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.     

Possibility for decreasing of mercury content in bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> by fish culture

ABSTRACT:   The bluefin tuna tested were reared for 22 months from eggs before the beginning of the experiment, and sampling was performed every 3 months over the following year. The experimental results showed that the mercury concentration in the muscle ranged from 0.32 to 0.85 μg/g, which is lower than that found in wild bluefin tuna of a similar size. Increase in the mercury concentration corresponding to the increase in body weight was not shown, and it was quite different with wild bluefin tuna. Furthermore, no significant relationship was found between the lipid concentration and the mercury concentration in muscle. Among the internal organs of cultured bluefin tuna, the heart (0.32–0.66 μg/g), liver (0.43–0.99 μg/g) and spleen (0.59–1.0 μg/g) contained higher concentrations of mercury. It was estimated that the full-cycle cultured bluefin tuna had been fed small fish containing lower concentrations of mercury, and that the mercury concentration of tuna would be almost equal throughout the year because the effect of mercury accumulation would be weakened by body growth. Therefore, it was concluded that selecting diet fish species might decrease mercury contents in cultured bluefin tuna.     

Multigenerational effects of 17β-estradiol and nonylphenol on euryhaline cladoceran <Emphasis Type="Italic">Diaphanosoma celebensis</Emphasis>

ABSTRACT:     The effects of parental exposure to 17β-estradiol (E2) and 4-nonylphenol (4-NP) on life history parameters of three successive generations of the euryhaline cladoceran Diaphanosoma celebensis were assessed under laboratory conditions. Less than 24-h-old neonates (P) were exposed to five sublethal concentrations of E2 (0.1, 1, 10, 100 and 1000 μg/L) and 4-NP (0.01, 0.1, 1, 10 and 50 μg/L) at 25°C. Age at first reproduction, reproductive period, fecundity and lifespan were investigated. Successive generations (F₁–F₃) were monitored further in the absence of toxicants. Results showed that cladocerans exposed to 10–1000 μg/L E2 produced more neonates at a younger age compared to the control. The same effects were also observed in the F₁ and F₂ but ceased in F₃. Cladocerans exposed to 1 μg/L 4-NP also produced significantly more neonates compared to the control, but this effect was not found in successive generations. The results suggest that vertebrate hormone can modify the reproduction of D. celebensis , and the effects are multigenerational.     

Size selectivity of escape holes in conger tube traps for inshore hagfish <Emphasis Type="Italic">Eptatretus burgeri</Emphasis> and white-spotted conger <Emphasis Type="Italic">Conger myriaster</Emphasis> in Tokyo Bay

ABSTRACT:   In Tokyo Bay, conger tube-trap fishers voluntarily deployed escape holes of at least 13 mm diameter to reduce the by-catch of young conger smaller than the marketable size of 35 cm total length. Comparative fishing experiments in Tokyo Bay were carried out using tube traps with seven hole diameters (3, 9, 13.5, 14, 15, 17, and 19 mm), to obtain the size-selectivity of the escape-hole size for inshore hagfish Eptatretus burgeri and white-spotted conger Conger myriaster . On the assumption of the geometrical similarity in the combination of body g and hole perimeter m at a given retention probability, a single master curve s ( R ) = exp(−13.52 + 11.31 R )/(1 + exp [−13.52 + 11.31 R ]) was estimated for the two species in terms of relative R  =  g / m using the Share Each LEngth's Catch Total (SELECT) process based on a multinomial distribution. Almost all conger and hagfish with a girth equivalent to the hole perimeter were able to pass through the hole. Thus, the two species have a high ability to escape through a narrow space by squeezing the body through the hole in the rigid PVC tube. Optimum escape-hole size is discussed from several objectives for conger tube-trap fishery management, e.g. reduction of hagfish by-catch. This study also specifies the conditions for pooling data when fishing experiments using more than two fishing gears are replicated.     

