Importance of the upper estuary as a nursery ground for fishes in Ariake Bay,Japan

To examine the importance of the upper estuarine areas of Ariake Bay as a nursery ground for fish, assemblages of larvae and juveniles were compared among various aquatic habitats. The upper estuaries of the bay (the Rokkaku and Hayatsue estuaries) are brackish, highly turbid waters with high tidal velocities, and differ substantially from the Isahaya area, which has been separated from the bay by a man-made dike, to the middle estuary (the Kikuchi estuary). Abundances of larvae and juveniles were higher in the estuaries than in the open bay and Isahaya areas. Abundant species in the upper estuaries were similar to each other, but differed from those of the middle estuary. This was primarily due to larvae and juveniles of fishes that occurred almost entirely in the upper estuaries, such as Acanthogobius hasta, Boleophthalmus pectinirostris, Coilia nasus, Cynoglossus abbreviatus, Nibea albiflora, Odontamblyopus lacepedii, Trachidermus fasciatus and Tridentiger barbatus. These results suggest that the upper estuaries play an important role as nursery grounds for fishes.     

A pre-leptocephalus larva ofConger myriaster (family Congridae) collected from Suruga Bay,Central Japan

One specimen of leptocephalus larva, measuring 16.0 mm in total length, was collected from the northern part of Suruga Bay (34°56′N, 138°39′E) by the T/V Bosei Maru II of Tokai University on November 7, 1982. This larva is identified asConger myriaster because of having melanophores under the eye, simple gut with melanophores, 142 total number of myomeres and the position of the last vertical blood vessel at the 52nd myomere. Judging from the body length, appearances of teeth and fins, and disposition of the anus, the present larva belongs to the preleptocephalus stage. The presence of this early larva in this area suggests that one of the spawning grounds ofC. myriaster exists in or near Suruga Bay in autumn.     

Selective mortality of larval Japanese seabass in Ariake Bay, Japan

This article describes the growth, mortality, and selection patterns in early larval stage of Japanese seabass Lateolabrax japonicus in Ariake Bay, Kyushu, Japan. Japanese seabass larvae were collected from the spawning ground in December 2007, and juveniles were collected from the nursery ground in March 2008. Otoliths were analyzed to produce daily records of size-at-age and growth rate that were compared between larvae and juveniles to determine whether selective mortality occurred. A weight-specific growth coefficient (G) and instantaneous mortality coefficient (M) were computed, and the recruitment potential was evaluated from the ratio of M:G. Selection for fast-growing and bigger larvae was evident during the 5–14 days after hatching (DAH). Selective mortality acted to preferentially remove fish that were slow growing and/or relatively small members of the cohort at least during the period examined. Trends in the growth rate differences between larvae and juveniles suggested that the selection process continued beyond 14 DAH although the exact duration over which selective mortality occurred was unknown. Survivors of Japanese seabass exhibited traits consistent with all aspects of the ‘growth–mortality’ hypothesis: faster growth, larger size-at-age, and shorter larval stage duration (LSD), i.e., larvae with faster growth, bigger size-at-age and a shorter LSD selectively survived the larval period. Larvae had higher M (0.323) than G (0.159), resulting in the M:G ratio of >1.0 (M:G = 2.031), suggesting that the larval cohort was rapidly losing biomass. Future studies should look to determine the duration over which selective mortality occurs and the timing of transition between M and G (M = G) and accumulation of cohort biomass.     

崂山湾人工鱼礁区星康吉鳗摄食生态及食物网结构

根据2015年4月至2017年1月于崂山湾人工鱼礁区地笼网和延绳钓捕获的279尾星康吉鳗样本,从胃含物组成、食性类型、摄食等级、营养生态位和营养级等方面对其摄食生态进行研究,同时结合海区许氏平鲉、大泷六线鱼、斑头鱼、褐菖鲉、花鲈等9种鱼类的胃含物分析结果,构建人工鱼礁区鱼类关键种的简化食物网模型.食性研究结果表明:星康吉鳗共摄食7类30余种饵料,虾类是其最主要的饵料类群,其次为鱼类和头足类,大泷六线鱼、方氏云鳚、鹰爪虾、玉筋鱼和日本鼓虾等是其优势饵料.星康吉鳗的饵料生物组成随肛长和季节发生显著变化.四季均以鱼类和虾类为主,春季胃含物中包括头足类,秋季包括头足类和蟹类,冬季亦有蟹类出现.肛长≤120 mm的星康吉鳗主要摄食鱼卵和鹰爪虾,120~130 mm肛长组主要摄食玉筋鱼和日本鼓虾,肛长>130 mm的星康吉鳗主要摄食大泷六线鱼和方氏云鳚.其摄食强度也随季节和肛长而变化,空胃率的季节性差异显著,平均胃饱满系数的季节性差异不显著,不同肛长组的空胃率和平均胃饱满系数均不存在显著差异.人工鱼礁区简化食物网结构显示:鱼类关键种的营养级均在3级以上,星康吉鳗的营养级为4.636,处于海区食物网的最顶端.虾类、蟹类、端足类和软体动物等是鱼类关键种的主要饵料,甲壳类、方氏云鳚、大泷六线鱼和玉筋鱼是高营养级鱼类花鲈和星康吉鳗的主要饵料.     

