Establishment of shell growth analysis technique of juvenile Manila clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>: semidiurnal shell increment formation

ABSTRACT:   The conventional acetate peel method was modified to analyze the shell growth pattern of juvenile Manila clam Ruditapes philippinarum as small as 2 mm in shell length (SL). In the outer shell layer along the axis of maximum growth, two types of growth increments were observed: distinct increments and indistinct increments, which, respectively, do and do not continue to the middle shell layer. The distinct increments were found to be formed every two days in intertidal and shallow subtidal zones by field enclosure experiments of juveniles with datum points marked with alizarin complexone. Growth patterns of juveniles (12 mm SL) collected from the Seaside Park of Yokohama in Tokyo Bay were analyzed to confirm the modified method. Mean daily shell growth rate from April to July 2005 ranged 120–142 μm/day, which was reasonable as compared with previous studies. It was impossible to backcalculate the growth to the settlement size (i.e. 0.2 mm SL) because of erosion of the outer shell surface, and the smallest backcalculated minimum shell length was 0.8 mm. Fluctuations in daily growth rate were high, ranging 29–315 μm/day, and did not show a clear two-weekly rhythm.     

Annual changes in distribution depths of bighand thornyhead <Emphasis Type="Italic">Sebastolobus macrochir</Emphasis> off the Pacific coast of northern Honshu,Japan

ABSTRACT:   Body size dependent distribution patterns of bighand thornyhead Sebastolobus macrochir were examined using bottom trawl surveys in the Tohoku area, off the Pacific coast of northern Honshu, Japan. In northern and southern Tohoku, distribution depths of ≤10-cm standard length (SL) fish increased from 500–600 m in 2003 to 600–700 m in 2005 with an increase in density of 11–20-cm SL fish at depths of 500–600 m. In 2004–2005, small fish (≤10 cm SL) were distributed in deeper waters than large fish (11–20 cm SL). In ≤20-cm SL fish, the main distribution depths changed from 300–600 m in 1997–2002 to 500–600 m in 2003 in southern Tohoku, but not in northern Tohoku. Stepwise multiple regression analysis showed that negative correlations were found in biomass densities between a few demersal fish species and bighand thornyhead at depths of 300–400 and 400–500 m in southern Tohoku. These results suggest that distribution of bighand thornyhead was affected by intra- and interspecific competitions in the Tohoku area.     

Growth and habitat of spotted halibut Verasper variegatus in the shallow coastal nursery area, Shimabara Peninsula in Ariake Bay, Japan

ABSTRACT:   To determine the growth performances and habitat characteristics of spotted halibut Verasper variegatus , successive samplings were conducted in the south-eastern coastal area of Shimabara Peninsula in Ariake Bay. The push-net samplings were performed at Kamaga beach from May 2003 to April 2004 to determine the horizontal distribution of larvae and juveniles, while the gill net samplings were done in the coastal waters of Tatsuishi beach from July 2003 to July 2004 to collect the larger juveniles and adults. A total of 478 individuals from metamorphosing larvae to 2-year-old fish (15.2–447.0 mm total length [TL]) were sampled. In particular, the 2003-year class fish were successively collected from May 2003 to June 2004 (15.2–350.0 mm TL; n  = 418) and the mean total length in March, June, September, December 2003 and May 2004 was 22.4, 82.5, 172.5, 203.9 and 296.4 mm, respectively. The present study found that metamorphosing larvae migrated into the estuarine tidal flats during March 2003; newly settled juveniles inhabited the shallow intertidal areas; and juveniles had a remarkably high growth in shallow coastal areas. It is suggested that young fish around 300 mm TL migrated from the nursery grounds in Ariake Bay to deeper waters around Tachibana Bay during May–June 2004.     

Radula development in abalone Haliotis discus hannai from larva to adult in relation to feeding transitions

ABSTRACT: The radula morphology of Haliotis discus hannai was examined by scanning electron microscope from the larval to the adult stage. The radula of competent larvae contained 11–13 transverse rows of teeth after 6–7 days at 20°C. The number of rows increased to 25–30 during the first several days after settlement, but then remained approximately constant throughout the post-larval period, increasing again in abalone larger than 4 mm in shell length (SL). In post-larvae < ~1 mm SL, only two pairs of lateral teeth (L1, L2) were present in the larval radula. An additional three pairs of lateral teeth (L3–L5) were added progressively as post-larvae grew from 0.9 mm to 1.9 mm SL. Marginal teeth were added steadily from one pair in larvae to 30–40 pairs at 3–4 mm SL, 70–80 pairs in 30–40 mm juveniles, and 70–90 pairs in 90–100 mm adults. The serrations on the working edges of the rachidian (R) and lateral teeth became less pronounced as the abalone grew. Nearly all serrations disappeared from the rachidian (R) and inner lateral teeth (L1, L2) by ~2 mm SL, and from the outer lateral teeth (L3–L5) by 20 mm SL. For abalone larger than 1.5 mm SL, the L3–L5 teeth became longer and more pointed, which increased the space between adjacent rows of teeth. Post-larvae < 1 mm SL had highly curved teeth with clearance angles of approximately or less than zero, whereas larger abalone had positive clearance angles. These radula developments appear to be related to transitions in feeding habits from microbial to macroalgal diets.     

