Australian Fish Species Research Articles

A review of the Arythmacanthidae (Acanthocephala) in Australia with the descriptions of a new genus and 6 new species

ABSTRACT Twenty-eight Australian fish species were infected with 18 taxa of Arhythmacanthidae; 11 characterised to species, 4 to genus and 3 to family. Diagnoses are provided for the genera Heterosentis, Hypoechinorhynchus, Paracanthocephaloides and Yamagutirhynchus n. gen. Heterosentis has four Australian species: H. hirsutus Pichelin & Cribb, 1999, H. paraplagusarium (Nickol, 1972), H. plotosi Yamaguti, 1935, H. lisitsynae n. sp., defined by a proboscis armature of 14–16 rows of 8–9 hooks, 4 large, 4–5 spiniform, and three indeterminate species, two from Western Australia, one from Queensland. Hypoechinorhynchus is represented by Hy. robustus Pichelin, 1999 and Hy. alaeopis Yamaguti, 1939. Paracanthocephaloides is represented in Australia by one indeterminate species and three new species: P. bartonae n. sp. has an armature of 14–16 rows of 3 large, 7 spiniform hooks; P. hustoni n. sp. 12 rows of 5–6 hooks, 2 large, 3–4 spiniform; P. shamsiae n. sp. 12 rows of 5–6 hooks, 2 large, 3–4 spiniform. Paracanthocephaloides cabelleroi (Guptar & Fatma, 1983) is returned to the genus Heterosentis. Paracanthocephaloides golvani Chandra, Hanumantha-Rao & Shyamasundari, 1984 is moved to the genus Gorgorhynchoides as G. golvani n. comb. Yamagutirhynchus n. gen. has a cylindrical proboscis with an expanded middle region. Yamagutirhynchus lymberyi n. sp. and Y. elliotae n. sp. both have proboscis armatures of 10 rows of 4–5 hooks; for Y. lymberyi the largest hooks are 42.5 μm long; for Y. elliotae, 51 μm.

Cryopreservation and Flow Cytometric Analysis of Ovarian Tissue in Murray River Rainbowfish, Melanotaenia fluviatilis.

Simple SummaryFreshwater fish populations are in global decline, with many Australian freshwater species expected to become extinct in the next twenty years. The storage of reproductive cells and tissues at extremely cold temperatures in bio-banks known as “Frozen Zoos”, allows for the indefinite storage of genetic material, meaning that in the event of an extinction, we have a genetic blueprint available to produce new individuals and reintroduce a species into the wild. Here we have developed a cryopreservation protocol for the storage of ovarian tissue from the threatened Murray River Rainbowfish. Many Australian freshwater fish species are threatened with extinction, our methodology provides a framework for the conservation of other fish species in Australia and globally.Freshwater fish populations are declining with many small, Australian fish species at risk of extinction within the next twenty-years. Cryopreservation of reproductive cells and tissues makes it possible to reproduce individuals from a species even after they are extinct in the wild. We describe the successful cryopreservation of ovarian tissue in the Murray River Rainbowfish, Melanotaenia fluviatilis (Order: Atheriniformes). Histology showed that oogonia are 13.70 µm ± 1.75 µm in size, stain positive for germ-line marker Vasa, and represent approximately 2.29 ± 0.81% of cells in the ovary. Flow cytometry was used to analyse ovarian cell suspensions, requiring an optimised tissue digestion protocol. We found that 0.25% trypsin with 1.13 mM EDTA produced cell suspensions with the highest viability (76.28 ± 4.64%) and the highest number of cells recovered per gram of tissue (1.2 × 108 ± 4.4 × 107 cells/g). Subsequent sorting of ovarian cell suspensions by flow cytometry increased oogonial cells in suspension from 2.53 ± 1.31% in an unsorted sample to 5.85 ± 4.01% in a sorted sample (p = 0.0346). Cryopreservation of ovarian tissue showed DMSO-treated samples had higher cell viability post-thaw (63.5 ± 18.2%) which was comparable to fresh samples (82.5 ± 7.1%; p = 0.36). Tissue cryopreserved in 2.0 M DMSO had the highest cell viability overall (76.07 ± 3.89%). This protocol could be applied to bio-banking programs for other species in the Melanotaeniidae, and perhaps species in other families and orders of Australian fish.

