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.     

Observations on the effect of salinity and photon fluence rate on the induction of sporulation and rhizoid formation in the green alga Enteromorpha prolifera (Müller) J. Agardh (Chlorophyta, Ulvales)

ABSTRACT: Although most members of the genus Enteromorpha are important edible green algae, some species are also potentially economically valuable crops. Samples of E. prolifera were obtained from the Yoshino River estuary, Tokushima, Japan and cultured in laboratory conditions at 10°C, a salinity of 20 psu, under white light with 12 h light : 12 h dark cycle and at a photon fluence rate (PFR) of 40 μmol/m² per s for 30 days. In the present study, the effect of salinity and PFR on the induction of reproductive cells and rhizoid formation were investigated. Synchronous formation of swarmers by thalli was induced in excised disks of 1.2 mm diameter after 2–5 days incubation. The optimum salinity for maturation of reproductive cells was between 5.0 and 52.0 psu, and between 13.2 and 45.3 psu for swarmer release, although the lower limit for swarmer release was 5.0 psu. Maturation of reproductive cells and swarmer release required a PFR higher than 16 μmol/m² per s. The minimum PFR for swarmer release was 8 μmol/m² per s. Many rhizoids were formed between 1.6 and 52.0 psu and photon fluence rates between 8 and 320 μmol/m² per s. Rhizoids were formed in a polarized manner.     

Migration of anadromous white-spotted charr <Emphasis Type="Italic">Salvelinus leucomaenis</Emphasis>, as determined by otolith strontium: calcium ratios

ABSTRACT:   The migratory history of anadromous white-spotted charr Salvelinus leucomaenis collected from Japanese coastal waters, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith, by means of wavelength dispersive X-ray spectrometry using an electron microprobe. Otolith Sr concentration or Sr : Ca ratios of anadromous S. leucomaenis , fluctuated strongly along the life history transect in accordance with the migration (habitat) pattern from sea to fresh water. The anadrmous S. leucomaenis showed phase L (low Sr : Ca ratio) from the core to the point 1000–2500 µm distant, averaging 1.3 × 10⁻³ to 2.7 × 10⁻³ and thereafter, the ratios increased sharply, being higher than 5.0 × 10⁻³ to 10.0 × 10⁻³. These findings indicated that otolith Sr : Ca ratios reflected individual life histories, enabling a sea habitat to be identified from a freshwater habitat in this species.     

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.     

Evaluation of coral bleaching condition <Emphasis Type="Italic">in situ</Emphasis> using an underwater pulse amplitude modulated fluorometer

ABSTRACT:   Photosynthetic activities of hermatypic corals (28 genera, c . 68 species and c. 92 specimen) were measured in November 2000 at Sekisei lagoon, Okinawa, Japan, using an underwater pulse amplitude modulated fluorometer. Maximum quantum yield (Fv/Fm) ranged from 0.61 to 0.70 and had an average value of 0.664 (standard deviation [SD], 0.0289). Following the measurement of Fv/Fm, quantum yield (Fm'-F)/Fm' at eight-leveled actinic-light intensities were obtained from all specimens. Values of electronic transport rates (ETR) were nearly the same under low photosynthetic active radiation (PAR; µmol quanta/m² per s) condition and varied with increasing PAR. The value of ETR at 100 µmol quanta/m² per s ranged from 21.3 to 30.0 and had an average of 27.8 (SD, 2.09). In August 2001, a coral bleaching event was observed in Sekisei Lagoon. During the event, photosynthetic activities of 21 specimens of eight species (seven genera) were measured. By applying two indicators, Fv/Fm and ETR at 100 µmol quanta/m² per s obtained in August 2000, 18 of 21 specimens were suggested under the bleaching process. In case of Porites lutea , seven colonies were visually evaluated for their condition of bleaching and were found to have two 'normal', three 'slightly bleached' and two 'heavily bleached'. From the density of zooxanthellae, colonies evaluated 'normal' or 'slightly bleached' did not show an apparent difference. However, they were clearly identified by Fm/Fv and ETR at 100 µmol quanta/m² per s.     