The amino-acid sequence of a lectin from conger eel, Conger myriaster, skin mucus.

The amino-acid sequence of a beta-galactoside-binding lectin isolated from the skin mucus of the conger eel Conger myriaster was determined. The lectin (30 kDa) was composed of two identical subunits of 135 amino acid residues with N-acetylserine at the N-terminus and no half-cystinyl residue. It was a 30-34% sequence identical to vertebrate beta-galactoside-binding lectin and proved to be a member of the S-type lectin family.     

Longline selectivity for white‐spotted conger Conger myriaster (Brevoort, 1856) in Haizhou Bay,China

Conger myriaster is one of the most commercially important fish stocks in the Haizhou Bay, China. As the type of longline fishing hook has a significant effect on its capture, three hook sizes (nos. 302, 303, 304) were compared in experiments conducted along the Haizhou Bay from September to November 2012. C. myriaster selectivity analysis using the different hook widths was obtained by analysing the catch rate, CPUE, total length distribution and selection curves. The log‐normal model equation was used to explore the longline selection, and anova was employed to analyse the difference in catch rate and CPUE among the three hook sizes. The longline selectivity for C. myriaster was well described by a log‐normal model equation. Hook no. 303 proved to have the highest catch rate, CPUE, and the estimated model lengths within three types of hooks tested in the experiments, in accordance with the fact that no. 303 is also the favourite hook used by local fishermen. Overall, the present study indicates that hook no. 303 has the best selection and is an appropriate size for sustainable utilisation of C. myriaster.     

Cultivation ofMonostroma nitidum (Chlorophyta) in a river estuary,southern Japan

The green seaweedMonostroma nitidum Wittrock is cultivated in brackish waters of southern Japan and an ecological survey of its cultivation was carried out in the estuary of R. Shimanto over three years. Artificial seed culture began by collecting many gametes in April. The zygotes adhered to a plastic settlement board (20–30 cm long and 10 cm wide). The cultivated zygotes in the indoor tank increased gradually in size from 8 to 40m till early September. Maturation of the zygote was promoted by providing dark conditions for 2–3 weeks. The production of a concentrated zoospore solution was achieved by adding freshwater 2–3°C above that of the zygote culture tank and a photon flux density of 100mol m^–2 s^–1).The culture nets were set our horizontally at a level exposed for 4 h and were harvested 3–4 times till March. The total production was approximately 6–10 kg dry weight per net during culture periods. The total production of nets harvested 3–4 times per year was greater than that of nets harvested only once.     

Effects of river flow on larval growth and survival of Japanese seaperch Lateolabrax japonicus (Pisces) in the Chikugo River estuary, upper Ariake Bay

The abundance and growth history of larval and juvenile Japanese seaperch Lateolabrax japonicus were investigated in the Chikugo River estuary, upper Ariake Bay, from 1990 to 2000. Growth during the larval period (up to 15 mm standard length, L _S, the size at recruitment into the estuary) was backcalculated using sagittal otolith microstructures by the biological intercept method. Growth rates in length declined at body sizes >14 mm L _S. High freshwater discharge through the Chikugo River was associated with high temperatures of the upper Ariake Bay where the larvae spend their planktonic life. Mean larval stage duration (days) from hatch to 15 mm ( D ₁₅) varied between 48·8 and 76·2 days and was inversely correlated with the estimated mean temperature history [mean daily temperature (° C) experienced by the larvae during the period from hatch to 15 mm, T ₁₅]. Mean abundance (number m⁻²) of larvae and juveniles was highest in years when T ₁₅, D ₁₅ and freshwater discharge were at intermediate levels. Although the abundance was not correlated with either of these variables, an exponential relationship between abundance and D ₁₅ was found when data collected during the highest river discharge years (1990, 1991 and 1998) were excluded. The increase in freshwater discharge through the Chikugo River probably had the potential to enhance or diminish Japanese seaperch recruitment in two ways: 1) it could increase recruitment probability by increasing temperature and larval growth and 2) high river flow also had the potential to decrease the probability of immigration into the river by increasing larval seaward dispersion, predation due to decreased turbidity and starvation due to decreased zooplankton prey abundance in the estuary.     