Can slowing the rate of water temperature decline be utilized to reduce the impacts of cold water pollution from dam releases on fish physiology and performance?

Cold water pollution (CWP) is caused by releases of unseasonably cold water from large, thermally stratified dams. Rapid and prolonged decreases in water temperature can have depressive effects on the metabolism, growth and swimming performance of fish. However, it is unknown if reducing the rate of temperature decrease could mitigate these negative effects by allowing thermal acclimation/acclimatization to occur. This study investigated the rate of temperature decrease as a potential CWP mitigation strategy in juvenile Murray cod Maccullochella peelii. M. peelii were exposed to a gradual, intermediate or rapid temperature decrease from 24 to 14°C. Energetic costs, locomotor performance, growth and survival were measured to determine if the initial thermal regime affected the thermal acclimation capacity of M. peelii. Cold exposure had significant acute and lasting depressive effects regardless of the rate of temperature decrease, although M. peelii showed varying degrees of thermal compensation in swimming performance and metabolism after 8 weeks of exposure to low temperatures. The short‐term effects of CWP‐like reductions in temperature are significant, but over time M. peelii can offset some of the depressive effects of CWP through thermal plasticity. This study highlights the importance of understanding physiological responses of fish to inform management and conservation. We conclude that rate of water temperature decline cannot be used to mitigate the sublethal effects of CWP on juvenile M. peelii but may still be useful for managing the negative effects in other native Australian fish species.

Fish want to see the light at the end of the tunnel

Picture a poorly designed city with enormous city blocks and few roads. It would probably be difficult to get around, so you might try to avoid going across town if you could. Now, if alleyways were created throughout this city as shortcuts, you might be more likely to walk across town. But what if those alleys were dark, sketchy and had a guy in a trench coat sharpening a knife? Even though you technically can use these alleys as shortcuts, you would almost certainly be too afraid to walk through them. Craig Franklin and colleagues from the University of Queensland in Brisbane, Australia, wondered whether riverine fish are also afraid of using dark alleys. Except the alleyways used by fish are called culverts and they allow rivers and streams to pass underground beneath streets. Culverts can vary in structure, from corrugated plastic tubes to rectangular channels, and function to redirect waterways, reduce erosion near infrastructure and physically connect upstream and downstream environments, but do they also alter the way fish move up and down rivers?The team wanted to know if the abrupt transition between a sunny stream and a dim culvert would act as a barrier to fish movement, so they made an experimental culvert: a 12 m long fish tank with water flowing through it and a light over one side while the other half was blacked out to simulate a natural culvert. In addition, the team included a viewing window in the middle to watch fish travel between the two sides. They then placed several native Australian fish species – one species at a time – in the experimental culvert at different locations to see if the light levels affected their movements.Overall, the team found that the experimental culvert affected fish behaviour. Australian smelt and fly-specked hardyhead strongly preferred the light half, rarely venturing to the dark half. These small species are most active during the day and rely heavily on sunlight to navigate their environment. Meanwhile, the Australian bass joined the dark side of the culvert, rarely visiting the light side. These fish are crepuscular, which means that they are mainly active at dawn and dusk, using their large eyes to see in low light conditions when ambushing unsuspecting prey.While there probably are no cane toads in trench coats sharpening knives in Australian culverts, fish that are active during the day might be afraid of predators – such as Australian bass – lurking in the shadows, reducing their ability to migrate through streams. This means that while culverts may be created with the best intention of connecting fish habitats, they may effectively perform as barriers if they are too dark. So, how much light do day-active fishes need to encourage them to pass through culverts?After testing various light levels, the team found that the light threshold for the daylight-loving species was very low. They do not need much light to find their way around in culverts. However, the researchers measured the light levels in various Australian culverts and found them to be dimmer than the minimum that the fish require, suggesting they may be hindering fish migrations. Fortunately, there is a simple solution to the problem: lights. The scientists suggest that dim lighting could be installed in culverts to help shy fish complete their journeys. Just like everyone in the world right now, daytime fishes also want to see the light at the end of the tunnel.

