Diel activity and vertical distribution of Lysianassoid amphipods dominant in Onagawa Bay, north-eastern Japan

ABSTRACT:   Baited traps were used over 24 h to reveal the diel activity and vertical distribution of three dominant lysianassoid amphipods ( Scopelocheirus onagawae , Anonyx omorii , Anonyx abei ) in Onagawa Bay, north-eastern Japan. The three species were the most dominant small crustacean scavengers in the bay. Most individuals were caught by traps deployed 0.3 m above the bottom, showing that they were active in the layers close to the sea bottom. No habitat segregation was found among species or developmental stages, suggesting that these scavengers rely on the food supply from bottom deposits. The three species increased remarkably in numbers of collected individuals at night, showing a rise in feeding activity. The two Anonyx species were collected only during the night, and S. onagawae was collected mostly during the night. The nocturnal activity appears to be an adaptation to reduce predation risks. However, juveniles of S. onagawae appeared even during the day, suggesting that feeding might take precedence over avoiding predation. Baited traps collected ovigerous females of S. onagawae but not of Anonyx species; the reason for the difference could not be determined.     

Diel variation in the seagrass ichthyofaunas of three intermittently open estuaries in south-eastern Australia: implications for improving fish diversity assessments

Diel variation in the ichthyofaunas associated with Zostera capricorni Ascherson was investigated in three intermittently open estuaries in the Illawarra region, New South Wales. Each estuary showed differing diel shifts in fish assemblages, which appeared to be related to estuary size. In the largest estuary (Lake Illawarra) significantly more species were caught during the night than the day for all months. In contrast, there was little diel variation in the fish assemblages at Werri Lagoon and Shellharbour Lagoon, although many species were only caught during the night at both estuaries. The distinct diel changes at Lake Illawarra was thought to be attributable to the relatively deep channels adjacent to the seagrass beds which are better habitats for larger fishes compared with the shallow sand bars without deep channels throughout the two smaller estuaries. The composition of fish species within the three estuaries were significantly different, although each assemblage was characterised by large numbers of small-sized fish (<100 mm FL) indicating the importance of intermittently open estuaries as fish habitats. It was concluded that night sampling provided a more complete picture of the ichthyofaunas associated with Z. capricorni . As a result, inclusion of night sampling in fish diversity assessments would increase the chance of catching diurnally rare species and therefore attain a better representation of the true community structure.     

Settlement of larval top shell <Emphasis Type="Italic">Turbo (Batillus) cornutus</Emphasis> in response to several marine algae

ABSTRACT:     The settlement of larval top shell Turbo  ( Batillus )  cornutus in response to seven macroalgal and three benthic diatom species was examined in the laboratory. The percentages of larval settlement differed significantly among algal species, and were significantly higher on two red algal species ( Marginisporum crassissima , an articulated coralline alga, and Gelidium elegans , an agarophyte) than on the green algae, brown algae and benthic diatoms tested. Marginisporum crassissima induced larval settlement most strongly throughout the experiments. The percentage of larval settlement on a crustose coralline alga (unidentified species), which is known as a suitable substratum for abalone larvae, was much lower than on M. crassissima and G. elegans , which have morphologically complex growth forms . The percentage of settled individuals on ethanol-killed M. crassissima was much lower than on intact M. crassissima . The results indicate that physical structure is unlikely to be the main inducer of settlement; therefore, settlement of top shell larvae seems to be strongly induced by chemicals from the two red algal species. The specific distribution of juvenile top shell in the field may be at least partly determined by the strong induction of larval settlement by articulated coralline and gelidiacean algae.     

