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Biology of the Mullet

Click a marker above to learn about the mullet and its anatomy.

Adipose Eyelid: As they mature, mullet grow an adipose eyelid. This is a transparent fatty tissue covering the eye, which leaves a narrow slit over the pupil.

Dorsal Fins: Mullet are one of the few fish species with two dorsal fins. They are considered a ray-finned fish, because the fins are composed of webs of skin supported by bony spines, rather than fleshy lobed fins. The mullet’s first dorsal fin contains 5 sharp spines, while the second has 8 soft rays.

Anal Fin: One of the easiest ways to identify a striped mullet is by the number of anal fin rays. The striped mullet’s fin has 8 rays, whereas the white mullet has 9.

Gizzard: Mullet have strong stomachs, similar to gizzards, and long intestines, allowing them to thrive on a primarily vegetarian diet.

Mouth: Mullet have a distinctively shaped triangular mouth with several rows of small teeth.

Gill Rakers: Typically, fish use their gill rakers to filter out debris from water as it passes over their gills while breathing. For mullet, they serve an additional purpose, allowing them to filter out things they want to eat. This includes algae, plankton, and various other vegetation.

Lateral Line: Mullet do not have an obvious lateral line - the organ most fish use to detect variations in water currents.

Eyes: Two bulbous eyes on stalks sit either side of the rostrum. These are compound eyes which have panoramic vision and are very good at detecting movement.

Chela: The first two pairs of pereiopods have claws or chela. The chela can grasp food items and bring them to the mouth. They can also be used for fighting and grooming.

Striped Mullet

Mugil cephalus

Distinctive Features:

The mullet’s body is roughly torpedo-shaped with a round head and small mouth with inconspicuous teeth and a blunt nose. The lips are thin, with a bump at the tip of the lower lip. Pectoral fins are short, not reaching the first dorsal fin. The origin of the second dorsal fin is posterior to the origin of the anal fin. The lateral line is not visible.

This mullet is often confused with the white mullet, Mugil curema. However, the white mullet has scales extending onto its soft dorsal and anal fins while the striped mullet does not. They may also be identified by the anal ray fin count — 8 for the striped mullet and 9 for the white mullet.

Coloration:

The body is grayish olive to grayish brown, with olive-green or bluish tints and sides fading to silvery white towards the belly. Dark longitudinal lines are formed by dark spots at the center of each scale on the upper half of the body, and run the length of the body. Young fish smaller than 6 inches (15 cm) in length lack stripes. There is a large dark blotch at the base of the pectoral fin. The pigmentation in the iris is dispersed and brown, a character that also helps to distinguish it from White Mullet.

Size, Age and Growth:

The maximum recorded length of the striped mullet is 47.2 inches (120 cm), with a maximum weight of 17.6 pounds (8 kg). Lifespan is reported to range somewhere between 4 and 16 years. Maturity is attained at approximately 3 years of age, corresponding to lengths of 7.9-11.8 inches (20-30 cm). Females mature at a slightly larger size than males. Growth rates along the gulf coast of Florida increase from west to east, from the panhandle along the peninsula, likely due to the temperature increase. Most growth occurs during the spring and summer months. Adults grow at a rate of 1.5-2.5 inches (3.8-6.4 cm) per year. Females are larger and grow faster than males of the same age.

Mullet in net

Food Habits:

Mullet are diurnal feeders, consuming mainly zooplankton, dead plant and marine animal matter. Mullet have thick-walled gizzard-like segments in their stomach along with a long gastrointestinal tract that enables them to feed on many of the things in their diet. They are an ecologically important link in the energy flow within estuarine communities. Feeding by sucking up the top layer of sediments, striped mullet remove dead plant and marine animal matter and microalgae. They also pick up some sediments which function to grind food in the gizzard-like portion of the stomach. Mullet also graze on epiphytes and epifauna from seagrasses as well as ingest surface scum containing microalgae at the air-water interface. Larval striped mullet feed primarily on microcrustaceans. One study found copepods, mosquito larvae, and plant debris in the stomach contents of larvae under 35mm in length. The amount of sand and other food matter in the stomach contents increases with length indicating that more food is ingested from the bottom substrate as the fish matures.

Mullet Roe

Reproduction:

The striped mullet is catadromous, that is, they spawn in saltwater yet spend most of their lives in freshwater. During the autumn and winter months, adult mullet migrate far offshore in large aggregations to spawn. In the Gulf of Mexico, mullet have been observed spawning 40-50 miles (65-80 km) offshore in water over 3,280 feet (1,000 m) deep. In other locations, spawning has been reported along beaches as well as offshore. Estimated fecundity of the striped mullet is 0.5 to 2.0 million eggs per female, depending upon the size of the individual.

The eggs are transparent and pale yellow, non-adhesive, and spherical with an average diameter of 0.72mm. Each egg contains an oil globule, making it positively buoyant. Hatching occurs about 48 hours after fertilization, releasing larvae approximately 2.4mm in length. These larvae have no mouth or paired fins. At 5 days of age, they are approximately 2.8mm long. The jaws become well-defined and the fin buds begin to develop. At 16-20mm in length, the larvae migrate to inshore waters and estuaries. At 35-45mm, the adipose eyelid is obvious, and by 50mm it covers most of the eye. At this time the mullet is considered to be a juvenile. These juveniles are capable of osmoregulation, being able to tolerate salinities of 0-35 ppt. They spend the remainder of their first year in coastal waters, salt marshes, and estuaries. In autumn, they often move to deeper water while the adults migrate offshore to spawn. However, some young mullet overwinter within the estuaries. After this first year of life, mullet inhabit a variety of habitats including the ocean, salt marshes, estuaries, and fresh water rivers and creeks.

Mullet Life Cycle:

Mullet spawn in salt water. Once hatched, the larvae make their way toward the coast and the juveniles settle in lower salinity water. They later school to freshwater estuaries where they grow to adults. In Florida, adults begin to spawn in the early fall October through January, returning to deeper salt water to spawn, as they cannot spawn in freshwater.

Includes excerpts from Florida Dept. of Natural History

Mullet Mavens