Mugil cephalus Linnaeus, 1758 (Mugiliformes: Mugilidae)
Species: cephalus, curema
Of the 17 genera and 66 species worldwide, the two that are native to Florida are the striped mullet (Mugil cephalus) and the white mullet (Mugil curema). Despite the fact that Mugilidae is primarily a marine family, all species of mullet are capable of living in various salinity levels. After reaching 1.6-2.8 inches in length (4-7 cm), a Mugil cephalus can withstand salinity levels from 0 parts per thousand (fresh water) to 75 parts per thousand (hypersaline water). Even so, Mugilidae are rarely found in a fresh water environment without access to the ocean (Bester, 2007, Hoese & Moore, 1998, Gilbert & Williams, 2002).
Because of their wide range of tolerable salinities, mugilidae must be able to find food in different habitats. Luckily, all species are omnivores, feeding on detritus (decaying organic material), epiphytes (small plant organisms growing on the exterior of larger plants), and polychaetes (sea worms). Juveniles smaller than 30mm in length are carnivorous, but later become reliant on detritus and epiphytic algae as their primary food sources. Their stomachs become gizzard-like and their intestines are 3-5 times their body length, indicating an herbivorous diet (Bishop & Miglarese, 1978). This diverse diet benefits both the mullet and the ecosystem. It is advantageous to mullet because they are able to utilize multiple food sources depending on what is most abundant. When detritus is too plentiful, it clouds the water and makes it hard for algae and other aquatic flora to photosynthesize. By eating plentiful detritus the mullet also allows the algae to grow. Similarly, if there is too much algae in the water, mullet will thrive on it and keep its population in check. By acting as a decomposer, primary consumer, and/or secondary consumer, mullet are very valuable to the food chain; even in high numbers they pose no real threat to the environment because they represent one of the most readily-available food sources for fish and predators of various sizes.
While mullet rarely exceed 6.5 cm, certain species have the potential to grow up to three feet! Individuals smaller than approximately 7.5 cm (depending on species) are considered juveniles or “finger mullet” and are often used for fishing bait. A mullet becomes sexually mature after three years or so and lives as an adult for four or five more years after that (four for males and five for females); the oldest recorded mullet was 13 years old (Texas Parks and Wildlife Department, 2005)!
Because mullet live in very shallow water, they are easy prey for birds and land-dwelling animals as well as aquatic predators. Due to the fact that the mullet grows slowly, they have adapted certain techniques in addition to a diverse diet to ensure the species’ survival. Schooling is a useful characteristic used by most fish because it not only allows more individuals to look out for predators and food, but also because it can confuse predators into thinking the school is a larger entity than a single mullet. It is not known whether olfaction is a sense used to school in mullet, but scientists have determined that sight plays a crucial role and that individuals can visually recognize conspecifics (Spotte, 1992). Jumping is a more uncommon technique used to avoid predation. Many types of fish will occasionally leap when being pursued, but mullet do it regularly as a preventative measure. By exiting the water, the light refraction of the surface makes the mullet leave the aquatic field of vision, confusing prospective consumers. Also because the diffusion of oxygen is many times greater in air than in water, mullet that are found in low-oxygen bodies of water (usually low or lacking in predators) can jump from the water (or gulp at the surface) to catch a quick breath (Cochran, 2003).
Mullet are also known to be hardy breeders and even though they usually spawn in shallow water, they have been noted spawning up to 32km offshore in water up to 40m deep. A population of M. cephalus in the Gulf of Mexico was once observed mating 80km offshore in water 1800m deep (Collins, 1985). Mating season depends on the species (M. cephalus mating occurs in fall and winter and M. curema spawns in spring). The eggs are a dull-tan color, transparent, and non-adhesive. A single female will lay one million to seven million eggs in a season. Eggs are left unguarded by their parents and hatch within a 36-50 hour incubation period depending on water temperature. Fry are 2.4mm at birth and have no mouth, paired fins, or branchial skeleton. They finish developing the physical characteristics of an adult by 16mm-20mm (Collins, 1985, Texas Parks and Wildlife Department, 2005).
Additional Historical Significance
Mullet have been an important food source for people in the Sarasota area since it was settled in the 1880’s by North Carolina fishermen. In 1879 mullet was the “fish most largely taken” from the west coast of Florida. Despite the fact that mullet are found worldwide, Florida’s populations seem to be the most desirable. Mullet in the western gulf and most areas of the world are supposedly oilier and have a “muddier” taste than those from the Florida area. Red tide, large numbers, and harsh weather caused the mullet fishing industry to be a fickle business. There was a boom in the fishermen’s prosperity from 1970 to 1995 when various Asian countries started serving the roe (eggs) as a delicacy with the finest roe coming from Florida. However in 1995 the state of Florida passed a law prohibiting the use of gillnets, which was the most effective way of catching mullet. The industry crumbled and most of the fishermen had to find new jobs. Thankfully, mullet populations seem to be safe. They are not listed as either endangered or vulnerable and continue to serve and help the ecosystem in Florida waters (Cortez: A Working Waterfront, 2007).
Striped Mullet (Mugil cephalus). 2005. Austin, TX: Texas Parks and Wildlife Department. http://www.tpwd.state.tx.us/huntwild/wild/species/mullet/
Cortez: A Working Waterfront. 2007. National Sea Grant Library. http://nsgl.gso.uri.edu/flsgp/flsgpm99004/flsgpm99004_part5.pdf
Bester, C. 2007. Striped Mullet Biological Profile. Florida Museum of Natural History.
Bishop, James M. & Miglarese, John V. 1978. Carnivorous Feeding in Adult Striped Mullet. American Society of Ichthyologists and Herpetologists. (705-707)
Cochran, Gary. 2003. Florida’s Fabulous Fishes (pp.46-47). Tampa, FL: World Publications
Collins, Mark R. 1985. Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (South Florida): Mullet. U.S. Fish and Wildlife Service. Biological report #82.
Gilbert, Carter R. & Williams, James D. 2002. Field Guide to Fishes (pp. 236-239). New York, NY: Chanticleer Press, Inc.
Hoese, H. D. & Moore, R. H. 1998. Fishes of the Gulf of Mexico (Second edition) (pp.172-173). Texas A&M University Press.
Spotte, Stephen. 1992. Captive Seawater Fishes (692-694). John Wiley & Sons, Inc.
Robins, C. Richard, Ray, G. Carlton & Douglas, John. 1986. A Field Guide to Atlantic Coast Fishes (212-213). New York, NY: Houghton Mifflin Company.