Nematalosa Erebi Research Articles

Spatial and Temporal Patterns in Fish Assemblages Following an Artificially Extended Floodplain Inundation Event, Northern Murray-Darling Basin, Australia

Water extraction from dryland rivers is often associated with declines in the health of river and floodplain ecosystems due to reduced flooding frequency and extent of floodplain inundation. Following moderate flooding in early 2008 in the Narran River, Murray-Darling Basin, Australia, 10,423 ML of water was purchased from agricultural water users and delivered to the river to prolong inundation of its terminal lake system to improve the recruitment success of colonial waterbirds that had started breeding in response to the initial flooding. This study examined the spatial and temporal patterns of fish assemblages in river and floodplain habitats over eight months following flooding to assess the possible ecological benefits of flood extension. Although the abundances of most fish species were greater in river channel habitats, the fish assemblage used floodplain habitats when inundated. Young-of-the-year (4-12 months age) golden perch (Macquaria ambigua) and bony bream (Nematalosa erebi) were consistently sampled in floodplain sites when inundated, suggesting that the floodplain provides rearing habitat for these species. Significant differences in the abundances of fish populations between reaches upstream and downstream of a weir in the main river channel indicates that the effectiveness of the environmental water release was limited by restricted connectivity within the broader catchment. Although the seasonal timing of flood extension may have coincided with sub-optimal primary production, the use of the environmental water purchase is likely to have promoted recruitment of fish populations by providing greater access to floodplain nursery habitats, thereby improving the ability to persist during years of little or no flow.

The importance of zooplankton in the diets of three native fish species in floodplain waterholes of a dryland river, the Macintyre River, Australia

The zooplankton of freshwater systems has been recognized as an important energy resource for fish of small body size that, in turn, provide energy to piscivorous fish consumers higher up the food web. This study evaluates the importance of zooplankton to the diets of three species of fish living in floodplain waterholes of an Australian dryland river. The species selected for study represent different trophic categories in waterhole food webs: Ambassis agassizii is a microcarnivore, Leiopotherapon unicolor is an omnivore, and Nematalosa erebi is a detritivore. Dietary differences among size classes of each species were also evaluated to understand possible ontogenetic shifts in zooplankton consumption. Ambassis agassizii fed primarily on zooplankton (99.9%, made up mostly of 81.6% Calanoida and 17.4% Moinidae), regardless of the size of individual fish. Leiopotherapon unicolor fed on zooplankton (47%, mostly Daphniidae and Moinidae) and aquatic insects (46.7%). Smaller individuals of Leiopotherapon unicolor (30–49 mm TL—total length) were responsible for 36.1% of the plankton consumed by the species. Nematalosa erebi fed on detritus (84.6%) with zooplankton (Calanoida, Moinidae, and Cyclopoida) contributing only 13.7% of the mean diet. Smaller individuals (40–69 mm TL) were responsible for 98% of the plankton consumed by Nematalosa erebi, and individuals of 40–49 mm (TL) fed exclusively on zooplankton (53.8% Moinidae and 46.2% Calanoida). Although the three fish species had different diets, reflecting differences in species-specific and ontogenetic morphological and behavioral characteristics, zooplankton formed the basis of the diet of all species when young. These results confirm the importance of zooplankton as a major food resource for three fish species and smaller size classes of these species in floodplain waterholes of the Macintyre River, Australia.

Food resource variability in an Australian dryland river: evidence from the diet of two generalist native fish species

To examine how food resource availability links with natural variation in primary productivity in the Moonie River, south-west Queensland, the diets of two native Australian fish species (Nematalosa erebi and Macquaria ambigua) were examined from fifteen waterholes in February, May and September 2006. N. erebi diets reflected strong ‘boom and bust’ patterns of food consumption, with high concentrations of benthic (non-filamentous) algae during boom (flow) times, moving to higher concentrations of filamentous algae and detritus during bust (no flow) periods. M. ambigua diets were primarily dominated by aquatic insects in all sampling periods. Although there was no clear ‘boom to bust’ pattern in relation to flow, M. ambigua secondary prey consumption revealed a compensatory switch between high energy prey (crustaceans) during more productive periods with terrestrial insects during less productive periods. The ability of both species of fish to switch from high to low concentrations of food quality under a variable environmental background allows them to persist through both high productive and low productive periods. This interaction between native biota and variable ‘boom’ and ‘bust’ conditions, and how changes to the natural hydrology will affect it is an important consideration of any future water resource development plans.