Diel vertical migration of myctophid fishes (Family Myctophidae) in the transitional waters of the western North Pacific

The diel vertical migration patterns of adult myctophid fishes were determined in the transitional waters of the western North Pacific off Japan, using day–night sampling from 20 to 700 m depths with a commercial otter trawl in the summer of 1995. A total of 12 species belonging to 9 genera were collected. Four patterns were recognized in the diel vertical migration of 11 of the 12 species. (1) Migrants showing clear day–night habitat separation with peak abundance above 200 m at night: Symbolophorus californiensis, Tarletonbeania taylori, Notoscopelus japonicus, Diaphus theta, Ceratoscopelus warmingi, and Diaphus gigas. (2) Semi-migrants, in which part of the population often remains in the daytime habitat at night. The distribution depths of migratory and nonmigratory individuals do not overlap: Stenobrachius leucopsarus . (3) Passive-migrants, in which there is no separation of day–night habitats, but the upper limit of daytime distribution depth shifts to a shallower layer at night, probably as the fish follow migratory prey: Lampanyctus jordani . (4) Nonmigrants: Stenobrachius nannochir, Lampanyctus regalis (> 140 mm SL), and Protomyctophum thompsoni . The day–night habitat temperature ranges are also given for the 11 species. No remarkable east–west differences were seen in the vertical migration patterns compared with previous knowledge of eight of these species in the eastern Pacific. The diel migration patterns are newly described for three other species endemic to the western Pacific. The standing stock of myctophids in the study area was conservatively estimated at 18.5 ± 4.7 g m⁻² (avg. ± SD).     

Individual consistency between diel activity during rearing and behavior after release in red tilefish <Emphasis Type="Italic">Branchiostegus japonicus</Emphasis> revealed by laboratory observation and acoustic telemetry

ABSTRACT:   To determine characteristics which may reflect the behavioral quality of red tilefish Branchiostegus japonicus after release, five wild and four hatchery-reared fish were observed in a laboratory and in the sea. The diel activity of the fish was recorded on video tape for 2 days in a tank, where the light condition was regulated to vary periodically over 24 h. The individuals were then released in Maizuru Bay and tracked using acoustic telemetry. Four wild individuals became most active at dawn during a day in the tank, and settled near the release area to stay for 28–104 days after release in Maizuru Bay. In contrast, one wild and four hatchery-reared individuals were not active at dawn, and then did not settle in Maizuru Bay after release. Among the four settled wild individuals, the more active a fish had been in the tank, the more distant the individual moved from the release point until its settlement. The diel activity pattern should be a factor deciding whether red tilefish would settle nearby after release, and the relative amount of activity during rearing is probably related to the degree of dispersion within the release area.     

Nocturnal and diurnal feeding by Galaxias auratus, a lentic galaxiid fish

Abstract –  We examined the diel feeding pattern, gastric evacuation and daily ration of a lentic, endemic Tasmanian galaxiid fish, Galaxias auratus . Analysis of stomach contents and consumption estimates based on collections of fish every 3 h over three 24-h periods in summer 2002/2003 revealed that feeding always occurred during both day and night, with no obvious peaks. We also estimated the gastric evacuation rate of G. auratus in a laboratory experiment using the two prey species found to be dominant in stomachs of field-sampled fish. The relationship was best described by an exponential model, with rate parameters ( R ) of 0.104 and 0.081 for the evacuation of the amphipod, Austrochiltonia australis , and the cladoceran, Daphnia carinata , at water temperatures of 11.5 and 16.5 °C, respectively. Daily ration of G. auratus in summer was estimated to be approximately 3% (dry body weight) using the models of Elliot & Persson and Eggers. Galaxias auratus appears to be unusual in that its feeding pattern cannot be classified as nocturnal, diurnal or crepuscular, but its gastric evacuation and daily ration estimates are still similar to other comparable Northern Hemisphere freshwater fishes.     

Diel migration patterns of Atlantic salmon smolts with particular reference to the absence of crepuscular migration

Abstract –  The real-time diel pattern of Atlantic salmon smolt migration was observed for 8 years using automatic resistivity counters verified by video surveillance. A clear dominant nocturnal migration was demonstrated early in the migration period, later becoming increasingly diurnal, until rates became approximately equal at day and night. Migration patterns were related to water temperature, such that when mean daily temperatures were below 12 °C, hourly rates of migration were significantly lower during the day than at night. When daily mean temperatures exceeded 12 °C, there was no significant difference between diurnal and nocturnal migration rates. Migration patterns showed a distinct suppression of migration at dawn and dusk throughout the migration period. It is hypothesised that this behaviour is an active decision and/or an adaptive strategy either to take advantage of increased food in the form of invertebrate drift or to reduce predation risk from actively feeding piscivores or both.     

