Sand Flathead Research Articles

Development of matrix-specific standards for LA-ICP-MS zinc analysis in sand flathead (Platycephalus bassensis)

The use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to analyse soft tissues is limited because of the lack of suitable certified reference materials resulting in difficulties with calibration. In this study, several laboratory-prepared thin agarose sections were tested as matrix-specific standards. Our results showed 1 mm thin agarose sections were suitable as calibration standards for LA-ICP-MS Zn analyses in fish muscle, especially when the signal intensity of 66Zn was normalised to 13C. The thin agarose standard sections were used for LA-ICP-MS Zn analyses in the muscle of melanised and non-melanised sand flathead collected from a polluted estuary and assigned with different melanisation scores. Zn levels in melanised regions of fish muscle were determined to be significantly higher than non-melanised regions across all melanisation scores, though Zn levels in the melanised regions of muscle were not significantly different between sand flathead with different melanisation scores. In non-melanised regions of muscle from fish with melanisation and fish unaffected by melanisation, Zn levels were around baseline levels. Overall, this study has successfully developed matrix-specific standards for LA-ICP-MS analysis of soft tissues, thus allowing broader application of this analytical technique in future environmental pollution studies.

Links between elevated zinc levels, diet and muscle melanisation in sand flathead (Platycephalus bassensis) from polluted estuaries

Muscle melanisation in sand flathead is defined as the presence of abnormal black spots in the fish's flesh and the phenomenon has been associated with Zn pollution in the environment. In this study, Zn levels in the fish muscle and crabs were analysed to investigate the role of Zn in causing muscle melanisation and the fish's uptake of Zn via its diet, crabs. An improved technique for extracting melanised fish muscle from fillets with black spots was developed. It enabled Zn levels in melanised muscle to be more accurately determined when compared to previous study and showed Zn levels were 2.1–3.5 times higher in melanised regions of muscle than non-melanised regions of muscle from fish with melanisation and fish unaffected by melanisation. This indicated elevated levels of Zn were localised in the melanised muscle. Muscle melanisation was potentially caused by Zn ions binding to the active site of tyrosinase, an enzyme involved in melanin production, likely facilitated by the presence of higher Zn than Cu in the polluted estuaries. A digestion reagent mixture suitable for microwave assisted acid digestion and analysis of Zn in the whole crab was developed using a mixture of HNO3 and H2O2. Zn levels in the whole crab were 1.5 times higher in 50% of the crab species studied from a polluted estuary compared to the same species from an unpolluted estuary. As sand flathead primarily feed on crabs, the fish's diet was a likely source of elevated Zn for the fish. Overall, this study has described new techniques useful for the study of melanised fish and heavy metal levels in the whole crab. The findings from this study also provided insights that will inform and guide the direction of future research on muscle melanisation in sand flathead.

The use of image analysis techniques for the study of muscle melanisation in sand flathead (Platycephalus bassensis)

Muscle melanisation in sand flathead is visible as black spots in the normally white flesh of fish. It is widespread in Tasmania, including at the Tamar Estuary, with increasing frequency of reporting by recreational fishers. The phenomenon is more prevalent in areas impacted by heavy metal pollution and has been linked to heavy metal accumulation. In this study, image processing software ImageJ was employed to study the phenomenon and to establish an objective rating system. A longitudinal profile plot was used to study the greying of the fillet. The degree of melanisation was rated based on the percentage surface area melanised on the surface and in transverse sections of fillets. A muscle melanisation scoring system for sand flathead was established based on visual interpretation using the macroscopic melanisation scoring criteria: melanisation scores 0 = <0.5%, 1 = 0.5–5%, 2 = 5–20%, and 3 = >20% (% = melanised surface area in proportion to the whole fillet). A refined image analysis technique was developed to quantify the percentage of melanised muscle surface area and the muscle melanisation scoring system was statistically validated. Sand flathead fillet with higher melanisation score was shown to be linked to increased intensity of greyness and greater numbers and size of black spots on the surface of fillets and within the flesh. The greying and black spots were primarily concentrated at the anterior region of fillet and around the dorsal vertebrae zone on transverse section of fillets. Overall, findings from this study established the use of image analysis techniques to validate visual inspection and to give a standardised and objective method to determine the degree of melanisation in sand flathead. As muscle melanisation appears to be linked to heavy metal pollution, the standardised scoring system would facilitate future research for environmental pollution and monitoring purposes.