Effects of temperature, salinity and irradiance on the growth of the toxic dinoflagellate Gymnodinium catenatum (Dinophyceae) isolated from Hiroshima Bay, Japan

ABSTRACT: Temperature and salinity ranges in which Gymnodinium catenatum (Hiroshima Bay strain) showed specific growth rates higher than 0.2/day were approximately 20–30°C and 20–32. The specific growth rate (μ), expressed as a polynomial equation as functions of temperature ( T ; °C) and salinity ( S ) were μ = (−6.84 × 10⁻⁴ T ² + 0.0354 T – 0.213) × (−1.03 × 10⁻³ S ² + 0.0579 S – 0.548)/0.31; the maximum growth rate (0.31/day) was obtained at 25°C and 30. From a comparison with field data recording temperature, salinity and light intensity, this species may be expected to bloom from summer to autumn in Hiroshima Bay.     

Larval settlement of the tropical abalone, Haliotis asinina Linnaeus, using natural and artificial chemical inducers

Many kinds of chemical and biological materials have been used as inducers of settlement of abalone larvae, as well as other species of marine gastropods, with responses being highly variable, even to the same chemical cue. The present study tested chemical inducers, γ-aminobutyric acid (GABA), δ-aminovaleric acid (5-AVA) and l -glutamic acid (GA) and the effects they have on larval settlement of Haliotis asinina . Additionally, a relatively inexpensive commercial substance, monosodium glutamate (MSG), was trialed. The datum provided shows all chemicals to be active inducers of settlement in this study, in order of effectiveness of 5-AVA, GABA, MSG to GA. Induction as adjudged from larval numbers settled was best at 6 h 62%, with 10⁻¹ mM 5-AVA. At 24 h, induction was the highest at 78% when exposed to 10⁻² mM 5-AVA. Larvae that were allowed to settle up to 72 h showed the highest numbers of settled larvae, and declined back to 60% when exposed to 10⁻² 5-AVA and 10⁻¹ mM GABA respectively. Monosodium glutamate, although third in settlement standings would bypass the other chemicals, with regard to cost versus yield. The assessment of settlement surface, rough or smooth proved to be irrelevant, which had no significant impact on larval settlement.     

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).     

Temporal variation of seasonality of egg production and the spawning biomass of Pacific anchovy, Engraulis japonicus, in the southern waters of Korea in 1983–1994

Embryonic mortality, egg production and the spawning stock biomass of Pacific anchovy, Engraulis japonicus , off Southern Korea during 1983–1994, and their biological response to oceanographic features in spring and summer, were analysed. The instantaneous mortality rate (IMR) of embryonic stages decreased in spring and increased in summer, with a range of 0.33–1.23 day^–1 in spring and 0.78–1.69 day^–1 in summer. Egg production in summer was three times that during spring and production was low in the late 1980s. Mean lengths of yolk-sac larvae and adult females were greater in spring than in summer, whereas spawning fraction and spawning stock ratio (spawning biomass:adult biomass) were lower in spring than summer. Estimated mean spawning stock biomass ranged from 141 × 10³ to 380 × 10³ MT in spring and from 221 × 10³ to 557 × 10³ MT in summer. Statistically, the seasonal and long-term trends of embryonic mortality, egg production and spawning stock biomass of Pacific anchovy can be explained largely by spring warming, summer cooling and by less abundant zooplankton in the late 1980s.     

Creation of artificial upwelling areas for brown trout, Salmo trutta, spawning in still water bodies

Abstract  Brown trout, Salmo trutta L., spawning sites were constructed by creating areas of artificial upwelling water, 252 ± 37 mL m⁻² min⁻¹ (95% CL), through appropriately sized spawning gravel substrate in 3 m² vessels buried in the bottom of a 150-m² pond. Natural spawning occurred in the vessels during autumn 2001–2004, with hatching and alevin swim up the following spring. In areas of upwelling, egg survival was 85–95%, while no live eggs were observed in areas without upwelling. In areas with upwelling, the maximum density of live eggs at the eyed stage was 570–1510 eggs m⁻². In spring 2004 and 2005, the density of alevins was estimated at 322 (±187) m⁻² and 567 (±217) m⁻², respectively, in areas with upwelling water, compared with 35.2 ± 25.4 m⁻² in areas without upwelling water in 2004.     

