Reproductive biology and per-recruit analyses of striped trumpeter (Latris lineata) from Tasmania,Australia: Implications for management

This paper profiles the reproductive biology of and investigates the resilience of Tasmanian striped trumpeter under different levels of fishing pressure and size at entry to the fishery using per-recruit analysis. The spawning season around Tasmania occurs in the austral spring, with peak spawning activity in September and October. Size at 50% maturity was estimated at 543 mm fork length (FL) for females (estimated age = 6.8 years) and 529 mm FL for males (estimated age = 6.2 years). Striped trumpeter is a multiple spawner with batch fecundity estimates ranging from 205,054 for a 2 kg fish (540 mm FL) to 2,351,029 for a 9.5 kg fish (800 mm FL). At the current minimum legal size limit of 450 mm total length (equivalent to approximately 425 mm FL), yield-per-recruit was estimated to be close to maximum, and spawning biomass-per-recruit (SPR) ranged from 35 to 52% of virgin stock, depending on the mortality estimates used. Although these SPR are at a level considered sustainable, this methodology does not incorporate temporal variability, specifically recruitment variability. Therefore, conservative management measures are recommended until a dynamic model is applied to the striped trumpeter population.     

Pentacapsula neurophila sp.n. (Multivalvulida) from the central nervous system of striped trumpeter,Latris lineata (Forster)

Striped trumpeter, Latris lineata, are being experimentally cultured by the Tasmanian Aquaculture and Fisheries Institute at Taroona, Tasmania. Fish surviving over 30 days post-hatching have frequently developed nervous aberrations associated with a severe granulomatous meningoencephalomyelitis. The myxozoan parasite Pentacapsula neurophila sp.n. was revealed as the parasite causing the disease in the striped trumpeter juveniles. Measurements made of isolated spores indicated that the organism was distinct from all previously described Pentacapsula species. This is the first report of a marine myxozoan parasite of the genus Pentacapsula in Australian waters.     

Sensitivity of striped trumpeter, Latris lineata, embryos to mechanical shock and simulated transport

The sensitivity of striped trumpeter, Latris lineata, embryos to transport was assessed through mechanical shock at four stages of embryonic development, and simulated transport at different densities and durations. Fertilised egg mortality due to mechanical shock was greatest for embryos shocked 3 and 27 h post-fertilisation (48.6% ± 4.1 and 36.0% ± 3.2, respectively; mean ± SE), and prior to blastopore closure. Mortality of embryos shocked 51 and 75 h post-fertilisation, and following blastopore closure, did not differ from un-shocked controls (9.5% ± 0.7). Density and duration of incubation affected the survival of embryos in a simulated transport trial. Embryonic mortality remained below 3% for all density treatments up to 24 h post-fertilisation. Significant mortality of fertilised eggs occurred when incubated at 5,000 embryos l⁻¹ (17.2% ± 6.9) for 48 h and was correlated with a drop in dissolved oxygen (DO) levels. Final DO concentrations decreased with increasing embryonic density and incubation duration. DO of embryos incubated at 5,000 embryos l⁻¹ was significantly lower than those incubated at 500, 1,000 and 2,500 embryos l⁻¹, at all incubation durations. Mortality was prevalent in treatments that had a final DO level less than 72% saturation at 14°C. Transportation of fertilised striped trumpeter eggs in seawater is recommended from 51 h post-fertilisation at 14°C, after blastopore closure and neural keel development and at densities of no more than 2,500 embryos l⁻¹ for 24 h transportation duration.     

Ultraviolet irradiation is an effective alternative to ozonation as a sea water treatment to prevent Kudoa neurophila (Myxozoa: Myxosporea) infection of striped trumpeter,Latris lineata (Forster)