Effects of fish size and water temperature on the acute toxicity of boron to Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> and red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

ABSTRACT:     The acute toxicities of boron were examined for Japanese flounder Paralichthys olivaceus and red sea bream Pagrus major in terms of fish size and water temperature. Japanese flounder of 0.1–70.0 g and red sea bream of 0.6–20.3 g were exposed to different concentrations of boron for 96 h at 20°C under semi-static conditions. In both fish species, the median lethal concentration (LC₅₀) for 96 h of boron increased linearly with increasing fish size, ranging from 108 to 252 mg B/L for the flounder, and from 97 to 172 mg B/L for the sea bream. The effect of water temperature on acute toxicity was examined for Japanese flounder of 0.6 and 1.5 g at 10, 15, 20 and 25°C, and for red sea bream of 0.6 and 2.4 g at 12, 15, 20 and 25°C. The toxicity of boron for the flounder increased linearly with increasing water temperature. The 96 h LC₅₀ values ranged from 299 to 108 mg B/L for the 0.6 g flounder and from 350 to 113 mg B/L for the 1.5 g flounder. A similar trend was shown for the 2.4 g red sea bream; however, the relationship for the 0.6 g red sea bream was not significant.     

Effects of water temperature on early development of Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis>

ABSTRACT:   To determine an optimal temperature range for efficient production of healthy eel larvae Anguilla japonica , the effect of water temperature on hatching, survival, and deformity rates was examined. The early ontogeny of morphological features in this species by incubating eggs at five different temperatures (19, 22, 25, 28 and 31°C) was examined. Hatching occurred at 24, 28, 46 and 58 h after fertilization when incubated at 28, 25, 22 and 19°C, respectively; no eggs hatched at 31°C. The growth rate of prefeeding larvae increased as water temperature was elevated and acquisition of feeding ability was also accelerated at higher temperature. Significantly high hatching rates (76–86%, P  < 0.05) and survival rates (61–86%, P  < 0.05) were observed at relatively high temperatures (22–28°C). The deformities were 'open lower jaw', 'pericardial edema', and 'notochordal bending', in which the mouth was deformed with a downward projecting lower jaw, the pericardial cavity was swollen, and the notochord was bent or twisted to various degrees, respectively. Open lower jaw and pericardial edema were especially predominant at 19°C, with rates of 68 and 92%, respectively, compared with 31 and 10% at 25 and 28°C, respectively. The occurrence of notochordal bending was not affected by temperature. The optimal temperature for incubation and rearing A. japonica eggs and prefeeding larvae is approximately 25–28°C.     

Analysis of bacterial communities in <Emphasis Type="Italic">Nannochloropsis</Emphasis> sp. cultures used for larval fish production

ABSTRACT:   Phytoplankton used in fish hatcheries is mass-cultured in the open air and usually contains large numbers of bacteria. In commercial fish production, the phytoplankton cultures are usually added into the larval rearing tanks; however, the numbers and types of bacteria introduced into the rearing tanks simultaneously are unknown. In this study, the bacterial community structures in Nannochloropsis sp. cultures were analyzed by using fluorescence in situ hybridization (FISH). A direct viable count (DVC)-FISH analysis was also performed as DVC is useful for the detection of actively growing cells. Total numbers of bacteria in Nannochloropsis sp. cultures ranged from 7.72 × 10⁵−2.39 × 10⁶ cells/mL. High proportions of the total bacteria (31.6–53.6%) in the Nannochloropsis sp. cultures showed growth potential. DVC-FISH analysis revealed that α-proteobacteria and the Cytophaga – Flavobacterium cluster were abundant in the bacterial community of actively growing cells. Thus, the high growth potentials of the distinct bacterial communities in Nannochloropsis sp. culture must influence the bacterial communities in larval rearing tanks.     

