Comparison of environmental conditions in two representative oyster farming areas: Hiroshima Bay,western Japan and Oginoham a Bay (a branch of Ishinomaki Bay), northern Japan

ABSTRACT:   Sea water environmental conditions over annual cycles were investigated and compared between two oyster farming areas, western Hiroshima Bay and Oginohama Bay (a branch of Ishinomaki Bay) in Miyagi Prefecture, to appropriately manage oyster culture or more efficiently utilize farming areas. The environmental parameters of temperature, salinity, nutrient concentrations (NO₂–N, NO₃–N, NH₄–N, PO₄–P, and SiO₂–Si) and size-fractionated chlorophyll- a (<0.2, 2–20, >20µm), and abundances of microzooplankton were measured in each bay at the surface, and 2 and 5 m depth layers. Differences in the annual mean values and results with monthly paired Student's t -tests showed that salinity was lower, and temperature, nutrient (especially PO₄–P) and chlorophyll- a concentrations, and abundance of microzooplankton, were higher in Hiroshima Bay than in Oginohama Bay. Differences in environmental conditions between inshore and offshore areas of each bay suggest that inflows of river water in western Hiroshima Bay and sea water from offshore had the most significant effects on the environmental conditions. It is concluded that such oceanographic and biological differences strongly affect the oyster farming system, especially regarding the optimum usage of offshore areas in Summer under clean, cold and stable seawater conditions, rather than food quantity in Hiroshima Bay, and under more abundant food conditions in Oginohama Bay.     

Toxicity to marine bivalves of culture supernatant fluids of the bivalve-pathogenic Vibrio strain NCMB 1338 and other marine vibrios

Abstract. Culture supernatant fluids from twelve Vibrio strains were toxic to spat of the European and Pacific oysters, Ostrea edulis L., and Crassostrea gigas L. At least three factors were present in culture supernates of one of the most virulent strains (NCMB 1338). The first was a heat-labile protein of molecular weight approximately 39000 which was lethal to oyster spat. This toxin was released during the stationary phase of culture and 72-h culture supernates contained 23·0LC₅₀ml when assayed against 2–3 mm Crassostrea gigas spat for 24 h at 20°C. Under the same assay conditions, 7-mm C. gigas spat were six times less sensitive to the toxin. The second factor was a relatively heat-stable ciliostatic toxin of molecular weight < 5000 and the third a proteinase of molecular weight 30000 which degraded gill segments of Mytilus edulis L. In addition, a haemolysin of molecular weight 20000 was produced. All these factors could be involved in the pathogenesis of 'vibriosis' in oyster larvae.     

A preliminary evaluation of physiological filtration variables for Crassostrea corteziensis (Hertlein, 1951) and Anadara tuberculosa (Sowerby, 1833) in shrimp aquaculture effluents

This study examined the main filtration variables [filtration rate ( FR ), clearance rate ( CR ) and assimilation efficiency ( AE )] of the Cortez oyster, Crassostrea corteziensis (Hertlein, 1951), and the mud cockle, Anadara tuberculosa (Sowerby, 1833), in shrimp aquaculture effluents at three different flux velocities (1.5, 3 and 4.5 L h⁻¹) using a 36-respirometer system, each with a 0.5 L capacity. Under inverted photoperiod conditions, free variations in the environmental parameters were allowed to mimic effluent conditions during a pair of 12-h trials. The FR s for both species (0.124, 0.328 and 0.402 L h⁻¹ for the Cortez oyster; 0.093, 0.189 and 0.345 L h⁻¹ for the mud cockle) were relatively low as compared with those reported for similar or related species. The CR s were higher for the Cortez oyster (20.04, 52.92 and 64.70 L h⁻¹) than for the mud cockle (10.96, 22.95 and 42.12 L h⁻¹); in both cases, the values were in the range reported previously for the last species. The AE for both mollusks (over 92% for the Cortez oyster and over 95% for the mud cockle) was very high and greater than that found by other authors for the same or related species. The three filtration variables were better at higher effluent flux velocities. These preliminary results strongly suggest that both species are good candidates to be considered for bioremediation of aquaculture effluents.     