山东南部皱纹盘鲍工厂化养殖试验研究

报道了山东南部皱纹盘鲍（HaliotisdiscushannaiIno）工厂化养殖试验研究的结果。自1995年1月19日至1996年5月19日，经16个月的培育，将平均壳长21．4mm，平均体重0．99g的幼的培育成平均壳长61．9mm（最大壳长72．0mm），平均体重28.5g的成鲍，成活率为93．2％。0．3m2的波纹权的养殖密度：鲍壳长为20．0～30．0mm时，养殖密度200～250粒为好；40．0mm以前，养殖密度150粒为宜；60．0mm以前，养殖密度50～80粒为佳。饵料以人工配合饵料为好。在鲍壳长40．0mm以前，在投喂人工配合饵料的同时，加上适量的新鲜海藻可以达到同样的增长和增重的目的。全投喂海藻增长和增重都较慢。     

Identification of juvenile abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis> based on number of open and sealed respiratory pores

ABSTRACT:   Changes in the number of respiratory pores (open pores) and their imprints (sealed pores) in post-larvae and juveniles were observed and compared for four abalone species Haliotis diversicolor , H. discus discus , H. madaka , and H. gigantea . The first open pore was evident at a shell length (SL) of 1.5 mm in H. diversicolor , 1.9–2.0 mm SL in H. discus discus , and 2.3–2.4 mm SL in H. madaka and H. gigantea . The number of open pores in H. diversicolor gradually increased with growth, with four to five pores at 2.5–18.0 mm SL and five to six pores at 18.0–27.0 mm SL. The other three species maintained four to five open pores after they reached 3.4–4.5 mm SL. The total number of open and sealed pores (TNP) was greater in H. diversicolor than in the other species at the same SL. Juvenile H. diversicolor were identified among field-caught abalone by the difference in the relationship between SL and TNP (SL–TNP relationship) and also by the monoclonal antibody reaction method. The results of the two methods were in perfect agreement, indicating that our method using the SL–TNP relationship is reliable for the identification of H. diversicolor .     

Vertical movements of Atlantic salmon post-smolts relative to measures of salinity and water temperature during the first phase of the marine migration

Abstract  The migratory behaviour of hatchery-reared Atlantic salmon, Salmo salar L., post-smolts during the first phase of the marine migration was examined to assess their susceptibility to salmon lice, Lepeophtheirus salmonis (Krøyer), infestations. Swimming depths of eight post-smolts relative to the measured salinity and temperature were monitored for an average of 11.4 h following release outside the mouth of the River Eio using depth sensitive acoustic transmitters. Vertical salinity and temperature distributions were simultaneously recorded along the migratory route. Mean swimming depth was 1.7 m (individual mean 0.5–2.1 m). There was no overall preference among all the post-smolts for specific salinity concentrations. Typically post-smolts migrated the majority (68%) of their time at salinities <20 psu (brackish water), and as a result outside the reported salinity tolerances of sea lice. Furthermore, post-smolts chose the warmest water layer during their coastal migration.     

Morphological and habitat characteristics of settling and newly settled Roughscale Sole Clidoderma asperrimum collected in the coastal waters of northeastern Japan

This report first describes the morphological and habitat characteristics of larval and juvenile Roughscale Sole Clidoderma asperrimum. Five metamorphosing larvae (22.1–31.7 mm standard length, SL) and 12 juveniles (23.7–46.4 mm SL) were collected from two locations in coastal waters of northeastern Japan, Shizugawa Bay (rocky habitats, 6–12 m depth) and Iwaki (sandy habitats, 10–50 m depth), respectively, using a hand net while SCUBA diving and a small trawl net during May–August in 2008 and 2010. Underwater observation in Shizugawa Bay revealed that metamorphosing larvae and juveniles that had settled on rocks or stones showed transparent and variegated body coloration, which is cryptic to a rocky habitat. Juveniles in Iwaki showed monotonic coloration. The settlement would occur during metamorphosis because the same larva observed on a stone subsequently swam with a left-lateralized body posture. The larval morphology was characterized by a dense covering of fine spines on the whole body surface. Spines on the ocular side developed steadily, gradually forming bony tubercles with growth, whereas those on the blind side regressed with development and finally disappeared in metamorphosed juveniles. Our results indicate that Roughscale Sole can settle and adapt to rocky and sandy habitats in coastal waters with wide depth range.     