An investigation of genetic connectivity shines a light on the relative roles of isolation by distance and oceanic currents in three diadromous fish species

Understanding connectivity is crucial for the effective conservation and management of biota. However, measuring connectivity directly is challenging and it is often inferred based on assumptions surrounding dispersal potential, such as environmental history and species life history traits. Genetic tools are often underutilised, yet can infer connectivity reliably. Here, we characterise and compare the genetic connectivity and genetic diversity of three diadromous Australian fish species: common galaxias (Galaxias maculatus), tupong (Pseudaphritis urvillii) and Australian grayling (Prototroctes maraena). For each species, we investigate the extent of genetic connectivity across a study region in south-eastern Australia (~700 km). We further determine the potential roles of contemporary ocean currents in shaping the patterns of genetic connectivity observed. Individuals across multiple rivers were sampled and >3000 single nucleotide polymorphisms were genotyped for each species. We found differences in genetic connectivity for the three species: common galaxias were highly connected, and Australian grayling and tupong exhibited patterns of isolation by distance. The degree of genetic connectivity for tupong and Australian grayling appeared unrelated to oceanic currents. This study indicates that the degree of connectivity for different diadromous species can vary greatly despite broadly similar life history strategies, highlighting the potential value of genetic tools for informing species-specific management plans.

Fish fins as a non-lethal alternative to muscle tissue in stable isotope studies of food webs in an Australian river

This study found a strong relationship between fin and muscle tissue in three Australian fish species, showing that non-lethally collected fin tissue can be used as a proxy for muscle tissue in isotopic trophic studies. We hypothesised that a strong linear relationship exists between fin and muscle δ13C and δ15N isotope ratios, and conversion equations can be developed where differences exist. We analysed fin and muscle tissues of three common species (Cyprinus carpio, Macquaria ambigua and Nematalosa erebi) from the Barwon–Darling River, New South Wales, Australia. There were significant differences between fin and muscle δ13C values for all species, and fin tissue was a good predictor of muscle tissue δ13C (r2=0.77 for all species). The relationship between δ15N values was less consistent, with a significant difference found in one species, but fin tissue was still a good predictor (r2=0.72 for all species). Developing species-specific tissue conversion models results in the least amount of error, but regional models result in similar error and are more accurate than general global models. These results are consistent with prior studies of different species. This study provides tissue conversion models for three species common to Australian lowland rivers, facilitating the inclusion of fish in food web studies with non-lethal collection methods.

Cryopreservation of testicular tissue from Murray River Rainbowfish, Melanotaenia fluviatilis

Globally, fish populations are in decline from overfishing, habitat destruction and poor water quality. Recent mass fish deaths in Australia’s Murray–Darling Basin highlight the need for improved conservation methods for endangered fish species. Cryopreservation of testicular tissue allows storage of early sperm precursor cells for use in generating new individuals via surrogacy. We describe successful isolation and cryopreservation of spermatogonia in an Australian rainbowfish. Testis histology showed rainbowfish spermatogonia are large (> 10 μm) and stain positive for Vasa, an early germ line-specific protein. Using size-based flow cytometry, testis cell suspensions were sorted through “A” (> 9 μm) and “B” gates (2–5 μm); the A gate produced significantly more Vasa-positive cells (45.0% ± 15.2%) than the “B” gate (0.0% ± 0.0%) and an unsorted control (22.9% ± 9.5%, p < 0.0001). The most successful cryoprotectant for “large cell” (> 9 μm) viability (72.6% ± 10.5%) comprised 1.3 M DMSO, 0.1 M trehalose and 1.5% BSA; cell viability was similar to fresh controls (78.8% ± 10.5%) and significantly better than other cryoprotectants (p < 0.0006). We have developed a protocol to cryopreserve rainbowfish testicular tissue and recover an enriched population of viable spermatogonia. This is the first step in developing a biobank of reproductive tissues for this family, and other Australian fish species, in the Australian Frozen Zoo.