Evidence for up-estuary transport of puffer Takifugu larvae (Tetraodontidae) in Ariake Bay, Japan

The present study determined whether puffer Takifugu rubripes and T. xanthopterus larvae use selective tidal stream transport (STST) for migration into the nursery area. The influence of the tidal cycle on the vertical distribution of Thkifugu larvae was investigated during a 24 h sampling period at one location off Shimabara Peninsula in Ariake Bay. Samples were collected in three depth layers, from near the sea floor to near the surface (5, 20 and 30 m depth). The change in vertical distribution in relation to tidal phase was not observed. This data did not support STST hypothesis. Diel vertical migration was observed irrespective of tidal phase, where larvae migrated to the middle layer during the night, and sank to the bottom layer during the day, however, larvae hardly emerged into the surface layer during the study period. In Ariake Bay, the residual current leads to a layered vertically stratified structure, in which surface water flows towards the mouth and the middle-bottom water flows toward inner part of the Bay. It is suggested that Takifugu larvae use not STST but residual currents for transport into the nursery ground, namely, undergoing nocturnal diel vertical migration in the water column between the middle layer and the bottom layer where the net flow is northward.     

Reproduction and embryonic development of the red stingray Hemitrygon akajei from Ariake Bay,Japan

Ichthyological Research - The reproductive system of the red stingray Hemitrygon akajei was described from 1,418 specimens, 682 males and 736 females, sampled year-round (2003–2014) from...     

Development of epidermal and mucosal galectin containing cells in metamorphosing leptocephali of Japanese conger

The epidermis of premetamorphic leptocephali of Japanese conger Conger myriaster consisted of only a few cell layers including congerin- (a galectin) containing club cells. The epidermis increased in thickness after metamorphosis, mainly due to a preponderant development of club cells. This suggested that the biological significance of congerins increased at this stage, which may be related to a change in life style. Epidermal mucous cells showed only limited distribution. Immuno-positive cells in the mucosal epithelia of the buccal cavity wall and oesophagus were not found in the youngest individuals. Though these cells were observed at the commencement of metamorphosis, the development of the epithelia and club cells was apparently retarded compared to that of the epidermis. No immuno-staining was found in the gills at any stages.     

Dietary habits of the fanray Platyrhina tangi (Batoidea: Platyrhinidae) in Ariake Bay, Japan

The dietary habits of the fanray Platyrhina tangi were investigated by analyzing the stomach contents of specimens collected in Ariake Bay, Japan. Of 334 stomach specimens, 324 contained food and 10 (3.0%) were empty. The mean percentage weight of stomach contents per unit of body weight was 0.59%. Thirty-seven taxonomic levels of prey were identified. The most common prey was shrimp, followed by fish and mysids. There were no differences in the composition of the diet between sexes, but an ontogenetic dietary shift was observed. Shrimps were the most common prey in all size classes. In addition, smaller individuals frequently ate mysids, and larger individuals often consumed fish. Dietary breadth values increased with size. Trophic level analysis revealed that trophic level increased with size; however, this species is consistently a secondary consumer. Dental sexual dimorphism was also observed. Specifically, mature males had much longer and sharper cusps than females and immature males. Since males and females had similar diets, dental sexual dimorphism may be related to their reproductive behaviour.     

Spatiotemporal occurrence and feeding habits of tonguefish,Cynoglossus lighti Norman, 1925, larvae in Ariake Bay,Japan

Spatiotemporal occurrence and feeding habits of tonguefish (Cynoglossus lighti Norman, 1925) larvae were investigated in an offshore area (>5 m in depth) of the inner part of Ariake Bay, Japan. All specimens were symmetric, free‐swimming larvae. Although their seasonal abundance and distribution in the study site varied from year to year, spawning started in June and the larval abundance was high in August and September with a wide distribution in the inner part of the bay. Both present and previous study results strongly suggest that larvae may settle primarily in the estuary and near‐shore areas of Ariake Bay after their wide distribution in the offshore area of the bay during the free‐swimming stage. Larvae showed a clear feeding rhythm in which they fed on prey mainly during the daytime. Larvae fed exclusively on copepods, and identified prey were mostly Paracalanidae (mainly Parvocalanus crassirostris), Microsetella norvegica, and Oithona davisae. Pre‐metamorphosis larvae fed primarily on Paracalanidae and O. davisae, whereas O. davisae formed a smaller proportion of the early‐metamorphosis diet. In early metamorphoses, larvae fed preferentially on Paracalanidae and M. norvegica.     