Spatial organisation of European eel (Anguilla anguilla L.) in a small catchment

Abstract –  Modelling-governing patterns of European eel ( Anguilla anguilla L.) distribution of four eel size classes (<150, 150–300, 300–450 and >450 mm) in the Frémur basin (northwest France) was done using artificial neural network (ANN) techniques and ecological profiles. Our results demonstrate the high predictive power of the ANN models. Some macro- and microscale factors, such as distance from the sea, depth and flow velocity, have the most significant influence on the models. Influence of distance from the sea appears to be very different from the spatial organisation usually described in river systems. In fact, the general tendencies of total eel densities according to the distance from the sea showed that densities increase weakly upstream. Another outcome was the variations in habitat preference according to the eel size, even if this species is spread over practically every type of microhabitat. Small eels were mainly found in shallow habitats with strong abundance of aquatic vegetation, whereas large eels tend to be found in intermediate to high depth with small to intermediate abundance of aquatic vegetation. Finally, we hypothesise that European eels change behaviour and microhabitat characteristic preference around a size of 300 mm.     

Life cycle of <Emphasis Type="Italic">Dilophus okamurae</Emphasis> (Phaeophyceae) and its associated invertebrate fauna in Onagawa Bay,Japan

ABSTRACT:   The life cycle of Dilophus okamurae and the associated benthic invertebrate fauna were studied monthly or bimonthly from June 1998 to September 1999 at a depth of 4–7 m in Onagawa Bay along the Pacific coast of north-eastern Honshu, Japan (38°28'N, 149°29'E). Dry biomass ranged from 230 g/m² in June to 10 g/m² in October. Sporophytes with tetrasporangia appeared during July to September 1998. Gametophytes with oogonia or antheridia were observed for the first time in May 1999 during observation. The absence of mature sporophytes in 1999 suggests that the life cycle is completed over two years. The sympatric gastropods Lirularia iridescens , Homalopoma sangrarense, Conotalopia minima and Cantharidus callichroa synchronized with seasonal changes in biomass of this algae. In contrast, Barleeia angustata and B. trifasciata fluctuated independently. The juvenile sea urchin Strongylocentrotus nudus appeared in the algal population starting in October at 0.7 mm mean test diameter at high density, and disappeared after March.     

Vertical distribution of jack mackerel Trachurus japonicus larvae in the southern part of the East China Sea

ABSTRACT:   The vertical distribution of jack mackerel Trachurus japonicus larvae was described based on discrete depth sampling using a MTD net system from the surface down to 100 m depth at 13 stations in the southern East China Sea between 27 February and 10 March 2002. Of the 20 782 fish larvae collected, T. japonicus larvae were most abundant, accounting for 37.0% of the total catch. The average abundance of the larvae was 419.0 individuals/10 m², with the average (± standard deviation [SD]) body length of 2.6 ± 0.3 mm (range 1.8–7.5 mm). The larvae were concentrated in the mixed layer, with peak densities in the 10–30 m layer. The average (±SD) weighted mean depth was 21.5 ± 7.8 m. There was no evidence of either diel or ontogenetic vertical migration for the early larvae of <5 mm. More than 90% of the T. japonicus larvae were collected in the water temperature ranging from 21 to 23°C. Vertical profiles of the larval densities and chlorophyll a coincided with each other, which might reflect the abundance of their main prey organisms, copepod nauplii and copepodites, since copepod production is known to be closely related with the chlorophyll a concentration.     

