Glaucosoma Hebraicum Research Articles

Implications of big, old, fat, fecund, female fish (BOFFFFs) for the reproductive potential of a demersal teleost stock

The ‘big old fat fecund female fish’ (BOFFFF) hypothesis suggests that larger, older female fish contribute disproportionately more to the reproductive potential of a stock than smaller, younger female fish. As fishing typically differentially removes larger, mature fish, this can negatively impact reproductive potential and impair the recovery of a depleted stock. In this study, the BOFFFF hypothesis was explored quantitatively for the endemic West Australian dhufish (Glaucosoma hebraicum) by estimating the relationships between total length (TL) of females and spawning season duration, spawning frequency and oocyte size. The impacts of these size effects on estimates of reproductive potential of the G. hebraicum stock were also explored using a per-recruit analysis. Larger (900 mm TL), older mature female G. hebraicum were shown to spawn for a longer duration (six versus two months) and on more occasions (155 versus 60 times) than smaller (350 mm TL), younger mature fish, and thus these larger females have higher annual fecundity. Larger, older mature G. hebraicum also spawn, on average, significantly larger oocytes with greater estimated energy content (474.6 μm diameter and 0.234 J versus 379.9 μm and 0.140 J). Due to these size effects, reproductive output of G. hebraicum scales hyperallometrically with fish body mass, rather than isometrically. Not accounting for these size effects in per-recruit analysis resulted in higher estimates of stock reproductive potential and thus stock status. Such overestimates, if used to inform management, have the potential to result in harvest rates being set too high which, in turn, could thus affect stock sustainability.

Glaucosoma hebraicum (westralian jewfish)

This datasheet on Glaucosoma hebraicum covers Identity, Distribution, Further Information.

Geostatistical tools to assess shifts in recreational fishing

The use of geostatistical indices to examine fishery-dependent data over time is novel. We assess the value of a range of these indices for describing trends in boat-based recreational fishing in Western Australia and areas of high effort and catches for two demersal species with varying biological characteristics, life histories and distributions. The number of blocks (10- × 10-nautical mile (~19- × 19-km) area) visited decreased by 40%, while the number of fishing trips with demersal species catch increased by 15%. Spatial indices showed a south-easterly shift in demersal catch per unit effort (CPUE) across survey years. The southerly shift of West Australian dhufish (Glaucosoma herbraicum) CPUE and subsequent return to the north likely to reflect the response of this temperate species to a marine heatwave. In comparison, CPUE of retained Baldchin groper (Choerodon rubescens) shifted north, whereas released catches shifted south with high probabilities of hotspots present associated with habitat structure. We identified hotspots of retained and released CPUE, highlighting potential areas where species experience high post-release mortality through barotrauma, and targeted spatial management strategies. Spatial indices allow quantitative definition of the structure of the fishery, identify high catch areas, and assess changes over time at a broader scale to sustainably manage multispecies fisheries.

Determining spatial patterns in recreational catch data: a comparison of generalized additive mixed models and boosted regression trees

Abstract Marine recreational fisheries (MRFs) are often highly spatially heterogenous, with effort concentrated into small areas, and fisheries spanning large environmental gradients. However, spatially resolved catch data is rarely collected in MRFs, preventing the study of spatial heterogeneity in catch. This study uses recreational catch reported in 10 × 10 nm blocks across eight degrees of latitude in Western Australia to map spatial predictions of the probability of a recreational catch on an average trip for two key species: West Australian dhufish (Glaucosoma hebraicum) and snapper (Chrysophrys auratus). Two spatial modelling techniques are compared for the analysis, generalized additive mixed models (GAMMs) and boosted regression trees (BRTs). We find that BRTs outperform GAMMs, but performance gains are small. We also find marked spatial variations in recreational catch probabilities: high catches of dhufish are found in the north of the study area, and low catches in the Perth Metropolitan area and in the south; snapper catches are highest in the north and low in the south. These patterns are used to identify important spatial processes in the fishery. The analysis also suggests that modelling approach (GAMMs or BRTs) has only a minor effect on outcomes of spatial catch analysis in MRFs.

