protein (DP) (28%, 30%, and 32%) and dietary lipid (DL) levels (4%, 6%, and 8%) on growth performance and flesh quality of grow-out striped catfish (Table 1). Nine extruded diets (DP28/DL4, DP28/DL6, DP28/DL8, DP30/DL4, DP30/DL6, DP30/DL8, DP32/DL4, DP32/DL6, and DP32/DL8) were prepared. Required ingredients were thoroughly ground and mixed according to the specified formulation (Table 1) to achieve a uniform particle size. The mixture was pre-conditioned and extruded using a single-screw extruder (P98-SANJIVANI, Nagpur, India), producing floating pellets with a diameter of 3 mm. Post-extrusion, the pellets were dried, cooled, and packaged into designated storage bags.

Table 1 Ingredients and proximate composition (% dry matter basis) of experimental diets.
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The prepared diets were transported to the experimental site (ICAR-CIFE, Powarkheda, Madhya Pradesh, India) and stored at a cool room temperature until use. The diets were formulated using highly palatable and digestible ingredients at permissible and commercially viable inclusion levels. Key protein sources included oilseed cakes such as deoiled soybean meal (DSBM), groundnut oilcake (GNOC), and mustard oilcake (MOC), alongside high-quality fishmeal (prime grade, TJ Marine Products Pvt. Ltd., Ratnagiri, India). Lipid requirements were met using fish oil and soybean oil (1:1). Deoiled rice bran (DORB), wheat flour, and corn starch served as carbohydrate sources. Additional additives included a vitamin-mineral mixture, carboxymethyl cellulose (CMC) as binder, butylated hydroxytoluene (BHT) as antioxidant, and betaine as attractant.

Fish were fed to apparent satiation twice daily, at 08:30 h and 17:30 h, with each feeding session lasting a minimum of five minutes per hapa. Daily feed intake was meticulously recorded to ensure precise data collection.

Experimental fish and conditions

The grow-out striped catfish used in this study were procured from the PRAYAS Fish Farm, Narmadapuram, Madhya Pradesh, India. The acclimatisation period, lasting four weeks, was conducted at the ICAR- Central Institute of Fisheries Education, Powerkheda Centre, Madhya Pradesh, India, within a farm facility (800 m2). During acclimatisation, the fish were fed a commercial diet containing 30% crude protein (CP) and 6% crude lipid (CL). After the acclimatisation period, the experimental fish, with an average initial body weight of 167.91 ± 0.03 g, were starved for 24 h and then randomly distributed to nine treatment groups, each based on a specific experimental diet. Each treatment group consisted of three replicates, with ten fish stocked per m3 / hapa. In total, 27 synthetic nylon mesh hapas [dimensions: 2 m (W) × 3 m (L) × 1.5 m (H), mes h size: 2 mm] were placed in an earthen pond covering 1.1 ha with a depth of 1.6 m. Pond water quality was maintained through partial water exchange using tube-well water, as needed. The hapas were secured with bamboo frames, and mosquito nets were used to cover their tops to prevent fish escape and predation. The feeding trial was conducted for eight weeks.

Water quality parameters

Water quality parameters (except temperature) were monitored twice a week and found within optimal ranges to support the growth of pangasius throughout the study26. The water temperature, recorded daily in the morning and afternoon using a digital thermometer (Eutech Instruments, India), averaged 28.7 ± 1.8 °C, with a range of 27.0 to 30.5 °C. Dissolved oxygen (DO) levels were measured using a DO meter (Lutron DO-5509, Madhya Pradesh, India), with an average of 6.4 ± 0.03 mg L⁻1, ranging from 6.3 to 6.9 mg L⁻1. The pH was measured with a pH meter (Hanna, Amit Engineering Equipments, Indore, India) and remained steady at 7.2 ± 0.13, within a range of 7.1 to 7.4. Additionally, total ammonia nitrogen was recorded with an average concentration of 0.02 ± 0.06 mg L⁻1, ranging from 0.02 to 0.03 mg L⁻1.

