Have you ever walked on a bridge over the water and seen a circular congregation of fish near shallow water? There are many possibilities of what they could be, but chances are, those fish are a school of mullet. Here in Florida, we have two species of mullet that we commonly encounter: the striped and white (Mugil cephalus and Mugil curema, respectively). These fish are super cool, and for many, delicious (mullet is a popular ingredient of smoked fish dip).
Mullet are euryhaline and eurythermal marine fish (Muhlia-Almazan et al. 2003). This means that mullet can live in areas with both a great range of temperature as well salinity. Mullet often find their way to freshwater bodies, like rivers. Because of these qualities, the distribution range of the mullet is quite large. Mullet live off of both Florida coasts, as well as both coasts of the United States.
These mullet average 8-12 inches in size and are covered in silver scales, with a dark spot on their pectoral fins, and a dark margin on their second dorsal fin and tails. The mullet spawn or lay their eggs at sea, and utilize estuaries as their nursery areas. Mullet feed on detritus (waste material) and micro and macroalgae. To do this, sometimes they ingest sand or silt (Fernandez et al. 2014).
The reason that I wanted to write about the mullet is because of the fantastic schooling aggregations that they form. Schooling behavior is an adaptation so that a single fish can be avoid being eaten and to confuse predators. We’ve seen examples of this in mainstream movies, most notably, Finding Nemo. What you might not know about schooling is that it can also be used to detect food sources more easily, achieve a maximum rate of energy intake, and escape a variety of predators (Pitcher 1986).
A terrific study conducted by Delgado de Carvalho et al. 2007 in Brazil indicated that white mullet have three main ways of schooling, which are directly tied to particular feeding habits: stationary, slow, and fast movements. Here are the main criteria of each:
- Stationary: Mullet form a loose group, face different directions, members are usually feeding. The school shape is circular and stays close to the bottom. These are often in nearshore habitats where the water is shallow.
- Slow-moving: This school is a more cohesive but still loose aggregation. These fish face the same direction, and more often than not, are feeding. They are distributed throughout the water column and eating despite their respective position.
- Fast-moving: This school is aligned, with synchronized movements. They are rarely feeding. These elliptical or circular-shaped schools form in mid-water, although sometimes they swim near the surface.
The next time that you’re near the water, I want you to pay close attention to the schools of mullet swimming around. Try to identify their type of schooling behavior, and think about what might be going on under the surface to provoke it. What might some other pros/cons be of hanging out in those types of groups?
Delgado de Carvalho, C., Marocco Corneta, C., Sanches Uieda, V. 2007. Schooling behavior of Mugil curema (Perciformes: Mugilidae) in an estuary in southeastern Brazil. Neotropical Ichthyology, 5(1), pp 81-83.
Fernandez, W., Dias, J., Boufleur, L., Amaral, L., Yoenama, M. 2014. Bioacumulation of trace elements in hepatic and renal tissues of the white mullet Mugil curema Valenciennes, 1836 (Actinopterygii, Mugilidae) in two coastal systems in southeasthern Brazil. Nuclear Instruments and Methods in Physics Resarch B 318, 94-98.
Muhlia-Almazan, A., Mulia-Melo, A., Alcaraz, G. 2003. Responses to temperature and salinity by white mullet mugil curema: possible explanation for the population decrease in Baja California Sur. Marine Freshwater Behavior Physiology, Vol. 36, No. 3, pp. 177-185
Pitcher, T. 1986. Functions of shoaling behavior in teleosts. The Behavior of Teleost Fishes. Pp. 294-337.