Research Article

Effect of Dietary Carbohydrate Forms on Zootechnical Parameters and Liver Histology of the Malaysian Mahseer, Tor tambroides

Sairatul Dahlianis Ishak1,2*, Sharifah Rahmah2*, Hung-Hui Chung3, Donald Torsabo4, Okomoda Victor Tosin4,5, Mohd Salleh Kamarudin6

1HiCoE, Institute of Tropical Aquaculture and Fisheries, Universiti Malaysia Terengganu, Kuala Nerus 21030, Terengganu, Malaysia; 2Faculty of Fisheries and Aquaculture Science, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia; 3Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan 94300, Sarawak, Malaysia.; 4Department of Fisheries and Aquaculture, College of Forestry and Fisheries, Joseph Sarwuan Tarka University (formerly Federal University of Agriculture Makurdi), Makurdi P.M.B. 2373 Makurdi, Nigeria; 5WorldFish, Ibadan, Nigeria.; 6Department of Aquaculture, Faculty of Agriculture, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia.

Received | June 07, 2026; Accepted | August 18, 2026; Published | August 29, 2026

*Correspondence | Sairatul Dahlianis Ishak, Sharifah Rahmah, HiCoE, Institute of Tropical Aquaculture and Fisheries, Universiti Malaysia Terengganu, Kuala Nerus 21030, Terengganu, Malaysia; Faculty of Fisheries and Aquaculture Science, Universiti Malaysia Terengganu,21030 Kuala Nerus, Terengganu, Malaysia; Email: [email protected], [email protected].

Citation | Ishak SD, Rahmah S, Chung HH, Torsabo D, Tosin OV, Kamarudin MS (2026). Effect of dietary carbohydrate forms on zootechnical parameters and liver histology of the malaysian mahseer, tor tambroides. Adv. Anim. Vet. Sci., 14(9):2083-2093.

DOI | https://dx.doi.org/10.17582/journal.aavs/2026/14.9.2083.2093

ISSN (Online) | 2307-8316

Copyright: 2026 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

The cyprinid Malaysian mahseer T. tambroides (Bleeker, 1854), is a high-valued finfish priced at approximately USD178 kg-1, with Malaysia currently the top global producer (FAO 2020; DOF 2021). This species is widely popular as game fish; white meat delicacy, and as a valuable ornamental fish (Lau et al., 2021). The inherently slow growth of T. tambroides limits production, leading commercial farmers to rely on wild-caught mature individuals to offset low yields (Ng and Andin 2011; Abduh et al., 2021). Since T. tambroides is an omnivore, its natural diet consists of smaller animals, molluscs, aquatic insects, and riverine fruits consumed for its high carbohydrate and lipid content (Tan 1980; Ambak and Jalal 2006). Boosting aquaculture production of this species through appropriate nutritional studies targeted at improving growth can reduce the tendency of wild fishing and mitigate the pressure on wild stock population.

Carbohydrates are intentionally included in aquaculture feeds to enhance pellet integrity, reduce nutrient leaching, and improve digestibility, ultimately supporting efficient nutrient uptake and farm profitability by serving as a cost-effective energy source (Sørensen 2012; Wu et al., 2021; Ren et al., 2021; Mohamed Nafees et al., 2022). While teleosts can utilize various carbohydrate forms, their capacity depends on species, developmental stage, size, and carbohydrate type (Zhou et al., 2022). Limitations in carbohydrate utilization are often linked to feeding behavior, digestive enzyme activity, and genetic variation among species (Shiau 1997; Stone 2010; NRC 2011; Adjoumani et al., 2022). Carnivorous and piscivorous species generally have low digestive carbohydrate activity levels, restricting their ability to digest complex carbohydrates efficiently, unlike herbivorous or omnivorous fish (Hidalgo et al., 1999; Chan et al., 2004; Jun-Sheng et al., 2006; Debnath et al., 2007; Kamalam et al., 2017; Corrêia et al., 2019). These species may benefit more from simple carbohydrates, such as monosaccharides, due to their higher digestibility and rapid absorption (Stone et al., 2003; Enes et al., 2008). However, starch supplementation has been shown to support growth in carnivorous aquaculture species like Atlantic salmon, Salmo salar (Hemre et al., 2002), European sea bass, Dicentrarchus labrax (Enes et al., 2011), cobia, Rachycentron canadum (Cui et al., 2010), hybrid striped bass, Morone chrysops×M. saxatilis (Rawles et al., 2008) and white sturgeon, Acipenser transmontanus (Deng et al., 2005).

