Fish Facts

FISH FACTS: Samson fish

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Samson fish grow to over 1.7 m long and in excess of 50 kg.

SAMSON fish (Seriola hippos) are Australia’ own private member of the kingfish/amberjack group. Unlike the worldwide distribution of their close cousin the amberjack (Seriola dumerili) and the Pacific-wide range of the venerable yellowtail kingfish (Seriola lalandi), sampson fish (or sambos) have a comparatively restricted distribution being found only around the southern states of Australia, Norfolk and Lord Howe Islands, while a couple of fish have even been recorded from northern New Zealand. Australia’s fourth species of Seriola is the highfin amberjack (Seriola rivoliana), which like its larger cousin the amberjack also occurs worldwide in tropical and warm temperate seas.

Growing to over 1.7 m long and in excess of 50 kg, adult sampson fish can be found around offshore reefs along the southern continental shelf in depths up to 200 m from Moreton Bay in Queensland to Shark Bay in WA.  Near Rottnest Island off Perth, large spawning aggregations occur during the summer months around specific offshore reefs and shipwrecks, where up to 30,000+ sampson fish may gather in water depths ranging from 80 to 200 m.  These aggregations are composed almost entirely of adult fish over the size at which 50% of sampson fish are mature (88+ cm) Tag returns suggest that individual fish return to the same spawning areas year after year on a regular basis. It appears that the fish are not feeding while at the spawning aggregation, though some will take lures and baits if presented with them.

An individual female sampson fish can spawn upwards of over 1.5 million eggs. After spawning the fertilized eggs are dispersed by the currents and hatch into juveniles that recruit in inshore waters to jellyfish, sargassum weed and other floating objects.  Growth of juveniles is very rapid.  One year olds around 35-40 cm long are grey with brown blotches on the head and flanks, and commonly frequent inshore reefs, jetties and other structures. Sexes are separate and both males and females reach around 60 cm long in their second year of life. After that females tend to grow faster than males, reaching maturity at over 88 cm in their fourth or fifth year. Growth slows after maturity with predicted fork lengths (and weights) for females 109 cm (17 kg), 122 cm (24 kg) and 131 cm (30 kg) at 10, 15 and 20 years of age. In comparison, male sampsonfish lag behind a little, averaging around 103cm (15 kg), 112 cm (19 kg) and 117cm (21 kg) at 10, 15 and 20 years old.  Maximum age for both sexes appears around 28-29 years old, which is longer lived than recorded for any other species of Seriola. The diet of adult fish in WA appears to be almost entirely composed of fish (pilchards, scads, yellowtail) and squid, with juveniles also feeding on smaller crustaceans including prawns.

Numerous recaptures of tagged fish have found that, like their biblical namesake, sampson fish are very strong swimmers.  The scale of the migrations some adult fish undertake to be part of the spawning action is impressive. For example, one fish tagged at the Rottnest spawning site was recaptured near Esperance on the south coast of W.A. (over 1000 km away) after being at liberty for only 26 days. The longest migration recorded was 2400 km for two sampson fish recaptured around 9 months later off Kangaroo Island in South Australia. Tag data also indicates individual fish may only stay within the aggregations for a short period of time (two weeks), but they return to the spawning area at around the same time each year.  The movements of fish towards the spawning grounds are almost universally up current, suggesting the behaviour developed through natural selection to compensate for down current dispersion of eggs and larvae. Similar behaviour has been demonstrated for many other species of fish living in rivers (e.g. golden perch, Murray cod) and inshore areas (tailor).

One of the concerns raised by recreational fishers and scientists was about survival rates of sampson fish released after being taken from deep water. However studies of fish taken from up to 195 m showed the vast majority survived. Overall post-release survival was around 91%, with the majority of deaths due to barotrauma (pressure damage) in some of the fish taken from water over 100 m deep. The main factor influencing survival of these fish was the surface interval – the sooner the fish were allowed to get back into the water and regain some depth, the better their chances of survival.  It turns out that sampson fish benefit from an anatomical feature (possibly evolved from a natural predatory requirement to change depth quickly while chasing prey), which allows the expanding gases from the swimbladder to escape through a “swimbladder vent” near the back of the fishes mouth. This acts as a “safety valve”, protecting the internal organs of the fish from pressure damage due to swim bladder overexpansion during the last 10-20 m of ascent. Divers have noted release of bubbles from the swimbladder vent in free swimming sampsonfish, suggesting the vent is used naturally. Obviously the same feature helps sampson fish avoid barotrauma damage and allows them to get back down that crucial first 10 or 20 m, especially if they are helped on their way by the fisher spearing them back into the water head first. This means that if best practice catch and release techniques are used with appropriate tackle selection, populations of sampsonfish targeted by recreational anglers should be able to be sustainably managed into the future. 

For a great read about the biology of sampson fish, see Andrew Rowland’s thesis which is available at

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