Characterization of depth-related changes and site-specific differences of microbial communities in marine sediments using quinone profiles

ABSTRACT:   Respiratory quinone compositions were analyzed by a high-performance liquid chromatography to characterize the depth-related changes and site-specific differences of microbial communities in marine sediments. Two deep-sea sediment samples and one coastal sediment sample were investigated from three sites on the coast of Japan, Sagami Bay, Suruga Bay and Tokyo Bay. Although depth-related changes in microbial community structures were observed, site-specific differences appeared to have greater influence on overall community structures. A variety of quinone homologs was commonly identified at all sampling sites and depths examined, but a few minor quinone fractions, mainly derived from Actinobacteria , were detected only at specific sampling sites. Methylmenaquinone-7 (MMK-7) was the major component throughout the examined depths in Sagami Bay and Tokyo Bay. Most abundant quinone homologs changed with each depth in Suruga Bay. Menaquinone-6 (MK-6) predominated in the 0 to 2-cm layer (19%). Below 0–2 cm, the most abundant homolog in each sampling depth was phylloquinone (K₁; 13%, 4–6 cm), MK-8 (19%, 8–10 cm) and MK-7 (13%, 16–18 cm). The microbial respiratory quinone profiling method shown here, successfully demonstrates the usefulness of this approach to characterize microbial communities in marine sediments.     

Comparison of spatiotemporal patterns in reproduction of the kuruma prawn Marsupenaeus japonicus between two regions having different geographic conditions in Kyushu, southern Japan

ABSTRACT:   The Yatsushiro Sea and Shibushi Bay are, respectively, located on the western and south-eastern coast of Kyushu, southern Japan. The Yatsushiro Sea is a shallow semi-enclosed inland sea, whereas Shibushi Bay is an open-type bay with a deep and wide mouth facing the open sea. The size at sexual maturity and spatiotemporal patterns of reproduction of the kuruma prawn Marsupenaeus japonicus (Decapoda, Penaeidae) were examined and compared between these two regions. In the Yatsushiro Sea, the size at sexual maturity was estimated to be 131 mm body length. However, the estimated size at sexual maturity was considerably larger (154 mm) in Shibushi Bay. The spawning season of M. japonicus was estimated to continue from April to September in the Yatsushiro Sea, whereas it was estimated to be longer in Shibushi Bay, from March to November. It is believed that the warm water temperature due to the strong effect of the Kuroshio Current prolonged the spawning season of M. japonicus in Shibushi Bay. The spawning grounds were estimated to be in areas deeper than 10 m in the Yatsushiro Sea and deeper than 20 m in Shibushi Bay. In Shibushi Bay, body size distribution of mature females was considered to be less affected by water depth in comparison with the Yatsushiro Sea, although older mature females larger than 200 mm body length also spawned outside of the bay.     

Shell growth and age determination of the brackish water bivalve Corbicula japonica in Lake Shinji, Japan

ABSTRACT:   Shell growth and age determination of Corbicula japonica were investigated from samples collected monthly at two sites and field growth experiments from November 1999 to November 2000 in Lake Shinji. Both specimens did not grow in winter when the water temperature was below 11°C, but grew rapidly from spring to early summer when the water temperature rose from 15°C to 30°C, before further growing slowly from summer to autumn after the main breeding period. The monthly marginal growth distribution of the samples indicated that the concentric groove on the shell surface was an annual growth ring. It is concluded that the age of C .  japonica in the i -ring group when the shell growth resumed in spring was i  + 0.5 ( i  = 1, 2, · · ·), because the first true growth ring was formed at 0–2 mm in shell length, which then faded with growth. Lee's phenomenon was observed in the age determination results, and thus the growth coefficient and the asymptotic shell length of the von Bertalanffy growth equation were not estimated from the samples. However, these parameters were estimated from the annual shell length increments of the experimental individuals, which were 0.331/year and 28.2 mm, respectively.     

Lateral migration of Arapaima gigas in floodplains of the Amazon

Abstract –  This study deduced in detail the lateral migration –those between river channels and floodplain habitats – of the pirarucu ( Arapaima gigas ), a giant, obligate air-breathing species of the Amazon Basin. Over a thousand samples of the pirarucu were taken through counts of the individuals performed at the moment of aerial breathing; these samples were taken in eight habitats of a floodplain near the Amazon River every week throughout an entire flood cycle. The lateral migration of the pirarucu accompanied water level fluctuations closely. As water levels rose, the pirarucu migrated to increasingly higher habitats in flooded forests and remained there during high water levels. As water levels declined, the pirarucu migrated first back to lower habitats of flooded forests, then to communicating channels, and, eventually, to the lakes, where they remained during low water levels. These results allow for a conceptual model of lateral migration of floodplain fishes.     

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.     

