Introduction
Dietary changes can negatively affect feed intake in fish, leading to suboptimal performance. To address issues of palatability, various feed additives have been explored. Sugarex AQUA is a proprietary neohesperidin dihydrochalcone (NHDC) formulation with enhanced solubility and sensory properties. Research in other livestock has shown that NHDC, can enhance feed intake and improve growth performance. However, data on its effects in aquaculture remain limited. This study aimed to evaluate the impact of Sugarex AQUA on feeding behaviour and performance of Atlantic salmon ( Salmo salar ) when added to low-palatability or medicated diets.
Materials and Methods
Groups of 30 162g Atlantic salmon ( Salmo salar ) were held in 30 500 L holding units forming part of a recirculating aquaculture system (RAS) with full strength sea water having a target temperature of 13 + 1o C and a with a l ight/dark cycle of 12/12 h. The trial was split into four two-week periods and t he fish in each holding tank were weighed in bulk every two weeks. Feeding behaviour was assessed using a fixed scoring system.
Six treatments were tested with five replicates per treatment . The first set of treatments consisted of a control diet formulation with or without supplemental Sugarex AQUA (CD and CDS respectively). The second set of treatments consisted of a low- palatability diet with or without supplemental Sugarex AQUA (LP and LPS respectively). The final set of treatments were similar to the first two treatments except during the second two-week period during which an antibiotic (oxytetracycline) was added to the feed with or without supplemental Sugarex AQUA (TM and TMS respectively). Sugarex AQUA concentration in the supplemented diets was 0.6 g/kg, equivalent to an inclusion level of 18ppm NHDC.
Data was checked using Shapiro-Wilk and Levene’s tests. T-tests or Mann-Whitney U tests (https://www.statskingdom.com) were used to compare similar diets (p < 0.05).
Results
No significant differences in fish weight or specific growth rate (SGR) were observed between fish fed diets CD and CDS. Feed intake was slightly higher in CDS-fed fish, and feed conversion ratio (FCR) was consistently improved. Sugarex AQUA inclusion gave an SGR and FCR improvement of 8% and 4%, respectively. Sugarex AQUA had a more pronounced effect on fish fed the LP diets, significantly improving fish growth in Periods 1 to 3. Feeding behaviour and feed intake were also significantly higher in LPS-fed fish. In Periods 2 and 3, fish fed the TMS diet clearly outperformed those on the TM diet, showing significantly higher SGRs. Although the difference in SGR was not statistically significant in Period 4, the TMS group maintained a stronger overall growth, with a SGR 26% higher than the TM group. From Period 2 onwards, feed intake and SFR were consistently better in the TMS group, remaining significantly higher through to the end of the trial. Additionally, fish fed TMS achieved better feed efficiency, with FCR being consistently lower than the TM group in all periods, most notably in Period 3, resulting in a 13% overall reduction in FCR compared to the TM diet.
Discussion
There were no clear benefits of adding Sugarex AQUA to the control diet. Conversely, Sugarex AQUA had a clear positive effect on feed intake and overall performance when included in the low-palatability diet for fish. The greatest impact was observed in Periods 1 and 2, diminishing over time, likely due to adaptation to the taste of the low-palatability formulation.
The results related to Sugarex AQUA use alongside antibiotics were also clear . No significant differences were observed in Period 1 but, when antibiotics were introduced in Period 2, feed intake and SGR significantly increased in the Sugarex AQUA-supplemented group. It was expected that, once antibiotics were discontinued, the differences between the two treatments would disappear. However, significant differences in feed intake and performance persisted through Periods 3 and 4 and across the entire trial period. These results suggest that antibiotic use may have had a lasting impact on fish performance even after treatment ceased. This effect could be attributed to changes in gut microbiota (Dhanasiri et al., 2024; Monticelli et al., 2024), although this was not investigated in this study. Over the full trial period, fish fed the medicated diet (TM) were significantly smaller and exhibited lower growth than those fed either the control diet (CD) or the Sugarex AQUA-supplemented control diet (CDS). On the other hand, NHDC has been shown to positively influence gut morphology and microbiota (Daly et al., 2016; Wang et al., 2024), which may have helped mitigate the negative effects of the TM diet. As a result, by the end of the experiment, there were no significant differences in SGR and FCR between fish fed TMS and those on the control diets with or without Sugarex AQUA.
Conclusions
The findings of this study indicate that Sugarex AQUA can be beneficial in two key situations commonly encountered in aquaculture:
References
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