Ontogenetic and diel changes in diets of two sympatric mudskippers Periophthalmus modestus and Periophthalmus magnuspinnatus on the tidal flats of Suncheon Bay, Korea

Variability in the diet breadth of two sympatric mudskippers Periophthalmus modestus and P. magnuspinnatus in the tidal flats of Suncheon Bay, Korea, was compared. The analysis of 494 P. modestus and 455 P. magnuspinnatus specimens revealed that both were carnivores, consuming mainly gammarid amphipods, polychaetes, insects, and crabs. However, adult P. modestus consumed greater proportions of polychaetes whereas P. magnuspinnatus ate more crabs. The diets of both species showed ontogenetic changes in diet; smaller individuals of both species consumed harpacticoid copepods and gammarid amphipods, whereas larger fishes of both species fed mainly on different preys. The stomach content index (SCI) of both species underwent significant size-related and diel changes; the values of both species were higher in the larger size classes and during the late afternoon. Levin’s index of diet breadths of both species were lower during the day than at night, indicating high prey selection during the daytime. Non-metric multi-dimensional scaling ordination emphasized that the dietary compositions of the smaller individuals of both species showed some obvious similarities, with dietary similarity gradually reducing with increasing fish size. This indicates that the two species consume gradually different types of prey as they grow, that is, resource partitioning may be occurring between larger P. modestus and P. magnuspinnatus.     

Horizontal distribution and seasonal variability of the epipelagic chaetognath Sagitta elegans in relation to hydrography in the western subarctic Pacific Ocean

The spatial distribution and seasonal variability of epipelagic chaetognaths along the Kurile Islands and off south-east Hokkaido, in the western subarctic Pacific Ocean. were investigated during the period from May 1990 to October 1992. Sagitta elegans was the dominant species among the epipelagic chaetognaths in the study area. Juvenile S. elegans were distributed mainly along the path of the mixed water which was determined by the acceleration potential anomaly (APA) at the iso-pycnal density surface of 26.6 σθ. The location of the path of The mixed water meandered around cyclonic and anticyclonic eddies. Catches of S. elegans were made at temperatures ranging from 4.5 to 22.2C. The juvenile distribution, however, was mostly restricted to between 1 and 4C of the potential temperature determined at the isopycnal density surface of 26.6 σθ. Variability in the juvenile abundance within the path of the mixed water could be caused by predation rather than by food limitation because microzooplankton, which are known to he prey for juveniles, were abundant enough to meet the food requirements of juveniles in the study area. Adults occurred in spring (April-May) and young individuals (juvenile and stage 1) were abundant in summer (June-July), when a strong thermocline developed. The main spawning period appears to be during April-May, with a possible second spawning period in the autumn.     

Fish fauna associated with drifting sea weeds in the Chikuzen Sea,northern Kyushu,Japan

ABSTRACT:   From 2002 to 2006, the fish fauna associated with sea weeds drifting in the Chikuzen Sea, northern Kyushu, Japan, was examined. The total numbers of species and individuals collected were 51 and 5475, respectively. The five dominant species, accounting for approximately 80% of the total individuals, were Rudarius ercodes , Stephanolepis cirrhifer , Petroscirtes breviceps , Sebastes thompsoni and Paramonacanthus japonicus . The number of species and individuals increased significantly with the increase in water temperature, reaching maxima during early summer and autumn, respectively. Combining the present and previous data (∼50 years ago), the appearance patterns of the fishes associated with drifting sea weed were classified into the following four types: (i) long periods (continuously for 3 months or more) and autumn (LA); (ii) spring (SP); (iii) summer (SU); and (iv) rare (R). In more than half of the species, there were no changes in the appearance patterns between the present and previous studies. However, in the present study, the appearance patterns of several species changed from LA to R ( Oplegnathus punctatus and Kyphosus cinerascens ) and from R to LA and SU ( Abudefduf vaigiensis and Hyperoglyphe japonica , respectively).     