Interactions between water depth, velocity and body size on fish swimming performance: Implications for culvert hydrodynamics

Understanding how fish traverse man-made barriers (e.g. road-crossings and culverts) ensures that engineering and design guidelines achieve positive outcomes for fish communities. Water velocity, depth and fish body size are interrelated factors that influence fish passage through culverts. Velocity barriers have been a major focus of culvert remediation efforts to improve fish passage, however wide culvert designs that aim to limit high water velocities, often create shallow depths in the culvert barrel that can potentially impede fish passage. Here, we quantified how water velocity, depth and body size interact to affect fish swimming performance and their ability to traverse a 12 m culvert-scale swimming channel. Juveniles and sub-adults of three large-bodied native Australian fish species, silver perch (Bidyanus bidyanus), Murray cod (Maccullochella peelii) and eel-tail catfish (Tandanus tandanus), were chosen to represent a range of body shapes, swimming styles and capabilities. Each species was swum in nine treatments, consisting of three velocities at three water depths, with their time to fatigue and traverse success rates over 8 m of flume length quantified. We found that B. bidyanus had an exceptional probability of traverse success, with larger individuals traversing faster than smaller sized fish, but they were physically hindered by shallow water depths. The interaction between velocity and depth was non-linear and highly affected the swimming performance and traverse success of M. peelii and T. tandanus, particularly for fish >250 mm and < 100 mm. Our results demonstrate the importance of considering size class and species-specific swimming capabilities in culvert design criteria.

Novel hydraulic guidelines can assist upstream fish passage through smooth box culverts

ABSTRACT Culverts are important hydraulic structures for delivering a range of valuable socioeconomic services; however, they are also known to have negative impacts on freshwater and estuarine river systems, including the blockage of upstream fish passage, particularly small-bodied fish species. Herein new guidelines are proposed for fish-friendly multi-cell smooth box culvert designs, with a focus on small-bodied Australian native fish species and juveniles of larger fish. The new set of hydraulic engineering design guidelines, in the process of being implemented in New South Wales (Australia), optimise culvert design for fish passage for water discharges Q < QT = 0.1× Qdes, for which the reduced-velocity zone (RVZ) represents 15% of the flow area where 0 < Vx < Ufish, with Vx the local time-averaged longitudinal velocity component and Ufish the maximum prolonged swimming speed of target fish species. After a presentation of the basic concepts, a design application is developed based upon a real-world case study in north-eastern New South Wales (Australia). The novel approach relies upon a sound understanding of the velocity flow in the box culvert barrel at less-than-design discharges to accurately characterise the RVZ next to the barrel walls and corners, combined with a detailed understanding of the swimming performance and behaviour of native fish species.

Assessment of the effects of microPIT tags on the swimming performance of small-bodied and juvenile fish

Monitoring the movements of fish enables management decisions to be based on the ecological requirements of the species in question. PIT tags are a cost effective, long-term method of tracking large numbers of fish. As this technology has improved, the size of PIT tags has decreased, enabling smaller species, and younger fish to be tagged and tracked. There is limited information available on the possible effects that these tags have on the survival rates and subsequent health of small fish. Swimming performance is a physiological measure that is easy to quantify in the lab and directly relates to an individual fishes health. We used swimming performance to assess the effect of microPIT tags (8.4 mm) on five small-bodied, and juveniles of five large growing native Australian fish species. In an initial trial to assess suitability for microPIT tagging, two of the small-bodied species had high mortality and were categorised as unsuitable for tagging. Sample sizes were increased for the remaining eight species to quantify potential effects of microPIT tags on swimming performance. For these eight species we found no significant effects of microPIT tags on their swimming performance.

