Comparative Ontogenetic Behavior and Migration of Kaluga, Huso Dauricus, and Amur Sturgeon, Acipenser Schrenckii, from the Amur River

We conducted laboratory experiments with kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii, to develop a conceptual model of early behavior. We daily observed embryos (first life phase after hatching) and larvae (period initiating exogenous feeding) to day-30 (late larvae) for preference of bright habitat and cover, swimming distance above the bottom, up- and downstream movement, and diel activity. Day-0 embryos of both species strongly preferred bright, open habitat and initiated a strong, downstream migration that lasted 4 days (3 day peak) for kaluga and 3 days (2 day peak) for Amur sturgeon. Kaluga migrants swam far above the bottom (150cm) on only 1 day and moved day and night; Amur sturgeon migrants swam far above the bottom (median 130cm) during 3 days and were more nocturnal than kaluga. Post-migrant embryos of both species moved day and night, but Amur sturgeon used dark, cover habitat and swam closer to the bottom than kaluga. The larva period of both species began on day 7 (cumulative temperature degree-days, 192.0 for kaluga and 171.5 for Amur sturgeon). Larvae of both species preferred open habitat. Kaluga larvae strongly preferred bright habitat, initially swam far above the bottom (median 50–105cm), and migrated downstream at night during days 10–16 (7-day migration). Amur sturgeon larvae strongly avoided illumination, had a mixed response to white substrate, swam 20–30cm above the bottom during most days, and during days 12–34 (most of the larva period) moved downstream mostly at night (23-day migration). The embryo–larva migration style of the two species likely shows convergence of non-related species for a common style in response to environmental selection in the Amur River. The embryo–larva migration style of Amur sturgeon is unique among Acipenser yet studied.     

Ontogenetic Behavior and Migration of Volga River Russian sturgeon, Acipenser gueldenstaedtii, with a Note on Adaptive Significance of Body Color

We conducted laboratory experiments with Volga River Russian sturgeon, Acipenser gueldenstaedtii, to develop a conceptual model of early behavior. We daily observed fish from day-0 (embryos, first life interval after hatching) to day-29 feeding larvae for preference of bright habitat and cover, swimming distance above the bottom, up- and downstream movement, and diel activity. Hatchling embryos initiated a downstream migration, which suggests that predation risk of embryos at spawning sites is high. Migration peaked on days 0–5 and ceased on day 7 (8-day migration). Migrants preferred bright, open habitat and early migrants swam-up far above the bottom (maximum daily median, 140cm) in a vertical swim tube. Post-migrant embryos did not prefer bright illumination but continued to prefer white substrate, increased use of cover habitat, and swam on the bottom. Larvae initiated feeding on day 10 after 170.6 cumulative temperature degree-days. Larvae did not migrate, weakly preferred bright illumination, preferred white substrate and open habitat, and swam near the bottom (daily median 5–78cm). The lack of a strong preference by larvae for bright illumination suggests foraging relies more on olfaction than vision for locating prey. A short migration by embryos would disperse wild sturgeon from a spawning area, but larvae did not migrate, so a second later migration by juveniles disperses young sturgeon to the sea (2-step migration). Embryo and larva body color was light tan and tail color was black. The migration, behavior, and light body color of Russian sturgeon embryos was similar to species of Acipenser and Scaphirhynchus in North America and to Acipenser in Asia that migrate after hatching as embryos. The similarity in migration style and body color among species with diverse phylogenies likely reflects convergence for common adaptations across biogeographic regions.     

Ontogenetic Behavior, Migration, and Social Behavior of Pallid Sturgeon, Scaphirhynchus albus, and Shovelnose Sturgeon, S. platorynchus, with Notes on the Adaptive Significance of Body Color

