Introduction
Flathead grey mullet (Mugil cephalus) is a catadromous, omnivorous fish species that has recently gained attention from researchers due to its potential as a sustainable, low-trophic-level candidate for aquaculture. Its omnivorous feeding habits and resilience to high temperatures make it particularly suitable in the context of climate change. For these reasons, the mullet represents an interesting model species for studying the interactions between environmental factors, such as temperature, growth performance, and feeding strategies. Understanding the effects of temperature is especially relevant in the current scenario of global warming. Optimizing feeding strategies in relation to environmental conditions is essential to improving aquaculture efficiency and sustainability. Among abiotic factors, temperature stands out as a key driver, significantly influencing metabolism, nutrient utilization, animal welfare, and gut health.
Materials and Methods
Two isoproteic experimental diets were formulated to contain two lipid levels (Diet 10% and Diet 15%) and were tested at two temperatures: 22 °C and 28 °C. Diets were administered to triplicate groups of 30 fish each (initial weight: 90.5 g) over a period of 100 days at both temperatures. During the trial, feed was provided to apparent satiation during a single 6 hour meal per day, and dissolved oxygen was maintained above 7.5 mg L⁻¹. At the end of the trial, final body weight (FBW), specific growth rate (SGR), feed intake (FI), and feed conversion ratio (FCR) were calculated. Samples for gut evacuation analysis were collected at 1, 3, 5, 7, 9, and 12 hours post-feeding, while samples for microbiota analysis were taken at 4 hours post-feeding. Differences among treatments and temperatures were considered significant at p < 0.05 (two-way ANOVA followed by Tukey’s test).
Results and Discussion
At the end of the trial, fish fed with 10% and 15% lipid diets at 28°C exhibited significantly higher final body weights compared to those fed the same diets at 22°C. A similar trend was observed for specific growth rate (SGR), with the exception that fish fed with 10% lipid diet at 22°C showed no significant differences when compared to those fed either lipids level at 28°C or the 15% lipid diet at 22°C. These findings indicate that fish reared at 28°C exhibited enhanced growth compared to those at 22°C, likely due to the warmer temperature being closer to the range (26–27°C) where improved growth performance has been reported in previous literature (Crosetti and Blaber, 2015). At 28°C, fish were presumably able to more efficiently utilize dietary nutrients to meet their energy demands, thereby supporting improved growth performance. In contrast, the reduced energy expenditure at 22°C may have limited nutrient utilization and growth. Regarding feed conversion ratio, fish fed with 15% lipid diet at 28 °C showed a tendency toward a lower FCR compared to all other treatments. However, fish fed with 10% lipid diet at 28 °C didn’t show significant differences in FCR across the different lipid levels or temperature conditions. Moreover, feed intake was significantly lower in fish fed with 15% lipids at both temperatures compared to those receiving the 10% lipid diet. These results suggest that flathead grey mullet exhibited superior feed conversion efficiency with the 15% lipid diet at 28°C, indicating minimized feed waste and enhanced nutrient utilization.
Conclusion
In conclusion, the growth of the mullet at 28°C remained consistent across both dietary treatments. However, considering feed conversion ratio and feed intake, fish exhibited improved growth when provided with a diet containing 15% lipids at this temperature. A comprehensive understanding of the protein and energy requirements of this emerging species at varying temperatures is essential for optimizing growth performance and developing effective aquaculture practices.
Acknowledgements
The project has received funding from the PRIN: progetti di ricerca di rilevante interesse nazionale – bando 2022; prot. 2022snlr4y. Mugil cephalus (linneus, 1758): the flathead grey mullet as a model for sex determination in fish with implications for aquaculture (acronym mugilsex)
References
Crosetti, D., Blaber, S.J.M. (Eds.), 2015. Biology, Ecology and Culture of Grey Mullets (Mugilidae). CRC Press, Boca Raton. https://doi.org/10.1201/b19927