Search

Riverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet‐dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow‐pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet‐dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta‐diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow‐habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future. [ABSTRACT FROM AUTHOR]

The impacts of mine contaminants on ecological connectivity in rivers and streams are poorly documented globally. We used acoustic telemetry to evaluate and refine conceptual models of fish movement in Magela Creek, a stream in the wet-dry tropics of Australia. This creek receives wastewater discharge from a nearby uranium mine, and a secondary objective was to describe behavioural responses of fish to one such discharge event. Of 55 fish (black bream Hephaestus fuliginosus, saratoga Scleropages jardinii, sharp-nose grunter Syncomistes butleri) tagged in dry season refuge pools 18 km upstream of the mine lease area (RPA [Ranger Project Area]), 16 (29%) moved downstream after the first wet season flows, using the RPA as habitat for 3–5 months before moving upstream to their previous locations as flows receded. Of 39 fish (spangled perch Leiopotherapon unicolor, barred grunter Amniataba percoides, black catfish Neosilurus ater) tagged ~ 8–12 km downstream of the RPA in the late wet season, only two were subsequently detected in the RPA. Direct and camera-based observations of 12 species of upstream-migrating fish during mine-water discharge in the late wet season showed no evidence of mine-water avoidance. Our results demonstrate that Magela Creek provides wet season habitat for fish within the RPA and acts as a migration pathway that connects lowland reaches and floodplains to upstream dry season refuges. Use by fish of waterbodies within the RPA highlights the need to manage the site to ensure that future contaminant egress and water quality do not adversely affect fish migration and habitat suitability. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sex‐specific reproductive roles contribute to sexual dimorphic morphological trait variations. In uniparental mouth‐brooding fishes, the mouth performs a reproductive function in addition to its key roles in feeding and respiration, resulting in the potential for sex‐specific functional performance trade‐offs. Trait differences related to parental care may occur when the individual matures or be restricted to periods when the parent is mouth‐brooding. This study explored sexual dimorphism and morphological trait adaptations related to feeding, breeding, respiration and locomotion performance in two paternal mouth‐brooding freshwater fishes (Glossamia aprion and Neoarius graeffei). Eight morphological traits were evaluated for sexual dimorphism (non‐brooder males vs. females) and male breeding state differences (brooders vs. non‐brooders). Male breeding state was a significant predictor of trait variation in both species. Brooders differed in buccal volume and in several feeding and locomotory traits compared to non‐brooder males. Non‐brooder males had bigger buccal volumes and relative eye diameters (G. aprion) and larger relative gape sizes (N. graeffei) compared to females, a potential response to both mouth‐brooding and feeding requirements. Although there were clear trait differences between brooder and non‐brooder males, further research is required to confirm whether individuals return to their former morphology once mouth‐brooding has ceased or if trait differences are maintained post‐brooding. This study highlights the importance of considering the potential impacts of intraspecific trait variation on the performance of critical life functions, such as feeding, respiration and locomotion across the life history. [ABSTRACT FROM AUTHOR]

Trait‐based models of ecological communities and ecosystem functioning often fail to account for intraspecific variation in functional traits, assuming that intraspecific variability is negligible compared with interspecific variability. However, this assumption remains poorly tested across vertebrate animals where past studies routinely describe species according to mean trait values without explicit consideration of individual trait variability. We assessed nine functional traits for 4254 individuals belonging to 15 freshwater fish species from 11 families in northern Australia, including body elongation, body shape, caudal peduncle throttle, eye size, eye position, gape shape, gape size, mouth position, and pectoral fin length. We quantified the extent and geography of intraspecific trait variability and its relationship with riverine hydrologic regimes using a structured sampling design. Using a combination of single‐ and multi‐trait analyses, we demonstrate that intraspecific trait variability can contribute up to 70% of the total trait variability depending on the attribute considered and averaged 31% across all traits. The magnitude of intraspecific trait variability also varied across the hydrological permanency gradient. Fish assemblages in intermittent streams subjected to frequent environmental disturbance had high intraspecific trait variability, most likely due to strong abiotic filters limiting interspecific divergence. Conversely, assemblages in perennial rivers with less harsh environmental filters but with a larger pool of species expressed lower intraspecific trait variability: This is most likely due to stronger resource competition (biotic filter), which promotes specialization of resource use and, consequently, interspecific divergence. Our study provides the first evidence of intraspecific trait variability driven by a disturbance gradient for an animal group and points to the need for additional research into the functional importance of intraspecific variability in animal ecology. A better understanding of the patterns, drivers, and implications of intraspecific trait variability will help guide mechanistic‐based predictions of the effects of environmental changes on community assemblage and ecosystem processes. [ABSTRACT FROM AUTHOR]