We conducted laboratory studies on the ontogenetic behavior of free embryos (first life interval after hatching) and larvae (first feeding interval) of pallid and shovelnose sturgeon. Migration styles of both species were similar for timing of migration (initiation by embryos on day 0 after hatching and cessation by larvae on days 12–13 at 236–243 cumulative temperature degree units), migration distance (about 13km), life interval when most distance was moved (embryo), and diel behavior of embryos (diurnal). However, the species differed for two behaviors: movement characteristics of embryos (peak movement rate of pallid sturgeon was only one-half the peak rate of shovelnose sturgeon, but pallid sturgeon continued the lower rate for twice as long) and diel behavior of larvae (pallid sturgeon were diurnal and shovelnose sturgeon were nocturnal). Thus, the species used different methods to move the same distance. Migrating as poorly developed embryos suggests a migration style to avoid predation at the spawning site, but moving from spawning habitat to rearing habitat before first feeding could also be important. Migrants of both species preferred bright habitat (high illumination intensity and white substrate), a behavioral preference that may characterize the migrants of many species of sturgeon. Both species were remarkably similar for swimming height above the bottom by age, and day 7 and older migrants may swim far above the bottom and move far downstream. A migration of 12 or 13 days will probably not distribute larvae throughout the population's range, so an older life interval likely initiates a second longer downstream migration (2-step migration). By day 2, individuals of both species were a black-tail phenotype (light grey body with a black-tail that moved conspicuously during swimming). Aggregation behavior suggests that black-tail is a visual signal used for group cohesion.     

Ontogenetic Behavior and Migration of Dabry's Sturgeon, Acipenser Dabryanus, from the Yangtze River, With Notes on Body Color and Development Rate

We conducted laboratory experiments with Dabry's sturgeon, Acipenser dabryanus, from the upper Yangtze River to develop a conceptual model of early behavior. We daily observed fish from day-0 (embryo, first life interval after hatching) to day-30 feeding larva for preference of bright habitat and cover, swimming distance above the bottom, up- and down-stream movement, and diel activity. Hatchling to day-12 embryos and days 13–24 larvae were similar for ontogenetic behavior, i.e., neither initiated a dispersal migration, both swam within 15cm of the bottom, both preferred bright habitat, and neither strongly preferred cover or open habitat. Embryos and larvae were weakly active day and night. Days 72–76 juveniles had a weak nocturnal downstream migration, indicating wild juveniles disperse from a spawning site. In other sturgeon species yet studied representing three genera on three continents, Dabry's sturgeon is the first that does not disperse as an embryo or larva. Development of Dabry's sturgeon is slow, requiring more cumulative temperature degree days per millimeter of larvae TL than is required for other sturgeons to develop into larvae. Thus, a dispersal migration that diverts energy from development may not be adaptive. The available information suggests the initial dispersal of early life intervals is likely done by females, which spawn in a dispersed spawning style, not the usual aggregated spawning style. Juvenile migrants had a black body and tail with a light line along the lateral scutes. The color of juvenile migrants shows that a dark body and tail is characteristic of Acipenser that migrate downstream as larvae or juveniles.     

Ontogenetic Behavior and Migration of Atlantic Sturgeon, Acipenser oxyrinchus oxyrinchus, and Shortnose Sturgeon, A. brevirostrum, with Notes on Social Behavior

Ontogenetic behavior of Hudson River Atlantic sturgeon and Connecticut River shortnose sturgeon early life intervals were similar during laboratory observations. After hatching, free embryos were photonegative and sought cover. When embryos developed into larvae, fish left cover, were photopositive, and initiated downstream migration. Free embryos may remain at the spawning site instead of migrating downstream because the risk of predation at spawning sites is low. The two species are sympatric, but not closely related, so the similarities in innate behaviors suggest common adaptations, not phylogenetic relationship. Atlantic sturgeon migrated downstream for 12 days (peak, first 6 days), shortnose sturgeon migrated for 3 days, and year-0 juveniles of both species did not resume downstream migration. Short or long migrations of larvae may reflect different styles related to the total migratory distance from spawning sites to juvenile rearing areas. Atlantic sturgeon need to move a short distance to reach rearing areas and they had a long 1-step migration of 6–12 days. In contrast, shortnose sturgeon need to move a long distance to reach all rearing areas. This may be accomplished by a 2-step migration, of which the brief migration of larvae is only the first step. Early migrant Atlantic sturgeon were nocturnal, while late migrants were diurnal, and shortnose sturgeon were diurnal. These diel differences may also be adaptations for long (Atlantic sturgeon) or short (shortnose sturgeon) migrations. Cultured shortnose sturgeon, and possibly Atlantic sturgeon, have a dominance hierarchy with large fish dominant when competing for limited foraging space. Social behavior may be more important in the life history of wild sturgeons than is generally recognized.     