Evaluation of spatiotemporal imputations for fishing catch rate standardization

As commercial fishing activity shifts to target different grounds over time, spatial gaps can be created in catch rate data, leading to biases in derived indices of fish abundance. Imputation has been shown to reduce such biases. In this study, the relative performance of several imputation methods was assessed using simulated catch rate data sets. Simulations were carried out for three fish stocks targeted by a commercial hook-and-line fishery off the southwestern coast of Australia: snapper (Chrysophrys auratus), West Australian dhufish (Glaucosoma hebraicum), and baldchin groper (Choerodon rubescens). For high-growth scenarios, the mean squared errors (MSEs) of geometric and linear imputations were lower, indicating higher accuracy and precision than that for base method (constant value) imputations. For low-growth scenarios, the lowest MSEs were achieved for base method imputations. However, for the final standardized and imputed abundance indices, the base method index consistently demonstrated the largest biases. Our results demonstrate the importance of selecting an appropriate imputation method when standardizing catch rates from a commercial fishery that has changed its spatial pattern of fishing over time.

Targeted demersal fish species exhibit variable responses to long-term protection from fishing at the Houtman Abrolhos Islands

Natural fluctuations in the abundance and length of targeted fish are often disrupted by acute environmental changes and anthropogenic impacts, particularly fishing pressure. Long-term assessments of targeted fish populations inside and outside areas closed to fishing are often necessary to elucidate these effects, yet few of these studies extend over long time periods. We assessed trends in the abundance and length of six targeted fish species in areas open and closed to fishing on seven occasions spanning a 9-year period (2005–2010 and 2013) at the Houtman Abrolhos Islands, Western Australia. Shallow (8–12 m) and deep (22–26 m) coral-dominated reef sites were sampled across four geographically separated island groups using baited remote underwater stereo-video (stereo-BRUV). Between 2005 and 2010, populations of Lethrinus miniatus, Lethrinus nebulosus, Plectropomus leopardus, and Chrysophrys auratus became increasingly dominated by larger individuals, potentially indicative of an ageing population. Between 2010 and 2013, however, there was a significant increase in the proportion of smaller L. miniatus, L. nebulosus, and P. leopardus in both open and closed areas, reflecting increased recruitment perhaps due to changing environmental conditions associated with a marine heat wave anomaly. This recruitment pulse was not observed for the other species in this study (Chr. auratus, Choerodon rubescens, and Glaucosoma hebraicum). Lethrinus miniatus, L. nebulosus, Chr. auratus, and P. leopardus were larger in closed areas relative to open areas; however, they were not more abundant. These complex responses to protection also varied across sampling years for certain species (e.g., P. leopardus). Monitoring changes over the long-term in areas open and closed to fishing provides a sound basis for separating environmental variability from that associated with fishing mortality, which is crucial for optimising fisheries management.

Sound production by the West Australian dhufish (Glaucosoma hebraicum)

Biological examinations of Glaucosomatid fish species have suggested that they could produce sound via swimbladder vibration, using "sonic" muscles. However, there have been few reported instances of it in the family. West Australian dhufish (Glaucosoma hebraicum) is an iconic teleost, endemic to Western Australia. Dissection of G. hebraicum in this study identified the presence of "sonic" muscle pairs in immature and sexually mature individuals. The muscle tissue originates in the otic region of the skull with its insertion at the anterior of the swimbladder. Recordings of sounds were acquired from two male G. hebraicum, at a range of 1 m, during capture. Calls comprised 1 to 14 swimbladder pulses with spectral peak frequency of 154 ± 45 Hz (n = 67 calls) and 3 dB bandwidth of 110 ± 50 Hz. The mean of all call maximum source levels was 126 dB re 1 μPa at 1 m with the highest level at 137 dB re 1 μPa at 1 m. The confirmation of sound production by G. hebraicum and the acoustic characteristics of those sounds could be used to gain a better understanding of its ecology and, particularly, whether the production of sound is associated with specific behaviors, such as reproduction.

