Marine aquaculture sustainability relies on finding suitable alternatives to dietary fish oil (FO) and fish meal (FM) for aquafeeds, due that most marine fish species cultured are placed high in the trophic chain, contrary to freshwater ones. In this sense, mullets are great candidates for marine aquaculture diversification due to their euryhaline, eurythermal and low-trophic nature, allowing more sustainable culture practices to be implemented.
The Mugilidae family comprises up to 71 species distributed in temperate regions worldwide. Its cultivation has been done for centuries by different cultures, in many cases by taking advantage of their migrating behaviour from the sea to coastal lagoons or estuaries and vice versa, facilitating them to be stored in confined areas. This adaptability to different salinity environments has also allowed the cultivation of many mullet species from freshwater to high-salinity water.
These attributes have increased the interest in mullets in recent years, and numerous studies from different regions have addressed some Mugilid’s gaps in knowledge around the world. The state of the art in Mugilidae reproduction, larval rearing, and fattening is summarized below:
Reproduction
Mullets are oviparous bisexual teleosts with external fertilization and development. The females have group synchronous ovaries and usually only spawn once yearly. Mullet species with the same habitat distribution usually have different spawning seasons throughout the year.
Like other marine teleosts, some mullet species present reproductive dysfunctions in captivity, which has produced that mullet aquaculture has traditionally been supported by wild fry collection . However, in recent years, the breeding of Mugilidae has been developed through the improvement of hormone-therapy protocols (for instance, LH-RH analogues and dopaminergic inhibitors) and culture management protocols, allowing the obtention of viable eggs and larvae at a commercial scale in some species.
Larval rearing
Compared with well-established aquaculture species, there is still a vast knowledge gap related to larval rearing, ontogeny, and nutrition requirements of grey mullets. Size at hatching, yolk sac and oil globule size, reabsorption patterns, moment of mouth opening and mouth size, etc., vary significantly among mullet species, affecting the different rearing protocols that must be implemented and studied for each species to optimize producers’ cost and effort.
Fattening
Mullets are very adaptable species; therefore, cultivation conditions and feed formulas are very adaptable to a wide range of conditions. For instance, salinity and dietary lipid sources can be efficiently modulated as a tool to optimize growth, feed utilization and lipid metabolis m to improve the synthesis of long-chain polyunsaturated fatty acids such as ARA, EPA and DHA.
Overall, although much research in different fields still needs to be done, mullets are promising species in the prospect of blue growth and sustainable aquaculture, which assessment must be done with a multi-species and multi-areas approach.