Use of neuroactive catecholamines to chemically induce metamorphosis of hatchery-reared flat oyster, Ostrea angasi, larvae

Low numbers and unreliable wild catch of the native flat oyster, Ostrea angasi , spat has resulted in the NSW flat oyster industry being reliant on hatchery-produced spat. The need to produce culchless spat in the hatchery stimulated investigation of several catecholamines to induce metamorphosis in O. angasi larvae. Larvae were treated with one of four neuroactive catecholamines (epinephrine, epinephrine bitartrate, l -Dopa and GABA) at one of four concentrations (10⁻³, 10⁻⁴, 10⁻⁵ or 10⁻⁶  m ) for one of three treatment durations (0.5, 1–2 h) to determine morphogenic action for culchless spat production. Epinephrine bitartrate at 10⁻³ and 10⁻⁴  m and epinephrine at 10⁻³, 10⁻⁴ and 10⁻⁵  m , for a treatment duration of 1–2 h, produced significantly greater numbers of spat and culchless spat, compared with any other treatment combination. The other catecholamines tested did not induce a significant increase in the total number of spat or culchless spat, over untreated controls. Separate trials found that long-term treatment (24 h) with epinephrine bitartrate and epinephrine at morphogenic concentrations inhibited metamorphosis. Consecutive daily use of epinephrine bitartrate increased the numbers of spat and culchless spat produced, but did not affect larval or short-term post-larval survival. Treatment with 10⁻³  m epinephrine bitartrate or 10⁻⁴  m epinephrine for 1 h is recommended for routine commercial production of culchless flat oyster spat.     

Conchiolin infection and surface coating Vibrio: shell fragility, growth depression and mortalities in cultured oysters and clams, Crassostrea virginica, Ostrea edulis and Mercenaria mercenaria

Abstract. A disease of cultured juvenile European oyster, Ostrea edulis , and American oysters, Crassostrea virginica , was characterized by infection of conchiolinous ligament and periostracum by surface-coating Vibrio spp. bacteria. A similar bacterium was isolated from diseased cultured hard clams, Mercenaria mercenaria , held in a facility about 300 km distance from the oyster hatcheries. The oysters demonstrated fragile, undercalcified peripheral shell and apparently excessive chalky deposits. Histological and scanning electron microscopical examination revealed that the oysters' eroded ligaments and perforated peripheral periostracum were infected with uniform rod-shaped bacteria. The infection appeared to interfere with normal proteinaceous and calcareous shell deposition and possibly with normal ligament function. Histological examination of the digestive system organs suggested that normal digestive processes were also interrupted. Two predominant bacteria were isolated from oyster samples and one predominant bacterium was isolated from clam samples. One of the isolates from oyster culture facilities was found almost exclusively associated with oyster shell surfaces and culture tank surfaces, this isolate was similar to the one taken from clam shell surfaces. The other predominant bacterium was found in water column samples in oyster culture facilities at levels from about 10⁵ to 10⁷ per ml. This isolate had a DNA base ratio (moles % G + C) of 43.6; the two surface-associated isolates had base ratios of 43.6 and 44.5%. These Gram-negative, oxidase positive, fermentive rods have been identified as a Vibrio spp. group. Specific antibody was produced which differentiated these bacteria from each other and from other similar isolates. Practical procedures for controlling the bacteria in shellfish culture systems are described.     

A habitat suitability index model for suspended tray culture of the Pacific oyster, Crassostrea gigas Thunberg

Abstract. A habitat suitability index (HSI) model for suspended tray culture of the Pacific oyster, Crassostrea gigas Thunberg, was constructed from existing information in the literature on oyster-environment relationships. In the model, biophysical data are used to rate aquaculture potential of coastal areas on a scale from 0.0 to 1·0. where 1·0 represents optimal conditions for growth and survival and 0·0 represents totally unsuitable habitat conditions. The model was tested with environmental, growth (increase in shell height) and secondary production (g· 100 oysters⁻¹ day⁻¹) data collected over a 14-month period for two age-classes of oysters transplanted to 10 locations along the coast of British Columbia. Canada. Regressions of HSI values calculated from entire study environmental data against oyster growth and secondary production were highly significant for both age-classes. Environmental data subsets representing short sampling programmers (1–3 months) resulted in HSI values significantly correlated to oyster growth, provided that some sampling occurred during periods of high food availability. HSI modeling techniques have potential application in site selection and coastal management of aquaculture.     