Previous nutritional studies have elucidated the dietary requirements of T. tambroides, for boosting growth during rearing. The dietary protein requirement of the fish has been determined to be between 40% to 48% based on its different life stages (Ng et al., 2008; Misieng et al., 2011). Its dietary lipid requirement is reported to be 5% minimum (Ramezani-Fard et al., 2012). Meanwhile, this species possesses all required enzymes for in vivo fatty acid synthesis namely fatty acyl desaturase (Fads2) and two elongases (Elovl5, Elovl2); indicating fully functional capacity for the fish to convert C18 linoleic and linolenic acids to eicosapentaenoic acid, docosahexaenoic acid, and arachidonic acid (Sam et al., 2021). Ishak et al. (2016) had also established the optimal dietary carbohydrate of T. tambroides to be 23.44% while the species was demonstrated to have limited ability to utilize complex starch from different crop sources in another study by Ishak et al. (2021). Carbohydrate utilization could be species-specific and carbohydrate complexity might be a factor in fish physiological changes. Despite growing interest in carbohydrate nutrition and utilization in tropical freshwater fish species, there remains limited information regarding the capacity of T. tambroides to efficiently utilize different carbohydrate sources. In particular, comparative data on the utilization of simple sugars (such as monosaccharides and disaccharides) versus complex polysaccharides is notably scarce for this commercially important species.

In this study, we investigate the effects of different dietary carbohydrate complexities (starch, glucose, and sucrose) on growth performance, efficiency of feed utilization, body nutrient composition, and liver histology of T. tambroides. These are relevant in understanding the outcomes of carbohydrate complexities in T. tambroides diet which can then be applied in rearing other related fish species in captivity.

Materials and Methods

Experimental flowchart

A summary of step-by-step work flow for the experiment is presented in Figure 1 followed by a detailed explanation of every step carried out during the experiment.

Preparation of experimental diets

Three diets were prepared to include carbohydrate forms of different complexities. Monosaccharides (D-glucose), disaccharides (sucrose) and soluble polysaccharides (corn starch) were purchased from Sigma-Aldrich (Merck, USA) and the feed formulations were computed through the WinFeed Least Cost Feed Formulation Software 2.8.4 (Cambridge, UK). D-glucose and sucrose were incorporated into the experimental diets for T. tambroides as the primary carbohydrate sources. A basal inclusion level of 50.0 g kg⁻¹ corn starch was retained in all diets to facilitate diet formulation and maintain a constant total dietary carbohydrate level of 234.4 g kg⁻¹. This carbohydrate level was based on the optimal dietary

 

requirement previously determined for T. tambroides by Ishak et al., (2016), as shown in Table 1. Local fish meal (NutriVet Trading, Malaysia) was used as the protein source, and a vegetable oil mixture of canola and sunflower oils was used as lipid source (Naturel™, Malaysia). All ingredients were then blended until homogenous by KitchenAid Countertop Stand Mixers (KitchenAid, USA) for 20 minutes. Mixtures were then conditioned to 40% wet basis content and sealed in Ziploc bags to allow moisture equilibration for 24 hours at room temperature. All diets were extruded using Brabender KE19 single-screw extruder (Brabender Gmbh and Co., Germany). For verification, the composition of glucose and sucrose in the tested diets were determined using high-performance liquid chromatography with separation performed by Varian 385-LC ELSD (Agilent Technologies), also shown in Table 1. Dilution of samples was done with acetonitrile:water (1:1 ratio) prior to chromatographic separation, before subjected to centrifugation and filtration using a nylon syringe filter, 0.45 μm. Filtered samples were next injected into a Prevail Carbohydrate ES 250 mm × 4.6 mm, 5 μm column (Alltech, USA). The mobile phase was acetonitrile: water (75:25 ratio) at 1.0 mL min− 1 flow rate. The values of percentage area under chromatographic peaks over the total area of peaks were used to determine sugar composition.