Barriers to hybridisation and their conservation implications for a highly threatened Australian fish species

AbstractHybridisation and introgression are natural phenomena that may lead to the transfer of adaptive alleles from one species to another and increased species diversity. At the same time, hybridisation and subsequent introgression threaten many species world‐wide through the loss of genetic and species diversity. In Australia, introgressive hybridisation between native and alien species has not typically been considered a significant threat to native biodiversity because of the taxonomic distance between native and alien biota. However, many native fish have been introduced outside their natural range. Recently, four taxa in the genus Melanotaenia have been nationally listed as threatened due to introgressive hybridisation with introduced Melanotaenia splendida. We examined pre‐ and post‐zygotic barriers to hybridisation between M. splendida and one of these threatened taxa—Running River rainbowfish (RRR)—to assess the potential for hybridisation to occur. We used dichotomous mate choice experiments to examine pre‐zygotic barriers and mating experiments to examine post‐zygotic barriers. Size was not a significant predictor of the proportion of time subjects spent with a potential mate, nor was there any significant difference in the amount of time subjects spent with potential mates of their own or the opposite species. Eggs from hybrid pairings with female RRR had a slightly higher hatching rate than those from hybrid pairings with female M. splendida, but neither were significantly different from intraspecies crosses. We could not identify any definite barriers to hybridisation, demonstrating that the introduction of “native” fish species outside their natural range poses a higher risk of hybridisation than previously thought. We call for better education around the consequences of moving “native” fish and the development of rapid response plans to deal with recently established alien populations of Australian fish species in order to prevent future extinctions due to introgressive hybridisation.

Utilising the boundary layer to help restore the connectivity of fish habitats and populations

Culverts are a major cause of habitat fragmentation in freshwater ecosystems, are a barrier to fish movement, and can be regarded as a significant contributor in the decline of freshwater fish populations globally. To try to address this, various culvert remediation designs have been implemented, including the installation of vertical baffles and the provision of naturalistic (rock) substrates. While remediation strategies generally aim to reduce the velocity of water flowing through the structure, there is often resistance to their use because the resultant reduction in culvert discharge can negatively impact upstream flooding while also resulting in debris clogging and increased culvert maintenance costs. In addition, baffles markedly increase water turbulence that may be detrimental to passage by some fish species or size classes. Here we present some novel remediation designs that exploit the reduced water velocity in boundary layers along the culvert wall to enhance fish passage without significantly compromising discharge capacity. These longitudinal designs produce an expanded reduced velocity zone along the culvert margins that generate minimal turbulence. We show that these novel designs are significantly advantageous to the swimming endurance and traversability for six small-bodied Australian fish species. We also provide data on how and why some culvert baffle designs may impede small-bodied fish passage. This data scales with increasing water velocity, encompassing inter-specific differences in swimming capacity. These results have broad implications for the movement of small-bodied fish species, and the successful recruitment of large-bodied commercially important species, where baffles have been implemented.

Predicting hydraulic structure-induced barotrauma in Australian fish species

When fish pass downstream through river infrastructure, such as dams and weirs, barotrauma may occur as a result of rapid decompression. In severe cases, barotrauma may lead to mortality. Different species are likely to respond differently to these decompressions. Therefore, to predict barotrauma for a specific species, surrogate species may not be a valid approach, and it may be necessary to examine each species individually. For the present study, Australian bass and carp gudgeon were exposed to a range of rapid decompressions using hyper- and hypobaric hydro-chambers and examined for injuries and mortality. Rapid decompression data from these two fish species, in addition to previously examined Murray cod and silver perch, were evaluated to determine which injuries were highly associated with and likely to predict mortality. Dose–response logistic regression models were developed for each species to predict injury and mortality over a range of rapid decompressions. These models are valuable for estimating injury and mortality rates for fish passing though river infrastructure and can be applied to specific sites where pressure profiles have been developed. Applying these models to current and future infrastructure can provide important insight into what measures or design alterations may be necessary to reduce negative effects of infrastructure on fish populations.