Parental care purportedly promotes individual reproductive success and improves offspring survival, but is thought to come at a cost to the adult carer. Reproductive costs can be physiological such as the resources parents spend on caring but also the morphological changes that are necessary to accomplish parental care activities. This study considers morphological and body condition changes in brooders of two paternal mouthbrooder fishes – which incubate eggs and guard young inside the buccal cavity – mouth almighty (Glossamia aprion) and blue catfish (Neoarius graeffei), from rivers of northern Australia. Potential costs associated with mouthbrooding were examined by quantifying body condition, feeding deterrence and changes in gut length and gill form across individuals from varying sex‐breeding state category (brooder males, nonbrooder males and females). Brooders of both species exhibited significantly lower values in some condition indices, and did not feed, suggesting that body reserves were being used and not renewed during mouthbrooding. Brooders of both species had shorter gut lengths than nonbrooders, potentially to reduce tissue maintenance costs during a time of restricted food intake and requirements. Both species also exhibited changes in gill form and structure compared to nonbrooders; indicating structural adaptive plasticity to mouthbrooding by allowing more space for egg brooding in the buccal cavity. For G. aprion and N. graeffei, caring for progeny seemingly required similar trade‐offs including nonphysiological activities (e.g. feeding) and responses, such as changes in condition, respiratory and digestive morphology, that potentially allowed brooders to compensate for parental care energy expenditure. [ABSTRACT FROM AUTHOR]

Setting ecologically based water‐extraction rules requires an understanding of the relationships between hydrology and the completion of aquatic organism life cycles. Successful reproduction of riverine fishes has been linked to hydrological variation across diverse climatic regions. However, the reproductive ecology for many species in wet–dry tropical northern Australia is poorly understood, and consequently there is little knowledge on how temporal (seasonal) and spatial hydrological variation influences fish reproduction in this region.This study aimed to quantify the hydrology‐related reproductive ecologies of freshwater fish across the wet–dry seasonal cycle and between differing hydrological classes in a northern Australian river (Daly River, Northern Territory) subject to increasing interest in water extraction. Sampling of larval and juvenile fish was undertaken over 1 year at eight sites classified into perennial and intermittent flow types. Fish spawning phenologies were developed and spatial–temporal dynamics in larval fish assemblages were investigated using model‐based multivariate and univariate analyses.Spawning occurred in all hydrological seasons, with low‐flow dry season periods identified as important for many fish taxa. For a different fish assemblage, spawning mostly occurred during high‐flow wet season periods. Larval assemblages in the wet season were more diverse than in the dry and wet–dry seasons. Perennial sites maintained higher diversity than intermittent sites year‐round; however, larvae were more abundant in intermittent sites for some taxa. Spatial and temporal differences in larval assemblages were largely explained by variation in the occurrence and relative abundance of three aseasonally spawning taxa (Craterocephalus spp., Melanotaenia spp. and Ambassis spp.) and the largely wet‐period spawning of Terapontidae spp.These results add to growing evidence of variation in spawning phenologies among fish species and the use of multiple hydrological phases for aseasonal reproduction. The diverse range of hydrological conditions used for spawning and rearing, and the differences between hydrological river classes among taxa, suggests that water‐extraction and environmental flow rules should aim to maintain hydrological conditions catchment‐wide during both low and high‐flow periods to reduce the risk of impacting fish reproduction. In particular, the results suggest that if perennially flowing sites began to flow intermittently, such as through over‐extraction of water or due to climate change, less diverse fish assemblages may result.This study expands our understanding of the relationships between hydrology and the reproductive ecology of freshwater fish in wet–dry tropical climates and may inform future ecologically based approaches to setting water‐extraction rules. [ABSTRACT FROM AUTHOR]

Flathead gobies (genus Glossogobius) include c. 40 small‐ to medium‐sized benthic fishes found primarily in freshwater habitats across the Indo‐Pacific, having biodiversity value as well as cultural and economic value as food fishes, especially in developing countries. To help resolve considerable confusion regarding the identification of some of the larger‐growing Glossogobius species, a systematic framework was established using nuclear genetic markers, mitochondrial DNA barcoding and phenotypic evidence for a geographically widespread collection of individuals from the waterways of tropical northern Australia. Species boundaries and distribution patterns were discordant with those previously reported, most notably for the tank goby Glossogobius giuris, which included a cryptic species. Genetic divergence was matched with accompanying unique visual characters that aid field identification. Additional taxonomic complexity was also evident, by comparison with DNA barcodes from international locations, suggesting that the specific names applicable for two of the candidate species in Australia remain unresolved due to confusion surrounding type specimens. Although flathead gobies are assumed to be widespread and common, this study demonstrates that unrealised taxonomic and ecological complexity is evident, and this will influence assessments of tropical biodiversity and species conservation. This study supports the need for taxonomic studies of freshwater fishes to underpin management in areas subject to significant environmental change. [ABSTRACT FROM AUTHOR]