Effects of the initial size, stocking density and sorting on the growth of juvenile Pacific abalone, Haliotis discus hannai Ino

During winter months, a novel overwintering mode of transferring juvenile abalones to open seawaters in southern China rather than keeping them in closed land-based nursery systems in northern China is a popular practice. The initial size, stocking density and sorting are among the first considerations when establishing an abalone culture system. This study aimed to investigate the effects of these factors on the growth of juvenile Pacific abalone, Haliotis discus hannai Ino, during overwintering. Juvenile abalones were reared in multi-tier basket form for overwintering in open seawaters in southern China for 106 days. The daily growth rates (DGRs) in the shell length of all experimental groups ranged from 67.08 to 135.75 μm day⁻¹, while the specific growth rates (SGRs) were 0.2447–0.3259% day⁻¹. Variance analysis indicated that both DGRs and SGRs in shell length were significantly affected by the initial body size and stocking density. Furthermore, the effects of stocking density on DGRs and SGRs varied with the initial size. However, sorting abalones according to their initial sizes may not be necessary in practice as sorting did not alter growth significantly at all densities in this study. Factors potentially affecting abalone growth such as genetic control and intraspecific competition were discussed.     

An experimental investigation on aspects of infectious salmon anaemia virus (ISAV) infection dynamics in seawater Atlantic salmon, Salmo salar L.

This study investigated infection dynamics of infectious salmon anaemia virus (ISAV) by conducting two experiments to examine minimum infective dose and viral shedding of ISAV. In terms of minimum infective dose, the high variability between replicate tanks and the relatively slow spread of infection through the population at 1 × 10¹ TCID₅₀ mL⁻¹ indicated this dose is approaching the minimum infective dose for ISAV in seawater salmon populations. A novel qPCR assay incorporating an influenza virus control standard with each seawater sample was developed that enabled the quantity of ISAV shed from infected populations to be estimated in values equivalent to viral titres. Viral shedding was first detected at 7 days post-challenge (5.8 × 10⁻² TCID₅₀ mL⁻¹ kg⁻¹) and rose to levels above the minimum infective dose (4.2 × 10¹ TCID₅₀ mL⁻¹ kg⁻¹) on day 11 post-challenge, 2 days before mortalities in ISAV inoculated fish started. These results clearly demonstrate that a large viral shedding event occurs before death. Viral titres peaked at 7.0 × 10¹ TCID₅₀ mL⁻¹ kg⁻¹ 15 days post-infection. These data provide important information relevant to the management of ISA.     

Comparison of habitat use during early life stage between ayu Plecoglossus altivelis and ice goby Leucopsarion petersi along the sanriku coast of Japan, as determined from otolith microchemistry

ABSTRACT:   The habitat use and migration of ayu Plecoglossus altivelis was compared to that of ice goby Leucopsarion petersi using otolith microchemistry analysis. Both species were collected along the Sanriku Coast. Otolith Sr : Ca ratios of ayu fluctuated strongly along the life history transect in accordance with the migration (habitat) pattern from fresh water to sea water. The Sr : Ca ratios of the center region averaged 3.2 × 10⁻³; thereafter, the ratios increased sharply, averaging 9.2 × 10⁻³, and were maintained at the higher levels until the outermost regions. By contrast, the Sr : Ca ratios of ice goby showed consistently high values along the life history transect of the otolith, ranging 9.0 × 10⁻³ in the center to 9.2 × 10⁻³ in regions outside the center, with further increases around the otolith edge. These findings indicate that ayu shows a typical amphidromous migratory pattern, while ice goby does not show the anadromous migratory pattern previously reported. The use of a freshwater environment during the early developmental stage in ice goby along the Sanriku Coast was less prominent than that of ayu in the same region.     

