The present study quantitatively describes a significant stock of carp (Cyprinus carpio L.), an exotic pest species, in a temperate riverine floodplain wetland. Intensity and duration of flooding influenced relative abundance, distribution and recruitment. Average growth (mm) in length was described with the von Bertalanffy growth model for males (L∞ = 489, k = 0.249, t0 = –0.519), and females (L∞ = 594, k = 0.177, t0 = –0.609) to age 28. Variation in growth was described with a lognormal distribution of k. Total mortality (Z year–1) was 0.268–0.407 for males, 0.311–0.422 for females, 3.24 for age-0 juveniles and 1.80 for age-1 juveniles. Natural mortality (M year–1) was 0.199 for males and 0.262 for females. Fishing mortality (F year–1) was <0.05 for males and 0.11–0.30 for females. Gonadal changes indicated extended spawning seasons peaking in September 1999 and October 2000. Median sizes and ages at initial maturation were 307 mm, 584 g and 1.1 years for males and 328 mm, 688 g and 2.7 years for females. Sex ratio varied significantly with age from equal as juveniles to a significant male-bias as adults. This description will enable better stock assessment and development of simulations that evaluate potential pest management strategies.

Approximately 40% of Australian freshwater fish species are of conservation concern, largely because of the impacts of river regulation, habitat fragmentation and alien fishes. Murray hardyhead is a threatened fish endemic to the southern Murray–Darling Basin in Australia, which has declined significantly in range and abundance since European settlement. Conservation of the species has relied largely on environmental watering of off-channel wetlands where isolated populations persist. This became problematic during recent drought (1997–2010) because of competing demands for limited water, and resentment towards environmental watering programs from communities that themselves were subject to reduced water entitlements. In response, emergency conservation measures prioritised the delivery of environmental water to minimise applied volumes. Captive maintenance programs were established for fish rescued from four genetically distinct conservation units, with varying levels of breeding success. Several translocations of wild and captive-bred fish to surrogate refuge sites were also conducted. Future recovery of the species should secure existing natural and stocked populations and translocate fish to additional appropriate sites to spread risk and reinstate natural pathways for dispersal. The approach to the conservation of Murray hardyhead during extreme environmental conditions provides insights to inform the management of fishes in other drought-prone regions of the world.

Many freshwater fishes are imperilled globally, and there is a need for easily accessible, contemporary ecological knowledge to guide management. This compendium contains knowledge collated from over 600 publications and 27 expert workshops to support the restoration of 9 priority native freshwater fish species, representative of the range of life-history strategies and values in south-eastern Australia’s Murray–Darling Basin. To help prioritise future research investment and restoration actions, ecological knowledge and threats were assessed for each species and life stage. There is considerable new knowledge (80% of publications used were from the past 20 years), but this varied among species and life stages, with most known about adults, then egg, juvenile and larval stages (in that order). The biggest knowledge gaps concerned early life stage requirements, survival, recruitment, growth rates, condition and movements. Key threats include reduced longitudinal and lateral connectivity, altered flows, loss of refugia, reductions in both flowing (lotic) and slackwater riverine habitats, degradation of wetland habitats, alien species interactions and loss of aquatic vegetation. Examples and case studies illustrating the application of this knowledge to underpin effective restoration management are provided. This extensive ecological evidence base for multiple species is presented in a tabular format to assist a range of readers.

Common carp Cyprinus carpio are an important pest species in Australia, yet little is known regarding their age and growth there. We examined otolith sections of common carp to validate their utility for age determination. For the 1999 year-class in Hut Lake near Barmah, we confirmed the absolute age at first annulus formation as age 1 by repeated sampling of a discrete young-of-year cohort. We confirmed the annual periodicity of annulus formation for common carp in a mark-recapture experiment when 19 recaptured adult common carp (from an original stocking of 141 fish marked by injection with oxytetracycline [OTC]) showed visible fluorescent marks on their otoliths. Time at liberty for these fish ranged from 6 to 25 months, and their ages on recapture ranged from 3 to 14 years. Increment counts outside the OTC mark agreed completely with time at liberty. We calculated precision estimates on age determinations as the average percent error (APE) and estimated the coefficient of variation (CV ϭ Ϫ0.15 ϩ 1.41APE) between readers and for each of two readers over time. Precision was assessed by rereading subsamples. The APE was less than 5% and CV was less than 8% in all cases. We conclude that examination of thin otolith sections is a suitable method for the determination of annual age estimates for common carp age 0-14.

Internationally, re-introductions of endangered species into their former ranges have largely failed. Here we assess a successful reintroduction program of the endangered trout cod (Maccullochella macquariensis) and examine factors contributing to this success. Stocking of marked fish (all stocked fish were marked) occurred between 1997 and 2006 in the Ovens River, south-eastern Australia, where trout cod were historically abundant but locally extinct by the 1980s. We found no natural recruits (i.e. from spawnings of stocked fish in the wild) over the age of six, indicating that natural recruitment started at most five years after stocking began. Of the 83 fish we examined for sexual maturity, 12 were immature, 20 were male, and 51 were female. The body length at which 50% of the population can be considered mature was 325 and 250 mm for females and males, respectively. The length at which 90% of the population was mature was 394 and 318 mm for females and males, respectively. The smallest mature female was 245 mm. Average relative fertility was 9 eggs g–1 fish weight. The results we obtained provide valuable insights into the aspects contributing to the success of reintroduction programs for endangered freshwater species.