Aquaculture is recognized as the most intensive and distinctive source of animal-derived protein. Its rapid expansion has made it one of the most promising and significant sectors of the economy (FAO, 2023). The increasing demand for edible fish, combined with the declining productivity of capture fisheries, is driving the growth and intensification of aquaculture in Bangladesh. To maximize growth and profitability, it is essential to provide cultured species with nutritionally balanced and enriched feed (Liang et al., 2022). Aquafeed is considered balanced when it contains an adequate amount of vital nutrients, has minimal negative effects on ecosystem integrity and human health, and remains financially viable. However, most feed manufacturers struggle to deliver high-quality aquafeed due to various issues, including the use of contaminated ingredients and a lack of high-quality feed components (Khatun et al., 2017). To enhance nutrient utilization and optimize growth performance, various additives, such as growth promoters, are currently being incorporated into fish aquafeed formulations.
Growth promoters, a type of feed supplement, consist primarily of chemical and/or biological components and are incorporated into aquafeed to enhance growth in cultured fish (Tacon, 2014). In fish culture, these promoters help fish convert feed into body mass more effectively, resulting in increased growth rates, improved feed efficiency, and shorter production cycles (Islam et al., 2017). Additionally, they bolster immunity, facilitate better digestion, and enhance nutrient absorption, all of which contribute to improved health, higher survival rates, and greater yields, ultimately increasing profitability for fish farmers (Doan et al., 2024). Recent studies indicate that β-glucan, dietary enzymes, vitamins, beneficial microbes, herbal extracts, and mineral premixes are some of the most widely used growth promoters in Bangladesh's aquaculture industry (Anwar et al., 2018; Rahman et al., 2017; Chowdhury et al., 2015). Commercial growth promoters such as GrowFast, AquaBoost, BioAqua, AquaPro, and Bio-Grow are also commonly used in aquaculture, typically added to pond water or mixed with feed (Salma et al., 2022). Charger Gel, a commercial growth promoter produced by Growel Formulations Private Limited, contains β-glucan, betaine, polysaccharides, and 1-3 D-glucan, and is frequently utilized by Bangladeshi fish farmers in aqua-feed (Khanjani et al., 2021; Meena et al., 2013).
Carp fish play a significant role in the aquaculture sector of Bangladesh. To fully harness the potential of carp culture, it is essential to develop innovative and efficient management measures. Carp fattening, a common short-term intensive aquaculture technique, is predominantly practiced in the northwestern region of Bangladesh (Hossain et al., 2022 a,b). Feed additives or growth promoters are crucial for fattening carp and optimizing feed usage to enhance production and economic outcomes. The use of feed additives is gaining popularity among fish farmers in Bangladesh due to their numerous advantages. However, despite the increasing availability of various growth promoters introduced by aqua drug and pharmaceutical companies, there is a notable lack of comparative evaluations regarding their effects on fish growth, meat composition, and palatability. These growth promoters have distinct mechanisms of action, necessitating separate testing of each group, with the results made available to aquaculturists. Additionally, some farmers apply these growth promoters randomly, often without understanding their efficacy or the proper dosages. This unregulated use may have detrimental effects on the meat composition and palatability of fish, which are largely overlooked in the country.
Labeo rohita is one of the most extensively grown species in carp fattening systems due to its high market value and strong consumer demand. Although naturally herbivorous, L. rohita efficiently utilizes supplementary feeds provided in aquaculture systems. By developing effective, low-cost feed formulations using locally available ingredients and growth promoters, fish farmers can significantly enhance profitability. However, limited studies have investigated the impacts of growth promoter-incorporated diets on different fish species, such as Oreochromis niloticus and Clarias batrachus (Islam et al., 2017; Islam et al., 2014). Few investigations have focused specifically on the effects of growth promoters on the growth and flesh quality of Indian major carps in Bangladesh. This highlights the need to examine how feed enriched with growth promoters influences these parameters in L. rohita. An optimal dose of growth promoter can enhance growth performance, improve muscle quality, and increase the palatability of fish, while suboptimal or excessive doses may diminish these benefits. This research aims to assist farmers in selecting the safest and most advantageous dose of growth promoter, leading to improved production performance, better flesh quality, and more cost-efficient carp farming. Therefore, the study investigated the effects of feed containing charger gel, a commonly used growth promoter, on growth, feed utilization, flesh nutrient profile, and palatability of the popular Indian major carp, L. rohita.