Growth and mortality of common octopus Octopus vulgaris reared at different stocking densities in Mediterranean offshore cages

Four ongrowing cycles of common octopus ( Octopus vulgaris ), each with two stocking densities, were carried out in an offshore area in order to evaluate the effect of the following variables on growth ( G , % body weight day⁻¹) and mortality ( M , % day⁻¹): weight ( W , 0.5–3.0 kg), temperature ( T , 14–26 °C), stocking density (SD, 6–46 kg m⁻³), size dispersion, expressed as coefficient of variation (CV, 13–42%) and significant wave height (SWH: 0.4–1.2 m). The assays were performed in an 8 m³ stainless-steel floating cage divided into two compartments of 4 m³ each. For the range of temperatures considered (14–26 °C), G depended significantly on T and SWH, with maximum G values being obtained at 18.5 °C and with an important negative effect of SWH. M depended significantly on T, W and CV, mortality being minimal at 18 °C. The two other variables had an antagonistic effect, mortality increasing with greater size dispersion – suggesting that animals should be graded throughout the process – although the effect diminished as the sizes increased. The results point towards two alternatives for the commercial ongrowing of octopus under the particular conditions of the present study: (A) two ongrowing cycles of 3.5 months to reach a final weight of 2.5 kg or (B) one 5-month cycle to reach a final weight of 3.5 kg.     

Effects of irradiance of various wavelengths from light-emitting diodes on the growth of the harmful dinoflagellate <Emphasis Type="Italic">Heterocapsa circularisquama</Emphasis> and the diatom <Emphasis Type="Italic">Skeletonema costatum</Emphasis>

ABSTRACT:   We investigated the effects of specific light wavelengths from light-emitting diodes (LEDs) on the growth of the dinoflagellate Heterocapsa circularisquama , which kills bivalves, and the diatom Skeletonema costatum , which is an important food source for bivalves. Growth of H. circularisquama was obviously inhibited at 590 nm and a photon flux density less than 75 μmol quanta/m²/s. However, growth of S. costatum was not suppressed by irradiance from any LEDs tested from near-ultraviolet to near-infrared wavelengths at 75 μmol quanta/m²/s. The growth rate of H. circularisquama in an experimental treatment group with irradiance provided by both cool-white fluorescent lamps (12:12 h L : D cycle) and a 590-nm LED (continuous irradiance) was 0.43/day. In the control group with irradiance provided only by cool-white fluorescent lamps (12:12 h L : D cycle), the growth rate was 0.63/day, indicating that growth of H. circularisquama was suppressed by 590 nm (less than 75 μmol quanta/m²/s) irradiance from the LED and the continuous irradiance. The use of 590-nm LEDs in bivalve culture at irradiance levels less than 75 μmol quanta/m²/s might encourage the growth of the useful diatom S. costatum without stimulating growth of the harmful dinoflagellate H. circularisquama .     

The growth rate of two species of microalgae used in shellfish hatcheries cultured under two light regimes

Abstract. The production potential of any shellfish hatchery depends on the capacity of its algal system. The hypothesis that microalgal cultures grown under 12:12h light:dark photoperiod may produce the same cell densities as those using constant light is tested.
Two species of marine microalgae used in shellfish hatcheries. Chaetoceros gracilis Schütt and Isochrysis galbana clone T-iso, were grown in cultures at 18°C, under continuous light (1.43 × 10⁷μ^-2day^-1) and 12:12h light:dark cycles (2.87 × 10⁷μE m^-2 day^-1). Both light regimes provided equal amounts of light per day. In the continuous light cultures the mean doublings per day for exponentially growing cells were 1.37 and 1.49 for C. gracilis and I. galbana respectively and for the 12:12h light:dark cycles were 1.47 and 1.56 respectively. After 14 days of growth, the numbers of cells per unit of volume showed no significant differences between the two light regimes. The results are discussed in terms of a review of other authors' findings and in terms of the usefulness of the continuous light method in producing algae to be used in shellfish hatcheries.     