Integrative species delimitation and community structure of nematodes in three species of Australian flathead fishes (Scorpaeniformes: Platycephalidae).

This study aimed to determine the integrative characterisation of nematodes from three species of edible flathead fishes (Scorpaeniformes: Platycephalidae) in New South Wales, Australia, and describe nematode communities within three species of flatheads. Tiger (Platycephalus richardsoni (Castelnau); n = 20) and sand flatheads (Platycephalus bassensis (Cuvier); n = 20), sourced from the Nelson Bay area, and dusky flathead (Platycephalus fuscus (Cuvier); n = 20) from the Manning River, Taree, were examined for the presence of nematodes. The nematodes were initially classified morphologically as 12 different morphotypes belonging to the families Anisakidae (Anisakis types I, II, and III, Contracaecum type II, Terranova types I and II), Raphidascarididae (Hysterothylacium types IV, VI, VIII, and H. zhoushanense larva), and Gnathostomatidae (Echinocephalus sp. larva), Capillariidae (Capillaria sp.), followed by genetic identification through sequencing of the internal transcribed spacer (ITS-1, 5.8S, ITS-2) regions. Phylogenetic analyses revealed the evolutionary relationship between the identified larval specimens in the present study with available GenBank larval and adult nematodes. Sand flathead was 90% infected with nematodes followed by tiger flathead at 85% and dusky flathead at 15%. Nematodes infecting estuarine dusky and oceanic sand and tiger flatheads contrasted markedly. The analysis of similarities (ANOSIM) showed significant differences (p < 0.001) in the composition of taxa within nematode communities between the three species of flatheads (global R = 0.208) with the highest difference being between sand and dusky flatheads (R = 0.308, p < 0.001). The findings of the present study provide a foundation for future investigations of the community composition, life cycles, and distribution of nematode populations in edible fish in Australia and explore and clarify their significance to public health.

Home range, site fidelity and synchronous migrations of three co-occurring, morphologically distinct estuarine fish species

Determining the movement behaviours of animals is essential for understanding population dynamics. This is fundamental for developing effective spatial management strategies and in assessing the response of species to anthropogenic disturbance. This study uses a Bayesian state-space model applied to acoustic transmitter data to describe the temporal and spatial movement patterns of three estuarine fish species commonly targeted by recreational anglers in southeast Australia: Black Bream (Acanthopagrus butcheri), Sand Flathead (Platycephalus bassensis), and Brown Trout (Salmo trutta). Despite morphological differences between the three species, several common traits were observed in their movement and behaviour. Of the 50 individuals across all three species that were tracked, the vast majority remained within the estuary where they were tagged for the duration of the study. While the home ranges of the three species differed in size, all individuals remained resident around the mid-estuary where the majority of fish were tagged were released. Each of the species also displayed seasonal migrations, presumably linked to spawning. The timing of the beginning of these migrations was well synchronised both within and among species, starting in late spring/early summer. This suggests that environmental factors such as water temperature and day length may play an important role in cueing spawning behaviour for each of the species. These migratory behaviours suggest adverse changes to estuarine conditions such as reduced river flows may have potential consequences for spawning success for some species and hence implications for fisheries management.

Metabolomics Provide Sensitive Insights into the Impacts of Low Level Environmental Contamination on Fish Health-A Pilot Study.

This exploratory study aims to investigate the health of sand flathead (Platycephalus bassensis) sampled from five sites in Port Phillip Bay, Australia using gas chromatography-mass spectrometry (GC-MS) metabolomics approaches. Three of the sites were the recipients of industrial, agricultural, and urban run-off and were considered urban sites, while the remaining two sites were remote from contaminant inputs, and hence classed as rural sites. Morphological parameters as well as polar and free fatty acid metabolites were used to investigate inter-site differences in fish health. Significant differences in liver somatic index (LSI) and metabolite abundance were observed between the urban and rural sites. Differences included higher LSI, an increased abundance of amino acids and energy metabolites, and reduced abundance of free fatty acids at the urban sites compared to the rural sites. These differences might be related to the additional energy requirements needed to cope with low-level contaminant exposure through energy demanding processes such as detoxification and antioxidant responses as well as differences in diet between the sites. In this study, we demonstrate that metabolomics approaches can offer a greater level of sensitivity compared to traditional parameters such as physiological parameters or biochemical markers of fish health, most of which showed no or little inter-site differences in the present study. Moreover, the metabolite responses are more informative than traditional biomarkers in terms of biological significance as disturbances in specific metabolic pathways can be identified.