Development and Aging of the Liver and Pancreas in the Domestic Carp, Cyprinus Carpio: From Embryogenesis to 15-year-old Fish

The cytology of development and aging of the liver and pancreas in domestic carp was studied in a large sample of EM and LM sections from larvae juveniles 1–10 year old adults and 15 year old experimentally stunted fish weighing 20g and of 110–120mm TL. The primordium of the two glands appears in embryos 3–4 days after fertilization as buds from the gut wall. Formation of the hepatic tubules is first seen in larvae 10 days after fertilization. Two types of hepatocytes are discernable: one with a pale cytoplasm and the other with a dense opaque cytoplasm; both extend microvilli into the sinusoidal space of Disse and bear intracellular bile canaliculi. With maturation and branching of the hepatic tubules a complicated hepatic muralium is formed. The pancreatic cells develop in 5–6mm TL embryos primarily along the blood capillaries and in 10–11 day old larvae exocrine A and B cells are seen prominent by their zymogen granules and spires and stacks of rough endoplasmic reticulum. Ripening of the Islets of Langerhans begin in larvae of 10mm TL. By 16mm TL two types of endocrine cells are visible. With aging three processes are recognizable in the liver: (1) increased branching of the blood net displaces the hepatic units and complicates the structure of the liver parenchyma; (2) a gradual increase in lipid vacuoles and debris deposition in secretory cells takes place; and (3) the number of melano-macrophage cells and melano-macrophage centers gradually increases. In 15-year-old experimentally stunted fish (110–120mm TL) the liver and pancreas resemble those of juvenile fish appearing much healthier than those of 8–10 year old large carp from commercial ponds. These findings provide evidence that aging is not a simple time-dependent mechanism but is also strongly modulated by environmental factors.     

Proliferation and germination of somatic embryos from embryogenic suspension cultures in <Emphasis Type="Italic">Phœnix dactylifera</Emphasis>

The present study demonstrates a procedure for the rapid development of a high number of somatic embryos from embryogenic suspension culture. This method might be efficient for mass propagation of Phnix dactylifera L. Embryogenic callus placed in liquid medium with 10^–5M ABA yielded an average 72 embryos per 100ml of culture medium within 2months, while those placed on solid medium yielded an average of 33, 20 and 16 embryos per 100ml of culture medium respectively for 10^–7, 10^–6 and 10^–5 M ABA after 4months. The combination of 2,4-DIchlorophenoxyacetic acid (2,4-D) (4.5×10^–7M), glutamine (6.7×10^–4M), and ABA (10^–5M) (L8 liquid medium) showed a beneficial effect on somatic embryos production compared to 2,4-D and glutamine alone, while this combination significantly (p<0.05) increased the accumulation of storage proteins (144 and 138mgg^–1 DW respectively for Jihel and Bousthami noir cultivars) in somatic embryos. The somatic embryos which underwent maturation on medium containing only 4.5×10^–7M 2,4-D and 10^–5M ABA (L6 liquid medium) accumulated more sugars (292 and 265mgg^–1 DW respectively for Jihel and Bousthami noir) than those matured on any other liquid medium. Histological studies revealed that somatic embryos (developed in L6 and L8 liquid media) accumulated less reserve compounds (proteins and sugars) than zygotic embryos. The addition of activated charcoal (0.25 and 0.5gl^–1) and phytagel^® (2.5gl^–1) to the germination medium may be useful for enhancing the germination of Phnix dactyliferasomatic embryos.     

Behavior of early life intervals of Klamath River green sturgeon, <Emphasis Type="Italic">Acipenser</Emphasis><Emphasis Type="Italic">medirostris</Emphasis>, with a note on body color

We studied ontogenetic behavior, migration, and wintering behavior of young Klamath River green sturgeon, Acipenser medirostris, in the laboratory to provide insight into likely behavior of wild sturgeon. Hatchling free embryos preferred cover but were poor swimmers and could not move farther than a few centimeters to cover. The poor swimming ability and cover preference of hatchlings suggests evolution for habitat selection of females to place eggs in habitat with cover for eggs (and hatchlings), and for egg characteristics (large, dense, and weakly adhesive) to cause rapid sinking into cover without drifting. A day or so after fish developed into larvae (first life interval feeding exogenously), day-12 larvae initiated a 12-day downstream nocturnal migration. A totally nocturnal migration is unlike other Acipenser migrants yet studied. Migrant larvae had a dark-colored body typical of other Acipenser species that migrate as larvae. Tail color was a dark black (black-tail phenotype) only during the early larva period, suggesting a morphological adaptation for migration, foraging, or both. Post-migrant larvae and early juveniles to day 84 foraged diurnally with a nocturnal activity peak. Day 110–181 juveniles moved downstream at night until water temperature decreased to about 8°C, indicating wild juveniles migrate downstream to wintering habitat. Habitat preference of month 9–10 wintering juveniles suggests wild juveniles are in deep pools with low light and some rock structure. Wintering juveniles were only active at night. Initiation and cessation of daily activity was at dusk and dawn during illumination changes of <1.0lx. This sensitivity to illumination has not been found before in sturgeons. During the first 10months of life, nocturnal activity of early life intervals is a dominant feature of migration, foraging, and wintering.     