Seasonal flooding, instream habitat structure and fish assemblages in the Mulgrave River, north-east Queensland: towards a new conceptual framework for understanding fish-habitat dynamics in small tropical rivers

Strong relationships between seasonal flooding, instream habitat structure and fish assemblages have been well documented in large tropical rivers (e.g. the flood pulse concept). However, the mechanics of these relationships are likely to differ substantially in smaller coastal rivers, such as those in Costa Rica, south-east Brazil and Australia’s Wet Tropics. These systems typically feature steep upland streams with short, deeply incised lowland channels and poorly connected floodplains. This hypothesis was investigated by documenting spatial and temporal variation in fish-habitat relationships in the Mulgrave River, north-east Queensland. Sampling was conducted at four lowland sites under a range of flow conditions, from dry-season baseflows to a one-in-ten-year flood. Longitudinal environmental gradients and fine-scale habitat patches were important in regulating fish assemblage structure during the dry season. However, high wet-season flows, constrained by the deep channel, acted as disturbances rather than gentle flood-pulses. In particular, the mobilisation of bed sediments led to scouring of aquatic vegetation and a dramatic reduction in habitat heterogeneity. Seasonal movements of fish led to significant changes in assemblage structure – from a community dominated by Neosilurus ater, Hypseleotris compressa, Awaous acritosus and Redigobius bikolanus during the dry season, to one dominated by Nematalosa erebi, Ambassis agrammus and Glossamia aprion during the wet season. Based on these observations, together with information from the literature, a conceptual model of fish-habitat dynamics is presented that is better suited to small tropical rivers than those developed in larger systems with expansive floodplains.

Determining diel variation in fish assemblages downstream of three weirs in a regulated lowland river

The diel variation in boat electrofishing catches was investigated on the lower Murray River (south‐eastern Australia), downstream of three low‐level weirs. Fish assemblage composition did not differ among three sites, but differed substantially between day and night. Significantly more small‐bodied species (e.g. Australian smelt Retropinna semoni, flyspecked hardyhead Craterocephalus stercusmuscarum, bony herring Nematalosa erebi and Murray rainbowfish Melanotaenia fluviatilis) and some large‐bodied predators (e.g. golden perch Macquaria ambigua) were caught during daytime samples. Significantly more flatheaded gudgeon Phylipnodon grandiceps, carp gudgeon Hypseleotris spp. and perch Perca fluviatilis were collected at night. The size composition of the fish assemblage also changed over the diel cycle. Significantly smaller goldfish Carassius auratus, flyspecked hardyhead, bony herring and Australian smelt were sampled during the day, while generally smaller individuals of golden perch and the common carp Cyprinus carpio were caught at night. These findings suggest that sampling during both day and night is required to adequately characterize riverine fish assemblages in the context of fish migration studies.

Patterns of connectivity between the Lake Eyre and Gulf drainages, Australia: a phylogeographic approach

Historical barriers to dispersal in freshwater environments can be detected in the genetic structure of organisms living within these environments. Over time, it is possible that a barrier for freshwater organisms becomes passable, allowing gene flow between adjacent populations. The Lake Eyre and Gulf of Carpentaria Basins are adjacent drainages in northern Queensland. Low topography and large-scale flooding events make it possible that connectivity events may have occurred between the drainages throughout history. Documented geological evidence also suggests historical connectivity between the basins in the Pliocene. The present study looked at two widely distributed species, the freshwater fish Nematalosa erebi and the freshwater prawn Macrobrachium australiense, and used mitochondrial sequence data to assess past connectivity between the basins and estimate the timing of these events. Both species showed significant divergence across the drainage divide. There was evidence of two fragmentation events in the N. erebi data and divergence estimates for these events were 160 000 and 350 000 years ago. It was estimated that there has been no dispersal of M. australiense across the drainage divide for over one million years. The discordant evolutionary histories observed suggest that the patterns reflect recent historical environmental events and life-history differences between the two species.