Proposal for stock-recruitment relationship for Japanese sardine <Emphasis Type="Italic">Sardinops melanostictus</Emphasis> in North-Western Pacific

ABSTRACT:   This study assessed the stock-recruitment relationship (SRR) for the Japanese sardine Sardinops melanostictus in the North-western Pacific. Of the 20 SRR models investigated, the Akaike information criterion (AIC) was the minimum (AIC = 551.2) when the data were separated into two groups (A and B) and the log-normal distribution was applied as the error term. Group A was constructed with SRR data from 1976–1987 and 1992–2004. Group B consisted of data from 1988–1991. The AIC minimum model was R  = 22.8 S  ×  e ^ε for Group A, where R , S , and ε denote the recruitment of sardine (individual number of 0-year old fish), spawning stock biomass (SSB), and error term, respectively. This model indicated that recruitment was proportional to the SSB and that no density-dependent effect operated over the range of SSB investigated (51 000–11.3 million t). Recruitment was markedly higher (lower) when the sea surface temperature (SST) of the Kuroshio Extension area in February was low (high). The essential SRR can simply be expressed as R  = 22.8 S  ×  e ^ε with the level of recruitment deviating from the model to a greater or lesser degree depending on the environmental conditions.     

Chemical composition of dried eyeballs from <Emphasis Type="Italic">Euphausia superba</Emphasis> and <Emphasis Type="Italic">Euphausia pacifica</Emphasis>

ABSTRACT:   Dried krill eyeballs were obtained from Euphausia superba and Euphausia pacifica by using a patented industry method and their chemical compositions were examined. Crude protein content was 77.7% and 80.8% of the dry matter of E. superba and E. pacifica , respectively. The dominating amino acids in both krill were glutamic acid, aspartic acid, glycine, arginine, leucine and tyrosine. Crude fat content was 10.9% and 5.4% of dry matter of E. superba and E. pacifica , respectively. The main lipid class of the extracted lipids was phospholipids at 88.5% in E. superba and 96.4% in E. pacifica . The dominating fatty acids in both krill were 22:6 ( n- 3), 20:5 ( n- 3), 16:0 and 18:1 ( n- 9). Astaxanthin (3, 3'-dihydroxy-β, β-carotene-4, 4'-dione) content of E. superba and E. pacifica was 566 mg/100 g and 252 mg/100 g of dry matter, respectively. Retinol of E. superba and E. pacifica was 153.0 mg/100 g (510 000 IU/100 g) and 57.6 mg/100 g (192 000 IU/100 g) of dry matter, respectively. The lipophilic extract of E. superba by using n -hexane contained 1923 mg/100 g of astaxanthin at approximately four times higher than the dried eyeballs.     

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 .     

Genetic identification of <Emphasis Type="Italic">Conger myriaster</Emphasis> leptocephali in East China Sea

ABSTRACT:   A subsample of Conger leptocephali collected in the East China Sea (ECS) was genetically analyzed and most were found to be the larvae of Conger myriaster , the most commercially important marine eel species in East Asia. However, these leptocephali (22.3–74.0 mm total length [TL]) did not have a complete row of lateral pigmentation, like the leptocephali of this species are commonly known to have when they are collected over the continental shelf or in coastal waters as they recruit. These leptocephali were in the western edge of the Kuroshio Current and the mixing zone over the shelf in the northern part of the ECS, and two smaller leptocephali (22.3, 46.5 mm TL) were collected to the south of the Ryukyu Islands. This evidence of an ontogenetic change in the presence of lateral pigmentation of C. myriaster indicates that previous efforts to determine the spawning area and recruitment patterns based on only morphological examination of Conger leptocephali in the region must be reconsidered. New research efforts based on genetic identification methods are needed to understand the spawning ecology and recruitment of this important fishery species.     

Evaluation of genetic diversity of eight grouper species <Emphasis Type="Italic">Epinephelus</Emphasis> spp. based on microsatellite variations

