Last week, in Lake Bonney, at Barmera, in South Australia’s Riverland, nearly 600 Murray cod — Maccullochella peelii, the big native of the Murray–Darling — went into the water. RecFish SA says about two tonnes. Some reach a metre. They are not fingerlings. Asher Dezsery, RecFish SA’s chief: the lake was cut off from the river, water quality failed, there were fish kills, the cod died out years ago. Now, “instant broodstock” — mature fish ready to breed. A recreational fishery that does not wait five years of fry.

The project is RecFish SA’s, with the new Recreational Fishing Authority and the recreation ministry. It sits in a A$6.6 million recreational fishing package. RecFish SA gets A$1.75 million over four years, including tagging and translocations. A million goes on rod holders and filleting tables. Minister Rhiannon Pearce was at the release, next to Berri Barmera mayor Ella Winnall. Winnall: not many in the community lack a rod in the shed or a boat licence. A “once in a lifetime” chance, she said, to stand next to so many mature cod.

Paul Humphries, an ecologist at Charles Sturt University, said the cod defines the basin. It is, to a degree, a habitat engineer: structure, water quality. It matters in the food chain. On carp, he promised no miracles. If there are small fish, the cod “will certainly have a go.” But it is a main-channel specialist. Carp breed too well for 600 fish to cut them. “It certainly can’t hurt.” That is the limit of the science he offered, not a victory brief.

Norman Wilson, an elder at the release, said he hoped some would move into the river and that they would come back to breed. “That’s their cycle; they’ll always come back to the same place.” In the government’s statement the fish is pondi, a totem, from stories. The lake was Nookampka. Wilson also spoke of the narrow channel back to the Murray. Lucas Weaver, on RecFish SA’s Riverland board: a “dream come true” for locals.

Murray cod fishing is closed now, to protect the spawning stock. The catch-and-release season opens in January. The local Pioneer wrote that Riverland anglers will, from next year, be able to seek it in Bonney. Golden perch, redfin, carp stay on the rod. The government noted that a week earlier thousands of rainbow trout went into Happy Valley Reservoir — another programme, another water, not this one.

A lake cut off from the river, with fish kills behind it, is not fixed on a Saturday. A mature stock is put where none was left. Whether they breed, whether they stay, whether the tourist comes with a boat — that will show in months, not in a statement. Dezsery spoke of ecosystem and tourism in the same sentence. The two are not confirmed together. They are put, together, in the water.

Image: Tangerineduel, Lake Bonney at Barmera, 27 August 2015, CC BY-SA 4.0, Wikimedia Commons. The photograph shows the lake, not the fish release.

Sources consulted: Hope for population boom as Murray Cod are reintroduced to Lake Bonney — ABC News; Two Tonnes of Murray Cod Stocked into Lake Bonney — RecFish SA.