Induction of triploidy in the turbot (Scophthalmus maximus): II. Effects of cold shock timing and induction of triploidy in a large volume of eggs

Triploidy was induced in the turbot (Scophthalmus maximus, L.) by applying cold shocks shortly after fertilization. The combined effects of the timing of cold shock commencement after fertilization, cold shock duration and cold shock temperature were investigated. Ploidy was assessed by counting the number of nucleoli per nucleus (NOR) in larvae and also by measuring erythrocyte size in juveniles. A clear peak in triploidy induction was obtained when shocks were started between 6 and 7 min after fertilization at a pre-shock temperature of 13–14°C. With this timing, shocks of 20-min duration at 0°C gave >90% triploidy, with survival about 80% of the untreated controls. In order to ensure both high triploidy rates and high survival, it was necessary to carefully maintain the water temperature just below 0°C. Experiments with small and large volumes of eggs were performed in order to determine how changes in the relative volumes of eggs and chilled water could affect survival and triploidy induction. The best combination to induce triploidy in the turbot was as follows: shock commencement 6.5 min after fertilization, shock duration 25 min, and shock temperature between 0 and −1°C. With this combination, 100% triploidy could consistently be induced with survival 60% of the untreated control. This was successfully applied to a large volume of eggs (300 ml; 1 ml 800 eggs) in order to mass-produce triploid turbot. Triploids had lower survival rate than diploids at hatching but similar thereafter, with the ability to complete the different stages of larval rearing, indicating the viability to produce triploid turbot under farming conditions.     

Improving growth in juvenile turbot (<Emphasis Type="Italic">Scophthalmus maximus</Emphasis> Rafinesque) by rearing fish in switched temperature regimes

The effect of thermal history (16 and 20°C) on growth of juvenile turbot, Scophthalmus maximus (initial mean weight 72.6 g, n = 157) was studied. Fish were divided into four groups, two groups remaining at constant temperature (C16, C20), while fish in the other groups were transferred from either 16 to 20°C (F16-20) or from 20 to 16°C (F20-16). Between 35 and 42 fish in each tank were individually tagged at the start of the experiment. The final mean weights were significantly higher in the F20-16 group (230 g) than in the C20 (213 g), F16-20 (211 g) and C16 (205 g) groups. The overall growth rate was highest in the F20-16 group (1.17% day⁻¹) but comparable in the three other groups (1.00–1.04% day⁻¹). Our findings indicate that, even at near-optimal temperature for a given size, the temperature history of the fish may influence future growth. Based on these indications, we conclude that as turbot grow larger, the temperature should be reduced to take advantage of the change in optimal temperature for growth with increasing fish size rather than rearing at constant temperatures.     

Acoustic characteristics of two feeding modes used by brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and turbot (Scophthalmus maximus)

Under conditions of intensive culture, the acoustic signals produced by fish during feeding depend on their feeding mode. Exclusive suction, as used by turbot, is characterised by a maximum acoustic energy in the frequency range 7–9 kHz and a sound duration of about one minute depending of time duration of pellet distribution. Suction feeding in conjunction with forward swimming, as employed by brown trout and rainbow trout, had a maximum acoustic energy in the frequency range 4–6 kHz and feeding sounds were measurable only for short periods (less than 1 s) in between two pellet distributions by hand. The brevity of these feeding sounds (ca. 1000 ms) requires adapting the turbot acoustic-detection systems to actively feeding fish for developing automated feed distribution systems feasible in trout aquaculture.     

The physiological response of the turbot to multiple net confinements

The effects of multiple net confinements on the physiological stress response of the turbot (Scophthalmus maximus L.) were investigated. To allow for repeated blood sampling from individuals, fish were cannulated in the afferent branchial artery and were exposed to multiple 9 min net confinement episodes separated by either 4 h or 24 h. In fish stressed twice 4 h apart cumulative effects in plasma cortisol, glucose and free fatty acid concentrations were evident after the second handling stress. Although plasma Na⁺ and Cl⁻ concentrations were not increased further by the second net confinement, the elevation in plasma concentrations were more sustained compared to turbot handled only once. In a second experiment where turbot were net confined five times, with a 24 h recovery period between each net confinement episode, there was no evidence of any physiological accommodation with repeated exposures. For most circulatory parameters, there was also no evidence of any cumulative effect apparent. Plasma glucose concentrations were, however, elevated to a significantly higher degree with repeated net confinements. Although turbot were tolerant to the handling procedures, with no mortalities recorded, episodes of multiple handling of this species should be separated by at least 24 h if cumulative physiological disturbances are to be avoided. The significance of cumulative increases in plasma glucose concentrations is discussed. Present address: Aquaculture Associates International, The Firs, Glasshouse Hill, Codnor, Derbyshire, DE5 9QT, UK     