 

Table 1: Diet formulation, proximate and sugar composition of the experimental diets (g kg-1) as-fed basis.

	Experimental diets
	Glucose	Sucrose	Starch
Ingredients
Fish meal	690.0	690.0	690.0
Vegetable oil	55.6	55.6	55.6
Vitamin premix †	10.0	10.0	10.0
Mineral premix ‡	10.0	10.0	10.0
Corn starch	50.0	50.00	234.4
Sucrose	0	184.4	0
Glucose	184.4	0	0
Proximate composition
Moisture	47.7	48.1	117.2
Protein	461.0	454.6	431.0
Lipid	93.4	87.3	101.7
Ash	87.2	90.1	105.5
Fiber	13.9	12.5	18.0
Carbohydrate	310.7	319.9	244.6
Gross energy (kJ g-1)	19.93	19.67	18.30
Sugar composition
Glucose	114.1	0.7	1.0
Sucrose	< 0.1	113.4	1.0
Maltose	< 0.1	< 0.1	1.0

 

† Vitamin premix (g kg-1); cellulose, 845.11; choline chloride, 75; ascorbic acid, 45; α-tocopheryl acetate (500 IU g-1), 8; myoinositol, 5; niacin, 4.5; Ca-pantothenate, 3; riboflavin, 1; pyridoxine, 1; thiamine mononitrate, 0.92; retinyl acetate, 0.6; vitamin K menadione, 1.67; biotin, 0.02; folic acid, 0.09; vitamin B12, 0.001; cholecalciferol, 0.083.‡ Mineral premix (g kg-1): CaHPO4.2H2O, 500; CaCO3, 215; MgOH, 124; KCl, 90; NaCl, 40; FeSO4 7H2O, 20; ZnSO4.7H2O, 4; MnSO4.H2O, 3; CuSO4.5H2O, 3; NaF, 1; KI, 0.04; Na2SeO3, 0.03; COSO4, 0.02.

 

Feeding trials and sampling

This experiment was conducted at the Department of Aquaculture Wet Laboratory, Universiti Putra Malaysia. Wild T. tambroides fingerlings were obtained from a localfish farm in Kelantan, Malaysia and subjected to three weeks of acclimatization. Following the acclimatization period, fish were graded to 180 individuals (initial body weight of 1.40 ± 0.01 g). Nine 60 L glass aquaria (38 cm × 75 cm × 35 cm) filled with dechlorinated municipal water were each stocked randomly with twenty fish and each unit was equipped with continuous aeration. Water parameters were maintained at 26.0±1.0 ºC temperature, 5.0±0.5 mg l-1 dissolved oxygen and 6.8±0.2 pH; with up to 30% water changes done twice weekly. Experimental diets were fed daily to fish for eight weeks at 4% body weight. Fish mortality and body weight were monitored and recorded throughout the trial. The quantity of feed used during the trial was recorded as feed intake.

At the end of the feeding trial, fish were fasted for 24 hrs. before sampling. Final body weight for all fish was measured. Subsequently, ten fish from each replicate were selected randomly and euthanised following anesthetization of 1gL-1 tricaine methanesulfonate (MS222). Internal organs, including the liver, were excised and weighed. Fat from the abdominal cavity was combined with that separated from the viscera and classified as intraperitoneal fat. Liver was preserved for histological analysis, while eviscerated fish were freeze-dried for proximate composition analysis. Remaining live fish post-sampling were consolidated and maintained in a common holding tank under standard care. All procedural steps for animal laboratory use complied with the MYCODE for the Care and Use of Animals for Scientific Purposes (LKH/GP/01/2019) as outlined by the Animal Welfare Board, Department of Veterinary Services, Malaysia.