Feeding ecology of fishes associated with Egeria spp. patches in a tropical reservoir, Brazil

Abstract –  This research characterised feeding ecology of fishes associated with patches of Egeria najas and Egeria densa , two submerged macrophytes, in Rosana Reservoir, Upper Paraná River basin, Brazil. Fishes were sampled using a 1 m² throw trap in patches of different macrophyte biomass and in three diel periods during a wet season. Fish diet (10 species) was primarily composed of autochthonous items (zooplankton, algae and aquatic insect larvae). Almost all intra-specific diet patterns had moderate to low levels of diet similarity, indicating a high variability in diet. Some species showed no diel patterns in feeding activity, whereas others were primarily diurnal or nocturnal. No differences in feeding activity were observed among habitats of medium and high macrophyte biomasses, and species tended to feed on the same items among these habitats. The most abundant fish species demonstrated low inter-specific diet overlap and appear not to compete for food resources. We suggest that Egeria patches are feeding grounds and shelter for small-sized fish species.     

Identification of <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> and <Emphasis Type="Italic">Undaria undarioides</Emphasis> Laminariales,Phaeophyceae using mitochondrial 23S ribosomal DNA sequences

ABSTRACT:   Mitochondrial 23S ribosomal (r) DNA were sequenced from two Undaria species. The 23S rDNA from seven Undaria pinnatifida individuals were 2707 bp in length, whereas the 23S rDNA from four Undaria undarioides individuals were 2708–2709 bp in length. We found 15–20 nucleotide substitutions and 1–2 gaps between U. pinnatifida (the major haplotype) and U. undarioides . Based on the differences in sequences, we carried out PCR/RFLP analyses to distinguish between U. pinnatifida and U. undarioides , which showed different PCR/RFLP patterns upon Hin fI digestion. Sequence differences and PCR/RFLP analyses of mt 23S rDNA are useful for species identification of Undaria species .     

南昌月亮湖夏季浮游动物昼夜垂直分布及迁移特征

2013年8月1日19∶00至2日18∶00,通过间隔1 h的定量采样,研究南昌市典型城市湖泊月亮湖中浮游动物(轮虫、枝角类和桡足类)的昼夜垂直分布规律。结果表明,月亮湖共发现浮游动物20种,其中轮虫16种,枝角类1种,桡足类3种;剪形臂尾轮虫(Brachionus forficula)、桡足类无节幼体(Copepoda Nauplii)和迈氏三肢轮虫(Filinia maior)为优势物种,分别占总捕获数量的48.27%、15.75%和11.11%。浮游动物主要类群和优势物种的Morisita指数均大于1,说明月亮湖中的浮游动物群落呈聚集分布。密度垂直分布和平均滞留深度分析结果显示,浮游动物垂直分布昼夜差异明显,夜间(19∶00-05∶00),浮游动物先聚集于月亮湖中层,01∶00后逐渐迁移到表层;白天(06∶00-18∶00),浮游动物逐渐从表层向中层和底层迁移;主要类群中轮虫、枝角类和桡足类的迁移均表现为夜间上升、白天下降、傍晚再上升,轮虫和桡足类的迁移幅度小于枝角类。优势种剪形臂尾轮虫和无节幼体的昼夜垂直迁移表现为夜升昼降,至傍晚再上升;迈氏三肢轮虫昼夜垂直分布差异显著(P0.05),但昼夜垂直迁移活动不明显。相关分析表明,水温、p H值和溶解氧对月亮湖浮游动物的垂直分布和迁移活动有显著影响。     

Annual and lunar-synchronized ovarian activity in two rabbitfish species in the Chuuk lagoon, Micronesia

