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The introduction and spread of non-native species poses a significant threat to the health of freshwater ecosystems, and has recently been identified as the single biggest danger to threatened species survival in Australia. Notwithstanding, the importation, trade and keeping of exotic and potentially invasive freshwater fishes in Australia is significant, resulting in greater propagule pressure and higher risk for deliberate or incidental release into native waterways. The jaguar cichlid (Parachromis managuensis) is an invasive cichlid that has established non-native populations in many countries throughout the world. In December 2014, the Department of Agriculture and Fisheries in Queensland was notified of an incursion of jaguar cichlids in a stormwater retention dam in the Pioneer River Catchment, Mackay, Queensland. Rotenone was applied to the dam in January 2015, and around 200 jaguar cichlid specimens at various life history stages were destroyed. Follow up surveys into mid-2015 did not detect the presence of any jaguar cichlid in the dam or in nearby creeks. In September 2017, the Department was notified of a wild capture of a mature jaguar cichlid in Fursden Creek, 1.5 km from the original incursion site. Follow up surveys in 2018/19 have also detected jaguar cichlid juveniles in surrounding tributaries, indicating successful establishment and naturalisation of the species in Australia for the first time. © Holmes et al.

The introduction and spread of non-native species poses a significant threat to the health of freshwater ecosystems, and has recently been identified as the single biggest danger to threatened species survival in Australia. Notwithstanding, the importation, trade and keeping of exotic and potentially invasive freshwater fishes in Australia is significant, resulting in greater propagule pressure and higher risk for deliberate or incidental release into native waterways. The jaguar cichlid (Parachromis managuensis) is an invasive cichlid that has established non-native populations in many countries throughout the world. In December 2014, the Department of Agriculture and Fisheries in Queensland was notified of an incursion of jaguar cichlids in a stormwater retention dam in the Pioneer River Catchment, Mackay, Queensland. Rotenone was applied to the dam in January 2015, and around 200 jaguar cichlid specimens at various life history stages were destroyed. Follow up surveys into mid-2015 did not detect the presence of any jaguar cichlid in the dam or in nearby creeks. In September 2017, the Department was notified of a wild capture of a mature jaguar cichlid in Fursden Creek, 1.5 km from the original incursion site. Follow up surveys in 2018/19 have also detected jaguar cichlid juveniles in surrounding tributaries, indicating successful establishment and naturalisation of the species in Australia for the first time. © Holmes et al.

Lates calcarifer supports important fisheries throughout tropical Australia. Community-driven fish stocking has resulted in the creation of impoundment fisheries and supplemental stocking of selected wild riverine populations. Using predominantly tag-recapture methods, condition assessment and stomach flushing techniques, this study compared the growth of stocked and wild L. calcarifer in a tropical Australian river (Johnstone River) and stocked fish in a nearby impoundment (Lake Tinaroo). Growth of L. calcarifer in the Johnstone River appeared resource-limited, with juvenile fish in its lower freshwater reaches feeding mainly on small aytid shrimp and limited quantities of fish. Growth was probably greatest in estuarine and coastal areas than in the lower freshwater river. Fish in Lake Tinaroo, where prey availability was greater, grew faster than either wild or stocked fish in the lower freshwater areas of the Johnstone River. Growth of L. calcarifer was highly seasonal with marked declines in the cooler months. This was reflected in both stomach fullness and the percentage of fish with empty stomachs but the condition of L. calcarifer was similar across most sites. In areas where food resources appear stretched, adverse effects on resident L. calcarifer populations and their attendant prey species should be minimised through cessation of, or more conservative, stocking practices.

The stocking of predators can have significant consequences on recipient aquatic ecosystems. We investigated some potential ecological impacts of stocking a predatory fish (Lates calcarifer) into a coastal river and a large impoundment in north-eastern Australia. L. calcarifer was mostly found in slower-moving, larger reaches of the river or in the main body of the impoundment where there was abundant suitable habitat. In the tidally influenced freshwater reaches of the coastal river, L. calcarifer predominately consumed aytid and palaemonid shrimp that were associated with local macrophyte beds or littoral grasses. In this area the diets of juvenile stocked and wild L. calcarifer were similar and stocked fish displayed a high degree of site fidelity. Further upstream in the river, away from tidal influence, and in the impoundment, fish were the main prey item. Cannibalism was uncommon and we suggest that, at the current stocking densities, there was little dietary evidence of predatory impacts from L. calcarifer on species of conservation concern. We caution against introducing novel predatory species such as L. calcarifer in or near areas that are outside their natural range and are known to support rare, threatened or endangered species.

OBJECTIVES: 1. Assess movements and ecological impacts of stocked barramundi in a model river and impoundment 2. Determine if barramundi stocking has any discernable adverse genetic impacts on wild populations in a previously stocked river system