Assessing the biomass of small fish with a split-beam sonar in the Murray River, Australia

Split-beam hydroacoustics revealed large numbers of small fish in the lower reaches of the Murray River in autumn. At slow-flow sites, acoustically estimated fish biomass could reach 102 kg/ha in mid channel, which compares with the biomass level of planktivorous fish in eutrophic lakes. These results were confirmed by direct catches with a push net of Australian smelt ( Retropinna semoni) and juvenile bony herring ( Nematalosa erebi) ranging in length from 18 to 150 mm. Fish densities in the river channel doubled at night compared to the day. The density and total biomass estimates from net catches were strongly correlated with the acoustic data. However, the catch estimates were only 50–60% of the acoustic measurements, which is explained by the limited netting efficiency. The two methods produced similar estimates of fish mean weights. These results suggest that the density and biomass of small fish in open water habitats of the river can be reliably determined with acoustics. The high biomass of planktivorous fish and the diverse zooplankton community found in the same habitat suggest that the fish probably exploit an advantageous ecological niche in the main channel of the Lower Murray. The high biomass of small fish in this reach of the river, which has previously been underestimated, provides a large potential food source for native predators.

Optimising Denil fishways for passage of small and large fishes

Abstract An 8‐m long experimental fishway was trialled at three different slopes [8.3% (1:12), 14.3% (1:7) and 20% (1:5)] to examine the potential of the single‐plane Denil fishway for the passage of small‐ and large‐bodied native fishes in Australia. Fish between 45 and 630 mm ascended the fishway. The lowest slope enabled the full size range of bony herring Nematalosa erebi (Günther), from 45 to 350 mm fork length, to ascend the fishway successfully as well as a higher numerical proportion; 88% at the 8.3% slope compared with 31% at the 20% slope (fish numbers per trial = 33–3936). These results dispel the notion that Denil fishways are inherently poor for small fishes. Manipulating the design parameters of slope, length, width and possibly depth‐over‐breadth ratio enables Denil fishways to pass a wide size range of fish, which may greatly extend their present application and enable them to make a greater contribution to the rehabilitation of diverse fish communities.

Population estimation methods to quantify temporal variation in fish accumulations downstream of a weir

Abstract Temporal changes in the population sizes of seven migratory species were assessed over a 2‐year period prior to the construction of a fishway on the Murrumbidgee River, Australia. Mark‐recapture (Chapman–Petersen) and Jackknife removal methods were used at 3‐month intervals to determine the composition and sizes of migratory fish populations. No difference in population size estimate was detected between the two methods. However, the Jackknife removal estimator generally provided less variable estimates for a greater number of species. Population sizes were greatest during summer and autumn when bony herring, Nematalosa erebi Günther, and common carp, Cyprinus carpio L., dominated the migratory community. Both estimators provided data essential to further the development of an appropriate fish passage facility and could be applied to other sites where the size of migratory fish populations is of interest.