A comparison of the stock structures of two exploited demersal teleosts, employing complementary methods of otolith element analysis

Complementary methods of otolith element analysis (IRMS of stable isotopes and laser ablation ICP-MS of trace elements) were used to elucidate the stock structures in Western Australia of the exploited demersal West Australian dhufish Glaucosoma hebraicum and Snapper Pagrus auratus. Residency of adults during their most recent part of life and the existence of important nursery locations were investigated by analysing otolith margins and cores, respectively, to evaluate the applicability of current spatial management.Stable oxygen isotope ratios (18O/16O) in both margins and cores of G. hebraicum otoliths increased with latitude and thus decreasing mean annual water temperature. Analyses of δ18O, stable isotope composition (SI; δ18O, δ13C) and trace element composition (TE; 25Mg, 88Sr, 138Ba) in otolith margins of G. hebraicum from four management areas on the west coast of Australia indicated that adults were resident in each area. Analyses of elements in otolith cores demonstrated that, by the early juvenile stage (<1year old), individuals will have recruited to the area where they will remain as adults.Analyses of δ18O and both SI and TE compositions in otolith margins of adult P. auratus indicated residency within each of three large bioregions (Gascoyne, GCB; West, WCB; South, SCB) along the west and south coasts of western Australia. As for G. hebraicum, the data also demonstrated residency at the finer scale, i.e. within the four management areas on the west coast. The lack of a conspicuous pattern in δ18O levels in P. auratus otolith cores implied that adults in each area recruited from a range of nurseries. Although both SI and TE composition demonstrated that there was substantial self-recruitment within the WCB and SCB and within two of the four areas of the WCB, stock(s) of P. auratus at the southern extent of the GCB are likely to be partially reliant on immigration.Elemental signatures in otoliths of G. hebraicum and P. auratus demonstrated that adults in each management area of the WCB could be treated as separate stocks. However, while recruitment of juvenile G. hebraicum to adult stocks would occur primarily from adjacent multiple nurseries within areas of the WCB, adult P. auratus in any one bioregion and at least two of the four areas within the WCB were derived from a range of nurseries, including across area and bioregion boundaries.

Response of diurnal and nocturnal coral reef fish to protection from fishing: an assessment using baited remote underwater video

Diel variation is known to alter the composition and structure of reef fish assemblages. What is unknown is how nocturnal fish assemblages respond to closed fishery area management. Diurnal and nocturnal reef fish assemblages at the Houtman Abrolhos Islands, Western Australia, were studied using baited remote underwater stereo-video systems (stereo-BRUVs). Surveys were conducted during the day and at night (using blue illumination) from three sites inside and three sites outside a closed fishery area (CFA). The relative abundance of 116 fish species from 41 families was recorded. Significant changes were observed in fish assemblage structure from day to night (driven by high dispersion at night) and in areas open versus closed to fishing (driven by increased abundance within the CFA). The effect of protection from fishing was consistent for both diurnal and nocturnal fish assemblages. Closer examination of six targeted fish species showed that their response to diel changes and the absence of fishing pressure varied from species to species. The targeted fishes Pagrus auratus and Glaucosoma hebraicum were sampled during the day and at night with both species responding positively to protection from fishing. Results suggest that the inclusion of diurnal and nocturnal fish assemblage data will provide an improved ability to assess the effectiveness of closed fishery area management.