Assessing the potential for trace organic contaminants commonly found in Australian rivers to induce vitellogenin in the native rainbowfish (Melanotaenia fluviatilis) and the introduced mosquitofish (Gambusia holbrooki)

In Australia, trace organic contaminants (TrOCs) and endocrine active compounds (EACs) have been detected in rivers impacted by sewage effluent, urban stormwater, agricultural and industrial inputs. It is unclear whether these chemicals are at concentrations that can elicit endocrine disruption in Australian fish species. In this study, native rainbowfish (Melanotaenia fluviatilis) and introduced invasive (but prevalent) mosquitofish (Gambusia holbrooki) were exposed to the individual compounds atrazine, estrone, bisphenol A, propylparaben and pyrimethanil, and mixtures of compounds including hormones and personal care products, industrial compounds, and pesticides at environmentally relevant concentrations. Vitellogenin (Vtg) protein and liver Vtg mRNA induction were used to assess the estrogenic potential of these compounds. Vtg expression was significantly affected in both species exposed to estrone at concentrations that leave little margin for safety (p<0.001). Propylparaben caused a small but statistically significant 3× increase in Vtg protein levels (p=0.035) in rainbowfish but at a concentration 40× higher than that measured in the environment, therefore propylparaben poses a low risk of inducing endocrine disruption in fish. Mixtures of pesticides and a mixture of hormones, pharmaceuticals, industrial compounds and pesticides induced a small but statistically significant increase in plasma Vtg in rainbowfish, but did not affect mosquitofish Vtg protein or mRNA expression. These results suggest that estrogenic activity represents a low risk to fish in most Australian rivers monitored to-date except for some species of fish at the most polluted sites.

Using telemetry data to develop conceptual models of movement to support the management of riverine fishes

As human demands for freshwater resources increase, there is growing concern for the long-term viability of native fish populations globally. Understanding the movements of fish, and how these are influenced by or respond to environmental changes, is a critical knowledge requirement for effective management; however, limited information on the ecological requirements of many fish species currently hinders our ability to sustainably manage fish populations. In this paper, we use four native Australian fish species with contrasting life histories as case studies to demonstrate how data derived from acoustic and radiotelemetry studies can be synthesised into conceptual diagrams to help scientists and managers develop targeted and effective conservation management strategies. Commonalities in the observed movement patterns were observed among the species despite their contrasting life histories, but there were also important differences that need to be recognised in the development of species-specific conservation management strategies. We conclude by discussing how such information has been or could be incorporated into conservation management actions, including the implementation of environmental flow releases and the identification of critical habitats.

Effects of environmental chemicals on fish thyroid function: Implications for fisheries and aquaculture in Australia

Numerous environmental stressors exert acute or chronic effects on the fish thyroid cascade. Such effects could be mediated via thyroidal alterations, imbalance of plasma T4 and T3 levels or damage to the structure of the thyroidal tissues (thyroid hypertrophy, hyperplasia). The thyroidal system is intricately linked to other endocrine systems in vertebrates including the control of reproduction. Disruption of fish thyroid function by environmental stressors has the potential to result in deleterious effects including the inhibition of sperm production, reduction in egg production, gonad development, ovarian growth, swimming activity, fertilisation and increase in larval mortality. Thyroid hormones play a major role in the development and growth of fish, particularly during their early life stages, thus, thyroid disruption by environmental stressors could inhibit the growth of fish larvae and juveniles in wild fish and cultured species, limit fish seed production and result in a decline in wild fisheries. This review highlights the effects of several environmental toxicants including PBDE, PCBs, PCDD and PCDF, PAH/oil, phthalates, metals, pesticides, mixed pollutants/chemicals, cyanide; and other stressors including acid (low pH) and ammonia, on fish thyroid function. Environmental sources of chemical stressors and appropriate water quality guidelines to protect the freshwater and marine species for the relevant pollutants are also discussed including (when available) the Australian guidelines (2000) and Canadian water quality guidelines (where Australian guidelines are not available). To date there has been no published research on the effects of anthropogenic environmental pollutants on the thyroid system of any native Australian fish species. However, the detection of high risk chemicals (notably PBDEs, PCBs, PAHs, metals and pesticides) in Australian waterways and Australian fish and shellfish implies that thyroid disruption of Australian wild fish and aquacultured species could occur. It is therefore imperative that the effects of such pollutants on the thyroid system of Australian native fish be investigated.