2. Materials and Methods
2.1 Ethics declarations
Fish were anesthetized with clove oil before dissection for sample collection. All procedures in this study adhered to the ethical guidelines of the International Council for Laboratory Animal Science (ICLAS).
2.2 Experimental site and periods
The experiment was conducted in twelve cages located at a pond near the Department of Fisheries, University of Rajshahi, Bangladesh, from July to September 2023, over a period of 90 days (Figure 1). Each cage, constructed from an iron rod structure and measuring 2.73 m³, was covered with a 5-mm mesh nylon net. An entrance was maintained on the upper side of each cage to facilitate feed delivery and to allow for easy fish handling during sampling.
2.3 Experimental design
In the experiment, four different feeds were used as treatments, each with three replicates. Among these feeds, a commercially available option (ACI carp grower) was selected as the control (T1), which did not include a growth promoter or charger gel. The other three feeds were prepared by adding charger gel at concentrations of 4, 6, and 8 g/kg of feed, designated as T2, T3, and T4, respectively.
2.4 Feed formulation
Three test feeds were created using locally available feed materials (Table 1). The proximate compositions of these ingredients were estimated following the methods outlined by the Association of Official Analytical Chemists (AOAC) (2005), and the formulation was conducted using spreadsheet analysis. To achieve an iso-protein diet across all treatments, the protein level of the prepared feeds was designed to match that of the control. All ingredients were weighed and thoroughly mixed with the appropriate amount of water to form a dough, which was then extruded into pellets using a pelletizer and sun-dried. After drying, the pellets were placed in labeled polythene bags, sealed, and stored at 4 °C until use. According to AOAC (2005) procedures, the proximate composition of the prepared feeds (Table 2) was determined and revealed no significant variation among the test feeds.
Table 1. Incorporation levels of the ingredients in the experimental feeds.
Table 2. Proximate composition (dry basis) of the trial feeds.
2.5 Stocking and feeding of experimental fish
A total of 130 juvenile L. rohita were collected from a nearby fish farm and transported to the experimental site with proper aeration. The fish were then allowed to acclimate for 7 days to the experimental conditions before the investigation began. During this time, they were fed commercial carp feed at 5% of their total weight. After acclimatization, 10 fish, each weighing approximately 150 g, were released into each cage. Once stocked, the fish were fed the experimental feeds at 5% of their body weight daily, divided into two equal feedings of 2.5% each, in the morning and evening.
2.6 Monitoring of water quality
During the experimental period, water quality indicators—such as pond water temperature, alkalinity, pH, dissolved oxygen (DO), carbon dioxide (CO2), and ammonia-nitrogen (NH3-N)—were checked biweekly. Water temperature and pH were recorded using a Celsius thermometer and a pH meter, respectively. Measurements of the other parameters were taken using a HACH kit (model: DR/2010, Hach Company, Germany). The water parameter values for each treatment remained within the optimal range for fish culture and did not vary significantly among the treatments.
2.7 Analysis of growth and nutrient utilization
During the stocking of fish, initial sampling was conducted to record the weight of individual fish using an electric balance with a precision of 0.10 g. Subsequent sampling was performed biweekly to monitor fish growth. Growth and nutrient utilization matrices were computed using the following formula,
Mean weight gain (MWG) =Mean final weight – Mean initial weight
Specific growth rate (SGR% / day) = [100 (ln FW – ln IW)/T]
Where, FW = final weight (g), IW = initial weight (g), and T = experiment period (days)
Survival rate = (Number of harvested fish/number of fish stocked) × 100
Feed conversion ratio (FCR) = Feed fed (dry weight)/live weight gain
2.8 Analysis of carcass composition
At the end of the trial, three fish from each cage were collected and sacrificed. After cleaning, the flesh was collected and stored in the freezer. Once in the laboratory, the flesh samples were analyzed using standard AOAC (2005) methods to determine their chemical composition by measuring crude protein, lipid, moisture, ash, and carbohydrate content.