Color vision, spectral sensitivity, accommodation, and visual acuity in juvenile masu salmon Oncorhynchus masou masou

ABSTRACT:   Color vision, spectral sensitivity, accommodation, and visual acuity were examined in juvenile masu salmon Oncorhynchus masou masou to obtain fundamental information about the visual system. Two types of S-potentials were recorded from 415 horizontal cells in isolated retinas from 34 cultured freshwater masu salmon (114–219 mm standard length, SL). Although horizontal cells recording S-potentials were not identified, the horizontal cells were confirmed because their responses were maintained while the stimulus remained. The variety of chromaticity (C)-type S-potentials indicated well-developed color vision. The analysis of the luminosity (L)-type S-potentials indicated that the peak spectral sensitivity was at 522 nm. S-potentials were also recorded in response to ultraviolet light. The direction and extent of lens movement induced by electrical stimulation was measured in 12 cultured masu salmon (99.0–142.5 mm SL). The results indicated that the visual axis was upward and forward, and that the range of accommodation was from 0.79 × SL in front of the eye to infinity. In histological analysis of the retinas of five wild smolts (100–118 mm SL), the maximum cone densities (276–345 cones/0.01 mm²) were detected in the ventral to temporal regions. The visual acuities assessed by histological methods were 0.069–0.075.     

Length and sex-specific associations between spiny dogfish (Squalus acanthias) and hydrographic variables in the Bay of Fundy and Scotian Shelf

The associations between spiny dogfish ( Squalus acanthias ) and hydrographic variables (temperature, salinity and depth) were examined in the Bay of Fundy and Scotian Shelf from 1970 to 1998. Data were obtained from standard groundfish bottom trawl surveys. Dogfish sex affected habitat associations. Males were found to occupy bottom water of significantly higher salinities and depths than that occupied by females. Length also significantly affected habitat associations. Smaller dogfish occupied relatively deep, high salinity bottom water compared with larger dogfish. Overall, the occupied temperatures, salinities and depths were significantly different from those which were available. Dogfish occupied warmer temperatures along a narrow range (6.62–9.19°C) compared with those which were available (1.57–9.35°C). Occupied salinity (32.70–34.43 ppt) and occupied depth (88.62–184.66 m) were also distributed along a narrower range than available salinity (32.16–34.79 ppt) and available depth (55.00–218.10 m). Sex-specific, length-specific and overall environmental preference by dogfish may bias traditional `offshore' groundfish surveys while large scale changes in hydrographic parameters may alter dogfish distribution and their interactions with other marine fauna.     

Dietary value of benthic diatoms for post-larval abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis> associated with feeding transitions

ABSTRACT:   The feeding behavior and growth of post-larval Haliotis diversicolor with initial shell lengths (SL) of approximately 500 μm (Exp. 1-1 and 1-2), 800 μm (Exp. 2), and 1200 μm (Exp. 3) were studied in a laboratory setting while they fed on four species of benthic diatom Achnanthes longipes , Cocconeis sublittoralis , Cylindrotheca closterium , and Navicula ramosissima . Exp. 1-1 and 1-2 revealed no marked differences in post-larval growth rates (mean 24–39 μm SL/day) among the diatom species. However, marked differences in growth rates among the species were revealed in Exp. 2 and 3. Three species, A. longipes , Co. sublittoralis, and Cy. closterium , produced faster growth (Exp. 2 mean 29–51 μm/day, Exp. 3 mean 36–44 μm/day) than N. ramosissima (Exp. 2 mean 18 μm/day, Exp. 3 mean 23 μm/day). Post-larvae fed N. ramosissima had lower digestion efficiency (42.8%) than those fed other diatom species (90.7–100%). Diatom extracellular substances appeared to be principally used from post-settlement to 800 μm SL, and diatom cell contents were required to produce rapid growth of larger post-larvae (>800 μm SL). It is likely that the availability of each diatom for post-larvae was affected by diatom morphology, attachment strength, frustule strength, and post-larval size.     

Effects of seasonality and migratory prey on body condition of Cichla species in a tropical floodplain river

Abstract –  In this study we examine trends in body condition of three Cichla species native to the Cinaruco River, Venezuela. Specifically, we characterise the potential subsidy provided by migratory Semaprochilodus kneri to Cichla by comparing condition among species, hydrologic seasons and different size-classes (based on the ability to consume S. kneri assuming gape-limitation). All three species had lowest body condition during the rising-water season (following the reproduction period). Only Cichla temensis had greater body condition during the falling-water season than low-water season. During the falling-water season, C. temensis >300 mm SL had significantly greater condition than smaller conspecifics. Annual migration of S. kneri into the river during the falling-water season provides a resource subsidy to large C. temensis . Transfer of whitewater production into nutrient-poor rivers by migratory fishes appears to be a general phenomenon in the major Neotropical river basins and may partially account for high standing stocks of large piscivores in these unproductive ecosystems.