Samples collection

Prior to the feeding trial, 4–5 fish were randomly selected and stored at − 20 °C to analyse their initial biochemical composition. After the eight weeks of feeding, all fish were fasted for 24 h before counting and weighing. Sixteen fish were randomly selected from each hapa and anesthetized with MS-222 at a concentration of 350 mg L⁻1. Three fish were preserved whole at − 20 °C for subsequent biochemical analyses. Another three fish were dissected to measure visceral organs, liver, and visceral fat weights, enabling the calculation of indices such as the viscerosomatic index (VSI %), hepatosomatic index (HSI %), gastrosomatic index (GaSI %), intraperitoneal fat index (IPFI %). From the same fish, six dorsal muscle blocks (5–8 g) were collected to evaluate water-holding capacity (WHC) and pH. The remaining ten fish were retained for sensory evaluation and additional biochemical analyses.

Growth performance and nutrient utilisation

The growth performance and body indicators, including weight gain (WG), weight gain percentage (WG%), specific growth rate (SGR), feed conversion ratio (FCR), feed efficiency ratio (FER), protein efficiency ratio (PER), and survival rate (%), were evaluated27 using the following formulas:

$$\text{WG }\left(\text{g}\right)=\text{Final wet weight }\left(\text{g}\right)-\text{Initial wet weight }\left(\text{g}\right)$$
$$\text{WG }\%=\frac{\text{Final wet weight }\left(\text{g}\right)-\text{Initial wet weight }\left(\text{g}\right)}{\text{Initial wet weight }(\text{g}))}\text{x }100$$
$$\text{SGR }\%\,\text{Day}=\frac{\text{ln of final wet weight }\left(\text{g}\right)-\text{ln of initial wet weight }(\text{g}) }{\text{Experimental period }(\text{days})}\text{x } 100$$
$$\text{FCR}=\frac{\text{Feed given }(\text{dry weight in g})}{\text{Body weight gain }(\text{wet weight in g})}$$
$$\text{FER}=\frac{\text{Body weight gain }(\text{wet weight in g})}{\text{Feed given }(\text{dry weight in g})}$$
$$\text{PER}=\frac{\text{Body weight gain }(\text{wet weight in g})}{\text{Protein intake }(\text{dry weight in g})}\text{x }100$$
$$\text{Survival }(\%)=\frac{\text{Total number of experimental fish harvested}}{\text{Number of experimental fish stocked}}\text{X }100$$

Body indices

The following body indices were evaluated using established formulas: hepatosomatic index (HSI), gastrosomatic index (GaSI), intraperitoneal fat index (IPFI), and viscerosomatic index (VSI).

$$\text{HSI }(\%)=\frac{\text{Final liver weight }(\text{g})}{\text{Final body weight }(\text{g})}\text{x }100$$
$$\text{GaSI }(\%)=\frac{\text{Final weight of total gut }(\text{g})}{\text{Final weight of whole fish }(\text{g})}\text{x }100$$
$$\text{IPFI }(\%)=\frac{\text{Final weight of visceral fat }(\text{g})}{\text{Final body weight }(\text{g})}\text{x }100$$
$$\text{VSI }(\%)=\frac{\text{Final visceral weight }(\text{g})}{\text{Final body weight }(\text{g})}\text{x }100$$

Biochemical composition of feed and fish

The proximate composition of feed and fish was carried out in accordance with28 official method. The moisture content of the samples was determined by oven drying (HAO-9325P; LABLINE Instruments, Mumbai, India) at 105 °C until a constant weight was reached. Total ash (TA) content was assessed by incinerating the samples at 550 °C in a muffle furnace (AI-7982; Sanjeev Scientific, Udyog, Ambala Cantt, India) until a constant weight was obtained. The crude protein (CP) content was calculated using the Kjeldahl method with a nitrogen-to-protein conversion factor of 6.25, by using a Kjeldahl apparatus (Classic DX VA TS; Pelican Equipments, Chennai, India). Crude lipid (CL) content was determined by Soxhlet extraction with petroleum ether as the solvent, performed using a Soxhlet apparatus (CBNSSP001; Pelican Equipments, Chennai, India). The crude fibre (CF) content was analysed using the FibroTRON (FRB-8, Tulin Equipment, India). The nitrogen-free extract (NFE) content of the diet and the total carbohydrate (TC) content of the whole body were calculated using the following equations27,29:

$$\text{NFE }(\%)=100-(\text{CP }\%+\text{CL }\%+\text{CF} \%+\text{TA} \%)$$
$$\text{TC }(\%)=100-(\text{CP }\%+\text{CL }\%+\text{TA } \%)$$

The contents of CP, CL, TA, and TC were reported on a % wet-weight basis for the fish sample.