Accuracy of pairwise methods in the reconstruction of family relationships, using molecular information from turbot (Scophthalmus maximus)

Many estimators and algorithms have been developed to infer the genealogical relationships from molecular marker data when there is no pedigree information. Most pairwise methods provide estimates in a continuous range that needs to be converted into genealogical relationships (namely full-sibs, half-sibs and unrelated) if there is a previous knowledge of the population structure. Transformations are usually based on arbitrary thresholds, but the possibility of correcting the coancestry estimates via explicit pedigree reconstruction methods has been suggested. Using molecular data for ten highly polymorphic microsatellite loci on a population of turbot (Scophthalmus maximus) with a known genealogy, the behaviour of four pairwise marker-based coancestry estimators and the molecular coancestry has been evaluated. The population consisted on 138 families with 4 full-sib individuals each and one family with 8 full-sib individuals (up to 15 half-sib families were also present due to the sharing of parents between some of the full-sibs families). Our results suggested that transforming the pairwise estimators and the molecular coancestry to family relationships through the establishment of thresholds performs slightly better than the explicit pedigree reconstruction method, when accuracy is measured in a pairwise basis. However, if joint relationships between more than two individuals were tested at a time, the threshold methods led to a high percentage of incongruous triads of full-sib individuals, with Mendelian incompatibilities appearing in congruous full-sib families (more than 70% and 60% in our study, respectively). The explicit pedigree reconstruction approach, due to its nature, is free from such problems. Therefore, the pedigree reconstruction approach seems to be a valuable tool to provide a congruent and compatible pedigree when the pairwise marker-based coancestry matrices or the molecular coancestry need to be transformed.     

Growth, survival, lipid composition and pigmentation of turbot (Scophthalmus maximus) larvae fed live-prey enriched in Arachidonic and Eicosapentaenoic acids

Turbot larvae were fed live-prey enriched with different levels of arachidonic (ARA) and eicosapentaenoic (EPA) acids to study the effects of these fatty acids on body composition and pigmentation success. Significantly reduced pigmentation was obtained in those fish fed medium and high ARA diets for 43 days. Growth and survival were the same for all groups. The incorporation of ARA and EPA in fish eyes, brains, livers and carcasses reflected the percentage of these fatty acids in the diets. ARA accumulation was similar in all tissues, but brain accumulated EPA was less efficient than the other tissues examined. A highly significant, negative correlation was found between the %ARA in turbot juvenile brain total lipids and pigmentation success. A weaker, positive correlation was found between brain EPA and pigmentation. Increasing dietary ARA affected the fatty acid composition of turbot brain phosphoglycerides more than increasing dietary EPA, especially in phosphatidylinositol (PI) and phosphatidylethanolamine (PE). A negative relationship was found between percentage normal pigmentation and ARA levels in brain phosphatidylcholine (PC), PE and phosphatidylserine (PS). Elevated levels of ARA in PI also resulted in malpigmented juveniles, but EPA:ARA ratios ≥1 in PI were associated with normal pigmentation. We conclude that, given a sufficiency of dietary docosahexaenoic acid (DHA), the optimum dietary level of EPA is not a function of DHA, but of dietary ARA.     

Lipolytic activities in developing turbot larvae as influenced by diet

The development of neutral lipase and phospholipase activities was studied in larval turbot fed live prey. Activities of neutral lipase and phospholipase (activity larva⁻¹) increased significantly between days 6 and 24 after hatching in turbot larvae. The specific activities of both enzymes (activity μg protein⁻¹) decreased in older larvae. Feeding of a microdiet for 3 days (days 10–13) affected the lipolytic activity of neutral lipase and phospholipase negatively, compared to the larvae fed on rotifers. Since neutral lipase activities in whole larval homogenates and in the gut were significantly lower, it suggests a reduced synthesis rate and a reduced secretion of the enzyme in larvae fed the microdiet. A correlation between neutral lipase and phospholipase activities was found in larvae fed rotifers, but not in larvae fed the microdiet. This may indicate different regulating and stimulating mechanisms for these enzymes. The contribution of exogenous enzymes from ingested live prey to the total larval enzyme activity was about 6% for neutral lipase and 10% for phospholipase on day 6. The exogenous prey enzymes accounted for only 2% of the total activities in 12-day-old turbot larvae, suggesting that enzymes from prey did not contribute considerably to the digestion of lipids. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of temperature and body weight on growth rate and feed conversion ratio in turbot (Scophthalmus maximus)

