The mulloway (Argyrosomus japonicus) is one of our iconic inshore fish species. In Australia, they can reach nearly 1.5m in length and a weight of 35kg
Mulloway belong to the Family Sciaenidae which is a large families of fishes containing close to 300 species. A notable trait of sciaenids is the ability to produce a "croaking" sound – hence the common name of some species being “croaker” or “drum”.
Species in family have special adaptations to making sounds and central to being able to do so is their very large swim bladder which allows the sounds produced to resonate. The purpose of the vocalisation varies between species but can be associated with attracting mates and communicating to each other in dirty water where vision is limited.
Mulloway have an Indo-Pacific distribution occurring in coastal waters surrounding Australia, Africa, India, Pakistan, China and Japan. In Australia, they are mostly found from north of Perth around the southern coastline of to at least the Burnett River in Queensland.
While the species is common in inshore and estuarine waters, large adults are found associated with offshore reefs. Juveniles are generally limited to estuarine and inshore areas.
Compared to other states, there has been limited research on mulloway in Queensland. Much work has been done understanding the species in NSW. Adult mulloway are thought to aggregate for spawning. They generally establish a home range and for subadult fish, this can be associated with deeper holes in estuaries.
What do they feed on?
In estuarine and inshore waters, small mulloway mostly eat crustaceans including prawns and a prawn-like animal called a mysid before transitioning principally to a diet of fish including species of mullet, gobies, herrings and yellowfin bream.
Rainfall strongly influences successful recruitment of juvenile mulloway and the suggested reason for this is that it increases the abundance of suitable prey for the small fish.
Mulloway reach 45-55cm after three years but can live for up to 30 years. The growth of males and females is similar until age 4-5 years (the approximate age at female maturity), after which females grow faster and attain greater lengths than males.
Mulloway are not the only species of sciaenid fish captured by anglers in Queensland. The teraglin (Atractoscion aequidens) is an offshore species which is captured from the waters offshore of Moreton Bay and then southwards into northern NSW.
There’s also the black jewfish (Protonibea diacanthus) which is a more northern species that is also known to form large aggregations for spawning. There are two other small species present in Moreton Bay which are often mistaken for juvenile mulloway – the little jewfish (Johnius borneensis) which only grows to about 35cm and Weber’s croaker (Johnius weberi) which only grows to about 25cm.
Mulloway in Queensland have a minimum legal size of 75cm and an in-possession limit of two fish. Survival rates of released mulloway can be low, so every effort should be made to quickly release a fish in good condition.
Dr Dazza is an Associate Professor of Environmental Science at Bond University
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