Mysterious yellow jewfish caught in upper Hunter River

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THERE was complete silence in the windless night as we watched the ebb tide drain out of the upper Hunter River. A school of nervous mullet shimmered on the water’s surface, indicative of a predator in close proximity.

I lobbed a gold hardbody lure a few metres behind the school, careful not to spook them. After giving it a quick crank down to depth, a twitch and pause retrieve was initiated to imitate a wounded fish in the pack. The lure was soon intercepted, with the commotion sending the mullet school into an eruptive frenzy.

A short fight ensued, including a couple of barra-reminiscent jumps in shallow water before a juvenile mulloway washed up at my feet. Even with mere moonlight it was clear to see this was no ordinary jewfish. A closer inspection with a head torch supported my initial suspicions; it was a “yellow jewfish.”

Of course, mulloway possess a characteristic bright yellow mouth, but on this individual, that colouration had extended along the underbelly, through its fins and across its flanks. We were quick to snap some images before returning the fish to the water. With a strong kick of the tail it swam off into the night, offering no indication of physical ailment.

My initial thoughts were that the yellow-colouration looked similar to that which can be found on a black jewfish, a different species to mulloway which inhabit estuaries and reef systems of Australia’s top end. However, finding one of these in the backwaters of a central NSW estuary seemed a far stretch.

With this fish leaving me with more questions than answers, I consulted jewie expert Dr. Julian Hughes, research scientist from NSW DPI, as to the possible causes of the abnormal colouration.

Julian sees more mulloway than most and proposed two potential reasons: the first being a condition called xanthism which causes normal pigments to be replaced by yellow ones. This is known to affect the entire fish, or sometimes only occur in patches or blotches. Although it is a condition found in lots of different salt and freshwater fish species, he has never seen it in mulloway.

The second potential cause was that the yellow colouration is a bi-product of the mulloway’s environment. Very turbid estuaries, such as the upper Hunter can lend jewies to go bizarre colours such as bronze, olive, brown, purple or almost black depending on how stained or dirty the water is. With the fish coming out of very dirty water, this seems a likely cause.

If you’d like to get involved in the science of jewfish, check out NSW DPI’s Research Angler Program: http://www.dpi.nsw.gov.au/fishing/recreational/resources/fish-tagging/researchangler

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