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Home › Sea Life Facts › Marine Species › Vertebrates › Scorpionfishes › Flathead

Facts about Flathead Fish (Platycephalidae)

[Flathead Phylum: Chordata] [Class: Actinopterygii] [Order: Scorpaeniformes] [Family: Platycephalidae]

One reason why these bottom-dwelling, ambush-predatory fishes are favourites with scuba divers is because they blend in with the sand and rubble surroundings.

This page contains facts and information about flatheads (Platycephalidae), such as where they live, what they eat, and how fish with a flat head reproduce.

Flatheads Habitat and Geographical Range

There are more than seventy (70) recognised species of flatheads and most of them inhabit the Western Indo-Pacific regions, especially:

• Indian Ocean (such as the Arabian Sea, the Bay of Bengal, Maldives, and Sri Lanka)
• Northern parts of Australia (a hotspot for diverse flatheads)
• Southeast Asia (e.g., Indonesia, Malaysia, the Philippine Islands)
• The Eastern Mediterranean Sea (thought to be due to the Lessepsian migration of marine species along the Suez Canal)

You should also catch sightings of these large benthic species in parts of the Great Barrier Reef, the Persian Gulf, East Africa, and the Red Sea.

They are a ray-finned marine fish that tend to spend most time sitting in wait around shallow coral reefs and rock formations (or shipwrecks) on the seafloor at depths between the shoreline and 100 metres.

But wait - there's more:

Even though they prefer geographical locations with marine or brackish water, some types of scorpionfish can live in rivers and estuaries.

The primary habitats for flathead fish are sandy and silty bottoms where they can bury themselves - leaving only their eyes and mouth exposed.

Pro Tip: The venomous Synanceia genus can produce overpowering protein-based neurotoxins. Even though the flathead fish spines also contain venom, especially on the dorsal fin and gill covers, it's less potent and unlikely to cause severe injury.

Flathead Characteristics and Behaviour

Some flathead adaptations and special features have helped them evolve into effective, bottom-dwelling, ambush predators.

The head is broad and flat with a triangular shape that enables them to bury themselves in sand, and then keep a low-profile. Some of the species also have bony ridges and spines located on top of the head.

They are highly camouflaged with various dark colours that match sand, silt, and oceanic rubble. Usually, only the mouth and eyes will be exposed as they sit still and wait to lunge at any passing prey.

Their large, upward-facing mouth is ideal for ambushing fish that swim directly above or for sucking small animals off the bottom. In fact, the flathead jaw opens upward somewhat like a trapdoor.

Here's the thing:

The eyes are high-set and mobile, and flathead fish are able to move them independently. Some species, such as crocodilefish, have eye flaps or elaborate pupils that break up the eye outline for enhanced camouflage.

Having a long and tapered body that gradually narrows to the tail is designed for short bursts of acceleration and sudden strikes of ambush predation.

Flatheads have two parts to the dorsal fins. The first section is short and spiny, sometimes with 8 or 9 spines. But the second dorsal is usually longer with soft rays.

However...

Even though the venom is less dangerous than the one found in true scorpionfishes, flatheads also have venomous spines, albeit 'mildly toxic' and not life threatening for humans.

Flathead Size and Weight

Onigocia grandisquama is one of the smallest flathead species, measuring about six (6) centimetres long. They're only found in a few places, such as the Gulf of Thailand and the Seychelles (Amirante Islands).

By comparison, the Dusky Flathead (Platycephalus fuscus) is one of the biggest. They can grow up to 1.2 metres long and weigh more than fifteen (15) kilograms.

What Do Flathead Fish Eat?

Physical structure and camouflage are vital for these ambush predators. Like lizardfish and scorpionfish, they are suction feeders that feed in a similar manner.

They capture prey with a sudden strike from their powerful jaw before sucking the food into their mouth. The daily diet of flathead fish usually includes:

• Bottom-dwelling invertebrates (e.g., sea snails)
• Cephalopods (cuttlefish, octopus, and squids)
• Crustaceans (such as crabs and mantis shrimps)
• Small bony reef fishes (especially gobies, silversides, and whiting)
• Polychaete worms (annelids)

Flathead Facts: A reduced swim bladder (which may also be completely absent in some flathead species) means they are poor swimmers over long distances. However, they can stay on the ocean floor for long periods of time with ease.

Types of Flathead Fish Species

Flathead Reproduction

The common reproductive strategies in flatheads (Platycephalidae) revolve around a process known as "broadcast spawning" that is usually triggered by lunar cycles or an increase in water temperature.

During these coordinated spawning events, males and females will release their eggs and sperm at the same time into the water column.

Females are extremely fecund (producing high numbers of eggs) and they tend to be much bigger and longer than the males.

Put another way, fertilisation and egg development will occur entirely in open water, and there will be no parental care.

So...

There is no elaborate pair bonding with flatheads. Instead, they move in small aggregations to shallow estuaries or nearshore sand flats. There may be some brief and subtle mating displays, such as side-by-side swimming, before they release their gametes.

Their eggs are tiny (less than 1 mm) and buoyant. The planktonic larvae floats for several weeks as it's dispersed over a large area by the prevailing currents.

After settling on the seabed, juveniles will be about two (2) centimetres long and they start adopting the familiar flathead characteristics of camouflage and body shape.

Predators of Flatheads

In their natural surroundings, most of the large coastal predators eat various species of flathead fish of the family Platycephalidae, including:

• Barramundi (Lates calcarifer)
• Groupers
• Sharks (especially great white sharks)
• Trevally

In addition, shorebirds (e.g., egrets, herons, pelicans) prey on juvenile flathead fish, and some marine mammals (e.g., dolphins, seals) are also involved in flathead predation.

Some of the contributing factors for a decline in some vulnerable areas include certain types of human behaviour (e.g. habitat loss due to coastal construction, excessive commercial and recreational fishing activities (including bycatch), marine garbage pollution, and warming seas).

Flathead Facts: The International Union for Conservation of Nature (IUCN) assessed most of the flathead phylum as "Least Concern" (LC).

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