Liver damage in brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), following administration of the cyanobacterial hepatotoxin microcystin-LR via the dorsal aorta

Purified microcystin-LR (MC-LR) was administered via the dorsal aorta to brown trout, Salmo trutta L., or rainbow trout, Oncorhynchus mykiss (Walbaum), and, within 24 h, a dose of 300 μ g MC-LR kg^–1 caused increased activities in the blood by enzymes originating mainly from the liver, i.e. lactate dehydrogenase (LDH) and alanine transaminase (ALT). A dose of 75 μ g MC-LR kg^–1 significantly increased liver enzyme activities in the blood of brown trout at 24 h, but was without effect on rainbow trout, whereas 25 μ g MC-LR kg^–1 had no effect on blood LDH or ALT activities in either species. However, histopathological analysis of liver from both species following administration of the lowest toxin dose showed hepatocyte swelling and necrosis. Liver damage was more severe in brown trout compared to rainbow trout following administration of 300 μ g MC-LR kg^–1, showing disruption of the parenchymal architecture. After 48 h, there was a dose-dependent increase in the hepatosomatic index in both species. It is concluded that brown trout are less tolerant to MC-LR than rainbow trout.     

Experimental pathogenicity of reovirus 13p2 for juvenile American oysters Crassostrea virginica (Gmelin) and bluegill fingerlings Lepomis macrochirus (Rafinesque)

Abstract. A viral agent (13p₂), isolated from clinically normal juvenile American oysters ( Crassostrea virginica ) and characterized as a new serotype of reovirus, was tested to determine if it could replicate and produce disease in experimental juvenile oysters. Because the virus replicated well in the bluegill fry (BF-2) fish cell line, fingerling bluegills Lepomis macrochirus were included in the pathogenicity experiments. Exposure of oysters to the 13p₂ virus in ambient seawater resulted in no significant mortality and no increased virus titres or histological lesions. Virus particles were not observed in tissues of exposed oysters when examined with transmission electron microscopy (TEM). Intraperitoneal inoculation of the 13p₂ virus into bluegills resulted in 44% mortality associated with a focal necrotic hepatitis. Evidence of virus replication, when evaluated histological or by virus titration, was observed in 94% of 32 inoculated fish. Samples of infected livers examined with TEM revealed typical cytoplasmic arrays of 13p₂ virus particles in affected hepatocytes. Rising virus titres and hepatic lesions also occurred in bluegills exposed to water containing the 13p₂ virus. These results indicated the natural host of the 13p₂ virus was not the American oyster, but that it was a significant pathogen for at least one fish species.     

Nutrient requirement for zoospore formation in two alariaceous plants Undaria pinnatifida (Harvey) Suringar and Alaria crassifolia Kjellman (Phaeophyceae: Laminariales)

ABSTRACT:   Sporophyll formation in two alariaceous plants, Undaria pinnatifida and Alaria crassifolia , was studied in relation to the nutrient requirements. The sporophylls of U. pinnatifida formed zoosporangia when they had N and P contents greater than 1.4 kgN/m³ and 0.74 kgP/m³. This indicates that these values are the critical nutrient levels for zoospore formation in U. pinnatifida . In the sporophytes of A. crassifolia , many sporophylls with zoosporangia showed nutrient contents higher than 6.25 kgN/m³ and 1.70 kgP/m³. These results suggest that the U. pinnatifida can form zoospores at lower levels of N and P contents than A. crassifolia . Both species often formed zoosporangial sori on the blades in the late period of each reproductive season. The fertile parts of the blade showed N and P contents higher than the critical levels. This phenomenon indicates that the blades have the capability to form zoosporangial sori if there is a sufficient accumulation of nutrients for zoospore formation. The zoospore formation on the blade seems to be accomplished by an overflow of excess nutrients from sporophylls into the blade, or by accumulating sufficient nutrients to form sori even if the sporophylls are not formed.     