ABSTRACT:   Genetic diversity among eight species of grouper, Epinephelus bleekeri , E. coioides , E. malabaricus , E. ongus , E. akaara , E. maculatus , E. merra and E. fuscoguttatus , was studied using six microsatellite loci, Em-01 *, Em-03 *, Em-07 *, Em-08 *, Em-10 *, and CA-07 *, with the aim of exploring the feasibility of using microsatellite data for species identification. The results showed high levels of genetic differentiation among species ( F _ST  = 0.4403 and R _ST  = 0.4954). Species identification based on fixed allelic differences was possible between E. coioides , E. ongus , and E. fuscoguttatus at Em-01 * and between E. fuscoguttatus and E. ongus at Em-08 *. Private alleles were found in all species, except for E. ongus . Pairwise F _ST ranged 0.238–0.578 ( P  < 0.008 Bonferroni correction), and Nei's genetic distance ranged 0.433–2.710. Size homoplasy was observed at Em-03 * 157 allele, which was characterized by a T–C transition at the 119th nucleotide site of PCR products. The genetic assignment test unambiguously assigned each individual to the correct species. Thus, this test can be used for species identification of unknown individuals when the multilocus genotypes of the six microsatellite loci are available. The phylogenetic (neighbor-joining) tree, which was constructed based on the genetic distance matrix, separated the eight grouper species into two main groups.     

Community and trophic structures of abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis> habitat in Sagami Bay,Japan

Abstract:   The community and trophic structures of the subtidal habitat of the abalone Haliotis diversicolor were examined in Nagai, Sagami Bay, Japan. Conventional community indices showed no significant differences among three sampling stations. The overall continuum of stable isotope ratios was structured into three different trophic linkages: (i) brown algae-dependent benthic food chain; (ii) red algae-dependent benthic food chain; and (iii) planktonic food chain. Brown algae and red algae likely play different roles with respect to carbon sources in the habitat. Conventional fractionation values indicated that the abalone H. diversicolor (δ¹³C = −12.4 ± 1.0‰, δ¹⁵N = 9.3 ± 0.5‰) feeds on the lamina of Undaria pinnatifida during juvenile and adult stages (8.0–65.6 mm shell length). Stable isotope signatures suggested that the juveniles of other abalone species as well as some amphipods and a sea cucumber Holothuria decorata are competitors of H. diversicolor , whereas some Muricidae gastropods such as Thais bronni and Ergalatax contractus are predators. The isotopic differences among macroalgal species and the subsequent transfer to consumers indicate that stable isotopic analysis is an effective means of studying food webs in an open rocky shore community with little influence from external primary production such as terrestrial vegetation.     

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.     

Maturity and reproduction of goneplacid crab <Emphasis Type="Italic">Carcinoplax vestita</Emphasis> (Decapoda,Brachyura) in Tokyo Bay

ABSTRACT:     Sexual maturity, morphological sexual dimorphism, and reproduction of the goneplacid crab Carcinoplax vestita were investigated in Tokyo Bay, Japan, from November 2002 to October 2003. The puberty molt in males was evidenced by changes in the relative size of the chelipeds and merus of the walking legs, and was estimated to occur at a size range of 13.20–18.85 mm carapace length. Post-pubertal females were identified by the relative size of the abdomen and puberty was estimated to occur at a size range of 12.81–15.46 mm carapace length. Sexual dimorphism in C. vestita was observed in all features that showed secondary sexual characteristics. Monthly changes of gonad index in males, and of seminal receptacle index and occurrence of sperm plugs in females were synchronized, and indicated that mating was intense in spring. Ovaries began developing in March. Ovigerous females were found in all months except December, but were clearly more abundant between August and October. Fecundity ranged from 7800 to 57 000 mature oocytes per female per batch and was highly correlated with body size. The results suggest that some females may spawn more than one batch per year.     

Difference in the level of paralytic shellfish poisoning toxin accumulation between the crabs <Emphasis Type="Italic">Telmessus acutidens</Emphasis> and <Emphasis Type="Italic">Charybdis japonica</Emphasis> collected in Onahama,Fukushima Prefecture