Six size groups of hatchery produced turbot (2–499 g) were reared at six constant temperatures (10–25 °C). The results were used to develop a mathematical model for growth rate and feed conversion in turbot. At each temperature there were linear relationships between logarithms of (a) specific growth rate (G%/day) and body weight (W g), and (b) feed conversion ratio (FCR) and W. The slopes of the regressions were linearly related to temperature and the intercepts of the regression changed with temperature according to a second order polynomial. The optimal temperature for growth (T_opt.G) is predicted to decline with increasing body weight: T_opt.G = 22.45 − 0.713lnW, i.e. 22.5, 20.8, 19.1 and 17.5 °C for 1, 10, 100 and 1000 g fish, respectively, and the growth rates of these fish sizes at their optimal temperature (G_max) were predicted to be 7.63, 2.73, 1.03 and 0.40%/day, respectively. The optimal temperature for feed conversion (T_opt.FCR) is also predicted to decline with increasing fish size: T_opt.FCR = 18.80 − 0.625lnW, i.e. 18.8, 17.4, 15.9 and 14.5 °C for 1, 10, 100 and 1000 g fish, respectively, and the predicted feed conversions of these fish sizes (FCR_min) were 0.44, 0.56, 0.68 and 0.82 for the present feed types. The growth model predicts that 2 g turbot can reach 743 and 619 g in 1 year when reared at T_opt.G and T_opt.FCR, respectively.     

Molecular evidence for the lack of transmission of the monogenean Sparicotyle chrysophrii (Monogenea, Polyopisthocotylea) and isopod Ceratothoa oestroides (Crustacea, Cymothoidae) between wild bogue (Boops boops) and cage-reared sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

In the Mediterranean area, wild fish have often been suggested as either the reservoirs of the causative agents or at least the carriers of the pathogens responsible for disease outbreaks in cultured fish. However, no epidemiological investigations on actual pathogen/disease interactions between farmed and wild fish have been conducted even for the most important fish pathogens. Only sporadic isolations and identifications of various pathogens in wild fish have been done and real associations with the pathological conditions that exist within the farm environment and vice versa have not been established. Monogenean ectoparasite Sparicotyle chrysophrii and isopod Ceratothoa oestroides are commonly found in the Mediterranean cage-reared sea bream and sea bass and in the surrounding wild fish population. Both species were recognized as pathogens that seasonally inflict serious losses in fingerlings and juveniles of sea bream and sea bass, being potentially propagated and exchanged during wild and caged fish interaction. In order to evaluate the degree of pathogens transfer between wild and farmed fish, we investigated genetic population structures of these two important parasitic pathogens inferred by mtDNA cytochrome oxidase I locus. Parasites isolated from wild and farmed fish on the two most productive Adriatic fish farms showed genetic heterogeneity, contradicting widely accepted hypothesis of cross-contamination, at least in case of S. chrysophrii and C. oestroides. As far as we know, this is the first report that in a study of pathogen transfer molecular evidence was employed to asses the genetic population structure of shared parasites.     

Genetic variations in survival of rohu carp (Labeo rohita, Hamilton) after Aeromonas hydrophila infection in challenge tests