ABSTRACT:   This study examined the annual and the lunar cycles of ovarian activity in the forktail rabbitfish Siganus argenteus (Quoy & Gaimard, 1825) and the spiny rabbitfish Siganus spinus (Linnaeus, 1758), which were collected from the Chuuk lagoon, Federated States of Micronesia. Gonadosomatic index (GSI) increased in May and June for S. argenteus . For S. spinus , GSI increased in March, and from July to September. During these periods, the ovaries of these species contained oocytes at the tertiary yolk stage or the maturation stage, suggesting that these months are the reproductive season of the two species. During the reproductive season, weekly collection of the fish according to the lunar phase revealed that high GSI occurred around the last quarter moon for S. argenteus and the new moon for S. spinus . In the ovaries, oocytes developed synchronously, and postovulatory follicles, an indicator of spawning, were observed after the respective moon phase, suggesting that these species are restricted lunar-synchronized spawners. Comparisons of the reproductive activity of the two rabbitfishes in the Chuuk lagoon with that in Okinawa waters revealed that there is a geographic difference in the reproductive activity between habitats. However, the lunar phase for exertion of synchronous gonadal maturation and spawning is common in both regions.     

Identification of ommastrephid squid paralarvae collected in northern Hawaiian waters and phylogenetic implications for the family Ommastrephidae using mtDNA analysis

ABSTRACT:   A total of 110 adult individuals from four ommastrephid (family Ommastrephidae) squid species ( Ommastrephes bartramii, Sthenoteuthis oualaniensis, Eucleoteuthis luminosa, and Hyaloteuthis pelagica ) were used to obtain diagnostic DNA markers for species identification. Restriction fragment length polymorphism (RFLP) analysis of a partial segment (855 bp) of the mitochondrial DNA cytochrome oxidase I (COI) gene amplified by polymerase chain reaction (PCR) revealed that the restriction profiles of two endonucleases ( Alu  I and Tsp 509 I) were diagnostic for species identification. The restriction assay partially supplemented with nucleotide sequence analysis successfully assigned 69 damaged and morphologically equivocal ommastrephid paralarvae collected in northern Hawaiian waters, identifying 60 O. bartramii , eight S. oualaniensis , and one E. luminosa . The family Ommastrephidae appears to be monophyletic. Although the phylogenetic relationships among genera were not resolved well due to apparent homoplasy and large genetic divergence between species, COI sequence data without transitions provided support for subfamily level relationships.     

Occurrence and distribution of larval and juvenile Japanese flounder Paralichthys olivaceus at sandy beaches in eastern Hiuchi-Nada, central Seto Inland Sea, Japan

ABSTRACT:   The occurrence and distribution of larval and juvenile Japanese flounder Paralichthys olivaceus and major demersal fish from May to September were examined at seven sandy beaches at the central Seto Inland Sea. The flounder appeared from late May to August and were mainly collected at a depth of 2–5 m. Settlement of larval flounder was seen from late May to late June. A total of 6412 individuals of 17 species representing 12 families were collected in the study area. The dominant fish species were Favonigobius gymnauchen (56.0%), Tarphops oligolepis (8.1%), Rudarius ercodes (7.8%), P. olivaceus (7.3%), Repomucenus spp. (7.0%) and Heteromycteris japonica (3.3%). The catches of flounder differed among beaches and months. The number of flounder in June at Ohama Beach, where the most flounder were collected, was 22.6 individuals per haul (400 m²). The density of the flounder correlated negatively to that of F. gymnauchen .     

Feeding ecology of dominant demersal fish species <Emphasis Type="Italic">Favonigobius gymnauchen,Repomucenus</Emphasis> spp. and <Emphasis Type="Italic">Tarphops oligolepis</Emphasis> at a sandy beach where larval Japanese flounder settle in the Seto Inland Sea,Japan

ABSTRACT:   Feeding habits of Favonigobius gymnauchen , Repomucenus spp. and Tarphops oligolepis were examined during the period from May to August in 1999, 2000 and 2001 at a sandy beach in the central Seto Inland Sea, Japan. The three species of fish accounted for more than 60% of all fish collected in terms of number of individuals. All three species mainly consumed small crustaceans. However, the major prey of F .  gymnauchen and Repomucenus spp. differed from that of T .  oligolepis . F .  gymnauchen and Repomucenus spp. mainly consumed mysids and small crangonid shrimp (<12 mm in body length), which predominated in the study area. T .  oligolepis actively selected only epifaunal mysids Nipponomysis ornata and avoided crangonid shrimp and gammarids . The frequencies of occurrence of fish in the guts of the three dominant species were very low, and larval and juvenile Japanese flounder were not observed in any of the three fish species. The diet of juvenile Japanese flounder was similar to that of the three species. From these results, it appears that these three fish are competing species for the flounder.     