Muscle melanisation of southern sand flathead (Platycephalus bassensis) in the Tamar Estuary, Tasmania, Australia

Tasmanian recreational fishers have reported the presence of dark pigmentations in the usually white fillets of southern sand flathead (Platycephalus bassensis), a phenomenon known as muscle melanisation. Based on histology, it is suggested that eumelanin and pheomelanin are involved in the occurrence of the phenomenon. A gross melanisation scoring system was validated through a comparison with an image analysis technique, that quantified the percentage surface area of the fillets affected by muscle melanisation. The occurrence of muscle melanisation was most severe in fish inhabiting Deceitful Cove, Tamar Estuary. This indicated that muscle melanisation in P. bassensis may be caused by yet to be identified site specific factors. No significant relationships were evident between the percentage surface area of melanised muscle with condition index, age, sex, maturation stage, fish weight, fish length and size of melano-macrophage centres in the liver or spleen. Overall, this study has provided critical information that will frame the direction and focus of future P. bassensis muscle melanisation research.

Muscle melanisation in sand flathead (Platycephalus bassensis) and links to elevated zinc levels.

Melanisation of muscle, observed as black pigmentation of the normally white flesh, has been reported in sand flathead from Tasmania and investigated in this study. There was a significant difference in the presence of melanised muscle in sand flathead from two sites within the Tamar Estuary (northern Tasmania), with higher proportion of sand flathead from Deceitful Cove with this condition. Presence of melanisation was not related to length or weight of the fish. No parasitic infections were detected in the muscles of the affected sand flathead. However, concentration of zinc in melanised regions of muscle in the affected fish was significantly higher, about 1.7 to 1.8 times, than non-melanised regions of muscle in the same fish. Furthermore, the concentration of zinc in melanised regions of affected fish was on average about 2.0 times higher when compared to muscle of unaffected fish that had no melanised spots.

Comparing indicators of recreational fishing in Port Phillip Bay, Australia, from 2008 to 2011 with variability from a background period (2003–07)

Understanding the effects of anthropogenic disturbances on marine environments that support recreational fisheries requires suitable monitoring data. Although catch rates are frequently considered to inform resource status for commercial fisheries, similar time series data are generally unavailable for recreational fisheries. This study is based on 9 years of data from boat-based recreational fishing surveys in Port Phillip Bay, Australia. Harvest rates and length distributions of the retained catches for three target species were statistically compared over 4 years following commencement of shipping channel dredging (2008–11) with variability from a background period (2003–07). Mean harvest rates were generally within historical ranges, with increases for snapper (Chrysophrys auratus) and King George whiting (Sillaginodes punctatus) and decreases for sand flathead (Platycephalus bassensis). Length–frequency distributions were not significantly different to the background period, except for increased mean length of snapper and King George whiting in 2011. This study demonstrates that data obtained from sampling recreational fishers can provide valuable information to monitor harvested resources and maintain social amenity for recreational fisheries during periods of anthropogenic disturbance. Trends in harvest rates from recreational fishing surveys may also complement catch rates from commercial fisheries for assessments of multisector fisheries or stand-alone assessments for recreational-only fisheries.

Hepatic expression of metal-related genes and gill histology in sand flathead (Platycephalus bassensis) from a metal contaminated estuary

Hepatic gene expression and gill histology were measured in sand flathead (Platycephalus bassensis) from a metal polluted estuary. The gene expression analyses were conducted on fish from two most polluted sites and a reference site. The metal-related genes were metal-regulatory transcription factor 1 (MTF1), transferrin (TF), ferriportin1 (FPN1), ferritin and metallothionein. The transcripts of MTF1, TF, and FPN1 were significantly higher in the liver of fish caught at polluted sites, suggesting these genes are potential biomarkers for environmental exposure to metal. Strong correlations were found between the transcripts of these three genes. Four types of gill lesions such as hyperplasia and lamellar fusion, epitheliocystis, telangiectasis, and deformed filament were observed in sampled fish. There was significant difference in the prevalence of epitheliocystis and telangiectasis between the fish from the polluted areas and reference area. Gill parasites were less prevalent in the flathead from polluted sites. The gill histopathological results indicated both pollutants and infections could contribute to gill lesions.