Subsequently growth parameters such as; weight gain (WG), and specific growth rate (SGR) were determined using the following equations:

FCR and PER, were determined using the calculations below:

Hepatosomatic index (HSI), viscerosomatic index (VSI) and intraperitoneal fat ratio (IPF) were calculated using the following equation:

Proximate composition analysis

Crude protein content was estimated via distillation using a 2400 Kjeltec Analyzer Unit (FOSS, Denmark) after 60 min sulfuric acid digestion at 100°C. Crude lipid content was estimated using a Foss Soxtec™ 8000 extraction unit (FOSS, Denmark). Estimation of crude fiber content in samples was determined by acid and alkaline digestions using Fibertec Cold and Hot Extractor Foss Tecator (FOSS, Denmark). Moisture content was measured by Infrared Moisture Determination Balance AD-4715 (AandD Company, Japan). Crude ash content was determined by high temperature combustion in furnace at 550°C for 6 hrs. Lastly, gross energy determination was performed using an Automatic Bomb Calorimeter AC 350 (LECO, USA). Major nutrient retention values (Protein retention value, PRV; Lipid retention value, LRV; Carbohydrate retention value, CRV; Energy retention value, ERV) were obtained from proximate analysis results and calculated using the equation:

Histology

The extracted livers during sampling were directly fixed in Bouin’s solution for 6 hrs, before keeping in 70% ethanol. Subsequently, tissues underwent sequential dehydration in graded ethanol concentrations following the standard histological method prior to paraffin wax embedment. Tissues were sectioned at 5µm, then subjected to haematoxylin and eosin staining before finally mounted in DPX following methods in Ishak et al. (2021). Slides were observed using AxioScope A1 microscope (Carl Zeiss MicroImaging GmbH, Germany).

Statistical analysis

Statistical analyses were performed with SPSS v20 (SPSS Inc., USA). Percentage data were arcsine-transformed before analysis. Results are presented as means of three samples ± standard error and were analyzed with one-way analysis of variance (ANOVA) after being subjected to the Shapiro-Wilk test for data normality and Levene’s test for homogeneity. Tukey’s Honestly Significant Difference (HSD) test was then used in determining difference when significance was detected at P<0.05.

Results

After 8 weeks of feeding trial, the growth performance, body indices, and feed efficiency of T. tambroides fingerlings fed with differing carbohydrate forms are shown in Table 2. Different carbohydrate complexities in the diets had no effect (p=0.402) on survival was observed between treatments although 100% survival was recorded in fish fed starch. However, the growth of T. tambroides was significantly affected (p<0.05) with starch feeding showing better final growth (2.32g±0.14) than fish fed glucose, along with significantly lower FCR (3.60±0.17) and higher PER (0.73±0.03) compared to fish fed either of the simple carbohydrates. Also, feeding the dietary starch recorded significantly higher SGR (0.60±0.02) too compared to those fed with sucrose (0.35±0.02) and glucose (0.38±0.02).

 

Table 2: Growth performance and feed efficiency of T. tambroides fingerlings fed with different carbohydrate forms for 8 weeks (Initial body weight = 1.40 ± 0.01 g).

	Experimental diets
	Glucose	Sucrose	Starch
Survival (%)	98.33±1.67	98.33±1.67	100.00±0.00
Final body weigh(g)	1.84±0.09b	1.93±0.05ab	2.32±0.14a
WG (%)	33.56±1.75b	37.66±2.08b	65.69±1.84a
SGR	0.35±0.02b	0.38±0.02b	0.60±0.02a
FCR	6.02±0.25a	5.73±0.16a	3.60±0.17b
PER	0.37±0.02b	0.40±0.01b	0.73±0.03a

 

Different superscripts in rows indicated statistical significance at P < 0.05. Values are presented as mean ±SEM (n=3). Experimental fish had an initial body weight of 1.40±0.01g.

 

Table 3 shows that the HSI value of fish fed starch and sucrose were higher than fish fed glucose diet, although there was no significant difference among glucose and sucrose treatments (p=0.004). No significant effects were observed for IPF (p=0.546) and VSI (p=0.265) between dietary treatments. Different carbohydrate complexities significantly affected (p<0.05) body composition except for the contents of ash and moisture is shown in Table 3. The highest (p<0.05) lipid content was recorded in fish fed starch at 110.3±1.3 g kg-1. Protein, energy, and fiber contents for fish fed the glucose diet were significantly lower (p<0.05) than both fish fed starch and sucrose diets. In contrast, fish fed starch had the lowest body carbohydrate content (p<0.05) than other treatments. Highest PRV (11.97±0.55%, p=0.000), LRV (54.30±2.38%, p=0.000), and ERV (32.75±1.50%, p=0.000) values were obtained in fish fed with starch but its CRV value was the lowest at 0.58±0.03% (p=0.002) as compared to other treatments.