Impact of a native predatory whelk on cultivated oysters (Crassostrea gigas) crops in San Quintin Bay, Mexico

San Quintin Bay (Baja, California, Mexico) is extensively utilized by artisanal farmers to cultivate Pacific oysters ( Crassostrea gigas ) using a rope/rack system. A large juvenile oyster mortality event was significantly correlated with the presence of native predatory whelks, Macron trochlea . Surveys, field and lab experiments were performed to identify the predatory behaviour of the whelk, determine factors affecting oyster mortality, and quantify the impact on oyster farmers. Macron trochlea was found to be a voracious, active predator, which can consume ∼4 juvenile oysters day⁻¹. Juvenile oysters suffer significantly higher mortality in the presence of whelks. Macron trochlea has the largest impact on small oysters. Once oysters grow to >30 mm they reach a size refuge above which there is much lower mortality. At average growth rates, an oyster can escape predation after ∼3 months. But, in areas of highest whelk densities, at average predation rates, whelks could consume the standing crop of juvenile oysters in approximately 43 days. For the artisanal oyster farmers of San Quintin this represents a substantial economic loss, which was unaccounted for previously. Farmers can reduce loss to whelk predation by seeding juvenile oysters in low whelk density areas until oysters reach the size refuge.     

Tissue distribution of vitamin D3 in Atlantic salmon Salmo salar: effect of dietary level

Atlantic salmon Salmo salar were given three dietary doses of vitamin D₃ for a period of 11 weeks: diet groups I, II and III received a 0.04, 2.21 and 28.68 μg g⁻¹ diet of vitamin D₃, respectively. The tissue distribution of vitamin D₃ was investigated, and between diet groups II and III, the level of vitamin D₃ found in the tissues was increased by a factor similar to the increased level in the feed. No effects were observed on weight gain, survival, plasma level of calcium, red blood cell count or haematocrit, relative to the dietary levels of vitamin D₃. The results showed that while the plasma concentration of 25(OH)D₃ increased between diet groups II and III, the concentration of 1,25(OH)₂D₃ decreased.     

Hydroacoustic assessment of the fish stock in Theodorushaven, a small Dutch harbour

Assessment of the fish stock in the Theodorushaven was conducted with a dual-beam hydroacoustic system. Species composition determined by a seine and trawl fishery showed large concentrations of fish in the harbour during winter. The hydroacoustic survey showed that the distribution of fish in the harbour area was stratified with fish near the bottom. The overall density in the harbour area was 0.67 fish m^–3. The density in the associated channel area was estimated at 0.1 fish m^–3. The coefficient of variation for the estimated total fish abundance was >25%.Fish >25 cm were not caught in the Theodorushaven fishery, although analysis of the sonar data indicated their presence. Fishery data from the adjacent Volkerak-Zoommeer showed that bream was the dominant species. Therefore, the biomass estimate of the stock >25 cm in the Theodorushaven was based on the standard length–weight relationship of bream. This resulted in maximum biomass estimates of 5800 kg ha^–1 for the harbour area and 1100 kg ha^–1 in the channel area. The minimum biomass estimate, based on the assumption that the more slender zander was the dominant species >25 cm, gave values of 4100 kg ha^–1 in the harbour area and 780 kg ha^–1 in the channel area.     

Phenotypic analysis in the Chilean oyster, Ostrea chilensis Philippi 1845: relationship between juvenile and adult growth rates

Abstract. The Chilean oyster, Ostrea chilensis Philippi, shows high phenotypic variability for growth rate within populations. In order to determine if the serial correlation of growth rate in oysters is positive, the correlation between shell height and live weight at different stages of the life cycle in a cohort of the Chilean oyster was estimated. Four size groups of individually tagged oysters selected on the basis of their shell heights were examined. The relationships for juvenile and adult oysters were found to be positively correlated throughout the study period. The correlation coefficients ranged from r = 0.28 to r = 0.83. For shell height the coefficient of determination for market size oysters was higher in 2-year-old (r²=0.88) than in 1-year-old oysters (r²=0.09). Shell height and live weight were more highly correlated at later stages of the life cycle. The results indicate that 2-year-old oysters have a size that is indicative of performance to market size and hence is an appropriate age to select the parents to be used in breeding programmes to improve the growth rate in O. chilensis . A high mortality was detected after the natural spawning period. A physiological stress hypothesis is proposed to explain the high summer mortality in O. chilensis in the Quempillen estuary, southern Chile.     