Myxozoan parasites are known pathogens of cultured finfish. Kudoa neurophila n. comb. (Grossel, Dyková, Handlinger & Munday) has historically infected hatchery‐produced striped trumpeter, Latris lineata (Forster in Bloch and Schneider), a candidate species for seacage aquaculture in Australia. We examined the efficacy of four water treatment methods to prevent K. neurophila infection in post‐larval (paperfish) and juvenile striped trumpeter. Treatments included dose‐controlled ultraviolet irradiation [hydro‐optic disinfection (HOD)], ozone with conventional UV (ozone), mechanical filtration at 25 μm and then foam fractionation (primary filtration), and 50‐μm‐filtered sea water (control). In post‐larvae (initially 10.3 ± 2.7 g, mean ± SD, 259 days post‐hatching, dph), the infection prevalence (PCR test) after 51 days was 93 ± 12% in the control, 100 ± 0% in primary filtration and 0 ± 0% in both ozone and HOD. Likewise, in juveniles (initially 114 ± 18 g, 428 dph), prevalence was 100 ± 0% in the control and primary filtration treatments with no infection detected in ozone and HOD. Concurrently, there was a 50–100% reduction in heterotrophic bacteria and 100% reduction in presumptive Vibrio sp. in sea water HOD and ozone treatments. HOD with a dose of ≥44 mJ cm^?2 UV was as effective as ozonation at >700 mV ORP for 10 min, in preventing K. neurophila infection.     

Induced resistance in rainbow trout, Oncorhynchus mykiss (Walbaum), to gill disease associated with the microsporidian gill parasite Loma salmonae

Branchial xenomas were detected by week 5 and disappeared by week 10 after naive juvenile rainbow trout, held at 14.5 °C, were fed or intubated with Loma salmonae ‐infected gill tissue preparations. Upon re‐challenge with L. salmonae , these fish were protected from disease and branchial xenomas did not develop. Branchial xenomas were never detected in naive fish held at 10 °C and exposed to L. salmonae . When these fish were re‐challenged with L. salmonae at 14.5 °C, they were also protected from the disease. Branchial xenomas also developed after naive fish, held at 14.5 °C, were injected intraperitoneally with a semipurified preparation of fresh spores, but generally did not develop after intraperitoneal injection with a preparation of spores subjected to freezing and thawing before use. Fish that had received fresh spores intraperitoneally were completely resistant to disease when re‐challenged via oral delivery of spores, whereas those that had received frozen spores were incompletely, but significantly, protected from disease compared with naive fish. We conclude that infection with L. salmonae induces strong protection towards the disease upon re‐exposure to spores, and that the protection does not depend on the completion of the parasite's life cycle, thus establishing the basis for further research on vaccine development for this disease.     

Natural outbreak of Streptococcus agalactiae (GBS) infection in wild giant Queensland grouper, Epinephelus lanceolatus (Bloch), and other wild fish in northern Queensland, Australia

Ninety‐three giant Queensland grouper, Epinephelus lanceolatus (Bloch), were found dead in Queensland, Australia, from 2007 to 2011. Most dead fish occurred in northern Queensland, with a peak of mortalities in Cairns in June 2008. In 2009, sick wild fish including giant sea catfish, Arius thalassinus (Rüppell), and javelin grunter, Pomadasys kaakan (Cuvier), also occurred in Cairns. In 2009 and 2010, two disease epizootics involving wild stingrays occurred at Sea World marine aquarium. Necropsy, histopathology, bacteriology and PCR determined that the cause of deaths of 12 giant Queensland grouper, three wild fish, six estuary rays, Dasyatis fluviorum (Ogilby), one mangrove whipray, Himantura granulata (Macleay), and one eastern shovelnose ray, Aptychotrema rostrata (Shaw), was Streptococcus agalactiae septicaemia. Biochemical testing of 34 S. agalactiae isolates from giant Queensland grouper, wild fish and stingrays showed all had identical biochemical profiles. The 16S rRNA gene sequences of isolates confirmed all isolates were S. agalactiae; genotyping of selected S. agalactiae isolates showed the isolates from giant Queensland grouper were serotype Ib, whereas isolates from wild fish and stingrays closely resembled serotype II. This is the first report of S. agalactiae from wild giant Queensland grouper and other wild tropical fish and stingray species in Queensland, Australia.     