A challenge test against Aeromonas hydrophila was conducted using 2062 rohu carp (Labeo rohita) fingerlings obtained from 52 dams and 87 sires (87 full-sib families) of two year-classes (2003 and 2004). Attempts to establish a cohabitant challenge model were not successful. Therefore, fish were challenged by intraperitoneal injection with A. hydrophila in two replicate tanks per year-class, and dead fish were collected hourly. The mortality reached its peak at 16–22 h after challenge and had almost completely stopped after 58 h. The test was terminated after 382 h at which the average survival was 43.9 and 48.9% in the two 2003 year-class tanks, and 77.1 and 35.8% in the two 2004 year-class tanks. Heritability estimates for survival were obtained from sire and dam threshold models (THR) and sire and dam linear repeatability models (LINR). For both types of models the heritability estimates based on data from single tanks were not consistent. For both year-classes, data from one of the two challenged tanks demonstrated significant additive genetic variation in survival during the A. hydrophila infection, whereas the heritability estimates were not significantly different from zero for the other tank. Further, genetic correlation between survivals in the two replicate tanks in each year-class was not significantly different from zero. The differential results from the replicate tanks demonstrate that additional challenge test experiments are needed before firm conclusions can be drawn about the magnitude of additive genetic variation for survival to aeromonasis in rohu carp. A cohabitant challenge model that allows the testing of important defence mechanisms in the skin and mucous membranes of the fish might have been more appropriate. To establish a valid cohabitant challenge model for rohu carp should be given high priority.     

Brachionus vs Artemia duel: Optimizing first feeding of Upogebia pusilla (Decapoda: Thalassinidea) larvae

Larval rearing of many marine organisms is dependent on the availability of live food. The aim of this study was to optimize larval first feeding for the mud shrimp Upogebia pusilla, by comparing the effectiveness of the two most commonly used live feeds: Brachionus plicatilis and Artemia sp. nauplii. Survival, larval duration, molt synchronism and megalop size were compared using five feeding treatments: Artemia from zoea I to IV (B0), Brachionus during zoea I and Artemia from zoea II to IV (B1), Brachionus during zoea I and II and Artemia during zoea III and IV (B2), Brachionus from zoea I to III and Artemia during zoea IV (B3) and Brachionus from zoea I to IV (B4). The proportion of larvae that reached the megalop stage was 0.00% in treatment B0, 3.33% in treatment B1, 33.33% in treatment B2, 66.67% in treatment B3 and 76.67% in treatment B4. Larvae fed on rotifers until zoea III or zoea IV stages had a higher survival but no differences were found either in time to reach megalop or in megalop size. This study demonstrates that rotifers are essential for the survival and development of U. pusilla early larval stages but that rotifers can be successfully replaced by Artemia nauplii in the zoea IV stage.     

Effects of experimental infection by Caligus rogercresseyi (Copepoda: Caligidae) on the common jollytail, Galaxias maculatus (Osmeriforme: Galaxiidae) (Jenyns, 1842) in Chile

Galaxias maculatus, the common jollytail, is a native smelt fish with a lacustrine or diadromous life cycle. In Chile, the rearing cycle of this fish includes a freshwater and a marine phase. Several diseases and parasites reported for the freshwater phase could be avoided by rearing the fish in salty or brackish water. Nonetheless, this alternative could result in Caligus rogercresseyi infections. The objective of this study was to evaluate experimentally the capacity of C. rogercresseyi to infect the common jollytail and the effects this parasite may cause to the fish. Prevalence and intensity of experimental C. rogercresseyi infections on G. maculatus were estimated and the effects of this parasitosis on the fish were evaluated on fish survival, weight loss, swimming behavior, and skin damage. Two experiments were carried out with adult fish taken from the Maullín Estuary. Fish were acclimatized to a salinity of 32 ppt and divided into two groups of 20 fish each. The experimental group was infected with copepodid stages of C. rogercresseyi and the other was used as a control. The fish were kept in individual tanks until observing ovigerous female copepods. C. rogercresseyi recognizes G. maculatus as a host under experimental conditions and optimal salinity for the parasite. Results show that under experimental condition copepodid stage can successfully infect the fish, developing to the adult stage, mating, and producing eggs (females). C. rogercresseyi caused alterations in fish behavior, superficial body damage, weight loss, and mortality. Rearing the common jollytail in salty water should take into consideration measures to control these infections as they can damage fish and affect surrounding wild fish populations. There are no records of this parasite in natural common jollytail populations; however, our understanding of the ecological role played by the common jollytail in C. rogercresseyi transmissions among sympatric host species could be greatly improved through further research related to host preferences and epidemiological data for different sympatric host species.     