Insight into nucleotide and Ca<Superscript>2+</Superscript> binding to carp α-actin

ABSTRACT:   Nucleotides and Ca²⁺ binding to α-actin prepared from ordinary skeletal muscle of carp Cyprinus carpio was studied. When bound Ca²⁺ was removed with ethylenediaminetetraacetic acid, carp α-actin denatured more rapidly than chicken α-actin. Kinetic studies of the denaturation process showed that in the absence of divalent cations, the binding constants of ATP to carp and chicken actin were 5.0 × 10⁴/M and 1.2 × 10⁵/M, respectively. Competitive binding of Ca²⁺ between actin and 8-amino-2-[(2-amino-5-methylphenoxy)methyl]-6-methoxyquinoline-N,N,N',N'-tetraacetic acid (Quin 2) showed that affinity of Ca²⁺ for carp actin was also lower than that for chicken actin by a factor of 1.6. These results indicated that carp actin could relatively easily denature due to the low affinities of these ligands. Enthalpy changes upon ATP binding to carp and chicken actin were −65 kJ/mol and −110 kJ/mol, respectively. Thermodynamic analyses of our results revealed that the entropy change associated with ATP binding to carp actin was significantly smaller than that to chicken actin, suggesting that structural stabilization upon ATP binding was less effective in carp actin.     

Underwater sound detection by cephalopod statocyst

Abstract:   The cephalopod receptor of particle motion was identified. In a previous study, it was suggested that statocysts served this function, but there was no direct supporting evidence, and epidermal hair cells had not been conclusively ruled out. Experiments on Octopus ocellatus were conducted using respiratory activity as an indicator of sound perception. Intact animals clearly responded to 141-Hz particle motion at particle accelerations below 1.3 × 10⁻³ m/s², and the mean perception threshold at this frequency was approximately 6.0 × 10⁻⁴ m/s². Specimens in which the statoliths had been surgically removed did not show any response for accelerations up to 3.9 × 10⁻³ m/s² at 141 Hz, which was approximately 16 dB greater than the mean perception threshold at this frequency. Specimens that had undergone a control operation in which the statoliths remained intact showed positive responses at 2.8 × 10⁻³ m/s² for the same frequency stimulus. This indicates that the statocyst, which is morphologically similar to the inner ear system in fish, is responsible for the observed responses to particle motion in O. ocellatus . This is the first direct evidence that cephalopods detect kinetic sound components using statocysts.     

Characterization of the quantitatively major collagen in the mantle of oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

ABSTRACT:   A quantitatively major collagen was isolated from the pepsin-solubilized collagen preparation of the mantle by differential salt precipitation and phosphocellulose column chromatography, and its constituent α components (α1 and α2) were purified by phosphocellulose column chromatography. The subunits were demonstrated to be genetically distinct from each other by peptide mapping and amino acid analysis. The amino acid composition calculated from those of the α1 and α2 components in 2 : 1 ratio coincided well with that of the major collagen from the mantle. These results suggest that the major collagen in the mantle of the oyster may have a heterotrimer structure (α1)₂α2.     

Nutritional evaluation of waste date fruit as partial substitute for soybean meal in practical diets of juvenile Nile tilapia, Oreochromis niloticus L.

The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g⁻¹) were formulated incorporating WDM at 0, 100, 200 and 300 g kg⁻¹ levels as partial substitutes for soybean meal (SBM). These were designated D₀ [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg⁻¹ diet], D₁ (279 g CP and 446 g CHO kg⁻¹ diet), D₂ (207 g CP and 495 g CHO kg⁻¹ diet) and D₃ (175 g CP and 578 g CHO kg⁻¹ diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different ( P  > 0.05). Protein efficiency rate (PER) was lowest in diet D₀ and increased with decrease of SBM content (D₁–D₃). A significant increase in whole body lipid content was recorded in fish fed diets D₂ and D₃. Results showed that WDM could be a substitute for SBM up to 300 g kg⁻¹ in practical Nile tilapia diets without compromising growth.     