Flesh quality indices

Sensory evaluation of muscle

The fish muscle samples were steamed at 100 °C for 5 min and then served on white plates to a panel of 10 trained evaluators from the ICAR-Central Institute of Fisheries Technology, Kochi, India30. All panel members possessed prior experience in assessing fish-based products. Mineral water was provided to cleanse the palate between tastings to ensure accurate sensory evaluation. The assessments were conducted in a specially designed sensory booth under controlled lighting conditions. The fillet samples were evaluated for key sensory attributes: appearance, colour, odour, taste, flavour, texture, and overall acceptability. A 9-point hedonic scale was used for scoring, where 9 indicated “like extremely”and 1 denoted "dislike extremely”.

Water-holding capacity (WHC) and pH

The water-holding capacity (WHC) and pH of the muscle were measured immediately after fish dissection. The method for calculating the WHC was adapted from31, along with some slight modifications. Approximately 5 g of wet muscle tissue was placed on a Whatman No. 1 filter paper and centrifuged at 5000 rpm for 10 min. Following centrifugation, the sample was reweighed to determine its weight. The WHC of fish muscle was calculated as follows:

$$\text{WHC }(\%)=\frac{\text{Weight of sample after centrifugation }(\text{g})}{\text{Weight of sample before centrifugation }(\text{g})}\text{x }100$$

The pH measurement method was adapted from32 using a digital pH meter. To determine the pH, 10 g of homogenized fish muscle was mixed with distilled water in a 1:2 (w/v) ratio, and the measurement was performed using a glass electrode digital pH meter (Testo 205, Germany).

Peroxide value (PV)

A 10% tissue extract in 25 mM sodium phosphate buffer (pH 7.4) was centrifuged at 3000 rpm for 15 min, and the supernatant was collected for lipid peroxidation analysis. Using a modified IDF33, spectrophotometric method, peroxides were quantified based on their ability to oxidise Fe2⁺ to Fe3⁺. In a 10 mL test tube, 0.1 mL of homogenate was mixed with a chloroform/methanol solution (to 10 mL), followed by 50 μL each of ammonium thiocyanate and Fe2⁺ solutions. After 5 min of incubation in the dark, absorbance at 500 nm was measured against a blank, and the peroxide value (PV) was expressed as milliequivalents of oxygen/kg.

Thiobarbituric acid reactive substances (TBARS) content

TBARS content was determined using the method of34. A 10 g fish muscle sample was homogenised with 50 mL distilled water (DW), then mixed with 47.5 mL DW and 2.5 mL 4N HCl (pH 1.5) in a 500 mL round-bottom flask. The mixture was heated, and 50 mL of distillate was collected within 10 min. Then, 5 mL of distillate was mixed with 5 mL of TBA reagent and incubated in a boiling water bath at 100 °C for 55 min. A blank was prepared similarly using DW. After cooling, the absorbance was measured at 538 nm to determine lipid oxidation.

Data analysis and statistics

The data were analysed statistically using SPSS version 25.0. A factorial two-way analysis of variance (ANOVA) was employed to examine the interaction effects of dietary protein and lipid levels on growth performance, body composition, body indices, and flesh quality in cultured fish. Two-way ANOVA followed by Duncan’s multiple range test (DMRT) was applied to assess the individual effects of dietary protein or lipid levels. If interaction effects were significant, a one-way ANOVA followed by Duncan’s multiple range test was conducted to evaluate the influence of one factor on the other. Statistical significance was measured at p < 0.05.

