What does flathead grey mullet eat?

Almost every angler who has failed to catch a mullet has failed for the same reason, and it is on this page rather than in a tackle box.

The flathead grey mullet is a detritivore. It feeds on decomposing organic matter, microalgae and the organic film coating sediment surfaces, ingesting sand and mud along with the food and grinding the mixture in a muscular, gizzard-like portion of the stomach. The gut is long, because extracting energy from that material is slow.

What that means is that the fish is not looking for an item of food. It is processing a surface. A discrete object presented in front of it — however well chosen — is not what its feeding behaviour is organised around, and the fish has no reason to treat it as food.

Both verified relationships describe this, and both use `consumes` rather than `preys_on`, because nothing here is hunted. That distinction is not pedantry: the graph previously had no way to state a non-predatory diet at all, and this species was one of the six left blocked because of it.

Juveniles are different animals in this respect, taking zooplankton before the adult feeding apparatus develops.

The ecological consequence is larger than the angling one. Detritivores move energy from the decomposition pathway back into the food web, and in estuaries — where mullet occur in quantity — that is a substantial part of why the system is as productive as it is.

The reputation of mullet as difficult is well earned and the explanation above is the whole of it: a grazing animal has no feeding response to a single item.

What anglers do about it follows directly, and it is unusually well reasoned for practitioner convention. The successful approaches present something of comparable texture and consistency to what the fish is already processing — bread in its various forms, and algae-based preparations — rather than something that imitates prey. In effect the angler is joining a grazing process rather than triggering a strike.

The second convention is location: mullet are drawn to places where organic material concentrates, and harbours, outfalls and weed-covered structure are fished for that reason rather than for cover.

Both are conventions rather than tested results, and both make more sense once the biology is stated. Mullet are also notably wary in the clear shallow water they favour, which compounds the difficulty and is a separate problem from the feeding one.

Both relationships are food categories rather than organisms, which is the correct granularity and not a shortfall. Neither establishes proportion, and in practice a feeding mullet takes detritus and living biofilm together in a way no diet study separates cleanly. Composition varies with sediment and location, and the juvenile zooplankton phase is a different diet not described by these relationships.