Microsatellite DNA analysis and hydrodynamic modelling reveal the extent of larval transport and gene flow between management zones in an exploited marine fish (Glaucosoma hebraicum)

AbstractDetermining the extent of dispersal in exploited marine fishes is essential for understanding their population dynamics and optimising management. The West Australian dhufish, Glaucosoma hebraicum, is a highly sought‐after, large and long‐lived reef‐dwelling species, endemic to south‐western Australia. Stock assessments indicate that this indicator species is overexploited. The fishery is managed using a zone‐based system, which implicitly assumes a high degree of demographic independence among zones. While tagging studies indicate limited movement of adult G. hebraicum, there is no understanding of the spatial scale of dispersal of its larvae and thus the true extent of interdependence of management zones. We analysed 13 microsatellite DNA loci to characterise the extent of gene flow, and conducted particle tracking simulations to model larval transport in this species. Genetic data demonstrated that some local recruitment was likely, but that on a broad scale gene flow between the management zones was extensive, and the entire fishery represents a single genetic stock. Hydrodynamic modelling predicted that the majority of dhufish larvae recruit from within the management zone where they are spawned, and that inter‐annual variation in current velocities has limited effect on the extent of larval transport. Because management zones are likely to be largely independent in terms of both larval and adult recruitment, heavy localised fishing pressure has the potential to reduce the abundance and reproductive capacity of this species in highly fished areas, but it should have limited impact on neutral genetic diversity.

Historical changes in fishing efficiency in the west coast demersal scalefish fishery, Western Australia: implications for assessment and management

Abstract Marriott, R. J., Wise, B., and St John, J. 2011. Historical changes in fishing efficiency in the west coast demersal scalefish fishery, Western Australia: implications for assessment and management. – ICES Journal of Marine Science, 68: 76–86. The west coast demersal scalefish fishery off the southern part of Western Australia has experienced technological creep over the past 20 years, resulting in improved fishing efficiency. The aim of this study was to obtain quantitative measures of efficiency improvements arising from the historical adoption of several important technologies from the surveys of experienced skippers. Survey results suggest that the relatively rapid adoption of Global Positioning Systems from 1989 to 1991 had a large and overriding effect on fleet-wide fishing efficiency. Additive effects from the fleet-wide adoption of colour sounders and hydraulic reels on effective fishing effort and the catch rates of West Australian dhufish (Glaucosoma hebraicum) and pink snapper (Pagrus auratus) were also demonstrated. Historical logbook data were independently analysed as a secondary check of these findings for three of the surveyed skippers, which identified that GPS adoption had a significant, positive influence on the catch rate for two vessels, but not for the third, highlighting potential variation in this response among skippers. The results have contributed towards improved understanding of the historical dynamics of the fishery and of the factors that have affected, at least in part, historical changes or, in some instances, a lack of change in observed effort and catch rates.

Influence of selected factors on the dietary compositions of three targeted and co‐occurring temperate species of reef fishes: implications for food partitioning

The dietary compositions of three medium to large targeted fish species, which co-occur over reefs in temperate waters of south-western Australia, were determined. These data were then used to ascertain statistically the extent to which body size, season and habitat influence the diets of these species and the degree to which food resources were partitioned among and within those species, and thus reduced the potential of interspecific and intraspecific competition. On the west coast, Bodianus frenchii (Labridae) and Epinephelides armatus (Serranidae) spent their whole life over prominent limestone reefs, as did Glaucosoma hebraicum (Glaucosomatidae) in all but juvenile life, when it lived over low-relief, limestone substrata. The dietary composition of each species changed with increasing body size, which, in G. hebraicum, was particularly pronounced at c. 300 mm total length (L(T)) and therefore at the size when this species shifts habitat. When the three species co-occurred over the same reefs, their dietary compositions were significantly different, with that of B. frenchii being by far the most discrete, reflecting a far greater contribution by sedentary taxa. Thus, the diet of B. frenchii was distinguished from those of the other two species in containing substantial volumes of bivalve and gastropod molluscs and echinoid echinoderms and essentially no teleosts. Although the diets of G. hebraicum and particularly E. armatus were dominated by teleosts, and especially for larger individuals, the former species ingested greater volumes of cephalopods and small crustaceans. The pointed jaws of B. frenchii, with their forwardly directed and interlocking anterior incisors, are ideally adapted for biting and retaining their invertebrate prey, which are attached to or reside within reef crevices. In contrast, the mouths of G. hebraicum and E. armatus are broader and rounder and contain numerous small, slender and inward-pointing teeth. These teeth, in conjunction with prominent backward-curved canines in E. armatus, facilitate the capture and retention of fish prey. Observations in situ indicate that G. hebraicum is a suction feeder, while E. armatus is predominantly a ram feeder. Although reef environments on the west and south coasts differ, the diet of B. frenchii on these coasts differed only slightly. Interspecific differences in diet, combined with size-related changes in dietary compositions and the occupation of different habitats by juvenile and adult G. hebraicum, reduce the potential for competition for food resources among and within B. frenchii, G. hebraicum and E. armatus and thus helps facilitate the coexistence of these species which historically have been abundant over reefs in south-western Australia.