Substrate Preferences of Juvenile Hatchery-reared Lake Sturgeon, Acipenser fulvescens

Substrate preferences of juvenile, hatchery-reared lake sturgeon, Acipenser fulvescens, from a Wisconsin population were examined relative to water temperature and velocity, fish size and time of day. Given the choice of a sand, gravel, rock or smooth plastic bottom, all sturgeon were strongly attracted to the sand substrate. Water temperature did not affect substrate preference, however small sturgeon (13.5cm mean FL) acclimated to 19°C were more active than those tested in 6°C water. Small sturgeon, under all conditions, were less sedentary in the early morning and late evening hours than during the daytime. Preference of small sturgeon for sand was slightly stronger when a current of 5cmsec^-1 was present. Substrate preference of larger sturgeon (24.3cm mean FL) was not affected by any of the parameters examined. In general, hatchery-reared lake sturgeon showed similar behaviors (with respect to substrate selection) as those previously described for the same population in the wild, making it possible that substrate preferences have a genetic component and likely that hatchery rearing does not alter instinctive behavior.     

The Effects of Increasing UV-B Radiation on Pigmentation, Growth and Survival of Coregonid Embryos and Larvae

In the northern regions UV-B radiation levels have increased due to ozone depletion. A two-week laboratory experiment was conducted to measure the effects of UV-B radiation on the pigmentation, growth, oxygen consumption rate and survival of whitefish, Coregonus lavaretus, and vendace, Coregonus albula, larvae. In May newly hatched embryos were exposed in laboratory aquaria to three CIE weighted UV-B radiation levels: subambient (daily dose 1.37kJm^–2), 9% (1.81kJm^–2) and 34% higher (2.24kJm^–2) than ambient. Control embryos and larvae were not exposed to UV-B. Larvae of whitefish and vendace that were irradiated with highest UV-B level had 32% and 31% more melanin than control larvae, respectively, which we interpret as an apparent induced response. In controls, the species difference revealed 53% more melanin in vendace larvae than in whitefish larvae. UV-B radiation had no effect on the mortality of either species, the survival being high in all treatments (>90%). Additionally, neither growth rate nor the metabolic rate of larvae of either species was affected by UV-B radiation. Thus, in relation to future scenarios UV-B radiation may not be a threat to whitefish or vendace larvae in current or expected radiation levels.     

Invasion of the North American Atlantic Coast by a Large Predatory Asian Mollusc

The large Asian gastropod mollusc Rapana venosa Valenciennes 1846 (Neogastropoda, formerly Muricidae, currently Thaididae) is reported for eastern North America in the lower Chesapeake Bay and James River, Virginia, USA. This record represents a transoceanic range expansion for this carnivorous species. This species has previously been introduced to the Black Sea, Adriatic Sea, and Aegean Sea. Ballast water transport of larval stages from the eastern Mediterranean or Black Sea is the suspected vector of introduction into the Chesapeake Bay; 650 adult specimens in the size range 68–165mm shell length (SL) have been collected from hard sand bottom in depths ranging from 5 to 20m at salinities of 18–28ppt. The absence of small individuals from local collections is probably related to bias in collection methods. Age of the specimens could not be determined. R. venosa is probably capable of reproducing in the Chesapeake Bay. Egg cases of R. venosa were collected from Hampton Roads, a section of the James River, in August 1998, and hatched over a 21-day period under laboratory conditions to release viable bilobed veliger larvae. Four lobed larvae developed 4 days post-hatching and apparent morphological metamorphic competency was observed 14–17 days post-hatching. Despite the provision of live substrates and/or metamorphic inducers no metamorphosis to a crawling form was observed for larvae cultured on the monospecific diet. In work performed during 1999 settlement was observed for larvae cultured on a diet of mixed flagellates and diatoms and subsequently exposed to local epifaunal species. Salinity tolerance tests were performed on larvae at 1–6 days post-hatching. No deleterious effects were observed at salinities as low as 10ppt with limited survival to 7ppt at 6 days post-hatch. Current distribution is considered in context with larval salinity tolerance tests and literature describing native Asian and introduced populations to assess potential for establishment and further range extension both within the Chesapeake Bay and along the Atlantic coast of North America. Establishment within the Bay mainstem to the Rappahannock River with minor incursions into the mouths of the southerly subestuaries is considered feasible. A projected breeding range on the Atlantic seaboard extending from Cape Cod to Cape Hatteras is considered as tenable. Potential impact of R. venosa on commercially valuable shellfish stocks throughout the projected range is cause for serious concern. Boring by the polychaete Polydora websteri is more prevalent in the younger whorls of the shell, and absent in shell laid down later in life. This pattern suggests that juvenile animals may prefer hard substrates and not adopt an infaunal lifestyle until a size in excess of 50mmSL, or after reaching maturity.     