Seasonal changes in respiration rates of copepodite stage V Calanus finmarchicus (Gunnerus)

Copepodite stage V Calanus finmarchicus were collected at locations on the continental shelf north of Scotland, in the Faroe–Shetland Channel and west of Ireland on six occasions covering winter, spring and summer from October 1993 to June 1995. Oxygen consumption by the overwintering and active spring/summer population of animals was determined at temperatures close to in situ temperatures. Laboratory measurements of oxygen consumption were also made at standardized temperatures (0°C, 5°C, 7°C and 12.5°C) to determine the sensitivity of animals to temperature change in the different seasons. Rates of oxygen consumption were very low (7–30 μmol O₂ gC⁻¹ h⁻¹) at in situ temperatures during the winter and early spring and significantly higher (105–219 μmol O₂ gC⁻¹ h⁻¹) for the active surface population in May and June. Animals collected from the overwintering population showed no significant response to changes in temperature. Due to the low respiration rates, the calculated rate of decrease in carbon content in diapausing copepodite stage CV was very low (approximately 0.250 μgC day⁻¹). The respiration rates were used to construct a model to estimate survival of the animals with an initial carbon content equivalent to that expected of animals in October. The results showed that in order to survive during winter and have enough energy for moulting and migration to the surface in the spring, these animals have to live at temperatures close to 0°C and be in a diapause state.     

Histopathology, electron microscopy and isolation of channel catfish virus in experimentally infected European catfish, Silurus glanis L.

Abstract Two groups of European catfish, Silurus glanis L., fingerlings were infected with channel catfish virus (CCV) by either intraperitoneal injection with 10⁵ TCID₅₀ of CCV, or bathing in water containing 10⁵ TCID₅₀ of CCV per 1·0 ml. The virus was isolated from spleen, intestine and brain of CCV-injected fish at day 1 and the titres ranged from 10^2·1 to 10^3·3 TCID₅₀/g. However, the tissue distribution of CCV was irregular and no virus was isolated after day 3 post-exposure. In CCV-bathed fish, the virus was isolated only from the liver of one specimen at day 3 post-exposure. No clinical signs of CCV disease developed in any of the fish. Specimens in each regime from all sampling periods showed some minor histopathological changes, but there were no differences between treatments. Lesions included oedema and focal haemorrhage in the liver and the spleen was congested. Electron micrographs of tissue samples showed the presence of a few virus particles around the nuclei of kidney, spleen and intestinal cells, and in or around a myelinated nerve within the optic lobes of infected fish during the first 4 days of infection.     

Quantitative real time PCR for the measurement of white spot syndrome virus in shrimp

Quantitative real time PCR, recently developed in molecular biology, is applied in this paper to quantify the white spot syndrome virus (WSSV) in infected shrimp tissue. The WSSV content in moribund shrimp of all species tested ( Penaeus stylirostris, P. monodon, P. vannamei ) ranged from 2.0 × 10⁴ to 9.0 × 10¹⁰ WSSV copies μg^–1 of total DNA ( n =26). In whole moribund post-larvae, 4.3 × 10⁹ WSSV copies μg^–1 of DNA were detected which is equivalent to 5.7 × 10¹⁰ WSSV copies g^–1 of post-larvae. The comparison of WSSV content between different tissues showed that muscle and hepatopancreas tissues contained 10 times less virus than gills, pleopods and haemolymph. With inocula of known virus content, bioassays by immersion challenge showed that a minimum of five logs of WSSV copies was necessary to establish disease in the challenged shrimp. In contrast, five logs of WSSV copies injected into shrimp muscle produced a LT-50 of 52 h. This real time polymerase chain reaction (PCR) technique is sensitive (four copies), specific (negative with DNA from shrimp baculoviruses and parvoviruses), dynamic (seven logs) and easy to perform (96 tests in <4 h).