USE OF THE INVASIVE MACROALGA Caulerpa racemosa AS A POTENTIAL FUNCTIONAL INGREDIENT FOR GILTHEAD SEABREAM Sparus aurata

Introduction

The use of marine macroalgae in aquaculture is gaining attention as a sustainable alternative for feed formulation, particularly in species such as gilthead seabream (Sparus aurata). The traditional reliance on fishmeal and fish oil poses significant economic and environmental challenges, driving the search for alternative nutrient sources, among which macroalgae stand out. Recent studies have shown that including 5% of species such as Gracilaria gracilis enhances immune and antioxidant status in seabream, improving growth performance and disease resistance (Passos et al., 2021). Among the most promising candidates, the green macroalga Caulerpa racemosa, native to Asia but widely distributed in tropical and temperate regions, is notable for its high content of bioactive compounds, including phenolics, flavonoids, fatty acids, terpenes, and alkaloids. Dietary supplementation trials in aquaculture species such as Cirrhinus mrigala have demonstrated that C. racemosa improves growth, digestive enzyme activity, and feed conversion ratio (Ragunath et al., 2024). Additionally, 240 mg/kg of its extract reduced intestinal damage in Litopenaeus vannamei infected with Vibrio parahaemolyticus (Pratiwi et al., 2022). These findings suggest that C. racemosa acts as a functional additive with nutritional, immunological, and environmental benefits, supporting sustainable aquaculture practices.

Materials and methods

Dried C. racemosa biomass was used to obtain lipophilic and aqueous extracts to evaluate antimicrobial activity against Vibrio anguillarum, Vibrio alginolyticus, and Photobacterium damselae using the disk diffusion method following Uddin et al. (2020). Additionally, 270 juvenile gilthead seabream (Sparus aurata) were randomly distributed into 15 fiberglass tanks (400 L; 18 fish per tank), with three replicates per treatment in an open seawater system under natural photoperiod. Fish were fed to apparent satiation twice daily, six days per week, using five experimental diets: a commercial control and four diets supplemented with 0.75%, 1.5%, 3%, and 6% C. racemosa biomass. Uneaten feed was collected, dried for 24 h, and weighed to calculate feed intake (FI) and feed conversion ratio (FCR). The trial lasted until fish doubled their initial weight, followed by final sampling for histological analysis.

Results and discussion

No antibacterial or bacteriostatic effects were observed in the in vitro analyses, as inhibition halos were absent in all tested extracts concentrations against the studied bacterial strains. In contrast, fish fed 0.75% C. racemosa showed the highest final weight, significantly differing from the 3% group. A similar trend was observed for specific growth rate (SGR), although differences were not significant. Feed utilization improved at 0.75%, showing the lowest FCR and significantly outperforming the 3% group. Preliminary histology analyses revealed comparable liver steatosis, glycogen accumulation, peripancreatic fat, and hyperemia among treatments. Moreover, a tendency toward reduced steatosis (~50%) was observed in the 0.75% treatment compared to the control (not statistically significant), along with increased fold length, area and globet cell count in the anterior gut, which suggests improved physiological functionality. Overall, all treatments performed similarly to the control, indicating that inclusion of up to 6% C. racemosa does not impair growth or tissue integrity in gilthead seabream (Sparus aurata). However, additional analyses of tissues and plasma are ongoing to better understand the full potential of this ingredient as a functional additive for sustainable aquaculture.

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Figure 1. Growth performance and feed conversion ratio of juvenile gilthead seabream (Sparus aurata) fed the experimental diets. Columns with different superscripts indicate significant differences among treatments (p < 0.05).

Acknowledgment

This study has been funded by the Calypso projects (1/MAC/1/1.1/0088, Interreg MAC Programme 2021-2027) and Cliraqua (EAPA_0103/2024, Interreg Atlantic Area Programme 2021-2027).

References

Passos, R., Correia, A. P., Ferreira, I., Pires, P., Pires, D., Gomes, E., ... & Baptista, T. (2021). Effect on health status and pathogen resistance of gilthead seabream (Sparus aurata) fed with diets supplemented with Gracilaria gracilis. Aquaculture, 531, 735888.

Pratiwi, A. F., Satyantini, W. H., Mahasri, G., Mukti, A. T., & Isnansetyo, A. (2022). The administration of Caulerpa racemosa extract in feed of whiteleg shrimp (Litopenaeus vannamei) after infected by Vibrio parahaemolyticus. J Aquac Fish Health, 11(2), 193-200.

Ragunath, C., & Ramasubramanian, V. 2024. Effect of dietary seaweed Caulerpa racemosa on growth, biochemical, non-specific immunity, and disease resistance to Pseudomonas aeruginosa in Cirrhinus mrigala. The Journal of Basic and Applied Zoology, 85(1), 12.

Uddin, S. A., Akter, S., Hossen, S., & Rahman, M. A. 2020. Antioxidant, antibacterial and cytotoxic activity of Caulerpa racemosa (Forsskål) J. Agardh and Ulva (Enteromorpha) intestinalis L. Bangladesh Journal of Scientific and Industrial Research, 55(4), 237-244.