Results

Growth performance and diet utilisation

The two-way ANOVA results (Table 2) demonstrated significant (p < 0.05) effects of dietary protein (DP) on growth performance, nutrient utilization, and flesh quality in striped catfish (Pangasianodon hypophthalmus). In contrast, dietary lipid (DL) had no significant impact (p > 0.05). Notably, a significant interaction effect (p < 0.05) was observed between DP and DL, indicating their combined effect influence on these parameters. DP levels significantly influenced (p < 0.05) growth parameters, including weight gain (WG), specific growth rate (SGR), feed efficiency ratio (FER), protein efficiency ratio (PER), and feed conversion ratio (FCR). All growth parameters were comparable among the 28–30% protein-fed groups. While FCR was lowest in the 28% protein (DP28) fed group, which increased significantly (p < 0.05) in the 30% and 32% protein-fed groups. However, no significant variation in FCR was observed between the DP30 and DP32 fed groups. DL levels did not exhibit any significant (p > 0.05) effect on the growth-related parameters. A significant interaction (p < 0.05) was observed between DP and DL on FBW, WG, WG%, SGR, FER, FCR, and PER. Interaction effects revealed that the effect of dietary protein levels was influenced by lipid levels in the diets as well. Thus, the diet combining DP28/DL4 shows the best growth performance with the lowest FCR.

Table 2 Growth and nutrient utilization of Pangasianodon hypophthalmus fed with varying levels of dietary protein and lipids.
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Tissue somatic indices

Two-way ANOVA indicated that dietary protein (DP) level, dietary lipid (DL) level, and their interaction (DP × DL) significantly (p < 0.05) influenced the body morphometric indices in growing Pangasianodon hypophthalmus (Table 3). HSI was significantly affected (p < 0.05) by the dietary protein levels, with lower values in the 28% protein fed group compared to the 30% and 32% protein fed groups. GaSI and VSI remained unaffected significantly (p > 0.05) by protein levels. IPFI was significantly lower (p < 0.05) in the 30% and 32% protein fed groups compared to their 28% counterpart. All body indices showed significant responses (p < 0.05) to varying dietary lipid levels. HSI increased progressively with the increasing lipid levels. GaSI showed the highest values at 8% lipid, followed by 4%, and the lowest at 6%. IPFI and VSI also increased significantly (p < 0.05) with the increasing lipid levels, with substantial changes at each level. A significant (p < 0.05) interaction between DP and DL was observed for all body indices. HSI increased significantly (p < 0.05) with the increasing DP levels, with the highest values observed at 30 and 32%, where values remained statistically comparable. DP and DL in combination had significant effects (p < 0.05) on all response parameters. DP28/DL4 group showed the lowest (p < 0.05) HSI values, while other groups showed non-significant differences (p > 0.05). IPFI was significantly higher (p < 0.05) in DP28/DL8 and lower (p < 0.05) in DP28/DL4 fed group.

Table 3 Body morphometric indices of Pangasianodon hypophthalmus fed with varying levels of dietary protein and lipids.
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Whole body composition

A significant effect (p < 0.05) of dietary protein (DP) and lipid (DL) levels was observed on the whole-body proximate composition of growing Pangasius hypophthalmus (Table 4). The interaction between DP and DL (DP x DL) also significantly influenced (p < 0.05) the whole-body CP and CL contents. Whole body CL content exhibited a significant increase (p < 0.05) with increasing DL levels, reaching a maximum in the DL8 group at DP levels of 30% or 32%. Conversely, lipid content declined when DP was reduced to 28%. Notably, the DP28/DL4 fed group exhibited elevated crude protein content alongside relatively low lipid content in the whole body. Also, DP and DL, individually and in combination, had a significant effect (p < 0.05) on total ash, total carbohydrate, and gross energy content.

Table 4 Whole body composition of Pangasianodon hypophthalmus fed with varying levels of dietary protein and lipids (% wet weight basis).
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Flesh quality indicators