Characterization of a host response to the myxosporean parasite, Ceratomyxa shasta (Noble), by histology, scanning electron microscopy and immunological techniques

Abstract. The tissue response of Salmo gairdneri Richardson, against the myxosporean parasite. Ceratomyxa shasta (Noble), was investigated using histological techniques, scanning electron microscopy and immunological methods. The progress of infection in C. shasta -susceptible and resistant steelhead and rainbow trout was examined by standard histological techniques and by indirect fluorescent antibody methods using monoclonal antibodies directed against C. shasta antigens. Trophozoite stages were first observed in the posterior intestine and there was indication that resistance was due to the inability of the parasite to penetrate this tissue rather than to an inflammatory response. Examination of a severely infected intestine by scanning electron microscopy showed extensive destruction of the mucosal folds of the posterior intestine. Western blotting and indirect fluorescent antibody techniques were used to investigate the immunological component of the host response. No antibodies specific for C. shasta were detected by either method.     

Dietary Arachidonic Acid Alters Tissue Fatty Acid Profile, Whole Body Eicosanoid Production and Resistance to Hypersaline Challenge in Larvae of the Temperate Marine Fish, Striped Trumpeter (Latris lineata)

We determined the effect of dietary arachidonic acid (20:4n-6, ARA) on tissue ratios of ARA/eicosapentaenoic acid (20:5n-3, EPA) and subsequent whole body production of the eicosanoids, prostaglandin F_2α (PGF_2α) and E₂ (PGE₂) in the marine larvae of striped trumpeter, Latris lineata. Larvae were also subjected to a hypersaline challenge (55 ppt) with an aim to determine possible relationships between tissue fatty acid profiles, prostanoid production, and their tolerance to osmotic challenge. From 5 to 23 days post-hatch (dph) larvae were fed live food, rotifers (Brachionus plicatilis), that had been enriched with one of five experimental emulsions containing increasing concentrations of ARA and constant EPA and 22:6n-3 (docosahexaenoic acid, DHA). Final ARA concentrations in the rotifers were 1.33, 3.57, 6.21, 8.21 and 11.22 mg g⁻¹ DM. Larval growth and survival was unaffected by dietary ARA. Tissue fatty acid concentrations generally corresponded with dietary fatty acids and final tissue ratios of ARA/EPA ranged from 0.9 to 4.9. At 18 and 23 dph whole body concentrations of PGF_2α and PGE₂ generally increased as more dietary ARA was provided in a dose-response manner, and a significant elevation in both PGF_2α and PGE₂ in larvae fed the highest dietary ARA concentration was recorded at 23 dph compared to larvae receiving the lowest concentration. At 18 dph, the highest cumulative inactivity following a hypersaline challenge occurred in larvae fed 8.21 or 11.22 mg ARA g⁻¹ DM, which was significantly greater than those receiving 3.57 mg ARA g⁻¹ DM. At 23 dph no relationship between inactivity of larvae subjected to a hypersaline challenge to dietary ARA was evident. In summary, dietary ARA altered tissue ARA/EPA ratios, prostanoid production and resistance to a hypersaline challenge in larval striped trumpeter. While increasing dietary ARA generally resulted in elevation of prostanoids as well as increasing the number of inactive larvae following a hypersaline challenge at 18 dph, similar trends between prostanoids and larval inactivity were not evident at 23 dph, suggesting the exact mechanisms and relationships between eicosanoids and larval osmoregulation warrants further investigation. Nevertheless the study provides preliminary data on the effect of dietary ARA on the prostaglandin production in marine fish larvae.     

The first‐feeding response of larval southern bluefin tuna,Thunnus maccoyii (Castelnau, 1872), and yellowtail kingfish,Seriola lalandi (Valenciennes, 1833), to prey density,prey size and larval density

We investigated the first‐feeding success of two species: southern bluefin tuna (Thunnus maccoyii) and yellowtail kingfish (Seriola lalandi) to determine if similar culture parameters can be used for both, especially when S. lalandi are held in the same tanks as prey for T. maccoyii. The feeding performance (proportion and intensity) was examined in three short‐duration (4 h) experiments: prey density, prey size and larval density. Increasing prey density from 0.5 to 25 rotifers mL^?1 increased the proportion of T. maccoyii and S. lalandi larvae feeding. Prey size alone did not affect feeding in either species. Seriola lalandi had a decreased proportion of larvae feeding when larval density reached 50 larvae L^?1 concurrent with a gradual increase in feeding intensity between 2 and 50 larvae L^?1. In T. maccoyii, there was no pattern to the effect of larval density on the proportion of larvae feeding. The overall feeding performance of larvae was higher in T. maccoyii than S. lalandi. Increased prey density improved the first‐feeding ability of T. maccoyii and S. lalandi larvae. The effect of larval density on S. lalandi feeding requires further investigation, to ensure that they remain feeding when provided as prey in T. maccoyii culture. The identification of factors in this study, which increase first‐feeding success, will improve the culture of both species.     

