Knowing the kinds of physical stress experienced by fish passing through hydropower turbines can help optimise technologies and improve fish passage. This paper assesses the hydraulic conditions experienced through three different low-head turbines (a very low head (VLH), Archimedes screw and horizontal Kaplan turbine), taken using an autonomous sensor. In total, 127 Sensor Fish deployments were undertaken across all three turbines, generating 82 valid datasets. Decompression was rare at the VLH and screw turbines and rarely fell more than 10 kPa below atmospheric pressure. In contrast, the Kaplan was capable of generating pressures as low as 55.5 kPa (~45 kPa below atmospheric pressure), over shorter periods of time. More severe ratios of pressure changes could, therefore, be expected for both surface- and depth-acclimated fish at the Kaplan than at the other turbines. Strike was another possible source of fish injury (detected in 69–100% of deployments), and although strike severity was highest at the Kaplan, strike was more likely to be encountered at the screw and VLH than the Kaplan turbine. Shear occurred only near the blades of the Kaplan, and not at severe levels. The results demonstrated that low-head hydropower facilities are not without their risks for downstream migrating fish.

Epizootic ulcerative syndrome (EUS) is a fish disease of international significance and reportable to the Office International des Epizootics. In June 2010, bony herring Nematalosa erebi, golden perch Macquaria ambigua, Murray cod Maccullochella peelii and spangled perch Leiopotherapon unicolor with severe ulcers were sampled from the Murray-Darling River System (MDRS) between Bourke and Brewarrina, New South Wales Australia. Histopathology and polymerase chain reaction identified the fungus-like oomycete Aphanomyces invadans, the causative agent of EUS. Apart from one previous record in N. erebi, EUS has been recorded in the wild only from coastal drainages in Australia. This study is the first published account of A. invadans in the wild fish populations of the MDRS, and is the first confirmed record of EUS in M. ambigua, M. peelii and L. unicolor. Ulcerated carp Cyprinus carpio collected at the time of the same epizootic were not found to be infected by EUS, supporting previous accounts of resistance against the disease by this species. The lack of previous clinical evidence, the large number of new hosts (n = 3), the geographic extent (200 km) of this epizootic, the severity of ulceration and apparent high pathogenicity suggest a relatively recent invasion by A. invadans. The epizootic and associated environmental factors are documented and discussed within the context of possible vectors for its entry into the MDRS and recommendations regarding continued surveillance, research and biosecurity are made.

Summary: The diversion of water from rivers removes millions of fish from Australian waterways each year. Modern diversion screens are available that can reduce fish losses by 90% and stop debris entering irrigation systems. Uptake of this technology in the United States has protected fish and infrastructure. However, application in Australia has been poor and both the problem and its solution continue to be overlooked. To address this, we summarise multiple lines of evidence of fish losses in Australia and propose a way forward. Large losses of fish at diversions have been reported for close to a century, providing compelling evidence of population‐scale impacts on native fish. We discuss the solution, outlining the progress being made to bring modern screening technology to Australia, including a social learning framework to improve how water is diverted and focussing on collaboration between the fisheries, agriculture and engineering sectors, and underpinned by science. We conclude that uptake of modern screens will rely on dialogue moving past whether a problem or solution exists, to the following: how screening can be better integrated with water and environmental management; where investment should be prioritised; and how screening could be funded. If Australia gets this right, substantial benefits can be realised, saving millions of native fish every year, bolstering native fish recovery programmes, reducing ongoing costs for water users and enhancing the economic and social value in regional areas by boosting manufacturing, service industries, tourism and recreational fisheries.

Irrigated agriculture and inland fisheries both make important contributions to food security, nutrition, livelihoods and wellbeing. Typically, in modern irrigation systems, these components operate independently. Some practices, commonly associated with water use and intensification of crop production can be in direct conflict with and have adverse effects on fisheries. Food security objectives may be compromised if fish are not considered in the design phases of irrigation systems. The 2030 Agenda for Sustainable Development provides a framework that can serve as a backdrop to help integrate both sectors in policy discussions and optimise their contributions to achieving the Sustainable Development Goals (SDGs). Inland fisheries systems do play an important role in supporting many SDG objectives, but these contributions can sometimes be at odds with irrigated agriculture. Using case studies of two globally important river catchments, namely the Lower Mekong and Murray–Darling basins, we highlight the conflicts and opportunities for improved outcomes between irrigated agriculture and inland fisheries. We explore SDG 2 (Zero Hunger) as a path to advance our irrigation systems as a means to benefit both agriculture and inland fisheries, preserving biodiversity and enhancing the economic, environmental and social benefits they both provide to people.2

Egg and larval fish that drift downstream are likely to encounter river infrastructure and consequently rapid decompression, which may result in significant injury. Pressure-related injury (or barotrauma) has been shown in juvenile fishes when pressure falls sufficiently below that at which the fish has acclimated. There is a presumption that eggs and larvae may be at least as, if not more, susceptible to barotrauma injury because they are far less-developed and more fragile than juveniles, but studies to date report inconsistent results and none have considered the relationship between pressure change and barotrauma over a sufficiently broad range of pressure changes to enable tolerances to be properly determined. To address this, we exposed eggs and larvae of three physoclistic species to rapid decompression in a barometric chamber over a broad range of discrete pressure changes. Eggs, but not larvae, were unaffected by all levels of decompression tested. At exposure pressures below ∼40 kPa, or ∼40% of surface pressure, swim bladder deflation occurred in all species and internal haemorrhage was observed in one species. None of these injuries killed the fish within 24 h, but subsequent mortality cannot be excluded. Consequently, if larval drift is expected where river infrastructure is present, adopting design or operational features which maintain exposure pressures at 40% or more of the pressure to which drifting larvae are acclimated may afford greater protection for resident fishes.