Gustatory receptor responses in marbled rockfish Sebastiscus marmoratus

Gustatory response of marbled rockfish Sebastiscus marmoratus was recorded from the facial nerve supplying the anterior palate. In amino acids, the lowest threshold was for L -proline at 10⁻⁶–10⁻⁵ M; in ATP-related substances, the value for inosine was approximately 10⁻⁵ M and in organic acids, the value for L -lactic acid was approximately 10⁻⁶ M. An almost complete self-adaptation was observed for stimulants after 5 s application. While a weak solution of L -lactic acid as adapting stimulus depressed the response to it completely, it did not appreciably affect the response to 10-times or more concentrated L -lactic acid solution. In contrast to a weak solution, a moderate solution caused a severe depression of the response to stronger solutions, resulting in a shift of the dose–response curve towards a high concentration range. Time for recovery from adaptation differed depending on chemicals and stimulus duration: for 10⁻⁴ M L -lactic acid, it took about 2.3 and 4.5 s for 1/2 recovery of response magnitude under unadapted condition from the adaptation after 1 s- and 5 s-stimulation, respectively. L -Lactic acid and L -alanine strongly depressed the response to each other, yielding a rightward shift of the dose–response curve. A similar profound cross-adaptation was also observed between inosine and 5'-inosinic acid. The possible role of gustation is discussed.     

Growth Characteristics of a Neurotoxin-Producing Chloromonad Fibrocapsa japonica (Raphidophyceae)

The effects of temperature, salinity, irradiance and pH on the growth of Fibrocapsa japonica (Raphidophyceae) were examined to determine how environmental factors affect the distribution of this species. Optimal growth was observed at temperatures of 15–25 C, salinities of 25–35 parts per thousand (ppt), irradiances of 60–140 μmol quanta/m² per s and pH between 7.5–8.5. Growth did not occur at temperatures below 10 C or above 30 C nor at salinities below 15 ppt. Fibrocapsa japonica grew when subjected to irradiances of 20–180 μmol quanta/m² per s, and could tolerate a pH range of 6.5–8.5.     

Suspension feeding of the ark shell <Emphasis Type="Italic">Scapharca subcrenata</Emphasis> as a function of environmental and biological variables

ABSTRACT:   To assess the roles of the ark shell Scapharca subcrenata in material cycling in the northern part of Ariake Sound (Mae-no-umi), Japan, filtration of the ark shell fed on small diatoms was examined as a function of environmental and biological variables. The clearance rate ( CR ) specific to the soft-body dry weight ( w ) of the animals (shell length, 8–26 mm) followed a power function of w with an exponent of −0.35. Over the range of 10–20°C, CR increased 2.7 times, and filtration did not occur below a salinity of 14 practical salinity unit. Neither food concentration (10–40 µg/L of chlorophyll- a ) nor weight-specific daily ration (0.5–6%/day in terms of ash-free dry weight) notably affected CR . Using this information on CR as well as data regarding abundance and size distribution, the population filtration rate was calculated to be 1.6 m³/m² per day in the ark-shell culturing ground of Mae-no-umi (mean water depth, ∼3 m), corresponding to the potential to locally process a volume of water equivalent to the water column within 2 days. Because the culturing ground accounts for 12% of Mae-no-umi (mean water depth, ∼8 m), the ark shell seems to play an important role in its material cycling.     

Cage culture of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) at different stocking densities in a shallow eutrophic lake

Postlarvae of Litopenaeus vannamei were acclimated and stocked in lake-based cages at the following stocking densities: 10, 20, 30 and 40 shrimp m⁻². Another set of shrimp was stocked in concrete tanks as reference samples at 30 shrimp m⁻². Significant differences were observed among stocking densities throughout the 95-day culture. The final weight at harvest decreased with increasing stocking density: mean weights of 23.3, 15.8, 13.0, 10.9 and 14.6 g for the 10, 20, 30, 40 shrimp m⁻² and reference tanks were observed respectively. There were no significant differences in survival throughout the culture period, ranging between 69% and 77%. Daily growth rates (range: 0.11–0.24 g day⁻¹) and specific growth rates (range: 3.54–4.34%) also differed significantly among stocking densities, both increasing with decreasing stocking density. The feed conversion ratio in the cages did not differ among the stocking densities, ranging from 1.53 to 1.65. The relationship between stocking density and mean individual weight at harvest followed the equation y =81.06 x ^−0.54 ( R ²=0.938) and that of stocking density and production (in g m⁻²) is y =58.01 x ^−0.46 ( R ²=0.834).