Daily rations and food availability of Japanese flounder Paralichthys olivaceus,small flounder Tarphops oligolepis and sand goby Favonigobius gymnauchen at a sandy beach in the central Seto Inland Sea,Japan

ABSTRACT:     To estimate the daily rations of Paralichthys olivaceus , Tarphops oligolepis and Favonigobius gymnauchen and to clarify diel variation in food availability to them, diel sampling was conducted over a 24-h period at a sandy beach in the Seto Inland Sea, Japan. The mean total length and body weight (BW) of P. olivaceus , T. oligolepis and F. gymnauchen were 32.6 mm (0.35 g), 23.7 mm (0.13 g) and 50.2 mm (1.03 g), respectively. The mean stomach contents index and percentages of stomachs with food were high during the day but low at night, indicating that these species are day-feeders. Paralichthys olivaceus and F. gymnauchen consumed mainly mysids and crangonids, whereas T. oligolepis fed chiefly on mysids. The estimated mean daily rations (95% confidence intervals) for P. olivaceus , T. oligolepis and F. gymnauchen made with the bootstrap method were 18.1 (9.3–31.3)%BW, 13.2 (7.9–24.3)%BW and 3.7 (1.7–7.4)%BW, respectively. Mysids were more abundant in the near-bottom layer during the day than at night, but the opposite was true for crangonids.     

Annual changes in the hatching period of the dominant cohort of larval and juvenile ayu Plecoglossus altivelis altivelis in the Shimanto Estuary and adjacent coastal waters during 1986–2001

ABSTRACT:   Larval and juvenile ayu from seven year-groups (1986, 1987, 1992, 1995, 1996, 1999 and 2000) were collected in the Shimanto Estuary and adjacent coastal waters. The present study focuses on the variation among year-groups in the hatching period estimated by age determination using the otolith. The hatching period of the dominant cohorts in the 1986, 1987 and 1992 year-groups occurred from late October to mid-November. A delay of the hatching period of the dominant cohort was observed from the 1995 year-group, which occurred in late November to early December, and the dominant periods in the 1996, 1999 and 2000 year-groups were observed from early to late December. It appears that the delay of the hatching period of dominant cohorts was not due to a delay of spawning, but a high mortality of early hatched larvae. The water temperature in autumn in the coastal waters adjacent to the Shimanto River has tended to rise over the past 20 years and this trend was especially notable in the late 1990s. The delay in the hatching period of the dominant cohort observed from the 1995 year-group was likely to be related to the rise in seawater temperatures in autumn.     

Preliminary telemetry data on the movement patterns and habitat use of European catfish (Silurus glanis) in a reservoir of the River Ebro, Spain

Abstract –  Knowledge of the movements and diel behaviour of the European catfish ( Silurus glanis ), the largest European freshwater fish, is limited to anecdotal information. In a preliminary telemetry study of European catfish, the spring diel movement patterns of five adult catfish were examined. After intraperitoneal insertion of the acoustic tags, the positions of the fish were recorded automatically in the Flix Reservoir (River Ebro, NE Spain). A marked nocturnal mobility pattern was observed throughout the study. During daytime, the catfish were consistently located in the littoral zone and spent extended periods of the day hidden in concealed habitats. Catfish movements were in a radial pattern, with upstream and downstream excursions followed by returns to a previously occupied location. Significant individual variations in movement pattern were observed among the tagged fish and within the 24 h cycle for each fish. Mean instantaneous swimming speed was 0.17 body lengths per second (BL·s⁻¹) at night but 0.09 BL·s⁻¹ during the daytime.