Comparative composition and shelf-life of fillets of wild and cultured turbot (Scophthalmus maximus) and Atlantic halibut (Hippoglossus hippoglossus)

Turbot and Atlantic halibut are highly valued fish species. However,very little is known about fillet shelf-life characteristics associated withboth species. Thus, fillet -tocopherol content and proximate compositionof wild turbot (1.5 kg) and Atlantic halibut (1.1 kg)caught off the south coast of Ireland and the north-west coast of Iceland,respectively, were investigated. In addition, the susceptibility of fillets, storedunder retail conditions, to lipid oxidation and colour change was studied.Proximate composition analysis showed that turbot had significantly highermoisture (P < 0.001) and lower protein (P < 0.001) contents compared toAtlantic halibut. Atlantic halibut incorporated significantly higher (P <0.001) levels of -tocopherol into fillets than turbot. Over 14 days ofstorage on ice, fillets from Atlantic halibut exhibited significantly lower (P =0.020) levels of lipid oxidation than those of turbot. However, malondialdehyde(MDA) concentrations were generally very low, never exceeding 0.6 gg^–1 fillet. Turbot maintained a significantly higher (P< 0.001) pH over the storage period. The lightness (L^* values) offillets from both species increased over 14 days of storage, but wassignificantly higher (P < 0.001) in Atlantic halibut than in turbot. Turbotdeveloped a relatively intense yellow colour during storage (decrease in hueangle and increase in b^* values), whereas this was not the case forAtlantic halibut. The results of this study demonstrate that fillets of wildAtlantic halibut stored on ice, were less prone to lipid oxidation anddiscolouration than those of wild turbot. However, quality changes in turbotwere very small showing that both fish have tremendous shelf-life capacities interms of lipid oxidation. These findings are considered in the context of knownmaterial for farmed fish.     

Microinjection of the antifreeze protein type III (AFPIII) in turbot (Scophthalmus maximus) embryos: Toxicity and protein distribution

Fish embryo cryopreservation has not been achieved. Different methods and alternative cryoprotective agents (CPAs) should be explored in order to succeed in this purpose. Antifreeze proteins (AFPs) are naturally expressed in sub-arctic fish species, and they inhibit the growth of ice crystals as well as recrystallization during thawing. Therefore, their introduction into embryos can be highly beneficial for vitrification purposes. In this study, AFP type III was introduced into turbot embryos, by microinjection into the yolk sac and the perivitelline space at F stage (tail bud).Toxicity and distribution of protein in microinjected embryos were established before testing the protein effect on embryo cryopreservation. AFP-FITC distribution within the embryo was analyzed by confocal microscopy at 5 min and 24 h after microinjection in F stage embryos. To test the sensitivity of microinjected embryos to CPAs, embryos were subjected to a protocol for the incorporation of a vitrifying solution that was specially designed for turbot embryos. Hatching rates after CPA incorporation were determined. Results indicate that embryos at late developmental stages are more resilient to microinjection, with embryo survival rates between 60 and 82%. Confocal microscopic images demonstrated that the protein was homogeneously distributed within the microinjected embryo compartment, but did not enter any other compartment. On the other hand, microinjected embryos successfully surmounted their incubation in the CPAs. This study explores new alternatives for cryopreservation suggesting the use of natural cryoprotectants (AFPs) in the protection of intra-embryo compartments, which are usually unprotected with the conventional cryopreservation protocols for fish embryos.     

Colonization of the gut in first feeding turbot by bacterial strains added to the water or bioencapsulated in rotifers

Two bacterial strains, 4:44 and PB52, isolated from turbot(Scophthalmus maximus L.) were used during a first feedingexperiment with turbot larvae. Bacteria were either added directly tothe water on the day of hatching of the larvae (day 0), orbioencapsulated in rotifers (Brachionus plicatilis) distributedon day 2 after hatching. The two bacterial strains were found to bepresent in the water of the rearing tanks throughout the experiment. Theaddition of bacteria influenced the species-composition of themicroflora associated with intensively produced rotifers added to thetanks, and resulted in colonization of the gut of the larvae by theadded bacterial strains. The strain 4:44 showed a peak on day 9 afterhatching, and reached a mean(sem) of 2.5(1.4) × 10⁴bacteria per larva, when added in a mixture with PB52, and 0.4(0.1)× 10⁴ bacteria per larva, when added alone. The strainPB52, on day 12 after hatching, reached 5.2(1.5) × 10⁴bacteria per larva when added in a mixture with strain 4:44, and12.5(0.7) × 10⁴ bacteria per larva, when added alone.The added bacteria colonized the gut turbot larvae, whereas thebacterial land, the survival and growth of the larvae were in most casesnot influenced in a negative way by the addition of bacteria.     

