Fact Sheet: Blowfish

Common blowfish Torquigener pleurogramma (Illustration © R.Swainston/www.anima.net.au)

Size and distribution

The common blowfish – also called the weeping toadfish or banded toadfish – can grow up to 22 centimetres long. It has dark vertical ‘tear’ lines down its cheeks and a dark brown line along its side.

The common blowfish is mainly found along WA’s lower west coast but is also sometimes seen as far north as Coral Bay and as far east as Esperance. It is also found in Queensland, New South Wales and South Australia.

A relative of the common blowfish, called the silver toadfish or northwest blowfish, inhabits northern Australian waters and is occasionally seen off WA’s lower west coast, as far south as Cape Naturaliste near Dunsborough. The silver toadfish is much larger than the common blowfish – growing up to 88 centimetres long, and has a silvery stripe down its body and a greenish-coloured back with dark spots. It is an aggressive species that can inflict serious bites.

Common blowfish are a marine species – found in the ocean and in the saline water of estuaries. In the Swan River Estuary in Perth, blowfish are most abundant near the estuary mouth at Fremantle, moderately abundant in the middle of the estuary and rare in the upper estuary. They usually prefer shallow water up to four metres deep but, in times of very high abundance, can be found at greater depths.

Distribution of common blowfish in WA

Silver toadfish, Lagocephalus sceleratus

Toxic family

The common blowfish, and its cousin the silver toadfish, belong to the family Tetraodontidae, which includes well over 100 species of toadfish and pufferfish, of which more than 25 are found in WA. Members of the Tetraodontidae family typically have torpedo-shaped bodies, soft skin instead of scales (sometimes imbedded with small spines) and fused teeth that form a beak.

Another characteristic of this family is a highly lethal toxin, called tetrodotoxin, present in the fishes’ skin, flesh and internal organs.

In Japan, fish from this family are known as ‘fugu’ and are considered a delicacy. Young chefs spend years learning how to prepare fugu. However, each year, a few people still die from eating poorly-prepared fugu dishes. In Australia, pets have died from eating blowfish washed up on beaches or left behind by fishers.

Pufferfish are the second most poisonous vertebrate in the world, the first being the golden poison frog.

Caught blowfish should be returned to the water immediately, rather than being left where dogs may eat them.

Oceans and estuaries

Common blowfish are a marine estuarine-opportunist species – typically found in nearshore marine waters and the lower to middle reaches of estuaries. They usually prefer shallow water up to four metres deep and estuarine conditions where the salinity is close to that of seawater. In the Swan-Canning Estuary in Perth, blowfish are most abundant from the estuary mouth in Fremantle to around Narrows Bridge, and rare in the upper estuary.

The reason why many blowfish live in estuaries is that there is often more food than in the ocean and less chance of being eaten by bigger fish. However, even the estuarine blowfish populations spend some of their lives in the ocean – see ‘Life of a blowie’.

What’s in a name?

Blowfish (and pufferfish generally) get their name from their ability to inflate their abdomens with water. This defence mechanism enables blowfish to look bigger and so warns off potential predators. Blowfish also inflate their abdomens with air on removal from the water and may have difficulty deflating. It is therefore best to put them back as quickly as possible.

Serious scavengers

Blowfish are opportunistic feeders, which means they eat a wide range of prey items depending on what is available. A study in the Swan-Canning Estuary found that small blowfish up to 13 centimetres in length mainly eat small crustaceans (for example, prawns) and marine worms known as polychaetes. Larger blowfish eat bivalve molluscs, such as mussels. They will also scavenge on larger prey, such as fish skeletons, and of course, as any fisher knows, blowies will form a feeding frenzy for bait and berley!

Some larger fish feed on blowfish, apparently without ill effect from their toxin. Blowfish have been found in the stomachs of tuna, tailor and mulloway.

Blowfish feeding on discarded bait

Life of a blowie

There is much we don’t yet know about the life cycle and population dynamics of blowies. Most of the research conducted on blowfish in Western Australia has occurred in the Swan-Canning Estuary.

These studies have shown that common blowfish live to at least 6 years old and reach sexual maturity when they are about 2 years old.

Mature blowfish migrate out of the Swan-Canning Estuary to spawn in shallow coastal waters along Perth’s coastline between October and January, with the peak spawning period being November to December. At these times, large schools of blowies have often been observed by fishers passing out to sea through the Fremantle heads.

Males and females release their sperm and eggs into the water where fertilisation occurs and the fertilised eggs develop into larvae. Once the larvae have developed into juvenile blowfish between 5 and 7 centimetres long – at about 7 to 9 months old – they enter the estuary and then stay there until they are sexually mature.