Rapid proliferation of the parasitic copepod,Salmincola californiensis (Dana), on kokanee salmon,Oncorhynchus nerka (Walbaum), in a large Colorado reservoir

Ecologically and economically valuable Pacific salmon and trout (Oncorhynchus spp.) are widespread and susceptible to the ectoparasite Salmincola californiensis (Dana). The range of this freshwater copepod has expanded, and in 2015, S. californiensis was observed in Blue Mesa Reservoir, Colorado, USA, an important kokanee salmon (O. nerka, Walbaum) egg source for sustaining fisheries. Few S. californiensis were detected on kokanee salmon in 2016 (<10% prevalence; 2 adult S. californiensis maximum). By 2020, age-3 kokanee salmon had 100% S. californiensis prevalence and mean intensity exceeding 50 adult copepods. Year and kokanee salmon age/maturity (older/mature) were consistently identified as significant predictors of S. californiensis prevalence/intensity. There was evidence that S. californiensis spread rapidly, but their population growth was maximized at the initiation (the first 2–3 years) of the invasion. Gills and heads of kokanee salmon carried the highest S. californiensis loads. S. californiensis population growth appears to be slowing, but S. californiensis expansion occurred concomitant with myriad environmental/biological factors. These factors and inherent variance in S. californiensis count data may have obscured patterns that continued monitoring of parasite–host dynamics, when S. californiensis abundance is more stable, might reveal. The rapid proliferation of S. californiensis indicates that in 5 years a system can go from a light infestation to supporting hosts carrying hundreds of parasites, and concern remains about the sustainability of this kokanee salmon population.     

Peculiar cases of intracardiac parasitism in the pilchard, Sardina pilchardus (Walbaum), by a pennellid copepod belonging to the genus Lernaeenicus

Abstract. The pilchard, Sardina pilchardus (Walbaum), is parasitized in coastal waters in the Languedoc-Roussillon region (South of France) by a copepod species which belongs to the genus Lernaeenicus (Siphonostomatoida, Pennellidae). These mesoparasites become established in various parts of the body of the host (eye, lateral muscle or muscle at the bases of fins). Examination of specimens which had penetrated at the root of pectoral fins revealed that some had penetrated the heart. A curious case of transcardiac parasitism was observed. Host tissue reactions caused by the presence of parasites are described.     

Salinity-induced quiescence in eggs of the calanoid copepod Acartia tonsa (Dana): a simple method for egg storage

We report the effect of salinity and temperature on the viability of stored culture-based subitaneous eggs of the calanoid copepod Acartia tonsa for use of copepods in fish larvae culture. Quiescence induction was recorded at 17 and 25 °C, in salinities from 0 to 30. Quiescence was strongly induced at 0 salinity and partially at 5 in both temperatures. Eggs incubated at 0 salinity for up to 12 days at both temperatures showed a decline in the fraction able to be induced into quiescence by abrupt salinity changes. The hatching success of eggs that were able to enter quiescence stabilized after a 1-day incubation and remained ∼25% viable for 12 days in 17 °C. On the contrary, the 25 °C trial showed a gradual decline in viability until stabilizing ∼10% at day 7 and onwards. Longterm 17 °C incubation for 35 days showed that eggs remained quiescent with a viability of ∼14%. Hence, we recommend salinity storage of A. tonsa subitaneous eggs as a relevant shortterm technique, and a suitable alternative to the recently proposed cold storage of eggs when eggs are to be shipped from the copepod producer to a given fish larvae hatchery.     