Genetic differentiation in hatchery strains and wild white shrimp Penaeus (Litopenaeus) vannamei (Boone, 1931) from northwest Mexico

Ten enzymatic systems were analyzed to determine allozyme genetic differentiation among three hatchery strains (A, B and C) of white shrimp, Penaeus (Litopenaeus) vannamei, commonly used in shrimp farming in northwest Mexico. A wild population from northern Sinaloa was used as a reference. Fifteen loci were detected, nine of which were polymorphic (ACP-1*, ACP-2*, AKP-2*, EST-2*, EST-3*, EST-4*, EST-5*, LAP*, and LDH*). Polymorphism of A, B and C were 53, 53, and 40%. The mean observed heterozygosity per locus was 0.071, 0.093, and 0.050 without any significant difference among them or with respect to the wild population (0.056). In all samples observed heteroxygosity was smaller than expected. The mean number of alleles per locus was 1.8 in A and 1.87 in both B and C. Strain A was the only sample without rare alleles. Only EST-3* and LAP* of strain A were in Hardy-Weinberg equilibrium; the other loci were in disequilibrium in all samples. High inbreeding values and heterozygote deficiencies were detected in all samples. Distribution of allelic frequencies was heterogeneous among the samples (G-test), involving all polymorphic loci and suggesting a genetic differentiation. According to Fst, a moderate genetic differentiation (7.4%) was detected among the samples. Greater differences were between strains A and C. Based on genetic distance, the samples were grouped into two pairs, B-C and A-wild. Strain A is a young strain related to the wild sample, whereas strains B and C have a different geographic origin than the wild sample.     

Immobilization antigen-independent protection of olive flounder (Paralichthys olivaceus) against Philasterides dicentrarchi (Ciliophora: Scuticociliatia) infection

To determine whether olive flounder (Paralichthys olivaceus) immunized with lysate of Philasterides dicentrarchi could be protected immobilization antigen (i-antigen) type independently, fish were immunized with lysate of ciliates obtained from in vitro cultures or ciliates obtained from infected fish. Fish immunized with ciliates obtained from infected fish were completely protected against artificial infection with in vitro cultured P. dicentrarchi, in spite of a weak or no serum agglutination activity against in vitro cultured ciliates. The present results indicate that i-antigen-independent protection was elicited by immunization of fish with the ciliates lysate, and the cultured ciliates would provide a good source for preparation of vaccines, which are cross-protective against various i-antigen types of P. dicentrarchi.     

A comparison of the population genetics of Lethrinus miniatus and Lutjanus sebae from the east and west coasts of Australia: Evidence for panmixia and isolation

Lethrinus miniatus and Lutjanus sebae are important commercial and recreational species of reef fish. Within Australian waters the former species is less widespread than the latter and has a discontinuous distribution, whilst the latter is continuously distributed in tropical Australian waters. The demographic attributes of these species (e.g. long life span, low rates of natural mortality) make them vulnerable to over-exploitation. Consequently, conservative harvest strategies including no-take zones for these species have been adopted by fisheries management agencies to control exploitation. Information on the genetic stock structure of these species is important for developing specific management strategies. However, little is known about genetic stock structures within and between east and west Australian populations of these species. The current study used the mitochondrial genome hypervariable region 1 (HVR1) of the control region to examine variation between two sites from both the east and west Australian coasts for each species. HVR1 for L. sebae did not differ genetically either within or between coasts (F_st < 0.018, p > 0.15) at the sites studied, suggesting a panmictic population structure. Similarly, L. miniatus did not differ significantly between sites sampled within coast. However, the west coast HVR1 for L. miniatus east and west coast populations, were discrete (F_st of at least 0.92, p < 0.0001). The degree of genetic sub-division between east and west coast populations indicates that they should be managed as discrete stocks. Further, when considering both species, the lower genetic (both haplotype and nucleotide) diversity in three of the four sites on the west coast of Australia, indicates that this region is genetically impoverished and neutrality tests suggest that selection is responsible. Consequently, west Australian populations will be less resilient to perturbations (e.g. fishing, climate change) than east Australian populations, which have higher genetic diversity.