Mullet fish are primarily bottom-feeders that eat organic detritus, microalgae, and the countless tiny organisms living in and on mud and sediment. Unlike the predatory fish most people picture, mullets make their living by grazing on the thin film of life coating the ocean and estuary floor, functioning more like underwater lawnmowers than hunters. Their diet shifts dramatically over a lifetime, and the way they extract nutrition from what looks like plain mud is one of the more underappreciated feats in coastal ecology.
What Adult Mullets Actually Eat
The flathead grey mullet (Mugil cephalus), the most widely distributed and studied member of the mullet family, feeds mainly on organic matter, detritus, and benthic microalgae. Mixed in with that material are foraminiferans (tiny shelled organisms), filamentous algae, protists, meiofauna, and small invertebrates.1Aquaculture. Ontogeny of the digestive system and eye of reared flathead grey mullet, Mugil cephalus (Linnaeus, 1758), and evaluation of lipid deposition in the liver according to the feeding protocol If you opened a mullet’s stomach, you would find a slurry of fine sediment particles, algal fragments, bits of decaying plant material, bacteria, and the microscopic animals that colonize all of it. The mix varies depending on where the mullet is feeding, but organic detritus and microalgae consistently dominate.
This puts mullets in an unusual category. Most fish of comparable size are either active predators chasing smaller fish and crustaceans, or filter feeders straining plankton from open water. Mullets do neither. They scrape, suck, and sift the bottom, extracting calories from material that most other fish ignore entirely. The ecological term for this is “detritivore,” and mullets are among the best-known detritivorous fish in coastal waters worldwide.
How Mullets Pick Through Mud
What looks like indiscriminate bottom-sucking is actually a surprisingly selective process. Research using radioactive phosphorus tracers and particle-size analysis showed that striped mullet strongly prefer very fine sediment particles when feeding from the bottom. These fine particles turn out to be far richer in absorbed organic material and in the bacteria, protozoa, and other microorganisms that cling to them than the coarser sand grains the mullet rejects.2Limnology and Oceanography. THE ECOLOGICAL SIGNIFICANCE OF FINE PARTICLE SELECTION BY THE STRIPED MULLET MUGIL CEPHALUS The result is that the organic content of what ends up in the mullet’s stomach is substantially higher than the organic content of the sediment it was feeding from.
Think of it like panning for gold, except instead of gold the mullet is concentrating the nutritious fraction of the mud. A mouthful of estuary sediment might be mostly mineral sand and silt with a thin coating of organic material, but the mullet’s mouth and gill apparatus sort and reject the larger, less nutritious particles while retaining the fine organic-rich fraction. This selectivity is key to how mullets survive on what seems like an impossibly low-quality food source. They are not eating mud; they are extracting the living film on and between the mud grains.
How Diet Changes as Mullets Grow
A mullet larva and a mullet adult live completely different dietary lives. In their earliest days, mullet larvae are planktonic feeders, drifting in open water and eating tiny zooplankton and phytoplankton much like most other larval fish. As they grow into larger juveniles and then adults, they shift toward the bottom-feeding, detritus-heavy diet described above.1Aquaculture. Ontogeny of the digestive system and eye of reared flathead grey mullet, Mugil cephalus (Linnaeus, 1758), and evaluation of lipid deposition in the liver according to the feeding protocol
What is interesting is why this transition happens. You might assume a fish switches food sources because its mouth or gut physically changes shape and forces a new feeding strategy. Research suggests the opposite for mullets: the dietary shift is driven by a change in feeding behavior, not by a physical modification of the feeding apparatus.1Aquaculture. Ontogeny of the digestive system and eye of reared flathead grey mullet, Mugil cephalus (Linnaeus, 1758), and evaluation of lipid deposition in the liver according to the feeding protocol The juvenile mullet could, in principle, keep eating plankton, but it chooses to start feeding from the bottom instead. This behavioral plasticity may explain why mullets as a group have been so successful across such a wide range of coastal habitats around the world.
By the time mullets reach adulthood, the planktonic phase of their diet is long gone. Adults are committed detritivores, and their digestive system has adapted to handle a steady diet of low-calorie, high-bulk material in ways that set them apart from most bony fish.