Seasonal change of dinoflagellates cyst flux collected in a sediment trap in Omura Bay, West Japan

Sediment trap samples were harvested bimonthly from 1998 to2000 and examined to better understand the species compositionand seasonal variation of dinoflagellate cyst flux in OmuraBay in Japan. Samples’ living cyst flux clearly showedseasonal variation with the higher flux number between autumnand winter. In total, 43 different cyst taxa were recorded,and these were composed of two different ecological groups.The first group included Protoperidinium compressum and Protoperidiniumsubinerme, which increased every autumn to winter. The secondgroup included Gonyaulax spp. and Pheopolykrikos hartmanniiand was trapped throughout the year. These two groups manifestedthe different flux patterns and were, respectively, heterotrophicand autotrophic in nutrition. In the heterotrophic group, protoperidinioidcysts were dominant. Vegetative cells of protoperidinioid areknown to feed mainly diatoms. Sample diatom flux also increasedfrom autumn to winter. Therefore, the increase of protoperidinioidcysts in autumn to winter was observed to correlate with diatomblooms. In contrast, the autotrophic group mostly consistedof Gonyaulacoid cysts and were generally observed throughoutthe year, although occurrence varied between species most likelyresponding to favorable environmental conditions. The resultsindicate that cyst production is closely related to differentnutritional modes.     

Genetic identification of fish eggs collected in Sendai Bay and off Johban,Japan

Mitochondrial DNA typing of 52 fish eggs collected in Sendai Bay and off Johban revealed ten haplotypes of the 225–251 bp region of 16S ribosomal DNA. Comparing with known sequences of fishes, we identified them as Trachurus japonicus (Carangidae), Pagrus major, Evynnis japonica (Sparidae), Paralichthys olivaceus, Pseudorhombus sp. (Paralichthidae), Pennahia argentata (Sciaenidae) and Platycephalus sp. (Platycephalidae). The occurrence of Trachurus japonicus and sparid eggs in the study area indicates significant extensions to the ranges of their spawning sites northward. Our method is useful for identifying fish eggs that are difficult to diagnose by morphology, and to uncover cryptic fish egg assemblages in the field.     

Isolation of epidermal cells and cDNA cloning of TNF decoy receptor 3 of conger eel, Conger myriaster

By using EDTA and a trypsin solution, we established a method for isolating the epidermal cells of the conger eel, Conger myriaster. We then identified TNF decoy receptor (DcR) cDNA in the species from a suppression subtractive hybridization library prepared from the epidermal cells stimulated with LPS. The full-length cDNA of conger TNF DcR (conDcR) consisted of 1479 base pairs, and the protein comprised 286 amino acid residues. Phylogenetic analysis indicated that conDcR was clustered into a DcR3 branch. ConDcR is likely to act as an important immune-regulating factor in inhibiting the apoptosis-inducing effect of TNF in the skin of conger eel.     

Comparison of the early life histories of two <Emphasis Type="Italic">Cynoglossus</Emphasis> species in the inner estuary of Ariake Bay,Japan

The larval distribution and feeding habits of Cynoglossus abbreviatus and Cynoglossus lighti were investigated around the Rokkaku estuary in Ariake Bay during October 2004 and March and April 2005. Cynoglossus abbreviatus started and completed metamorphosis at larger sizes than C. lighti. Developmental phases consisted primarily of individuals at metamorphosis and postmetamorphosis, which were mainly distributed inside and just outside the Rokkaku River in March–April for C. abbreviatus and October for C. lighti. Tidal changes in vertical distribution just outside the river mouth differed between the closely related species; C. abbreviatus was distributed in the surface and middle layers at flood tide, and aggregated near the bottom (where the current speed was lowest) at ebb tide. Cynoglossus lighti stayed mainly near the bottom during all tidal phases. Larvae of both Cynoglossus species selectively fed on copepods (Pseudobradya sp.), which were scarce in the waters. These facts suggest that the nursery grounds of the two Cynoglossus species were different in terms of their tidal vertical distribution patterns.     

DSP toxin contents inDinophysis fortii and scallops collected at Mutsu Bay,Japan

Cell densities of toxic phytoplankton species responsible for diarrhetic shellfish poisoning (DSP) were monitored at a sampling site in Mutsu Bay, Japan, in 1995.Dinophysis fortii almost completely dominated the toxic phytoplankton community. Okadaic acid (OA) and dinophysistoxin-1 (DTX1) contents in bothD. fortii cells and midgut glands of scallops collected at the same sampling site were determined by HPLC — fluorometry. DTX1 was detected fromD. fortii and scallops. The contents of DTX1 inD. fortii changed markedly during the experimental periods (5–252 pg cell^–1). The highest concentration of DTX1 in the midgut glands of scallops coincided with the period of relatively high cell densities ofD. fortii with the highest content of DTX1 (252 pg cell^–1). The results demonstrate that toxin content in the cells is an important factor affecting the toxicity of shellfish.