Do bigger dusky flathead have better eggs?

Tara Hicks with the largest flathead in her sample.

Tara Hicks with the largest flathead in her sample.

As if a keen fisherman ever needs an excuse to go fishing….but for one local Mallacoota resident, Keith Simpson the chance to be involved in a research project studying Dusky Flathead, a species very popular with recreational fishers, certainly
gave him that extra impetus.

The “fishing expert” provided more than 200 fish for honors student Tara Hicks who began her project on the
“Body size, fecundity and egg quality relationships in Dusky flathead (Platycephalus fuscus) from Victorian
waters” in July last year for a project funded by the Department of Environment, Land, Water and Planning
(Fisheries). She is supervised by Dr Keller Kopf and Dr Paul Humphries.  For the project, Tara had to source fish across its size range. To that end she asked the local fishers in Mallacoota to help out by donating their fish frames (what’s left after the fillets are removed).

“I had one particular retired man who was amazing,” says Tara who lives in the popular holiday town in Far East Gippsland. “He donated most of the fish I got from Mallacoota. He was brilliant. He brought fish around nearly every other day. I got permits for a few people to take some larger fish, as you are not allowed to take dusky flathead over 55cm in Victoria, and he was one of them. The stories he would tell me about dusky flat head were also very interesting….he is a nice person interested in fishery and its sustainability.”

Tara, who analysed around 500 fish in total, hired a commercial boat operator to take her out mesh netting on two nights to target larger fish (more difficult to collect ) and was able to get some more fish that way. She also purchased fish from the Lakes Entrance Fishermen’s Cooperative.

“In summer, when it is very busy, I would go down to the wharf at Mallacoota and get frames from people coming in from fishing,” says Tara. “I had to incorporate different sampling
methods to end up with a representative sample. I looked at fish from 20 cm to 82 cms but they can get a lot bigger than that, up to 1.2m. The largest fish I got came from one of
the anglers I put on the permit.”
Tara found that the number of eggs (fecundity) increased with body size i.e. the larger females had a greater number of eggs. “That was expected because the relationship between body size and number of eggs is present within all fish species,” says Tara. “But for egg quality, there was no change across the size range, larger females did not have better quality eggs than smaller females.  This result was unexpected. In some species of fish, bigger mothers produce better eggs.”

Tara spent three weeks in Hobart at CSIRO Marine and Atmospheric Research, working with Dr Peter Nichols analysing the lipids and fatty acids in the fish ovaries. This information is used as an indicator of egg quality. She also looked at egg size (also an indicator of egg quality) and found that didn’t change in relation to the fish size.The information will be fed back to the Department.
“There was no reproductive biology information previously on this species in Victoria, so this will help guide better management,” says Tara who hopes to write a journal paper out
of her research. She will also give a presentation on her findings to the Mallacoota community and the Australian Society for Fish Biology later this year.

Project funded by Department of Environment, Land, Water and Planning.

$49,639. Principal researchers Kopf, R.K & Humphries, P.

About ilwscsu
The Institute for Land, Water and Society is one of four Centres of Research Excellence within Charles Sturt University, Australia. Its principal focus is on integrated research which contributes to improved social and environmental sustainability in rural and regional areas.

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