A Large-scale, Hierarchical Approach for Assessing Habitat Associations of Fish Assemblages in Large Dryland Rivers

Multiple-scale assessments of fish-habitat associations are limited despite the fact that riverine fish assemblages are influenced by factors operating over a range of spatial scales. A method for assessing fishhabitat assemblages at multiple scales is proposed and tested in a large Australian dryland river, the Barwon–Darling River. Six discrete mesohabitat types (large wood, smooth bank, irregular bank, matted bank, mid-channel and deep pool) nested within 10 km long river reaches were sampled. Individual reaches were, in turn, nested within four larger geomorphological zones, previously identified along the river. Fish assemblages varied significantly between mesohabitat types and at different spatial scales. Golden perch (Macquaria ambigua), Murray cod (Maccullochella peelii peelii) and common carp (Cyprinus carpio) were strongly associated with large wood, but golden perch and Murray cod exhibited higher habitat specificity than carp. Bony herring (Nematalosa erebi) were more common in shallow edgewater habitats. At the riverscale, regional differences in the fish assemblage occurred at scales closely corresponding to geomorphological zones and these differences were associated with changes in the relative abundance of species rather than the addition or replacement of species. The proposed hierarchical framework improves the efficiency of fish surveys in large rivers by viewing meso-scale fish-habitat associations in the context of larger-scale geomorphological processes.

The fishes of Lake Kununurra, a highly regulated section of the Ord River in northern Western Australia

The Ord River, situated in the east Kimberley region of Western Australia, is regulated by two darns that supply irrigation water for tropical agriculture. The regulation of water in the 55 km span of river between these dams has resulted in this section now resembling a lacustrine rather than riverine environment that is reflected in its name, Lake Kununurra. Utilising various sampling techniques we captured/observed 4157 fish from 19 species in 13 families, whilst the presence of a further three species was confirmed by reliable sources. Nematalosa erebi, Craterocephalus stramineus and Melanotaenia austrahs were the three most widespread and abundant species, being encountered throughout the lake and representing -66% of all fish recorded. Ambassis sp., Arius midgleyi, A. graeHei, Glossamia aprion, Amniataba percoides, Hephaestus jenkinsi, Glossogobius giurus and Toxotes chatareus were found throughout the lake but generally at fewer sites and in smaller numbers (-30% of all fish) than the three dominant species. The remaining species Neosilurus ater, Strongylura kreHtii, Leiopotherapon unicolor, Syncomistes but/eri, Lates calcari{er, Mogumda mogumda, Oxyeleotris lineolatus and Ambassis madeayi were generally found at few sites and in low numbers, and accounted for less than 4% of the overall catch. The regulation of the Ord River has apparently altered the species composition and abundances in Lake Kununurra. For example, marine/estuarine species, commonly encountered in the freshwaters of large northern Australian Rivers, are largely absent, while species such as L. unicolor, which is one of the most abundant species in nearby rivers and tropical Australian rivers in general, contributed to <1°/,) of the total catch.

Fish assemblages of an Australian dryland river: abundance, assemblage structure and recruitment patterns in the Warrego River, Murray - Darling Basin

Fish in dryland rivers must cope with extreme variability in hydrology, temperature and other environmental factors that ultimately have a major influence on their patterns of distribution and abundance at the landscape scale. Given that fish persist in these systems under conditions of high environmental variability, dryland rivers represent ideal systems to investigate the processes contributing to and sustaining fish biodiversity and recruitment in variable environments. Hence, spatial and temporal variation in fish assemblage structure was examined in 15 waterholes of the Warrego River between October 2001 and May 2003. Fish assemblages in isolated waterholes were differentiated at the end of the dry 2001 winter but were relatively similar following high summer flows in January 2002 as a consequence of high hydrological connectivity among waterholes. Small, shallow waterholes supported more species and higher abundances than large-deep waterholes. Large, deep waterholes provided important refuge for large-bodied fish species such as adult yellowbelly, Macquaria ambigua, and the eel-tailed catfish, Tandanus tandanus. Recruitment patterns of bony bream (Nematalosa erebi), Hyrtl’s tandan (Neosilurus hyrtlii) and yellowbelly were associated with high flow events and backwater inundation; however recruitment of yellowbelly and bony bream was also evident following a zero-flow period. Departures from typical flood-induced seasonal spawning patterns may reflect opportunistic spawning behaviours appropriate to the erratic patterns of flooding and dry spells in dryland rivers.