Immunophysiology of Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus (Mitchill), and the relationship to parasitic copepod, Dichelesthium oblongum (Abilgaard) infection

The copepod parasite, Dichelesthium oblongum, is known to infect the Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, within the area near New York city, USA, known as the NY Bight. The gross pathology associated with the juvenile and adult copepod stages along with the parasite's link in causing changes in sturgeon osmoregulatory capabilities has led us to investigate the host immunophysiology in relation to this host-parasite system. All the host variables, which included gill Na(+) -K(+) -ATPase activity, serum alkaline phosphatase (AP) and white blood cell differential counts, were affected in a non-linear manner by the copepod parasite. The parasites increased the host gill Na(+) -K(+) -ATPase activity and serum AP along with the percentage granulocytes while decreasing the percentage lymphocytes. A new method, developed to sample and preserve white blood cells in the field for future flow cytometry analysis, proved adequate. The effects of fish size, location and time of sampling were accounted for by the use of generalized linear models, and their effects on the host variables are discussed.     

Early insulin and glucagon response associated with food intake in a teleost, the striped bass (Morone saxatilis)

To determine the existence of preabsorptive reflex responses in fish, plasma glucose, insulin and glucagon were measured in striped bass (Morone saxatilis) pre-feeding (baseline: 0 min) and at five times post-feeding (5, 10, 20 and 40 min) following a 15 h fast. Two diets were fed, a basal agar-gel diet, and the agar-gel diet supplemented with a previously identified feeding stimulant mixture comprised of L-alanine, L-serine, betaine and inosine-5-monophosphate at equimolar concentrations (0.1 mol l). After 11 days, blood samples were obtained from the caudal vein. In fish fed the stimulant diet, plasma insulin increased at 5 and 10 min post-feeding but fish fed the basal diet had lower levels than baseline after 5, 10 and 20 min. Glucagon levels were increased in fish fed the stimulant diet at 0–10 min post-feeding, then decreased to levels similar to fish fed the basal diet. Glucose levels were elevated in both treatments post-feeding and were similar in both treatments. These results indicate that there is an early phase of reflex insulin and glucagon secretion in fish, shortly after the beginning of a meal, as has been described in mammals and birds. Furthermore, feed palatability may play an important role in insulin and glucagon secretion.     

Growth,settlement and survival of Dicathais orbita (Neogastropoda,Mollusca) larvae in response to temperature,diet and settlement cues

The southern Australian whelk, Dicathais orbita, is a potential candidate for aquaculture, as both seafood and for bioactive compound production. Larval rearing experiments to determine the effects of temperature and diet on the growth and survival of D. orbita larvae under laboratory conditions comprised five different unicellular algal diets of two brown algal species; Isochysis galbana and Chaetoceros muelleri, two green algae; Tetraselmis seucica and Nannochloropsis oculata, and a mixture of all four strains for larvae maintained at 16 and 22°C. Absolute growth, specific growth rate (SGR) and survival were determined regularly. Larvae reared at 22°C on a mixed diet, or brown algae, performed significantly better than those reared on green algal diets alone. Preliminary trials with settlement cues were undertaken on different aged larvae to determine when larvae become competent. An array of natural cues (carrion, Xenostrobus pulex, adult mucus and Ulvella lens), as well as concentrations of KCl was tested. KCl(concentration of 20 mM) induced the greatest settlement, however, no larvae metamorphosed under the conditions provided. This study confirms long‐lived planktotrophic larval development for Dicathais orbita with higher development rates at the higher water temperatures. Further studies will optimize culture conditions and cues for settlement and metamorphosis.     

Morphometric changes in a strain of the lineage 'Nevada', belonging to the Brachionus plicatilis (Rotifera) complex

The rotifer Brachionus plicatilis is an important component of aquaculture as a larval feed. Its taxonomic status has been recently re-defined as a species complex, consisting of at least 14 new species/lineages. This study deals with the lineage Brachionus 'Nevada', which has been shown to occur in European hatcheries. A strain of B . 'Nevada' was mass cultured using two commonly applied feeding regimes and analysed in terms of its morphometry. A new formula was proposed for the calculation of volume, which can be used as an index of adequacy of rotifers as feed for fish larvae. The results were related to life cycle parameters. The pre-reproductive and reproductive phases were divided into distinct size groups. Differences were also found between the two diets in morphometry and demography. Rotifers of a larger size (yeast-based diet) showed a lower growth rate and a longer reproductive period, lifespan and mean generation time compared with smaller-sized rotifers (Culture Selco^®-based diet). In terms of lorica length, the present study's strain of B . 'Nevada' (238.5 μm) was intermediate between values reported for Brachionus ibericus (193.5 μm) and B. plicatilis sensu stricto (299 μm).