ABSTRACT:     The difference in paralytic shellfish poisoning (PSP) toxin accumulation in the crabs Telmessus acutidens and Charybdis japonica was investigated at Onahama, Fukushima Prefecture, from 2002 to 2005. The level of toxin accumulation in the hepatopancreas of T. acutidens corresponded to that of mussels when examined on a yearly basis. In 2003, some crabs had a high toxicity of approximately 1000 MU, which compares to one-third of the human minimum lethal dose. Therefore T. acutidens should be monitored as a vector species of PSP toxin. The toxin profile of T. acutidens was also investigated. Because an increase in highly toxic species of PSP toxins with a decrease in low toxic species, such as N -sulfocarbamoyl-11-hydroxysulfate toxins, was not clearly observed between consecutive samples, toxin transformation in T. acutidens was considered to have a minimal impact on toxicity. PSP toxins were also detected in several specimens of C. japonica , but the highest toxicity was only 7.4 MU/g in the hepatopancreas. Because C. japonica is widely distributed in the coastal waters of Japan, investigation of toxin accumulation in the crab should be continued, including its investigation in different areas of water from Onahama, where the causative dinoflagellates of PSP occur in different conditions.     

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

ABSTRACT:     The biomass of bighand thornyhead Sebastolobus macrochir was increased by the high recruitment success of the 1999–2002 year classes off the Pacific coast of northern Honshu, Japan. In this study, the growth of bighand thornyhead was examined over a 9-year period from 1996 to 2004 in this area. The growth of the 1999 year class and the 2000–2002 year classes was reduced at 3 and 2 years old, respectively, while the 1999–2002 year classes were smaller than the 1993–1998 year classes. In 2-, 3- and 4-year-old fish, the relationship between abundance and mean standard length was expressed by negative linear regressions, while fish became smaller when abundance of the year class was larger. Mean bottom temperatures were stable at depths of 350–900 m; variations in water temperature were small in the main distribution area of bighand thornyhead. We discuss the factors affecting the growth of bighand thornyhead via changes in the demersal fish community and feeding habits.     

Reproduction of sea urchin <Emphasis Type="Italic">Loxechinus albus</Emphasis> in Chiloé Island,Chile

ABSTRACT:   During 1986–1989, the seasonal maturation and gonad index (gonad weight/body weight × 100) of adult Loxechinus albus were examined at nine sites, and the appearance of four-armed echinopluteus larvae was investigated at three sites off the eastern coast of Chiloé Island, Chile. Spawning occurred during November–January when the gonad indices fell to a minimum, the number of mature specimens decreased and four-armed larvae appeared, corresponding to the rise in water temperature. The number of four-armed larvae appearing at the northern site was markedly less than that at the southern site. The sea urchins matured in January and February immediately after spawning at many sites and a high percentage of maturation lasted for a long period at some sites. These findings are considered to be associated with high food availability and annual narrow ranges of water temperature.     

Mass-processing method for aging otoliths of walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> using black resin

ABSTRACT:   The reliability of a mass-processing aging method for walleye pollock Theragra chalcogramma was examined. The method is a half-otolith method, in which 10–20 otoliths are embedded simultaneously in black resin and the mass-processed half plane section is viewed under reflected light (black-resin method). Seasonal periodicity of otolith growth was confirmed by the monthly observations of the percent of translucent zone at the otolith edge, and interannual variation in age distribution detected the progression of dominant year-classes. These results support the assumption that the translucent zone is formed once a year. The black-resin method was compared to the break–burn method, which is the standard technique for this species. The estimated ages of these methods were not biased throughout the age range examined. The coefficient of variation in the black-resin method (4.9–5.7%) was similar to those of the break–burn method (3.5–5.5%). These results suggest that the black-resin method is reliable as an aging method for walleye pollock.     

Induction of (<Emphasis Type="Italic">Z</Emphasis>)-8-heptadecene in marine green alga <Emphasis Type="Italic">Bryopsis maxima</Emphasis> by mechanical wounding

ABSTRACT:   After mechanical wounding of the marine green alga Bryopsis maxima in a phosphate buffer, one main organic component was released to the solution. The organic compound was characterized by a molecular ion at 238  m/z by gas chromatography–mass spectrometry (GC-MS) and was deduced as 8-heptadecene by the fragment pattern. To identify the stereochemistry of 8-heptadecene, synthetic ( Z / E )-8-heptadecene was coinjected to the solution of wounded B. maxima . Comparing retention times and mass spectra with the synthetic sample, the target hydrocarbon obtained from wounded B. maxima was coincident with ( Z )-8-heptadecene.