Introduction
In recent years, environmental enrichment (EE) has attracted increasing attention in the field of animal science as a key strategy to improve animal welfare. Although environmental enrichment has been widely investigated in terrestrial species, its application in aquaculture remains relatively limited (Ojelade et al., 2022). Flathead grey mullet (Mugil cephalus) is a catadromous, omnivorous fish species that has recently attracted growing scientific interest due to its potential as a sustainable, low-trophic-level option for aquaculture. In the context of a rapid global changing understanding how sand-based environmental enrichment could enhance growth performance along with related physiological responses in flathead grey mullet is crucial for improving aquaculture sustainability.
Materials and Methods
An experimental diet was formulated to contain low fishmeal (3%) and soybean meal (10%) levels. Diet were administered to triplicate groups of 18 fish each (initial weight: 124.5���g) over a period of 60 days at both different environmental enrichment (three of these tanks had been filled with 15 kg of sand each). 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), feed conversion rate (FCR) and serum biochemistry were calculated. Differences among treatments were considered significant at p < 0.05 (Student's t-test).
Results and Discussion
Environmental conditions significantly influenced fish growth performance (Figure 1) and serum biochemistry (Figure 2) of flathead grey mullet. The presence of sand appears to significantly modulate final body weight and specific growth rate. Feed conversion rate and feed intake were not influenced by environmental conditions. Cortisol and lactate levels were lower in EE fish, indicating reduced stress, while total protein levels were higher, suggesting improved nutritional and physiological status (Goikoetxea et al., 2021). These patterns suggest enhanced energy allocation and reduced chronic stress under EE conditions. Consistent with the natural presence of sand in the diet of wild individuals (Whitfield et al., 2012), these findings support the hypothesis that sand inclusion in recirculating aquaculture systems may improve digestive efficiency, likely by promoting proper gizzard functionality.
Conclusion
Although the flathead grey mullet is not considered a high-value species, its wide environmental adaptability and potential for sustainable production make it a promising candidate for diversified aquaculture systems. The development of rearing protocols that minimise environmental impact while supporting biodiversity will be essential for ensuring that future aquaculture practices remain both productive and ecologically responsible.
Figure 1
Figure 1. Final body weight, specific growth rate, feed conversion rate and feed intake of flathead grey mullet at two environmental enrichments (with/without sand). Different letters indicate significant difference.
Figure 2
Figure 2. Cortisol, Lactate and Total Proteins of flathead grey mullet at two environmental enrichments (with/without sand). Different letters indicate significant difference.
References
Goikoetxea, A., Sadoul, B., Blondeau-Bidet, E., Aerts, J., Blanc, M.-O., Parrinello, H., Barrachina, C., Pratlong, M., Geffroy, B., 2021. Genetic pathways underpinning hormonal stress responses in fish exposed to short- and long-term warm ocean temperatures. Ecol. Indic. 120, 106937. https://doi.org/10.1016/j.ecolind.2020.106937
Ojelade, O.C., Durosaro, S.O., Akinde, A.O., Abdulraheem, I., Oladepo, M.B., Sopein, C.A., Bhadmus, A.S., Olateju, M., 2022. Environmental enrichment improves the growth rate, behavioral and physiological response of juveniles of Clarias gariepinus under laboratory conditions. Front. Vet. Sci. 9. https://doi.org/10.3389/fvets.2022.980364
Whitfield, A., Panfili, J., Durand, J.-D., 2012. A global review of the cosmopolitan flathead mullet Mugil cephalus Linnaeus 1758 (Teleostei: Mugilidae), with emphasis on the biology, genetics, ecology and fisheries aspects of this apparent species complex. Rev. Fish Biol. Fish. 22. https://doi.org/10.1007/s11160-012-9263-9