Yasi legacy for barramundi

When Cyclone Yasi smashed a barramundi sea-cage farm in the Hinchinbrook Channel in February 2011, more than 250 tonnes of farmed barramundi made their bid for freedom.

What was originally seen as a boon for fishers has yielded valuable insights for JCU scientists.

Professor Dean Jerry, Head of Aquaculture at JCU, said researchers were using DNA pedigree technologies to determine the proportion of farmed barramundi now residing in the channel.

“Concerns were raised about the long-term impact these escapees could have on the genetic fitness of the wild population,” he said.

“The issue is that hatchery-produced fish are usually highly related, exhibit low levels of genetic diversity, and are subject during artificial rearing to a completely different suite of selection pressures than may be present in the wild.

“This can produce fish which are perfect for farming, but not necessarily representative of fish in the wild.”

Honours researcher Tansyn Noble enlisted help from local recreational and commercial fishers to catch barramundi in and adjacent to the channel and to provide small samples cut from the fins of fish so that she could extract DNA.

Professor Jerry said DNA parentage analysis was then used to determine if fish could be assigned to broodstock parents of the farmed fish.

“Tansyn’s analysis found that 30 per cent of barramundi caught by fishers represented escapees,” he said.

“Alarmingly, around half the escaped farmed fish in the channel had originated from the same male and female parents.”

Professor Jerry said the researchers’ work had demonstrated the usefulness of DNA parentage analyses to identify the farm escapees.

“There is now an urgent need to learn from this unfortunate event and understand the long-term effects on wild populations of large escape events like this.

“The results are also relevant to situations where stocked barramundi transverse spillways of impoundments in large numbers, as happened in the Gladstone area last year in an overflow of Awoonga Dam.

“These two types of fish escapes occur regularly. This study is the first of its kind in a tropical fish species and will be useful for future monitoring. It provides valuable information for managing the barramundi sea-cage industry and sustainable restocking programs.”

Issued: 13 June, 2013

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