The liver cross sections of T. tambroides fingerlings from each treatment showed normal staining character of the hepatocytes, intact cellular and sinusoid structure with no steatosis, or any evidence of nucleus degeneration or negative differences (Figure 2). Previous histological observations showed that liver morphology of T. tambroides is significantly altered by difference in carbohydrate sources and inclusion levels (Ishak et al., 2016; Ishak et al., 2021). These dietary factors generate excess carbohydrate, which fish metabolize and then store in hepatic tissues as glycogen and lipid vacuoles (Kamalam et al., 2017).

 

Table 3: Body indices, body proximate composition (g kg-1) per fed basis and nutrient retention percentage of T. tambroides fingerlings fed with different carbohydrate forms for 8 weeks.

	Body composition
	Glucose	Sucrose	Starch
Body indices
HSI (%)	1.03±0.08b	1.32±0.15ab		1.66±0.12a
VSI (%)	3.53±0.17	3.16±0.21		3.04±0.19
IPF (%)	0.66±0.10	0.66±0.08		0.81±0.10
Proximate composition
Moisture	726.5±2.0	705.3±10.2	692.0±9.5
Protein	150.5±1.6b	162.8±2.3a	161.8±1.9a
Lipid	67.9±0.8c	81.8±1.2b	110.3±1.3a
Ash	39.8±0.5	36.1±0.7	36.7±0.9
Fiber	0.4±0.2b	1.7±0.0ab	3.5±1.5a
Carbohydrate †	15.4±1.6a	14.1±2.3a	4.3±2.0b
Gross energy (kJ g-1)	16.90±0.45b	17.68±3.0ab	18.70±1.3a
Nutrient retention values
PRV (%)	4.52±0.25c	6.86±0.17 b	11.97±0.55a
LRV (%)	10.42±0.57c	23.34±0.39b	54.30±2.38a
CRV (%)	2.75±0.03a	2.34±0.04a	0.58±0.03b
ERV (%)	10.63±0.68c	14.47±0.49b	32.75±1.50a

 

Initial body proximate composition (g kg-1) was 732.0 moisture, 160.1 protein, 71.9 lipid, 32.6 ash, 2.5 fiber and 3.4 carbohydrate. Initial gross energy was 18.50 kJ g-1.† Carbohydrate = 1000 g kg -1 – (moisture + protein + lipid + ash). Different superscripts in rows indicate statistical significance at P < 0.05. Values are presented as mean±SEM (n=3).

 

 

Discussion

The growth rate of T. tambroides observed across all treatments in this study was relatively slow, aligning with the species’ inherent biological characteristics (Enes et al., 2010). Diets containing starch resulted in improved growth, body indices, and feed efficiency compared to those supplemented with glucose or sucrose. This agrees with the findings of Xu et al. (2020), who reported poor weight gain, and specific growth rate in brook trout, Salvelinus fontinalis fed dietary glucose or sucrose as compared to those fed diets with dextrin or pre-gelatinized corn starch. Nile tilapia also fed a glucose-based diet was reported to show lower weight gain compared to those fed on sucrose diet (Zhou et al., 2022). The poor utilization of glucose observed could be due to faster glucose absorption in the gut because of its simple molecular structure which can result in inefficient metabolism. In contrast, the absorption of starch with a complex molecular structure in the gut is slower and result in the suppression of the innate immunity, increased oxidative stress and distortion in glucose metabolism (Enes et al., 2011; Xu et al., 2020). Similar preferences for dietary starch over simple dietary carbohydrates were also observed in omnivorous freshwater fishes such as southern catfish, Silurus meridionalis (Fu 2005), hybrid tilapia, Oreochromis niloticus × O. aureus (Tung and Shiau 1993; Lin and Shiau 1995), and the gibel carp, Carassius auratus gibelio (Tan et al., 2009).