In gape-limited predators, gape size restricts the maximum prey size a predator is capable to ingest. However, studies investigating the energetic consequences of this relationship remain scarce. In this study, we tested the hypothesis that gape-size variability influences individual body condition (a common proxy for fitness) in one of the largest freshwater teleost predators, the barramundi. We found that individual barramundi with larger gapes relative to body size had higher body condition values compared to conspecifics with smaller gapes. Body condition was highest soon after the wet season, a period of high feeding activity on productive inundated floodplains, and body condition decreased as the dry season progressed when fish were restricted to dry season remnant habitats. The increased condition obtained during the wet season apparently offsets weight loss through the dry season, as individuals with large gapes were still in better condition than fish with small gapes in the late-dry season. Elucidation of the links between intraspecific variability in traits and performance is a critical challenge in functional ecology. This study emphasizes that even small intraspecific variability in morphological trait values can potentially affect individual fitness within a species' distribution. [ABSTRACT FROM AUTHOR]

Nurseryfish are unique among fishes in that the males carry the fertilized eggs on a supraoccipital hook on their head. In an attempt to learn where, when, and at what salinities spawning occurs, an ichthyoplankton net was towed at 14 stations in the Adelaide River from the mouth (38 ppt) to the most upstream sections of the river (0.1 ppt). Larval nurseryfish (5-27.5 mm SL) were collected, preserved and measured, and water chemistry parameters were recorded with each sample. Larvae were found in the mid-reaches of the river during July-October, most commonly at salinities between 13.6-0.5 ppt. Salinities increased as the dry season progressed. Larvae were not taken at salinities higher than 19 ppt, nor did they occur in the upper-most reaches of the river system during this time of the dry season. What nurseryfish do and where they occur during the massive influx of freshwater runoff during the wet season (November-April) remains a mystery. Electrofishing for nurseryfish proved to be ineffective in the Adelaide River due to its extraordinary turbidity which made recovery of stunned fish difficult and fresh material of males carrying eggs remains elusive. Two historic photographs showing males carrying eggs are described. [ABSTRACT FROM AUTHOR]

This study was undertaken to determine the spawning season of the nurseryfish, a species with a unique method of parental care found only in northern Australia and southern New Guinea. Monthly samplings with an ichthyoplankton net at the same locality in the Adelaide River over multiple years yielded no larval nurseryfish in February, March, April and May. Larvae first appeared in June and were collected each month until January. From this we conclude that the nurseryfish spawning season in the Adelaide River is June-January. Twelve other larval fish species from 10 families were collected in the plankton tows with nurseryfish. Larval nurseryfish are readily identified and separated from other larval fishes by their peculiar rib anatomy, an important diagnostic character of Kurtus. The development of the unusual rib anatomy is examined with three-dimensional micro-computerised tomography scans of 12-21-mm standard length (SL) specimens. The bony protection of the swim bladder formed by the ribs is visible in the smallest postflexion specimens examined and is essentially complete by 19mm SL. These ecological and anatomical observations add another pixel to the big picture of nurseryfish life history. [ABSTRACT FROM AUTHOR]

The Nurseryfish Kurtus gulliveri is found in estuarine and freshwater reaches of tropical rivers in northern Australia and southern New Guinea. Nurseryfish have been recorded in salinities ranging from fresh-water to seawater (salinity <0.5-36‰), but almost nothing is known of their movements. We conducted core-to-edge transect analyses of 87Sr/86Sr in the otoliths of 16 male and 14 female Nurseryfish collected from a tropical river in northern Australia to examine their movements across a freshwater--estuarine salinity gradient. Comparisons between water and otolith 87Sr/86Sr showed that most fish had 87Sr/86Sr values indicative of periods of saline (salinity > 4‰) residence during their early life history, usually followed by a distinct transition into brackish (0.5-4‰) or fresh water (<0.5‰) later in life. No differences were discernible between the salinity histories of male and female Nurseryfish. Analysis of the relationship between the otolith core-to-edge distance and fish mass indicated that most growth occurred in brackish water. We conclude that Nurseryfish are euryhaline rather than diadromous and that analysis of water and otolith 87Sr/86Sr is an effective method for assessing the movements of tropical riverine fishes and the potential importance of fish migration in driving foodweb subsidies. [ABSTRACT FROM AUTHOR]

Emerging infectious diseases are increasingly originating from wildlife. Many of these diseases have significant impacts on human health, domestic animal health, and biodiversity. Surveillance is the key to early detection of emerging diseases. A zoo based wildlife disease surveillance program developed in Australia incorporates disease information from free-ranging wildlife into the existing national wildlife health information system. This program uses a collaborative approach and provides a strong model for a disease surveillance program for free-ranging wildlife that enhances the national capacity for early detection of emerging diseases. [ABSTRACT FROM AUTHOR]