2.9 Palatability test of cooked fish
The experimental fish were first prepared for cooking, and the sensory evaluation of the cooked fish was conducted following the procedure outlined by Rahman and Shikdar (2025).
2.10 Statistical analysis
After confirming the normality of the data, statistical analysis was conducted using one-way analysis of variance (ANOVA), followed by Duncan's multiple-range test. Variations were deemed statistically significant at P < 0.05, and all analyses were performed using SPSS–21 (Statistical Product and Service Solutions) software./p>
3. Result
3.1 Growth and nutrient utilization of the test fish
The results demonstrated that the test fish in T2 exhibited significantly elevated MWG (199.37±1.94), PWG (163.68±2.66), and SGR (1.14±0.01), followed by the fish in T3, while lower values were recorded in the T1 fish group. The best FCR was reported in the fish of T2 at 2.07±0.03, compared to the other treatments. There were no significant variations in MWG, PWG, SGR, and FCR between T1 and T4. And also, the SR of the fish did not differ across the treatments (Table 3).
Table 3. Growth and feed utilization matrices of the fish under the treatments.
3.2 Carcass composition of the fish
Carcass composition of the fish flesh was analyzed to evaluate changes in nutritional quality resulting from the incorporation of charger gel in the feed (Table 4). Fish fed with feed containing charger gel exhibited better flesh composition than the control group. The T2 group showed a significantly higher level of crude protein (16.61±0.13) and lipid (2.37±0.08) compared to the other experimental groups. However, fish in the T4 group had significantly higher carbohydrate content (2.62±0.24). The average moisture content did not vary significantly among the groups.
Table 4. Carcass composition of fish among the treatments.
3.3 Palatability of cooked fish
A panel of consumers rated the flavor, texture, and taste of the cooked fish using the organoleptic sensory scoring system, with the mean values presented in Table 5. The fish flesh from T2 received a notably higher flavor score (8.80±1.09) compared to the other treatments. The highest taste score (8.60±1.78) was recorded for the flesh from T4, while the lowest was for T1 (7.20±1.09). T3 achieved a significantly higher texture score (8.20±1.09), followed by T2, T4, and T1. Overall, the fish from T2 outperformed the other treatments in terms of flavor, taste, and texture, as illustrated in Figure 2.
Table 5. Organoleptic assessment scores of the cooked fish among treatments.
4. Discussion
4.1 Growth and feed utilization
To increase fish production, particularly in the artificial feed-driven aquaculture practices of Bangladesh, fish farmers have gradually begun using various commercial growth promoters. However, the proper selection and dosage of these growth promoters are crucial, as unregulated or excessive use can negatively impact fish growth and nutrient utilization. The present investigation observed that the fish group fed a diet containing 4 g/kg of charger gel exhibited better growth and feed conversion ratio (FCR) compared to other treatments. According to the manufacturer's specifications, charger gel contains β-glucans, 1-3 D-glucan, betaine, and polysaccharides. In a scientific report, Meena et al. (2013) noted that β-glucan serves as an immunostimulant, enhancing growth, survival, and immunity against infectious diseases in fish and shellfish. Previous research has demonstrated that incorporating charger gel or other β-glucan-containing growth promoters in aquafeed enhances the growth performance of several fish species. For example, our findings align with those of Ray et al. (2016), who reported a significant increase in the specific growth rate of L. rohita due to the inclusion of β-glucan. Additionally, our results are consistent with those of Hussein et al. (2016), who documented that adding commercial feed additives to the diets of Cyprinus carpio improved growth and nutrient utilization compared to other groups. In a comparative analysis of various growth promoters, Islam et al. (2017) found that charger gel was the most effective in promoting the growth of walking catfish, outperforming two other growth promoters. Similar results were noted by Islam et al. (2014) in tilapia and Islam et al. (2023) in Rohu regarding growth and feed utilization parameters.