Regional‐scale effects of flow regulation on lowland riverine fish communities in New South Wales, Australia

AbstractLowland reaches of 40 rivers in New South Wales, Australia, were designated as ‘regulated’ or ‘unregulated’, depending upon the degree to which flows were modified by the operation of a dam upstream. Five replicate rivers of each type were selected from the North Coast, South Coast, Darling and Murray regions in the State. Fish communities in each river were sampled in summer and winter in two consecutive years. Regulated and unregulated rivers contained significantly different fish communities, although communities in each region retained characteristic features. The proportion of native species in the total catch was greater in unregulated rivers in all regions, ranging from 27% in the Murray region to 100% in South Coast rivers. In regulated rivers, native species made up 20% of the catch in the Murray region compared with a maximum of 99% in the North Coast. Carp, Cyprinus carpio, were the main alien species contributing to changes in the proportional abundance of native fish. Native species most affected by river regulation were western carp gudgeons, Hypseleotris spp., bony herring, Nematalosa erebi, and striped gudgeons, Gobiomorphus australis. Fifteen native species showed some effect of river regulation on their population structures. Individual species showed positive, negative or mixed positive and negative, effects of regulation, at population, species or community levels. Three abundant alien species and seven native species showed only positive or mixed responses, whereas 13 native species exhibited only negative effects. Flow regulation has reduced the resilience of New South Wales rivers and native fish communities to invasion by alien species. New research has commenced to investigate whether recently introduced environmental flow rules are effective in reducing the effects of river flow alteration on fish communities in New South Wales rivers. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Profenofos residues in wild fish from cotton-growing areas of New South Wales, Australia.

The organophosphorus (OP) pesticide profenofos (O-4-bromo-2-chlorophenyl O-ethyl S-propyl phosphorothioate) is used heavily in cotton-growing areas of eastern Australia toward the end of the growing season. European carp (Cyprinus carpio), bony bream (Nematalosa erebi), and mosquitofish (Gambusia holbrooki) were collected from the cotton-growing areas around Wee Waa, New South Wales, to determine the relationship between profenofos residues and acetyl-cholinesterase (AChE) activity in wild fish. Profenofos concentrations in water, sediment, and fish tissue reflected its general level of use; levels in March 1994 were significantly higher than in 1993 and generally decreased in May, 6 wk after cessation of spraying. Residues in carp and bony bream generally correlated with concentrations in water and sediment, although residues in fish tend to persist longer at some sites. Acetylcholinesterase inhibition was a useful indicator of profenofos exposure within a season, particularly if linked with residue measurements. Bony bream and gravid female mosquitofish recovered AChE levels more slowly than carp or nongravid mosquitofish. Recovery in creeks was generally more rapid than in lagoons.

Hydrological persistence and the ecology of dryland rivers

The flow regime of Cooper Creek, central Australia, is subject to a summer-monsoonal climate and aseasonal cycles associated with the El Nino–Southern Oscillation (ENSO). Analysis of a 48-year hydrograph indicates that floods tend to occur in clusters associated with La Nina episodes. The influence of ENSO is apparent in lagged correlations between discharge and values of the Southern Oscillation Index (SOI), and in measures of coherency derived from cross-spectrum analysis. Hydrological persistence is indicated by partial auto-correlations between floods in successive years. In a cluster of five floods over 1987–1991, cumulative effects were apparent in wetland habitat areas, in water temperature and transparency, and in the recruitment patterns of five fish species: Nematalosa erebi (Clupeidae), Hypseleotris klunzingeri (Gobiidae), Melanotaenia splendida tatei (Melanotaeniidae), Retropinna semoni (Retropinnidae) and Gambusia holbrooki (Poeciliidae). During serial floods, native fish appear to have a recruitment advantage over the exotic Gambusia. Hydrological persistence and its ecological correlates warrant consideration in research, planning and management, particularly in regard to the water resources of arid and semi-arid regions. Copyright © 2000 John Wiley & Sons, Ltd.