The haematology of six species of native catfish from northern Australia

Haematology has the potential to be a valuable tool in determining the health status of wild fish populations and wider ecosystem health. However, limited haematological data are available for wild Australian fish species, and the interpretation and nomenclature of leukocytes is variable and inconsistent in fish. The morphology and cytochemical reactions of erythrocytes, thrombocytes and leukocytes of 189 wild eel-tailed catfish (Tandanus tandanus), Wet Tropics tandan (Tandanus tropicanus), Hyrtyl’s tandan (Neosilurus hyrtlii), black catfish (Neosilurus ater), lesser salmon catfish (Neoarius graeffei), and silver cobbler (Neoarius midgleyi) are described. Erythrocytes, thrombocytes, lymphocytes, monocytes and heterophils in all six species are morphologically similar to those reported in other Siluriformes. Basophils and eosinophils are rarely reported in fish; however basophils were observed in peripheral blood smears of T. tropicanus and N. ater, and eosinophils were observed in N. graeffei. Periodic acid Schiff positive granular leukocytes were observed in N. graeffei, N. midgleyi, N. ater and T. tandanus. This is the first report on the leukocyte morphology and cytochemistry of any native Australian catfish species, and provides useful baseline data for future assessments of fish health and ecosystem integrity in Australia.

Activity of Endogenous Muscle Proteases from 4 Australian Underutilized Fish Species as Affected by Ionic Strength, pH, and Temperature

Storage conditions may influence the hydrolytic activity of endogenous muscle enzymes postmortem, rate of autolysis of myofibrillar proteins, and biological properties of hydrolyzed end products. This study investigated the effect of ionic strength, pH, and temperature on the activity of endogenous calpain-like, cathepsins B and B+L measured in crude extract obtained from deepwater flathead, silver warehou, ribaldo, and ribbonfish muscles. Activity of calpain-like enzymes in 3 examined species was significantly higher at pH 6.5 than pH 6.0 or 5.5. Raising the reaction temperature increased (P < 0.05) calpain-like activity in ribaldo. Endogenous activity of cathepsin B in ribbonfish and silver warehou declined significantly with increasing ionic strength at pH 6.5 to 6.0. The obtained results will further expand our understanding of the impact that postmortem storage conditions have on the activity of endogenous fish proteases with respect to quality and bioactivity of fish proteins and potentially diversify utilization of underutilized fish species.

Proteolytic activities in fillets of selected underutilized Australian fish species

The hydrolytic activity of major endogenous proteases, responsible for proteolysis of myofibrillar proteins during post-mortem storage, may be an indicator of the textural quality of fish which influences consumer purchasing behaviour and thus market value of the final product. Furthermore, it may also influence the type and bioactive properties of the peptides released during post-mortem proteolysis of myofibrillar proteins. This study compared the activities of cathepsins B, B+L, D, H and calpain-like enzymes in crude muscle extracted from 16 Australian underutilized fish species. Fish species had a significant effect on the activity of these enzymes with barracouta showing the highest cathepsins B, B+L, D and H activities. Activities of cathepsins B and B+L were higher than cathepsin H for all studied species. The more commercially important rock ling and tiger flathead demonstrated higher cathepsin B+L activity, whereas gemfish and eastern school whiting showed higher activity towards cathepsin B. Underutilized fish species showing higher endogenous protease activities may be suitable for fish sauce production, whereas those with lower protease activities for surimi processing.

Balancing conservation and recreational fishery objectives for a threatened fish species, the Murray cod, Maccullochella peelii

AbstractMurray cod Maccullochella peelii (Mitchell) is a large, iconic Australian fish species targeted by anglers but also listed as nationally threatened. A consultative process that included conservation and fishery interests helped to develop a population model for this species and agree on management scenarios to be tested. The modelled scenarios illustrated that threats to populations (risk of decline) can be substantially reduced and catch rates increased through harvest slot length limits (HSLL) rather than minimum legal limits (MLL). A 600‐ to 1000‐mm HSLL provided lower risk of decline and greater catch rates than the existing 500‐mm MLL, but better results were achieved with a 400‐ to 600‐mm HSLL. Importantly, a range of other impacts (fish kills, stocking, thermal impacts, larval mortalities, habitat changes) were recognised and incorporated. This study provides an example of the utility of a population model to improve management decision‐making for both conservation and fishery objectives.