Organoleptic and sensory attributes

Significant differences (p < 0.05) were observed in fillet organoleptic and sensory profiles across all dietary treatments. Hedonic attributes, as evaluated by consumer preference, are summarised in Fig. 1. Remarkably, fish from the DP28/DL4 fed group showed the highest mean consumer-liking scores. Sensory panel assessments identified statistically significant differences (p < 0.05) in the muscle slabs of fish fed various experimental diets. To our knowledge, this study represents the first evaluation of how the varying levels of DP and DL levels impact the sensory properties of grow-out P. hypophthalmus. Irrespective of DP and DL levels, the tested samples were positively characterised by their appearance, texture, flavour, and taste, with no significant negative attributes reported. The most frequently noted attributes regarding appearance were the juicy, moist texture and white flesh observed in the DP28 and DL4-6 treatment groups. Flavour characteristics were predominantly described as fresh, particularly in the DP28/DL4 fed group fish. Texturally, fillets were generally rated as easy to flake, while taste was consistently described as good. Negative sensory descriptors such as musty or earthy odor and taste were minimally perceived and did not reach statistical significance (p < 0.05). Overall, consumer-liking scores were highest for samples from the DP28 and DL4-6 treatment groups, underscoring the favorable sensory attributes associated with these diets.

Fig. 1
figure 1

Spider diagram representing the sensory profile analysis of muscle tissue from Pangasianodon hypophthalmus fed different DP and DL levels. Attributes were evaluated using a trained sensory panel (n = X) on a 9-point hedonic scale. Values represent means of sensory score (p < 0.05).

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pH and water-holding capacity (WHC)

The effect of dietary protein (DP) and dietary lipid (DL) levels on the physicochemical properties of Pangasius hypophthalmus flesh was assessed through one-way and two-way ANOVA (Table 5). Two-way ANOVA revealed that DP and DL had a significant effect (p < 0.05) on both pH and WHC. pH was significantly affected (p < 0.05) by protein levels, with higher values in the 32% protein fed group compared to the 28% and 30% groups. WHC was significantly lower (p < 0.05) in the 30% protein group compared to the 28% and 32% fed groups. The individual effect of dietary lipid revealed that pH showed significant variation (p < 0.05) with the highest values in the 4% lipid group, followed by 8% and 6% groups. WHC remained unaffected by lipid levels (p > 0.05). Significant interactions (p < 0.001) were observed between DP and DL for pH and WHC. The DP28/DL4 group showed the highest pH, while DP28/DL8 showed the lowest. WHC was highest in DP28/DL4 and lowest in DP30/DL4. Differences in WHC across treatments were statistically significant (p < 0.05), with lower lipid levels generally associated with increased WHC.

Table 5 pH, Water-holding capacity (WHC), peroxide value (PV), and Thiobarbituric acid reactive substances (TBARS) values of Pangasianodon hypophthalmus fed with varying levels of dietary protein and lipids.
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Lipid peroxidation (LPO) of muscle

Varying DP and DL levels had a significant effect (p < 0.05) on the flesh peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) and key lipid oxidation parameters (Table 5). Individual effects of DP and DL were significant (p < 0.05) for both PV and TBARS. PV and TBARS were significantly higher (p < 0.05) in the 30% protein fed group compared to other groups. Both PV and TBARS increased significantly (p < 0.05) with increasing lipid levels, except for TBARS, which showed the lowest values at 6% dietary lipid. The DP and DL in combination had a significant effect (p < 0.05) on TBARS, while PV showed no significant change (p > 0.05)). TBARS values were higher in DP30/DL4, DP30/DL8, and DP32/DL8 groups. The DP28/DL4 diet exhibited the lowest PV and TBARS values. In contrast, higher lipid diets, such as DP30/DL8 and DP32/DL6, showed elevated PV and TBARS.