An assessment of the effectiveness of a vertical-slot fishway for non-salmonid fish at a tidal barrier on a large tropical/subtropical river

Fishways for salmon in temperate rivers have often been successful, but salmonid-type fishways for non-salmonid species in tropical and subtropical rivers have frequently failed. This study assessed the effectiveness of modifying a salmonid-type pool-and-weir fishway into a vertical-slot design on a tidal barrage on the subtropical Fitzroy River, in Queensland, north-eastern Australia. In 38 paired samples of the top and bottom of the fishway, over 16 months, 29 fish species and over 23 000 fish were collected at a maximum rate of 3400 per day. This study shows much greater potential for success with a vertical-slot fishway as relatively few fish negotiated the original pool-and-weir design. Common species using the vertical-slot fishway included blue-catfish (Arius graeffei [Ariidae]), bony herring (Nematalosa erebi [Clupeidae]), striped mullet (Mugil cephalus [Mugilidae]), barramundi (Lates calcarifer [Centropomidae]), and long-finned eels (Anguilla reinhardtii [Anguillidae]). Freshwater shrimp (Macrobrachium australiense [Palaemonidae]), juvenile crabs (Varuna litterata [Grapsidae]) and long-finned elvers did not ascend the full length of the fishway and specific fishways for these species are recommended. Fish between 25 and 640 mm in length ascended the fishway, although the passage of smaller size classes of immature fish was restricted and this may be important for the sustainability of these migratory populations. The barramundi (200–640 mm) which ascended the fishway were all immature fish. However, during a period of low river flows enlarging the width of the vertical-slot from 0.15 to 0.45 m only encouraged a small number of larger fish (890 mm maximum length) to enter. The strong diel movement patterns of many species will need to be considered in future fishway design. Blue-catfish could ascend the fishway in 2 h, but many fish remained in the fishway and this behaviour may cause crowding and a reduction in fishway capacity. Further work is needed to assess the proportion of fish finding the fishway entrance. However, the findings suggest that vertical-slot fishways with lower water velocities and turbulence than salmonid fishways have great potential to pass the diverse migratory fish fauna of subtropical and tropical rivers. Copyright © 1999 John Wiley & Sons, Ltd.

Natural-series radionuclides in traditional North Australian aboriginal foods

Activity concentrations of the radionuclides 226Ra, 210Pb, 210Po, 238U, 234U, 230Th, 232Th and 227Ac were measured in edible flesh of traditional Aboriginal food items from the Magela and Cooper Creek systems in the tropical Northern Territory of Australia. Fish, buffalo, pig, magpie goose, filesnake, goanna, turtle, freshwater shrimp and freshwater crocodile were studied. Activity concentrations in water were also measured to enable the calculation of concentration ratios (CRs). For most edible flesh samples, activity concentrations followed the approximate order: 210Po≫ 226Ra> 210Pb>[ 234U∼ 238U]>[ 230Th∼ 232Th]. The 210Po/ 210Pb activity ratio was particularly high (greater than 100) for pig flesh. CRs for fish species fall into two groups. Group 1 (bony bream and sleepy cod) had CRs about five times higher than for group 2 (eight other species). CRs for turtle flesh were similar to those for fish in group 1, while those for turtle liver were about a factor of 10 higher. CRs for magpie goose, filesnake, freshwater shrimp, goanna and crocodile flesh were also of the same order as for fish in groups 1 or 2. Calculations of dose resulting from release of wastewaters from uranium mining operations in the region show that the dominant pathway would be uptake of radionuclides, especially 226Ra, by freshwater mussels, followed by radionuclide uptake by fish.