Using a multi-biomarker approach to assess the effects of pollution on sand flathead (Platycephalus bassensis) from Port Phillip Bay, Victoria, Australia

Hepatic gene expression and liver histology were examined in sand flathead (Platycephalus bassensis) from six locations in Port Phillip Bay, Victoria, Australia. Four sets of genes including thyroid-related genes (D1, D2, TTR, TRα and TRβ), metal metabolism-related genes (MT, MTF1, TF, Ferritin and FPN1), apoptosis-related genes (Diablo/SMAC1, Diablo/SMAC2 and CYP1A) and an endoplasmic reticulum stress biomarker gene (GRP78) were examined in female flathead using qRT-PCR. TRβ and Diablo/SMAC1 gene expression was significantly up-regulated in fish from all polluted sites compared to those from a reference site. The transcripts of TRα and FPN1 were significantly higher in flathead from Corio Bay, while the hepatic mRNA of TTR and GRP78 were significantly lower in those fish. Positive correlations were observed between Diablo/SMAC1 and CYP1A, D2 and TRβ, TRα and TRβ. This study demonstrates that application of pathway-based biomarker genes and histopathology can provide comprehensive information on the impact of environmental pollutants on fish.

Thyroid hormone related gene transcription in southern sand flathead (Platycephalus bassensis) is associated with environmental mercury and arsenic exposure

Arsenic (As) and mercury (Hg) are ubiquitous elements known to disrupt thyroid function in vertebrates. To explore the underlying mechanisms of Hg and As on the fish thyroid system, we investigated the associations between muscle concentrations of Hg and As with thyroid-related gene transcription in flathead (Platycephalus bassensis) from a contaminated estuary. We sampled fish at several sites to determine the hepatic expression of genes including deiodinases (D1 and D2), transthyretin (TTR), thyroid hormone receptors (TRα and TRβ) and related them to Hg and As levels in the same individuals. Negative correlations were observed between Hg levels and D2, TTR, TRα and TRβ, whereas positive associations were found between As concentrations and TTR and TRβ. These results suggest that Hg and As exposures from environmental pollution affect the regulation of genes important for normal thyroid function in fish. These thyroid-related genes could be used as biomarkers for monitoring environmental thyroid-hormone disrupting chemicals.

Health Status of Sand Flathead (Platycephalus bassensis), Inhabiting an Industrialised and Urbanised Embayment, Port Phillip Bay, Victoria as Measured by Biomarkers of Exposure and Effects.

Port Phillip Bay, Australia, is a large semi-closed bay with over four million people living in its catchment basin. The Bay receives waters from the Yarra River which drains the city of Melbourne, as well as receiving the discharges of sewage treatment plants and petrochemical and agricultural chemicals. A 1999 study demonstrated that fish inhabiting Port Phillip Bay showed signs of effects related to pollutant exposure despite pollution management practices having been implemented for over a decade. To assess the current health status of the fish inhabiting the Bay, a follow up survey was conducted in 2015. A suite of biomarkers of exposure and effects were measured to determine the health status of Port Phillip Bay sand flathead (Platycephalus bassensis), namely ethoxyresorufin-O-deethylase (EROD) activity, polycyclic aromatic hydrocarbons (PAH) biliary metabolites, carboxylesterase activity (CbE) and DNA damage (8-oxo-dG). The reduction in EROD activity in the present study suggests a decline in the presence of EROD activity-inducing chemicals within the Bay since the 1990s. Fish collected in the most industrialised/urbanised sites did not display higher PAH metabolite levels than those in less developed areas of the Bay. Ratios of PAH biliary metabolite types were used to indicate PAH contaminant origin. Ratios indicated fish collected at Corio Bay and Hobsons Bay were subjected to increased low molecular weight hydrocarbons of petrogenic origin, likely attributed to the close proximity of these sites to oil refineries, compared to PAH biliary metabolites in fish from Geelong Arm and Mordialloc. Quantification of DNA damage indicated a localised effect of exposure to pollutants, with a 10-fold higher DNA damage level in fish sampled from the industrial site of Corio Bay relative to the less developed site of Sorrento. Overall, integration of biomarkers by multivariate analysis indicated that the health of fish collected in industrialised areas was compromised, with biologically significant biomarkers of effects (LSI, CF and DNA damage) discriminating between individuals collected in industrialised areas from observations made in fish collected in less developed areas of the Bay.

