Mullet fish are common sights in coastal and estuarine environments worldwide. Found in shallow, brackish waters, these fish navigate the interface between freshwater rivers and the saltwater sea. They are recognized for a highly specialized feeding strategy that centers on consuming materials often ignored by other fish.
The Primary Diet: Detritus and Algae
Mullet are primarily detritivores and herbivores. The bulk of what a mullet consumes is detritus, which is decomposing organic matter mixed into the mud and sediment of the seafloor and riverbeds. This material consists of decayed plant fragments, microbes, and minute invertebrate remains, making it a low-quality but constantly available food source.
A significant part of their foraging is dedicated to grazing on microscopic plant life, such as benthic diatoms and microalgae films. These organisms form a nutrient-rich layer on the surface of rocks, submerged vegetation, and the upper layer of mudflats. The relatively low nutritional density of this food requires the mullet to process large volumes of material to extract sufficient energy for survival.
This preference for small, fixed, or decaying matter distinguishes them from many predatory coastal fish. By consuming this organic material, mullet play a functional role in cycling nutrients back into the ecosystem.
Specialized Feeding Apparatus
The mullet’s feeding method is a highly refined process tailored for scraping and filtering fine particles from the substrate. Their mouth is small, thick-lipped, and positioned slightly downward, which is ideal for sucking or scraping the surface layer of mud, sand, and rocks. This inferior mouth orientation allows them to efficiently target the microscopic algal and detrital films that coat the bottom.
Once the sediment and water are ingested, the fish utilizes a specialized filtration system located within its gill arches. Long, closely set gill rakers function like a sieve, separating the fine, edible organic particles from the surrounding water and sediment. These comb-like structures trap the microscopic food before the water is expelled through the gill openings.
The process of gathering this food involves ingesting large amounts of sand or mud along with the nutritious particles. The ingested sediment is not an accidental byproduct, but rather an integral component required for the next stage of digestion.
Unique Digestive System
To process a diet high in cellulose and abrasive sediment, the mullet possesses a unique internal adaptation: a muscular, gizzard-like stomach. This specialized stomach is structurally similar to the gizzard found in birds and is built with thick, muscular walls. This adaptation compensates for the lack of teeth capable of grinding tough plant matter before swallowing.
The sand and mud that the mullet intentionally ingests act as internal grinding stones within this muscular pouch. The strong contractions of the gizzard walls crush and triturate the ingested material, physically breaking down the cell walls of algae and detritus. This mechanical breakdown is necessary to release the limited nutrients from the low-quality food source, which might otherwise pass through the system undigested.
Following the gizzard, the mullet has a relatively long intestine, an anatomical feature common in fish that feed on plant material. This extended intestinal length provides a greater surface area and more time for the final absorption of the already mechanically processed nutrients.