On the other hand, other omnivorous, freshwater cyprinids such as rohu, Labeo rohita and mrigal carp, Cirrhinus mrigala were found to better utilize dextrin, (a lesser complex carbohydrate than starch) for growth over glucose and sucrose (Erfanullah and Jafri 1995; Singh et al., 2006). The blunt snout bream, Megalobrama amblycephala is also reported to have a growth response to dextrin over higher complexity carbohydrates like cellulose, wheat starch, corn starch, and over simple carbohydrates like maltose, sucrose and glucose (Ren et al., 2015). These findings suggest that growth response to dietary carbohydrate forms may be species-dependent regardless of whether they are in the same family or not. In general, T. tambroides’ poor use of glucose and sucrose for growth could be related to their low degree of energy metabolism. Fish may have a low rate of energy consumption and a high rate of energy supply when using carbohydrate as a fuel. The rate of energy supply may be overabundant after excessive glucose consumption, resulting in persistent hyperglycemia (Krishnan and Rohner, 2019). Many factors affecting dietary carbohydrate utilization in fish could be linked to this putative process, which requires further investigation. While the experimental diets were formulated to be isonitrogenous and isolipidic, proximate analysis revealed variations in the final composition. Specifically, the calculated carbohydrate content was significantly higher in the glucose (310.7 g kg⁻¹) and sucrose (319.9 g kg⁻¹) diets compared to the starch control (244.6 g kg⁻¹). This difference of approximately 66–75 g kg⁻¹ in total carbohydrate content represents a limitation of this study, as the higher carbohydrate and energy load in the simple sugar diets could have acted as a confounding factor. Consequently, the poor growth performance and metabolic dysfunction observed in the glucose and sucrose groups might be influenced not only by carbohydrate complexity but also by the absolute amount of dietary carbohydrates.

Excess carbohydrates in vertebrates are converted to glycogen and lipids in adipose and liver tissues via cytosolic polymerisation (Kamalam et al., 2017). Our study showed that T. tambroides fed starch had a significantly higher HSI than those fed glucose. An increased hepatosomatic index (HSI) is a non-specific indicator of liver enlargement and may reflect hepatic glycogen accumulation, lipid deposition, or a combination of both rather than steatosis alone (Li et al., 2021). Therefore, the absence of steatosis in routine histological sections does not necessarily exclude carbohydrate-induced hepatomegaly or enlarged liver. In freshwater fish, excessive dietary starch has been associated with mixed hepatic lesions involving both glycogen and lipid accumulation. For example, dietary starch levels exceeding 100g kg⁻¹ induced concurrent hepatic glycogen and lipid accumulation in largemouth bass (Micropterus salmoides) (Zhang et al., 2020), while high-starch feeding also increased the hepatopancreas index and promoted marked hepatic glycogen deposition accompanied by liver injury (Zhong et al., 2022). Likewise, excessive dietary starch can stimulate hepatic lipogenesis while suppressing fatty acid oxidation, further contributing to liver enlargement (Liu et al., 2023; Xie et al., 2024). Collectively, these studies indicate that elevated HSI should be interpreted as a general marker of altered hepatic energy storage rather than evidence of lipid accumulation alone.

Accordingly, the absence of steatosis in the present study does not contradict the observed increase in HSI. High-carbohydrate diets can induce glycogenic hepatopathy characterized by hepatocyte swelling and marked glycogen accumulation without significant hepatic lipid deposition (Zou et al., 2025), while routine hematoxylin and eosin staining may not detect mild lipid accumulation (Villasante et al., 2022). Furthermore, the low CRV does not preclude hepatic glycogen storage because excess glucose may be preferentially stored as liver glycogen (Li et al., 2021), whereas the high LRV suggests that enhanced lipogenesis may also have contributed to liver enlargement. Thus, the elevated HSI most likely reflects combined alterations in carbohydrate and lipid metabolism, with glycogen-dominant hepatomegaly being the most plausible explanation unless confirmed otherwise by glycogen- or lipid-specific analyses (Li et al., 2021; Zou et al., 2025; Withyachumnarnkul et al., 2025). This agrees with the findings in blunt snout bream, M. amblycephala fed high dietary carbohydrates which recorded significantly higher values in HSI (Adjoumani et al., 2022), though it remains highly species-dependent as rainbow trout, O. mykiss (Pfeffer et al., 1991), and jundiá, Rhamdia quelenand (Corrêia et al., 2019) have shown no significant HSI differences across varying carbohydrate complexities.