Contaminant (PAHs, OCs, PCBs and trace metals) concentrations are declining in axial tissue of sand flathead (Platycephalus bassensis) collected from an urbanised catchment (Port Phillip Bay, Australia)

Concentrations of PAHs, OCs, PCBs and trace metals were determined in the white muscle of sand flathead Platycephalus bassensis collected at 6 locations in Port Phillip Bay during 2015. No PAHs, OCs or PCBs were detected in the white muscle of sand flathead at any of the locations, however measurable levels of As, Cu, Hg, Se and Zn were detected at all sites. Only As and Hg exhibited regional difference in white muscle concentrations, with As present only in a non-toxic organic form and Hg measured at levels that are comparable to levels reported in reference sites in other studies. All contaminants detected in the white muscle of sand flathead collected in Port Phillip Bay in 2015 were below Australian Food Standards guideline values, and by world standards, the Port Phillip Bay sand flathead population is considered minimally contaminated. Furthermore, tissue contaminant concentrations appear to be decreasing over time.

The use of acoustic accelerometer tags to determine seasonal changes in activity and catchability of a recreationally caught marine teleost

Abstract Understanding the way catchability of exploited fish species varies due to changes in individual fish behaviour is a seldom addressed but important requisite for extracting accurate information on fish abundance from catch per unit effort (cpue) data, particularly from baited gears. In this study, cpue data analysis was combined with analysis of movement and activity data from acoustic telemetry tags to determine the nature of seasonal changes in cpue of the recreationally caught sand flathead (Platycephalus bassensis) in a coastal bay and estuary in southeast Tasmania, Australia. Water temperature had a significant influence on cpue of sand flathead with lower catches at lower temperatures. Yet, even at the relatively small scale of this study (10 s of km), the mechanisms in which temperature affects cpue were highly area specific. In the shallow, estuarine part of the study area, changes in cpue were driven by changes in availability, due to seasonal movements of fish in and out of the area. In the deeper bay at the mouth of the estuary, on the other hand, changes in cpue with temperature were most likely driven by temperature-related changes in activity. At lower temperatures, fish were less active, indicating that fish will have a lower probability of encountering bait as well as lower feeding motivation due to lower metabolic debt. This shows the importance of the inclusion of an environmentally influenced catchability parameter in stock assessment models that utilize cpue data from baited gear types, which is often only done implicitly on a coarse temporal scale by accounting for changes in cpue with season. Our study furthermore highlights the usefulness of acoustic telemetry in a fisheries context beyond the basic study of fish movement, allowing the monitoring of activity levels of exploited fish in relation to environmental parameters in the field.

Tailoring codend mesh size to improve the size selectivity of undifferentiated trawl species

AbstractTiger flathead, Neoplatycephalus richardsoni (Castelnau), and sand flathead, Platycephalus bassensis Cuvier, are undifferentiated and managed with a common legal minimum length (LML). The Commonwealth Trawl Sector (CTS) and the Tasmanian Danish‐seine fishery (TDSF) use a minimum codend mesh sizes of 90 and 70 mm, respectively. The codend mesh size should be tailored to the LML, which is based on the length of first maturity of females (M50). This study found the length–girth relationship of N. richardsoni and P. bassensis was not significantly different. Using the covered codend method, these two species had 50% retention lengths (L50) of 294 ± 2 and 307 ± 3 mm, in 70‐mm and 90‐mm codends, respectively. L50 estimates for mesh sizes from this study and others produced a curvilinear relationship: y = 120 ln(x) − 214, with an r2 of 0.8504. The size at maturity (M50) for female N. richardsoni was 337 mm, which is larger than the estimate for female P. bassensis (247 mm). There is a mismatch between the estimates of L50, the estimates of M50 and the LMLs in each fishery, leading to suboptimal exploitation of female Platycephalus. The model produced in this paper recommends a codend mesh size of 98 mm for both fisheries to exploit Platycephalus species sustainably.