The Gizzard and a Very Long Gut
If you have ever heard someone say mullets have a gizzard, it is true, and it is genuinely unusual. Most fish do not have gizzards. Mullets are one of a relatively small number of fish lineages that evolved a muscular, thick-walled stomach section that functions much like a bird’s gizzard, grinding food mechanically before it moves further down the digestive tract.3PubMed Central. True grit? Comparative anatomy and evolution of gizzards in fishes Sand and grit swallowed along with organic material get pressed and churned against the stomach walls, helping to break down algal cell walls, detrital clumps, and the tough outer layers of microorganisms that would otherwise pass through undigested.
Mullets also have an exceptionally long intestine relative to their body length. This is a common trait across detritivorous animals, whether fish, birds, or mammals. When your food is low in caloric density, you need more gut surface area and more transit time to squeeze every bit of nutrition out of it. A predatory fish eating concentrated protein from other animals can afford a short gut, but a mullet processing mouthful after mouthful of algae-laced silt needs the extra length.
Together, the gizzard and the elongated intestine make mullets efficient at a feeding strategy that would starve most similarly sized fish. They can thrive in environments where the primary food resource is the microbial and algal communities coating sediment surfaces, something few competitors can exploit as effectively.
Where and When Mullets Feed
Mullets are found in estuaries, lagoons, coastal bays, and the shallow nearshore waters of tropical and temperate oceans on every continent except Antarctica. Estuaries are their primary feeding grounds, and for good reason: the mixing of freshwater and saltwater in estuaries creates nutrient-rich conditions that support thick microbial mats, algal films, and dense accumulations of organic detritus on the bottom. For a fish that eats exactly those things, estuaries are an all-you-can-eat buffet.
Feeding habits shift with the seasons and with migration. Mullets are well known for their coastal migrations, and their feeding intensity changes as they move between habitats. In southern Brazil, for instance, local ecological knowledge and scientific study both describe mullets feeding actively in estuaries but also feeding in the open marine environment during migration, likely to meet the energy demands of both travel and reproduction.4Neotropical Ichthyology. Local ecological knowledge of fishers about the life cycle and temporal patterns in the migration of mullet (Mugil liza) in Southern Brazil Female mullets in particular need extra protein and lipids during the period when their eggs are developing.
In cooler months, some mullet populations reduce feeding significantly or stop eating almost entirely. Fishers in subtropical and temperate regions have long observed that mullets caught during winter migration runs tend to have emptier stomachs than those caught in summer feeding grounds. This is consistent with what researchers see in other migratory fish: when the priority shifts to reproduction and movement, feeding takes a back seat.
What Mullets Eat in Aquaculture
Mullets have been farmed for centuries in various parts of the world, particularly in the Mediterranean, the Middle East, and Southeast Asia. Their willingness to eat low on the food chain makes them appealing for aquaculture because you do not need to feed them expensive fishmeal-heavy diets the way you would with carnivorous species like salmon or sea bass.
Researchers have tested a range of plant-based and algae-based feeds for captive mullets. One approach that has shown particular promise uses the green seaweed Ulva (commonly known as sea lettuce) as a major feed ingredient. In trials with striped mullet fingerlings fed diets containing different levels of Ulva meal, the best weight gain and feed efficiency came from a diet containing about 20% Ulva meal alongside a protein content of roughly 40%.5Aquaculture Research. Growth enhancement and muscle structure of striped mullet, Mugil cephalus L., fingerlings by feeding algal meal-based diets A separate yeast-based diet enriched with vitamin E performed comparably well. These results underscore the mullet’s natural affinity for algae and its ability to thrive on feeds that would be nutritionally inadequate for most farmed fish.
In traditional polyculture systems, mullets are sometimes raised alongside other species in ponds or enclosed lagoons. The mullets graze on the algae and organic debris that accumulate naturally on the pond bottom, effectively cleaning the system while growing to market size. This makes them valuable not just as a direct food product but as a biological maintenance crew in mixed aquaculture operations.
The Mullet Family Beyond the Grey Mullet
When people say “mullet fish,” they usually mean the flathead grey mullet, but the family Mugilidae contains dozens of species spread across the globe. While the broad dietary strategy is consistent across the family, not every mullet species eats exactly the same things in exactly the same proportions. Some lean more heavily on filamentous algae, others take in more animal material in the form of tiny worms and crustaceans, and the balance depends partly on what is available in the local habitat.