Discussion

This study evaluated the effects of varying dietary protein (DP) and lipid (DL) levels on growth performance, nutrient utilisation, whole-body proximate composition, and flesh quality of grow-out striped catfish (Pangasianodon hypophthalmus). The findings indicate that dietary protein and lipid levels significantly influence the growth dynamics and flesh quality. The combination of 28% protein (DP28) and 4% lipid (DL4) shows highest WG and SGR along with the lowest FCR, indicating better nutrient utilisation. Further, the diets containing 28% protein and low lipid (4%) levels showed higher or similar growth rates with other treatments while reducing the whole body lipid deposition. The FCR, which measures the efficiency of converting feed into body mass, improved 28% dietary protein but plateaued at a higher inclusion level, suggesting that beyond a certain protein level, the efficiency of feed conversion did not improve further35. On the other hand, the study found that variation in DL levels had no significant impact on growth matrices, indicating that lipid levels alone are not a key factor in determining growth outcomes. These results suggest that optimizing protein and lipid levels in diets promotes maximal growth while minimizing excess fat accumulation, aligning with previous research highlighting the advantages of efficient dietary energy allocation for lean tissue development11. He et al.36 demonstrated that balanced protein and lipid levels improved growth performance and reduced fat accumulation in juvenile Furong crucian carp. Talukdar et al. (2020) reported that optimum dietary protein level with moderate lipid levels improved growth performance along with reduced lipid storage in grey mullets. The study also revealed that dietary lipid levels exceeding 6%, despite increasing energy density, stimulated lipogenesis, and reduced protein utilisation efficiency. This metabolic shift was evidenced by elevated body lipid levels at higher lipid levels. Balanced dietary composition facilitated efficient energy partitioning toward somatic growth rather than lipid deposition, as supported by reduced lipid storage observed in earlier body composition analyses. These findings align with37 reported similar benefits of optimised lipid levels in the diet of tilapia, and38 who found that excessive lipids in black carp diets increased lipid deposition and oxidative stress. Higher lipid diets (DP28/DL6 and DP28/DL8) demonstrated comparable WG but increased FCR and reduced protein utilisation efficiency, inconsistent with studies linking high-lipid diets to suppress protein efficiency due to lipogenesis11,39). The DP28/DL4 diet can be used for improved feed efficiency, reduced environmental impact, and production of high-quality, lean Pangasius for human consumption. The growth results underscore the importance of optimising DP and DL levels to promote efficient growth, minimise lipid accumulation, and preserve flesh quality in striped catfish, providing practical insights for sustainable aquaculture practices.

Both DP and DL levels significantly influenced the hepatosomatic index (HSI), a key marker of liver health and nutrient metabolism. Lower HSI values observed in the low protein and lipid levels, as in DP28/DL4 fed group, indicate reduced hepatic lipid accumulation, suggesting improved energy utilisation efficiency in the group. These results are inconsistent with the findings in Sebastes schlegeli (rockfish), where lower dietary lipid levels enhanced liver health13,40. Gastro somatic index (GaSI) values varied with dietary lipid levels, showing higher values in high-lipid fed group (DP28/DL8). However, the DP28/DL4 fed group exhibited normal GaSI values, indicative of optimised digestive efficiency under moderate protein and lipid levels41. Intraperitoneal fat index (IPFI) increased with higher DL levels and lower protein levels, peaking in DP28/DL8 group. These results indicated lipogenesis and deposition in the peritoneal region because of the higher level of lipids in the DL8 group and higher digestible carbohydrates used in the 28% protein-fed group. Conversely, the DP28/DL4 group showed the lowest IPFI, reflecting reduced visceral fat deposition. Excessive lipid intake led to undesirable fat accumulation, particularly in the abdominal region, corroborating findings from previous studies42,43. The higher viscerosomatic index (VSI) at higher lipid levels indicated that dietary lipid levels showed a more significant influence on visceral fat deposition than dietary protein content. Optimal VSI values in the DP28/DL4 group reflect balanced energy distribution, aligning with studies on Acipenser dabryanus (Yangtze sturgeon), where optimised lipid intake minimised visceral fat deposition44,45. Overall, significant effects were observed for all morphometric indices (HSI, GaSI, IPFI, VSI) with the variation in DP and DL levels, indicating the lipid deposition in striped catfish from dietary lipids and carbohydrates, as both varied in the treatments. Thus, the 28% protein and 4% lipid diet can promote efficient protein utilisation, reduce lipid deposition and maintain physiological homeostasis.

