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Home › Sea Life Facts › Marine Species › Vertebrates › Jawfish

Interesting Facts about Jawfishes

[Jawfish Phylum: Chordata] [Class: Actinopterygii] [Order: Blenniiformes] [Family: Opistognathidae]

Mouthbrooding in fishes refers to a process of gathering up fertilised eggs and keeping them safe inside the mouth until they hatch.

This section contains fun and interesting facts about 80 species of jawfish (Opistognathidae), such as where these remarkable mouthbrooders live, what they eat, and how jawfishes reproduce.

Geographical Range and Habitats of Jawfish

They are best known for their mouthbrooding habits and their burrow-digging nature.

But the best places to find jawfishes are tropical and subtropical seas, especially:

• Eastern Atlantic (Cape Verde, Canary Islands, West Africa)
• Western Atlantic (Bahamas, Caribbean Sea, Florida, Gulf of Mexico)
• Eastern Pacific (California, the Galápagos Islands, and Peru)
• Indo-Pacific (Eastern Africa, the Red Sea, Micronesia, and Polynesia)

They are typical bottom-dwelling marine fishes. Hence, some of the densest diversity of the jawfish species occurs across the Caribbean and most of the western and central portion of the Indian Ocean.

Jawfish prefer marine habitats that are shallow and near intertidal coastal zones, usually between two (2) metres and forty (40) metres deep.

They tend to flourish best near sand, rubble, and fossil hash rock substrates (smashed shells) where they can dig (and live inside) vertical burrows close to coral reef formations.

Interesting Fact: Jawfishes very rarely stray far from their selected microhabitats and the relative safety of their burrows. Instead, they are often seen hovering above the entrance of the excavation site, so they can scurry back inside if they feel threatened.

Jawfish Characteristics and Behaviour

Many jawfishes look quite similar to the goby fish family. But, in fact a jawfish is closer to being a blenny fish than any of the gobies.

They are all distinctive in their own way. But the appearance and behaviour of jawfish helps to identify them from other small vertebrate fishes.

For example:

The overall body shape is cylindrical and slender, which is ideal for reversing into a burrow. However, the head and mouth are much larger than fishes of a similar size.

Moreover, the downturned mouth of a jawfish creates a grumpy-looking expression of "disapproval". In fact, they use their extensible lower jaw to scoop up silty substrate and to store fertilised eggs during reproduction.

The cryptic colouration of most jawfishes helps them blend in with the seafloor colours that surround them. Hence, most are a mix of browns and grays with some mottled markings or patterns.

Jawfish Size

It is rare for any jawfish species to grow bigger than ten (10) centimetres long (4 inches). Yet, the biggest jawfish is Opistognathus rhomaleus and full grown adults can reach a total body length close to fifty (50) centimetres long (20 inches).

The frozen jawfish (genus Opistognathus cryos) is one of the smallest. Recently discovered in Taiwan, it measures less than seven (7) centimetres long (2.5 inches).

Fun Fact: The ecological role of jawfishes should not be underestimated. Not only does the continuous burrowing contribute to sediment turnover, often providing shelters for small invertebrates in abandoned burrows, they are also an important source of food for some of the large ambush predators, such as groupers and moray eels.

What Do Jawfish Eat?

Being typical carnivores means that most jawfish eat a lot of small invertebrate animals that wander near to their benthic burrows.

They also have a diet shaped by a "sit-and-wait" feeding style, patiently hovering outside their burrow for things like:

• Amphipods
• Benthic crustaceans
• Copepods
• Fish eggs
• Juvenile fishes
• Mysis shrimp
• Mollusk larvae
• Other small invertebrates
• Polychaete worms
• Small crabs

Pro Tip: Some aquarists keep jawfish as part of a fish keeping hobby, mostly for their burrowing traits and the male mouthbrooding behaviour. Most jawfishes kept in captivity will eat brine shrimp, mysis shrimp, and finely chopped seafood.

Types of Jawfish Species

How Do Jawfishes Reproduce?

It's a well-known fact that jawfish keep eggs in their mouth, but why do they do it? In fact, it is an important part of their reproductive strategies.

Jawfish Courtship Ritual

Generally, jawfishes are a monogamous species that either form long lasting pair bonds or they develop temporary pairs specifically for the breeding season.

The mating ritual begins when the male performs his courtship display close to the chosen nest site (his burrow).

Here's the thing:

Courtship involves some quick darting movements, a display of the open mouths, and sometimes a change in body colouration.

More often than not, spawning takes place as the sun is setting or during the night. After a female lays a clutch of her sticky eggs, the male goes ahead and fertilises them without any delay.

Unlike the open-substrate spawner strategy of many reef fishes, the male jawfish scoops up the fertilised eggs and stores them inside his mouth.

Jawfish Male Mouthbrooding

Only the male of the species will incubate the eggs in his mouth. He does so until they hatch, which usually takes at least five (5) days. During this brooding period:

• The male will not eat at all. Instead, he focuses on protecting the fertilised eggs.
• The male will aerate the eggs and try to keep them oxygenated by gently "churning" them inside his mouth.

Jawfish eggs hatch into planktonic larvae that drift in the open ocean (pelagic) for several weeks, helping to ensure a wide dispersal.

Once they have developed enough, juvenile jawfish will settle on a suitable sandy or rubble area and start digging their own burrows.

Threats and Predators

Jawfishes can be a territorial species, but they are also burrow-dependent. As a consequence, a number of natural predators and human-related pressures influence their long term survival rates.

In the wild, natural predators of jawfish are mainly ambush predators or opportunistic hunters that can dig them out of their burrow, such as:

• Groupers
• Lionfish
• Moray eels
• Octopuses
• Rays
• Sharks
• Snappers
• Wrasses

Other contributing factors for the decline in a few vulnerable areas include certain types of human behaviour (e.g. coral reef destruction and degradation, overfishing, marine pollution, and excessive 'wild-catch' for the aquarium trade).

Pro Tip: According to a 2012 assessment released by the IUCN Red List of Threatened Species, the conservation status of most jawfish species is "Least Concern" (LC).

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