Long term trends of Hg uptake in resident fish from a polluted estuary

Mercury contamination of fish is dependent upon a system’s ability to transform inorganic Hg into biologically available forms; however, fish biometrics also play an important role. To assess long term trends in Hg concentrations in sand flathead (Platycephalus bassensis) a polynomial model, corrected for fish length, was used to evaluate temporal trends and spatial variability, while growth rates were estimated using the Von Bertalanffy length-at-age model. Hg concentrations showed no decrease over time, and generally remained near recommended consumption levels (0.5mgkg−1). Previously reported spatial differences in Hg concentrations were not supported by the data once the models were corrected for fish length. Growth rate variation accounted for a large part of the previously published spatial differences. These results suggest that inclusion of fish biometrics is necessary to facilitate an accurate interpretation of spatial and temporal trends of contaminant concentrations in long term estuarine and marine monitoring programs.

Occurrence and abundance of anisakid nematode larvae in five species of fish from southern Australian waters

The aim of the present study was to conduct, in southern Australian waters, a preliminary epidemiological survey of five commercially significant species of fish (yellow-eye mullet, tiger flathead, sand flathead, pilchard and king fish) for infections with anisakid nematodes larvae using a combined morphological-molecular approach. With the exception of king fish, which was farmed and fed commercial pellets, all other species were infected with at least one species of anisakid nematode, with each individual tiger flathead examined being infected. Five morphotypes, including Anisakis, Contracaecum type I and II and Hysterothylacium type IV and VIII, were defined genetically using mutation scanning and targeted sequencing of the second internal transcribed spacer of nuclear ribosomal DNA. The findings of the present study provide a basis for future investigations of the genetic composition of anisakid populations in a wide range of fish hosts in Australia and for assessing their public health significance.

Implications of Age, Size and Region on Mercury Contamination in Estuarine Fish Species

This study investigated the effects of age and length on mercury contamination in four fish species; yellow-eye mullet (Aldrichetta forsteri), black bream (Acanthopagrus butcheri), sand flathead (Platycephalus bassensis) and sea-run brown trout (Salmo trutta) from the Derwent Estuary, Tasmania, Australia, and examined the implications of these findings for public health monitoring. Mean mercury levels exceeded the Food Standards Australia and New Zealand maximum permitted level (0.5 mg kg �1 ) for all species except yellow-eye mullet. Mean levels in black bream were significantly higher (p<0.05) than other species and consequently are a particular concern for human health. Regional differences (p< 0.05) in mercury levels in sand flathead were not obviously correlated with metal levels in the sedi- ments. However, age and length significantly (p< 0.05) influenced mercury levels in brown trout and sand flathead, with age being more strongly related to intraspecies differences. In addition, movement and distribution within the estuary and trophic status appeared to be important factors in contribution to interspecific variation. Consequently, a sound under- standing of fish life history and biology is important in identifying species which may be susceptible to accumulating mercury and hence pose a potential threat to human health.

Spatio-temporal variability in reproductive ecology of sand flathead,Platycephalus bassensis, in three Tasmanian inshore habitats: potential implications for management

Temporal and spatial variability in gonad development, duration of spawning period, and size ⁄ age at maturity were investigated in sand flathead, Platycephalus bassensis. A 3-year study (2001–2003) revealed that variation in gonad weight with somatic weight was a function of an interaction between season and study location (Coles Bay, Georges Bay, and Tamar River estuary). Highest gonad weight was recorded in Coles Bay in early summer, which in comparison to Georges Bay, was approximately 50% higher and occurred 3 months later. Tamar River mature individuals were reproductively inactive during the spawning season. The proportion of mature individuals at different stages of maturity differed significantly among the three locations across all times. Coles Bay individuals were reproductively active from October to March, while in Georges Bay females with hydrated oocytes were seen in September but were absent from the population by November. Interannual variation in initiation and duration of spawning activity was evident in each location. Apart from male size at maturity, for both sexes the size and age at maturity (L50) was higher in Georges Bay compared to Coles Bay. The results emphasize the necessity of temporal and spatial management based on population differences in reproductive ecology.