Phylogeny of Glaucosomatidae inferred from molecular evidence

Most species of glaucosomatids (Teleostei: Glaucosomatidae) are endemic to Australia, except Glaucosoma buergeri that is widely distributed from Australia to Japan. This study elucidated phylogenetic relationships among glaucosomatids based on the morphological characters of the saccular-otolith sagitta, in addition to molecular evidence of mitochondrial 16S rDNA, cytochrome oxidase I (COI) and cytochrome b (cyt b) sequences, and nuclear rhodopsin sequences. The topologies of individuals' phylogenetic trees, based on 16S rDNA, COI and cyt b sequences, were statistically indistinguishable from one another, and were only slightly different from a tree based on rhodopsin sequences. These molecular tree topologies, however, differed from species relationships in morphology-based phylogenetic hypothesis proposed in previous studies. Specimens of G. buergeri from Australia and Taiwan showed differences in the sagitta and molecular differentiation at the four genes, suggesting a possible speciation event. Both molecular and morphological evidences indicate that Glaucosoma magnificum is the plesiomorphic sister species of other glaucosomatid species. Glaucosoma hebraicum is the sister species of a clade composed of G. buergeri and Glaucosoma scapulare. Molecular and morphological evidences also support the species status of G. hebraicum.

Density and size of reef fishes in and around a temperate marine reserve

The effects of marine reserve protection on the density, size, biomass, sex-ratio and overall assemblage structure of reef fishes were investigated at Kingston Reef Sanctuary, Rottnest Island, Western Australia. Significant trends in response to reserve protection were found for two species of top predators and several serially protogynous labrid species. The relative density and biomass of the heavily targeted Glaucosoma hebraicum was 10 and five times greater within the sanctuary respectively. Similarly, the biomass of the serranid, Epinephelides armatus, was 3.2 times greater in the sanctuary, although this difference was owing to a greater mean length not relative density. The male : female sex ratio for the labrid, Ophthalmolepis lineolatus, was significantly different between sanctuary and non-sanctuary sites, with the density of male O. lineolatus significantly greater within the sanctuary. Rottnest Island waters are largely restricted to recreational fishing, therefore these results suggest that a range of fish species around Rottnest Island are affected by recreational fishing, and that these effects are found in taxa beyond the primary target species. The patterns in the effects on bycatch species suggest that fishing-related mortality may be exerting a greater control on these populations than that exerted by natural predation.

Protection from fishing alters the species composition of fish assemblages in a temperate-tropical transition zone