The DP28/DL4 treatment exhibited significantly higher protein retention and energy utilisation efficiency than the other groups. These findings corroborate previous studies suggesting that moderate protein intake and balanced lipid supplementation enhance protein synthesis without inducing metabolic inefficiency46,47. In contrast, as observed in the DP32 groups, excessive dietary protein is often excreted, leading to reduced growth efficiency48,49. This observation aligns with reports by Wang et al.50 who demonstrated similar patterns in lipid deposition with increasing dietary lipid levels, emphasizing the role of dietary lipids in enhancing energy density and lipid storage. However, some earlier researchers have also observed potential risks associated with excessive lipid intake, including hepatic lipid accumulation51. The gross energy values observed in this study suggest that DP28/DL4 facilitates balanced energy distribution without promoting excessive fat deposition. The significantly higher energy levels of the DP28/DL4 fed group appear to stem from the optimal protein-sparing effect. Optimum dietary lipid provide an alternative energy source, allowing dietary protein to be preferentially allocated for growth and tissue repair52,53. Additionally, the significantly lower ash content in the DP28/DL4 fed group than in the DP32 groups indicates reduced mineral wastage, likely due to improved nutrient absorption facilitated by a balanced protein-lipid ratio. Similar observations have been reported in mandarin fish, where a balanced dietary protein-lipid enhanced nutrient utilisation and reduced whole-body ash and mineral content35.

This study demonstrates that DP and DL levels significantly influence sensory characteristics and overall acceptability of Pangasius. Among the treatments, a diet of 28% protein and 4% lipid (P28/L4) showed significantly higher sensory scores, with overall acceptability, outperforming other groups. These results align with those of Iv and Robel54 who reported that moderate protein levels and low lipid content enhance sensory qualities in freshwater fish. The superior texture observed in DP28/DL4 fed fish suggests improved muscle fibre development and protein deposition, consistent with Sankian et al.35 at optimum protein and lipid levels. High taste scores further support the quality of this diet, likely due to improved nutrient utilisation and muscle macro and micronutrient composition. Similar findings in striped bass55 also highlight the benefits of balanced protein-lipid diets for enhancing sensory appeal. In general, higher dietary lipid levels (6% and 8%) resulted in lower sensory scores across all protein concentrations, indicating adverse effects on flesh quality. Excess dietary lipids may impair texture and flavour56,57.

Water holding capacity (WHC) of food is defined as the ability to have its own water or water added through the application of force58. The increased pH and WHC suggest enhanced muscle integrity and water retention, which are critical for the post-harvest quality of fish muscle59,60. Furthermore, fish-fed diets with balanced protein and lipid levels (DP28/DL4) exhibited enhanced WHC, reflecting improved muscle integrity and water retention key parameters for maintaining post-harvest quality56.

Lipid peroxidation (LPO) markers such as PV and TBARS were also estimated from flesh, as these biochemical markers are critical for evaluating the long-term impact of diet on fish health, and flesh quality61. LPO indices also highlighted that the DP28/Dl4 diet showed the lowest value, and the low lipid (4%) and protein (28%) are optimal for maintaining oxidative stability and flesh quality in Pangasius. Lower PV and TBARS values reflect reduced oxidative stress, thereby preserving the nutritional and sensory properties of the fish62. Liu et al.63 found that excessive dietary lipids led to increased oxidative stress and compromised flesh quality in common carp, which parallels the observed trends with higher dietary lipid levels. Conversely56, reported that although higher dietary lipid levels enhanced growth rates in mandarin fish, they also induced oxidative stress, indicated by elevated TBARS levels.

Conclusions

This study demonstrates that balanced dietary protein (28%) and lipid (4%) levels (DP28/DL4) optimize the growth performance, nutrient retention, and flesh quality in striped catfish (Pangasianodon hypophthalmus). The DP28/DL4 diet significantly improved feed efficiency, reduced fat deposition, and enhanced sensory attributes, making it a sustainable and cost-effective feed for the aquaculture of striped catfish. Whole-body proximate analysis indicated a synergistic effect of DP and DL on nutrient retention, with DP28/DL4 exhibiting the highest protein retention and minimal lipid deposition. Flesh quality assessments highlighted higher water-holding capacity (WHC), pH, and sensory attributes, including texture, flavour, and overall acceptability of fish fed DP28/DL4. Conversely, higher lipid levels (6%−8%) were associated with increased fat deposition and oxidative instability in the flesh. These findings offer valuable insights for optimizing nutrients for aquafeed formulations to enhance both production efficiency and product quality of Pangasius while meeting the environmental sustainability goals. Future research should explore long-term and species-specific applications to further advance sustainable aquaculture practices.