The results from this experiment also showed that T. tambroides fed starch had higher PRV and ERV in accordance to Deng et al. (2005) where white sturgeon fed with starch diet had higher PRV and ERV than their glucose-fed counterparts. Similarly, jundiá fed diet with starch showed higher PRV compared to those fed diets containing fructose, sucrose and maltodextrin (Corrêia et al., 2019). PER value indicated that T. tambroides fed starch displayed a greater protein-sparing effect than fish fed glucose and sucrose, a similar effect was also described in the olive flounder, P. olivaceus (Lee et al., 2003). On the contrary, grass carp and Chinook salmon, Oncorhynchus tshawytscha can efficiently utilize glucose for protein-sparing (Tian et al., 2004; Araujo et al., 2023). Nonetheless, protein-sparing effect was not observed in gilthead sea bream, Sparus aurata, GIFT tilapia, and European sea bass, D. labrax when fed different carbohydrate complexities indicating that these species have similar efficiency for the utilization of both starch and glucose (Enes et al., 2006, 2008, 2010; Qiang et al., 2014). Furthermore, elucidating carbohydrate utilization in metabolic pathways, especially physiological responses to dietary energy from carbohydrates will be valuable in formulating a species-specific diet (Salati and Amir-Ahmady, 2001; Trushenski et al., 2006). Understanding the ideal carbohydrate form and complexity as an exogenous glucose source for dietary inclusion can spare the use of essential amino acids in gluconeogenesis pathway, thus encouraging the protein-sparing effect (Kamalam et al., 2017; Panserat et al., 2019).

Conclusion

The findings conclude that T. tambroides benefits from the inclusion of higher carbohydrate complexity in its diet, in comparison to simple carbohydrates like sucrose and glucose. Carbohydrate utilization is species-specific, and carbohydrate complexities is a regulating factor in fish physiological changes. This study also provides baseline formulation incorporating the use of starch, considering the complexity of different carbohydrates and their availability.

Acknowledgements

This study was funded through ScienceFund 04-01-04-SF1713 titled “Dietary carbohydrate utilization by the Malaysian mahseer, Tor tambroides” granted by the Malaysian Ministry of Science, Technology and Innovation. We would like to express our gratitude to Mr. Jasni and laboratory officers from the Department of Aquaculture, Faculty of Agriculture Serdang for their technical assistance throughout the feeding trials.

Novelty statement

This study is the first to investigate the effects of dietary carbohydrate complexity on growth, feed utilization, and metabolic responses in Tor tambroides. Our results demonstrate a clear preference for complex starch over simple sugars (glucose and sucrose), leading to superior growth performance, body indices, feed efficiency, and protein-sparing effects.

The findings reveal species-specific metabolic traits, including poor simple-sugar utilization and elevated HSI primarily associated with glycogen accumulation rather than steatosis. These insights fill a key knowledge gap in the nutritional physiology of this slow-growing cyprinid and support the formulation of optimized, species-specific aquafeeds.

Authors contributions

S.D.I conceived and designed the study, performed the feeding trial, laboratory analyses, data interpretation, statistical analysis and drafted the original manuscript. S.R contributed to data interpretation and critical revision of the manuscript. H.C, D.T. and O.V. T. assisted in manuscript revision, data curation and data interpretation. M.S.K. provided supervision, resources, and critical revision of the manuscript. All authors read and approved the final version of the manuscript.

Generative ai and ai assisted technology statement

The author(s) acknowledge the use of Grammarly and Grok AI to assist with grammar checking, language refinement, reference formatting. These AI-assisted tools were not used as authors and did not replace the intellectual contributions or scholarly judgment of the author(s). All AI-assisted outputs, including content, references, and interpretations, were carefully reviewed, revised, verified, and approved by the author(s). The author(s) accept full responsibility for the accuracy, integrity, and final content of the manuscript.

Conflict of interest

The authors has no conflicts of interest to declare regarding the publication of this article.

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