Juvenile blowfish

A single stock

It is thought that blowfish larvae originating from various spawning events along the coast are transported and mixed by ocean currents, leading to the creation of a single genetic stock along WA’s lower west coast. This means that blowfish spawned in the ocean from Swan-Canning Estuary stock may enter the estuary as juveniles or stay in the ocean – or travel to nearby sheltered coastal waters such as Cockburn Sound at Rockingham.

Studies show blowfish grow at different rates in different locations. After one year in the Swan-Canning Estuary, blowfish are an average 8.5 to 10 centimetres in length, compared to 7.4 centimetres at Rockingham, and 6.5 centimetres at Jurien Bay and Dongara.

Blowfish bonanza?

Many people think that there are more blowfish today than there were in the past.

However, historical records show that there were also periods of high blowfish abundance in the past. In 1973, fishing writer Ross Cusack observed that blowies had occurred in large numbers along the WA coast during the periods 1930–1935 and 1954–1955. In the late 1960s, there was a period of respite with fewer blowfish around, but by the early 1970s, the high numbers were back, he noted.

“Blowies have infested the entire WA coastline from east of Esperance, north to Shark Bay and they now thrive in every estuary. The time has come to wonder just how bad our blowfish plague can get.” (Ross Cusack, 1973)  

This compares to a comment in a WA Museum document, dated 1979:

“Blowfish have been extremely abundant in the lower-middle (Swan) Estuary for many years.” (WA Museum, 1979)  

Observations of high blowfish numbers are clearly not new. However, it is possible that the abundance of blowfish has increased in some estuaries and popular coastal fishing areas.

A decline in rainfall and freshwater river flow has occurred throughout south-western Australia since the mid-1970s, leading to more ‘marine’ conditions in estuaries for longer throughout the year. As blowfish tend to prefer more saline conditions, this is a possible reason for them becoming more widespread in some estuaries for longer in the year. Additionally, blowfish are attracted to locations where people often fish, so local populations could increase with increased fishing activity over time.

A school of common blowfish

How to avoid blowfish

Leaving blowfish to die on the shore or jetty is cruel and could lead to the fatal poisoning of pets such as dogs. If you catch blowfish you should treat them like any other unwanted fish and release them as carefully and quickly as possible.

Here are some tips to help avoid catching these so-called ‘nuisance’ fish:

• Try using bigger hooks and less berley.  Bigger hooks will reduce the change of hooking blowies as they have relatively small mouths, and reducing your berley use will mean you are less likely to attract them in.
• Blowfish often gather around popular fishing spots, so try finding new fishing locations away from the crowds.
• Try using lures rather than real bait and berley. If you want to catch Australian herring, for example, try using a metal slice or soft plastic.
• In order to keep blowfish numbers down around your favourite fishing spot, take your unused bait home rather than throwing it into the water, or dispose of it in a bin well away from the water.

Not to be mistaken for…

Globe fish are related to blowfish and pufferfish. Globe fish are distinguished by their more rounded body shape, and long yellow spines on their head and body that become erect if their body inflates. They also have 4 dark bars down their sides and yellow markings at the base of their spine.

Globe fish at Busselton Jetty

Bibliography

FishBase
www.fishbase.org

Hutchins, B. & Swainston, R. 1986.
Sea Fishes of Southern Australia.

Hutchins, B. & Thompson, M. 1995.
The Marine and Estuarine Fishes of South-western Australia.
A Field Guide for Anglers and Divers.

Cusack, R. 1973.
Menace Under the Water.
(in The West Australian)

Potter, I.C., Cheal, A.J. & Loneragan, N.R. 1988.
Protracted estuarine phase in the life cycle of the marine pufferfish Torquigener pleurogramma.

Smith, K.A. 2006.
Fisheries Research Report No. 156. Review of fishery resources and status of key fishery stocks in the Swan-Canning Estuary.

Glossary

Abundance
Number of fish in a stock or population

Bivalve mollusc
A class of mollusc (sea snail) that has a shell with two hinged halves, such as clams, mussels, oysters and scallops

Crustaceans
Animals with hard, jointed external skeletons, such as crabs, shrimp, lobster and prawns

Larva (plural: larvae)
The stage of a fish between hatching and becoming a juvenile

Native
Exist naturally in an area or location

Polychaete
A class of worms, usually marine

Stock
A population of fish within a certain geographical area where members of that population breed with each other

Toxin
A poison produced by the cells of plants and animals

Illustrations ©R.Swainston/animafish.com