4.2 Carcass composition of fish
The nutritional content of feed influences the carcass composition of fish (Orban et al., 2007). Protein and fat levels in the fish carcass are commonly used as indicators to evaluate the nutritional and health conditions of fish (Ahmed et al., 2022). This investigation observed that the addition of charger gel to aquafeed can improve the overall nutritional value of the carcass in L. rohita. Analysis of the carcass composition revealed significant variations in protein content, with the highest value (16.61±0.13) reported in fish fed with a diet incorporating charger gel at 4 g/kg compared to the other groups. Consistent with these findings, Islam et al. (2023) reported that the crude protein content of the flesh from fish receiving charger gel was significantly greater than that of fish fed without it. Earlier studies have shown that β-glucan, the principal active component of charger gel, positively impacts protein deposition in fish (Hoang et al., 2018; Rufchaie and Hoseinifar, 2014). The present results also indicated that fish receiving a 4 g/kg dose of charger gel had significantly increased crude lipid content (2.37±0.08) in their muscles compared to the other treatments. Similar findings were reported by Islam et al. (2023), who noted that fish fed with charger gel-enriched diets had significantly higher carcass lipid content than those in the other treatments. Schmidt et al. (2017)found that feeding Starry flounder (Platichthys stellatus) with β-glucan-supplemented feed resulted in elevated lipid levels. Conversely, Hoang et al. (2018)observed that young Pompano fish (Trachinotus ovatus) fed higher β-glucan diets had lower lipid levels in their body composition. This variation may be attributed to the biochemical responses of different fish species to dietary β-glucan and requires further research for a more definitive conclusion. The supplementation of charger gel in L. rohita feed did not show any significant variations in moisture and ash content.
4.3 Palatability of cooked fish
The organoleptic scores from the palatability test of cooked fish indicate that the incorporation of charger gel may alter the sensory qualities of cultured fish. According to panelists' comments on palatability attributes, the fish treated with charger gel-enriched feed (4 g/kg) received the highest overall organoleptic score (24.80±2.27) compared to the other treatments. These findings are supported by Islam et al. (2023), who reported that fish fed charger gel-enriched feed achieved the highest organoleptic scores in palatability when compared to other growth promoters such as Aquazyme and Eon Fish Grower. Additionally, Rahman and Sarker (2019) noted enhanced palatability in L. rohita due to dietary multi-enzyme additive supplementation, which aligns with the present results. Furthermore, the current findings are consistent with those of Sultana et al. (2020), who described that dietary vitamin C influences the taste and flavor of L. bata. The higher palatability score of the T2 fish group may be attributed to their relatively higher carcass fat content. Lipids are known to significantly affect flavor and texture, primarily due to the presence of free fatty acids and the formation of volatile oxidation products (Shahidi and Weenen, 2006). However, studies on the effect of growth promoter-incorporated feed on fish palatability are limited, highlighting the need for further research to draw definitive conclusions.
5. Conclusions
The study indicates that, compared to the selected commercial feed, the inclusion of locally accessible feed ingredients and growth enhancers leads to improved growth, carcass quality, and enhanced palatability of L. rohita. Notably, the most economically favorable outcome was achieved with the incorporation of 4 g/kg of charger gel in the formulated feed. In Bangladesh, the increasing use of growth promoters in fish feed presents risks due to potential misuse by uninformed farmers influenced by manufacturers. To address this issue, the study calls for further research to establish appropriate dosage recommendations and evaluate the long-term effects of incorporating growth promoters in large-scale fish farms.
Acknowledgements
The authors would like to express their gratitude to the Rajshahi University Research Grant at Rajshahi University, Bangladesh, for providing financial assistance for this study.
Funding information
The research is funded by Rajshahi University Research Grant (5/52/RU/Fish-6/2023-2024) at the University of Rajshahi, Bangladesh.
Data availability
Data will be made available on request.
Informed consent statement
Informed consent was obtained from all subjects involved in the study.
Conflict of interest
The authors declare no conflict of interest.
Authors’ contribution
Conceptualization: Imon Kumar Shikdar and Md. Mahabubur Rahman; Methodology and data collection: Imon Kumar Shikdar, Isma Khatun Liza and Md. Risad Sarkar; Data analysis: Imon Kumar Shikdar and Isma Khatun Liza; Manuscript writing: Imon Kumar Shikdar and Isma Khatun Liza; Review and editing, supervision, and validation: Md. Mahabubur Rahman. All authors critically reviewed the manuscript and agreed to submit the final version of the manuscript.