River regulation and fish communities in the Murray‐Darling river system, Australia

AbstractFish communities from four catchments in the Murray—Darling river system were analysed in relation to climate, hydrology and river regulation. Using the annual proportional flow deviation as a measure of river regulation, the Paroo River catchment was assessed as unregulated, the Darling River catchment as mildly regulated and the Murrumbidgee River and River Murray catchments as highly regulated. A total of 11010 fish, representing nine native and three alien species, was caught during high and low flow seasons in the four catchments. Native species, such as golden perch Macquaria ambigua (Percichthyidae), bony herring Nematalosa erebi (Clupeidae) and spangled perch Leiopotherapon unicolor (Teraponidae), dominated fish communities in the Paroo and Darling catchments, but alien species, mostly carp, Cyprinus carpio (Cyprinidae), were also abundant. Both native and alien species were more abundant in these catchments after flooding, but there was little change in species composition between high and low flow seasons at the catchment level. Carp dominated communities in the Murray and Murrumbidgee catchments. There was a significant trend for reduced species diversity in increasingly regulated catchments. River regulation may alter the relative abundance of native and alien fish by desynchronizing environmental cycles and the reproductive cycles of native species. Ordination of species abundances showed discrete fish communities that reflect the geographical separation between catchments. Differences between communities are related to opportunities for dispersal, the environmental tolerances of dominant species and the modifying effects of river regulation. Fish communities in lakes exhibited less seasonal variation than riverine communities within the same catchment, indicating the greater seasonal stability of lakes compared with regulated and unregulated river reaches. Management of fish resources needs to include catchment‐specific strategies within current State and basin‐wide management programmes.

Polycyclic Aromatic Hydrocarbons in Biota from the Brisbane River Estuary, Australia

Six species of aquatic organisms from the Brisbane River estuarine system were sampled and their tissues analysed for polycyclic aromatic hydrocarbons (PAHs). These were the sea mullet,Mugil cephalus, bony bream,Nematolosa come, blue catfish,Arius graffei, mud crab,Scylla serrata, pelican,Pelecanus conspicillatus, and silver gull,Larus novaehollandiae. PAHs in the muscle (fish and birds) and soft (crab) tissue samples were isolated by first hydrolysing these samples and then solvent extraction followed by column chromatography. The compounds were then identified and quantified by gas chromatography and gas chromatography coupled with mass spectrometry. The samples contained low levels of PAHs that ranged in molecular weight from 128 (naphthalene) to 252 (benzo[k]fluoranthene). The highest total PAH level of 195ng g−1, wet weight, was recorded in mullet samples whereas the blue catfish samples yielded the lowest level of 43ng g−1. Relative ratios of low molecular weight (≤3-rings) compounds to those with high molecular weights (≤4-rings) suggested a petroleum related origin for the PAHs detected in the organisms. Results indicated that significant biomagnification of PAHs in the estuarine ecosystem sampled is highly unlikely. Characteristics such as the trophic level and size/age were not significant factors in determining the corresponding tissue PAH levels in the fish and crab species. Tissue lipid content, however, was found to be a primary factor in determining the PAH concentrations in fish species. PAH levels recorded in the samples are comparable to those levels reported from similarly urbanized areas in other geographical locations.

Acute and chronic toxicity of endosulfan to two Australian cladocerans and their applicability in deriving water quality criteria

The acute and chronic toxicity of endosulfan was determined in two Australian cladocerans, Ceriodaphnia dubia and Moinodaphnia macleayi. For C. dubia, the 48-h nominal EC50 (immobilization) was 490 μg/L and the chronic NOEC for reproductive impairment was 10 μg/L. For M. macleayi, the 48-h nominal EC50 (immobilization) was 215 μg/L, and the chronic NOEC was 20 μg/L. A water quality guideline for endosulfan based on cladoceran chronic toxicity may be estimated at 2 μg/L by using an application factor of 0.1 and the LOEC value for C. dubia of 20 μg/L. A much lower guideline of 4 ng/L may be obtained if the acute/chronic ratio calculated for C. dubia is applied to the lowest LC50 value determined for an Australian fish, 0.2 μg/L in the bony bream, Nematolosa erebi. This suggests that the concentration of endosulfan for Australian waters should be less than the level of 10 ng/L given in the Australian Water Quality guidelines for (fresh and marine waters) aquatic ecosystems. Factors which may modify these conclusions under site-specific conditions are discussed.