Closure of areas to fishing is expected to result in an increase in the abundance of targeted species; however, changes to populations of species not targeted by fishermen will depend upon their role in the ecosystem and their relationship with targeted species. The effects of protection on targeted and non-targeted reef fish species at the Houtman Abrolhos Islands, Western Australia were studied using baited remote underwater stereo–video cameras. Video images were collected from shallow (8–12 m) and deep (22–26 m) reef sites inside a Marine Protected Area (MPA) at each of three island groups and from three replicate fished locations at each of these groups that span a temperate-tropical transition area. The MPAs were established in 1994 and vary in size from 13.72 km2 at the Pelsaert group in the south to 22.29 km2 at the Easter group to 27.44 km2 at the Wallabi group in the north. The relative abundances of 137 fish species from 42 families were recorded. Large differences in fish assemblage structure existed between MPA and fished locations, and also between shallow and deep regions. Targeted fish species Plectropomus leopardus, Lethrinus miniatus, Lethrinus nebulosus, Pagrus auratus and Glaucosoma hebraicum were more abundant inside MPAs than in areas open to fishing. Their abundance inside MPAs was between 1.13 and 8 times greater than their abundance at fished locations. For non-targeted fish species many were more abundant in areas open to fishing, e.g. Coris auricularis, Thalassoma lutescens, Thalassoma lunare, Dascyllus trimaculatus, however others were conversely more abundant inside MPAs, e.g. Gymnothorax spp, Kyphosus sydneyanus, Scarus microhinos, Chromis westaustralis, Chaetodon spp. This study demonstrates that the removal of abundant targeted species from an ecosystem by fishing can indirectly impact non-fished species and alter the trophic structure of fish assemblages.

A comparison of temperate reef fish assemblages recorded by three underwater stereo-video techniques

Three underwater stereo-video techniques were used to sample the relative densities and species richness of temperate reef fish assemblages at three reef locations and two habitats (high- and low-relief reef) within Hamelin Bay, south-western Australia. The three techniques compared were diver-operated stereo-video strip transects, baited remote stereo-video and unbaited remote stereo-video. While unbaited remote stereo-video and diver-operated stereo-video transects recorded greater species richness at high compared to low-relief reefs, baited remote stereo-video recorded similar species richness at the two habitat types. The diver-operated stereo-video system was manoeuvred through caves and under overhangs recording small, cryptic, cave-dwelling species that were not recorded by either remote video techniques (Trachinops noarlungae, Trachinops brauni, Chromis klunzingeri, Trachichthys australis). Both remote video techniques recorded greater species richness and relative density of the most common species of Labridae, Ophthalmolepsis lineolatus. Baited remote video recorded the rarer, large predatory fish species (e.g. Seriola hippos, Glaucosoma hebraicum, Heterodontus portusjacksoni). None of the techniques sampled small cryptic fish families such as Gobiidae or Blenniidae. A combination of survey techniques is recommended for comprehensive fishery-independent studies that aim to sample broad components of fish assemblages.

Mortality of the demersal West Australian dhufish, Glaucosoma hebraicum (Richardson 1845) following catch and release: The influence of capture depth, venting and hook type

Cages were used to investigate the mortality after catch and release angling of the demersal reef fish Glaucosoma hebraicum (Family Glaucosomatidae), a recreationally and commercially important species in southwestern Australia. The effects of capture depth, venting the swim bladder, two types of hooks and anatomical hooking location, on mortality of G. hebraicum were examined by simulating actual catch and release fishing by recreational anglers. Additional factors (length of fish, duration of caging and the ability of released fish to swim) were included in a logistic regression. Only depth ( p < 0.01), duration of caging ( p = 0.01) and hook location ( p = 0.01) were significant factors in predicting whether or not a fish died after release. Mortality of G. hebraicum increased with depth of capture from 21% at 0–14 m to 86% at 45–59 m. Timing of mortality within the experiment (duration of caging) varied with depth due to the severity of barotrauma. Overall, 51% of all G. hebraicum caught in the experiment died. Most deaths (38.4% mortality of the total catch) were attributed to barotrauma while the remainder (13.2%) was caused by damage by hooks. The high post-release mortality of G. hebraicum at any given depth compared to other demersal species is best explained by their susceptibility to barotrauma. This additional source of mortality must be considered when setting sustainable catch levels for controls on exploitation rates. Traditional management strategies that assume the survival of undersize or excess fish that are returned to the water are not appropriate for G. hebraicum, particularly in deeper waters. Alternative management options must be developed to protect this slow growing, long-lived species.

