Mullets, you say? Many of us, even those already engaged in aquaculture, aren’t too familiar with them – but some of the most famous civilisations loved eating and even farming these delectable silver fish.
Mullets, together with carps, were some of the first fish to be cultured in ponds and still hold a dominant role in both Mediterranean and Middle-Eastern food cultures. Egyptian hieroglyphics depict locals catching and farming mullets a staggering 4,300 years ago.
And, throughout history, the fish have not been confined to any social class: records indicate that mullets were the favourite fish of ancient Roman nobles, while also playing a key role in the food culture of coastal aboriginals in Australia. In Hawaii mullet were so popular they were named the “king fish” or 'ama'ama. Today mullets are still highly prized, even becoming the ‘most expensive food fish’ in the Philippines, selling for over US$100 per kilogram.
There are over 70 species of mullet distributed across the globe, most preferring coastal waters. They are considered euryhaline species, meaning they can handle salt, brackish and fresh water equally well. They are very efficient in converting food to body mass. Even better, they are predominantly herbivorous and can filter zooplankton from the water, earning them an overall trophic score of 2.0.
Other benefits include their high-quality flesh and eggs, which are considered a delicacy. Fisherfolk regularly joke that mullets are the best fish you never caught. Fisherman Eric Williams noted in his blog that: “Once you’ve had your first smoked mullet, you’ll never go back. Trust me.”
These accounts reveal that mullets are highly marketable fish which can handle a wide variety of culture conditions. They are also excellent candidates for sustainable aquaculture due to their herbivorous feeding behaviour. As Nash and Shehadeh summed up back in 1980, “the Mugilidae have the brightest future of all marine and brackish-water finfish in the developing technology of aquaculture.” And as soon-to-be Dr Luciano Vílchez-Gómez, who was interviewed for this article explains: “Mullets are the past, present and future of aquaculture.”
A surprising mix of countries – including Indonesia, Korea, Israel, Italy and Egypt – currently make up the list of top mullet-producing nations. Together, aquaculture producers in these countries are responsible for an annual output of almost 200,000 tonnes. Egypt has for many years been the top producer of mullet, producing about 150,000 tonnes in 2016.
Culture systems and methods
Most mullets are cultured in Egypt’s delta region where a mix of farming methods are used for various salinity gradients. About 75 percent of the farmers use simple earthen ponds, but some fish are also cultured in floating cages, in rice fields and in desert systems which have been integrated with agriculture. Most of the culture is done extensively to semi-intensively. Surprisingly, all stocked juveniles still originate in the wild.
In 2016 for example, a staggering 92.9 million fry were caught in the wild. The practice has raised serious concerns about overfishing. However, collection employs large numbers of coastal residents who often have no alternative means of earning a living, making it difficult to prohibit the practice. All told, these collectors target three main species of mullets, with the flathead grey mullet (Mugil cephalus) by far the most popular. Collectors of flathead grey mullet receive approximately US$17.30 per 1,000 fry.
Although the national government of Egypt and organisations like the United States Agency for International Development (USAID) have assisted in the development of hatchery protocols and have funded the construction of a hatchery, it is very hard to compete with the significantly lower prices of wild-caught fry. Prices of hatchery-reared mullets are up to 15 times that of wild-caught fry, so optimisation is sorely needed to make the technology more commercially feasible.
Without strict controls, the fisheries of these wild fry are bound to collapse within a few years. Hatcheries are the solution and investors can fund further research and development. As a plus, hatchery-reared fry offer many advantages, performing much better in captive conditions, having more uniform growth rates and often carrying far fewer pathogens – eventually resulting in better returns for farmers.
Hatchery production can also contribute to improving the health of overfished stocks through so-called stock-enhancement programmes, wherein large numbers of fry are released back into the wild. An NOAA-backed restocking project in Hawaii is performing well, though questions are being raised about possible competition between wild and released fingerlings.
The European Union (EU) and its member states have also realised the future potential of mullet aquaculture in the Mediterranean. The flathead grey mullet has been selected as one of six priority species by the EU-funded Diversify project.
The five-year initiative, which has just ended, was driven by its objective of advancing the knowledge and practical application of the culture of new and emerging finfish species to satisfy an expanding European market with a variety of sustainably farmed fish.
The project explains that: “There is increasing interest in the culture of the omnivorous grey mullet as a high-quality source of protein and as a species which requires little to no dietary fish meal. Moreover, the salted and dried roe (bottarga) from gravid females is considered a highly prized delicacy in the southern Mediterranean and Asia, greatly adding value to the culture of the species.”
The project was able to further work out the hatchery production of mullets and overcome the other unknowns for the species. One of the main barriers was successfully spawning quality eggs in captivity. Researchers based at Israel Oceanographic and Limnological Research in Eilat, Israel, have worked on overcoming reproductive dysfunction for captive individuals and they have developed an expanded tool box for successful breeding. A second issue which needed to be tackled was the weaning of grey mullet fry, which the project successfully bridged as well.
To move the sustainability of the feed input a step further, Luciano Vílchez-Gómez, who besides being a lawyer and having a degree in aquaculture, has been working on utilising waste streams as part of his PhD in biotechnology at the University of Murcia.
As he explains: “We are throwing away many resources each day, with a high environmental cost, while recycling of by-products can be perfectly achieved by microbial eaters such as mullet.”
As he passionately continues: “Mullet have their ecological feeding habits close to natural carbon recycling as they are situated very low in the trophic chain.” This makes them a perfect candidate for his research trials in which he has been using yeast from local beer breweries to feed mullets and breams. The results are extremely promising and will be presented during his thesis defence in March 2020.
The way forward
In the meantime, the Egyptian government has released a proposal for a large hatchery in the Sinai Desert with a planned annual production capacity of 10 million fry. Everything seems to be in place for the private sector to capitalise on this opportunity to commercialise the sustainable production of mullets.
From being farmed by the ancient Egyptians and Romans, Mullets might finally be ready for the future. But who will take the lead?