The white mullet (Mugil curema), for instance, is frequently found in the same estuaries as the flathead grey mullet but may show subtle differences in which microhabitats it feeds in and what proportion of animal versus plant material ends up in its gut. These differences can matter ecologically because they reduce direct competition between species sharing the same stretch of estuary. Two species feeding side by side but emphasizing slightly different food fractions can coexist more easily than if they were eating identical diets.
Despite these differences, all mullet species share the core adaptation: they are built to process large volumes of low-quality food from the bottom. The gizzard, the long gut, and the fine-particle selectivity are family-wide traits, not quirks of a single species.
Microplastics and the Cost of Bottom Feeding
The same feeding strategy that makes mullets efficient detritivores also makes them particularly vulnerable to swallowing microplastics. Tiny plastic fragments and fibers settle into the sediment and mix with the organic particles that mullets actively select for. A study comparing wild flathead grey mullets with captive ones found that 60% of wild mullets had ingested microplastics, averaging about four plastic items per fish. By contrast, only about 17% of captive mullets had any microplastics, averaging roughly 0.2 items per fish.6PubMed Central. Microplastic Contamination of Wild and Captive Flathead Grey Mullet (Mugil cephalus)
The most common plastic items found were small fibers, predominantly green in color and under 2 millimeters in size. Polypropylene accounted for the largest share of the plastic types identified, followed by polyethylene.6PubMed Central. Microplastic Contamination of Wild and Captive Flathead Grey Mullet (Mugil cephalus) These are the two most widely produced plastics on the planet, found in everything from packaging to fishing gear to synthetic clothing fibers that wash out of laundry machines and eventually reach coastal sediments.
The stark difference between wild and captive fish makes the mechanism clear: it is not that mullets are especially attracted to plastic. They simply cannot distinguish plastic particles from the organic detrital particles they evolved to target. A fiber the same size and shape as a bit of decomposing seagrass gets swept up in the same mouthful. For a fish that feeds by vacuuming fine particles from sediment, microplastic contamination is an almost unavoidable consequence of living in polluted waters.
Why Mullets Matter to Fishers and Ecosystems
Mullets occupy a peculiar niche in coastal food webs. By feeding on detritus and microalgae at the very bottom of the food chain, they convert organic material that most fish cannot use into fish biomass that predators higher up the chain absolutely can. Snook, tarpon, sharks, dolphins, pelicans, and ospreys all feed heavily on mullets. In many coastal ecosystems, mullets are the primary link between the microbial decomposer community and the charismatic predators that people actually notice.
For recreational and commercial fishers, mullets serve double duty. They are caught directly for food in many parts of the world, particularly in the Mediterranean and parts of Asia and Latin America, where mullet roe (bottarga) is a prized delicacy. And they are used widely as bait for catching larger game fish. The role of mullets as both a food fish and a bait fish means their populations matter to a broad range of people who may never think about what the mullet itself was eating.
Their detritivorous feeding also has a direct physical effect on their environment. By constantly disturbing and reworking sediment, mullets help cycle nutrients through the water column. Organic matter that would otherwise stay buried in the mud gets processed through the mullet’s gut and released in a form more accessible to other organisms. In shallow lagoons and estuaries with high mullet densities, this bioturbation can measurably influence nutrient dynamics. The fish are not just living in their habitat; they are actively reshaping its chemistry through the simple act of eating.
Mullets as Bait and What They Bite On
If you fish with mullets as bait, you already know that a fresh-cut mullet chunk will attract nearly every predator in the estuary. But if you are trying to catch a mullet itself, the task is notoriously frustrating. Mullets do not bite hooks readily because they are not predators looking for prey items. You are essentially trying to hook a fish whose natural diet is microscopic particles scraped off mud.
Anglers who target mullets directly use techniques adapted to this reality. Tiny hooks baited with bits of bread, dough, or algae sometimes work. Cast nets are far more common and effective. Some fishers use chum made from oatmeal or bread to attract mullets into shallow water where they can be netted. In parts of Florida and the Gulf Coast, cast-netting schools of mullet near the surface is a time-honored tradition, and the fish are valued both for eating and for use as cut bait.
Mullets do occasionally take a hook, especially when small pieces of shrimp or worm are presented near the bottom. Juveniles are somewhat more willing to bite than adults, likely because their diet still includes a higher proportion of small invertebrates. But even experienced mullet anglers will tell you that patience and a cast net outperform a rod and reel when the target is a committed detritivore that would rather suck algae off a rock than chase anything resembling conventional bait.