Haemoglobin and oxygen transport of the West Australian dhufish, Glaucosoma hebraicum Richardson, and other species

To better understand the possible role of deoxygenation of haemoglobin in the pathogenesis of exophthalmos in the West Australian dhufish, Glaucosoma hebraicum Richardson, some oxygen transport properties of haemoglobin from this species were determined and compared with haemoglobin from black bream, Acanthopagrus butcheri (Munro), snapper, Pagrus auratus (Bloch &amp; Schneider) and King George whiting, Sillaginodes punctata (Cuvier). Dhufish had a single haemoglobin with a pronounced Root effect. Snapper and black bream blood had six and five types of haemoglobin, respectively. The magnitude of the Root effect of haemoglobins in the haemolysate was demonstrated by comparing oxygenation and total deoxygenation at pH 8 with relative deoxygenation at pH 6.9. Dhufish haemoglobin demonstrated a large Root effect, with the Root effect of King George whiting, snapper and black bream being of lesser magnitude. Deoxygenation of all haemolysates was more pronounced in the presence of adenosine triphosphate (ATP). Seasonal changes in haematological parameters and ATP content of dhufish blood were not evident. The Root effect is discussed in the context of its possible role in oxygen supply to the retina and adaptation to the fish's habitat and the environment.

The effect of CO 2-rich ground water on the West Australian dhufish ( Glaucosoma hebraicum)

The effect of high CO 2 saline ground water on the blood oxygenation properties of the West Australian dhufish was evaluated following ill thrift of wild caught dhufish held in the water. The Bohr factor was calculated for whole blood from captively bred dhufish to assess the potential effect of increased pCO 2 on oxygenation of dhufish haemoglobin. Blood pH, pCO 2, electrolytes and haematological parameters were determined for two groups of captively bred dhufish held long term in seawater and high pCO 2 ground water, respectively. Chemical analysis of the two water sources was performed. Ground water in dhufish tanks had a pH of 7.7 (seawater pH 8.1) and pCO 2 6.45 mm Hg (seawater 1.50 mm Hg). Dhufish whole blood had a large Bohr factor. Dhufish acclimated to ground water had increased plasma pCO 2, HCO 3 −, haemoglobin content, haematocrit and erythrocyte counts. The increase in haemoglobin content was the result of an increase in erythrocytes.

Infection of the gonads of Glaucosoma hebvaicum by the nematode Philometva lateolabracis: occurrence and host response

The prevalence of infection of the West Australian dhufish Glaucosoma hebraicum off the lower west coast of Australia by Philometra lateolabracis was greater among females than males, which contrasts with the situation with Pagrus auratus in waters off New Zealand. Live P. lateolabracis were represented solely by females and were found only in the gonads of fish of mature size (L50 at first maturity = c. 300 mm) caught between December and April and thus during the spawning period of dhufish. Since the gonads were largest during that period, they, and particularly ovaries, would provide an abundant food source in the form of blood. The prevalence of the parasite (live + dead individuals) increased with host body size to reach a maximum of c. 80% in the 700–799 mm length class of females and c. 50% in the largest length class of males. During the spawning period of G hebraicum, P. lateolabracis developed from small, non‐gravid females to large gravid females, representing an increase in mass of more than 200 times. The maximum length of P. lateolabracis (470 mm) in G hebraicum is the greatest yet recorded for this species. Gonadosomatic indices provided no evidence that infection by P. lateolabracis leads to a conspicuous atrophy of the ovaries, which contrasts with the situation with the gonads of some of the teleosts infected by Philometra species, and presumably reflects, in part, the small volume of the ovary occupied by P. lateolabracis (c. 3%) and the low intensity of infection (mean = 2.0, maximum = 7). Although the presence of live P. lateolabracis did not stimulate an obvious tissue response by the ovaries during the spawning period of G. hebraicum, both the dead and any live parasites that remain after spawning become encapsulated in fibrous tissue.