MACROALGAE-DERIVED MULTIBIOTIC SUPPLEMENTATION IN GILTHEAD SEABREAM: PHYSIOLOGICAL AND WATER QUALITY RESPONSE TO A MODERATE HYPOXIA CHALLENGE

Introduction

In modern aquaculture, the substitution of fish meals by vegetable-based diets shows compatibility in carnivorous species, but may produce physiological alterations that can be modulated by nutraceutical compounds derived from macro- and microalgae (Perera et al., 2020). At the same time, rising temperatures and high stocking densities reduce dissolved oxygen availability, which can trigger internal changes leading to physiological stress (Martos-Sitcha et al., 2020). Stress also affects the intestinal microbiota, which can be modulated through symbiotic nutraceuticals to provide beneficial properties to the individual (Egerton et al., 2018). Gut enzyme–bacteria interactions are also key for digestibility and protein utilisation, which influence ammonia, nitrate and nitrite release to the environment (Hlordzi et al., 2020). In this context, the present study evaluated the physiological response and water-quality changes in Sparus aurata fed with a macroalgae-derived multibiotic supplement under normoxic and moderate-hypoxia conditions.

Materials and Methods

The experiment was carried out in Servicios Centrales de Investigación en Cultivos Marinos (SCI-CM, Universidad de Cádiz, Spain). A total of 180 gilthead seabream (Sparus aurata) juveniles (54.58±0.05 g average body mass) were distributed into 9 tanks (300 L, n=20 fish per tank), where three experimental groups were constituted to be fed with: i) a control diet (CTRL), or the same formulation supplemented with a ii) 1% and iii) 3.5% with the nutraceutical compound Prebiodo II produced by Biotechnology Biopolym S.A. (Granada, Spain). Feeding was performed ad libitum by twice daily meals for 91 days. Feed intake was controlled weekly and biometric samplings were performed every 4 weeks. After the feeding period, a hypoxia challenge was performed on the 3 experimental groups, being subjected to moderate hypoxia (35-40% O2 saturation) during 24 hours. Biological samples allowed analysis of plasma, muscle and hepatic metabolites (glucose, glycogen lactate, triglycerides, cholesterol and proteins) and plasma cortisol. In addition, water samples were taken for water quality analysis (ammonium and nitrite concentration).

Results and Discussion

In general, an effect on the parameters can be seen in relation to the Prebiodo II supplementation dose. Plasma cortisol levels showed a decrease in the supplemented groups both during normoxic and hypoxic conditions, while a lower lactate level was observed in these groups during a mid-hypoxia process, promoting a clear shift between aerobic and anaerobic metabolism, especially in those fish fed with supplemented diets (Fig. 1A, 1B). An inverse pattern was observed in hepatic glucose and glycogen values, responding to glucose mobilisation to maintain homeostasis. The good circulation, transport and energy use could be corroborated with the other parameters taken, showing an improvement in performance and metabolic status as a consequence of better nutritional absorption and water quality (Table 1, Fig. 1C). Overall, dietary supplementation modulated the physiological response to moderate hypoxia, improved feed efficiency and reduced mesenteric fat deposition, supporting the potential application of macroalgae-derived multibiotic compounds during stress-prone production phases in gilthead seabream.

Table 1. Results of Feed Efficiency (A), Mesenteric Index (B) and Intestine Length Index (C). Results expressed as mean ± SEM, and analysed by one-way ANOVA analysis. Different letters represent statistically significant differences between groups (p-value<0.05).

Metabolite/Group

CTRL

B 1%

B 3.5% p-value

FE (%)

0.71 ± 0.02^a

0.76 ± 0.02^ab

0.78 ± 0.01^b

0.041

MSI (%)

1.08 ± 0.09^a

0.82 ± 0.09^ab

0.58 ± 0.06^b

<0.001

ILI (%)

97.89 ± 4.00^a

81.05 ± 4.38^b

83.89 ± 4.80^b

0.014

B

C

A

B

C

A

Figure 1. Plasma cortisol (A), lactate (B) and nitrite in water (C). Results expressed as mean ± SEM, and analysed by two-way ANOVA analysis. Different letters represent statistically significant differences between groups (p-value<0.05).

Acknowledgment

This work was supported by the Project OTRI-2021/134 funded by Biotechnology Biopolym S.A. (Granada, Spain). Lucía Moreno acknowledges the INICIA-TC-MASTER grant co-founded by the University of Cádiz and Biotechnology Biopolym S.A.

References

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Hlordzi, V., Kuebutornye, F.K.A., Afriyie, G., Abarike, E.D., Lu, Y., Chi, S., Anokyewaa, M.A. (2020). The use of Bacillus species in maintenance of water quality in aquaculture: A review. Aquaculture Reports. Vol 18, 100503.

Martos-Sitcha, J.A., Mancera, J.M, Prunet, P., Magnoni., L.J. (2020). Editorial: Welfare and Stressors in Fish: Challenges Facing Aquaculture. Frontiers in Physiology, 11, 162.

Perera, E., Sánchez-Ruiz, D., Sáez, M. I., Galafat, A., Barany, A., Fernández-Castro, M., Vizcaíno, A.J., Fuentes, J., Martínez, T.F., Mancera, J.M., Alarcón, F. J., Martos-Sitcha, J.A. (2020). Low dietary inclusion of nutraceuticals from microalgae improves feed efficiency and modifies intermediary metabolisms in gilthead sea bream (Sparus aurata). Scientific Reports, 10, 18676.