Estimation of Standing Stock and Decomposition Rates of Labile Organic Matter in Waters of Novorossiisk Bay,Black Sea

The annual dynamics of the decomposition rate, standing stock, and residence time of labile organic matter as an index of full self-purification were investigated in Novorossiisk Bay, Black Sea. The results are suggestive of fairly effective processes of biological self-purification in polluted waters of the bay. The decomposition rate was highest (0.3–0.7 mgO₂/l per day) during the summer, and it decreased by 4–8 times in winter. The residence time of labile organic matter was 97–104 days in winter and 8–11 days in summer. Oxygen consumption rates measured in different areas of the bay conformed to their trophic status and were not above the normal level for summer.     

<Emphasis Type="Italic">Uncisudis posteropelvis</Emphasis>, a new species of barracudina (Aulopiformes: Paralepididae) from the western North Pacific Ocean

Six specimens (2 flexion larvae: 9.5–10.4mm in notochord length; 4 postflexion larvae: 12.3–18.2mm in standard length) collected from the western North Pacific are tentatively ascribed to the genus Uncisudis of the tribe Lestidiini of the subfamily Paralepidinae (Paralepididae) in sharing remarkably elongate and filamentous pelvic fin rays, their tips reaching the origin of the anal fin. They are described as Uncisudis posteropelvis sp. nov. in uniquely having the insertion of pelvic fins closer to the origin of anal fin than to the posterior end of dorsal fin base among lestidiine species. Addition to this character, the new species has remarkably elongate and filamentous dorsal fin rays, the short distance between anus and origin of anal fin (4.2–6.1% of standard length, SL), the posteriorly located pelvic fins (prepelvic length 69.4–71.5% SL), dorsal fin rays 10, anal fin rays 28–29, myomeres 41–42+38–40=80–81 (vertebrae 38+41=79), and peritoneal pigment spots 11–12. The occurrence of larvae differing in pigment pattern from the present new species suggests another undescribed species of Uncisudis in the western South Pacific.     

Feeding greatly enhances swimming endurance of settlement-stage reef-fish larvae of damselfishes (Pomacentridae)

Previous studies of the swimming endurance abilities of late-stage larvae of reef fishes have used laboratory swimming chambers and, with one exception, unfed larvae. Based on the exceptional study, we predicted that fed larvae should have much greater endurance than previously reported for unfed larvae. We tested the swimming endurance of the fed late-stage larvae of 6 pomacentrid species and found that all could swim at least twice as long as unfed larvae. The 3 species with larger larvae (12–14mm standard length: SL) all grew during these experiments in spite of being forced to swim 23.3h per day. The 3 species with smaller larvae (10–11mm SL) did not show consistent growth. Unfed laboratory measures of swimming endurance are, therefore, very conservative, and are probably more of an indication of the reserves available to the larvae than a realistic indication of how far the larvae are capable of swimming in the field.     

Biodegradation of monochloroacetic acid used as a sole carbon and energy source by <Emphasis Type="Italic">Xanthobacter autotrophicus </Emphasis>GJ10 strain in batch and continuous culture

Batch and continuous mode degradation of monochloroacetic acid used as a sole carbon and energy source in the concentration range of 0.9–48.4 mM by pure culture of Xanthobacter autotrophicusGJ10 was investigated. The substrate was completely degraded in each flask in batch system. Partial substrate inhibition occurred at the concentrations exceeding 25.4mM. Temporary accumulation of glycolic acid in the medium indicated that dehalogenation was undergoing faster than further utilization of glycolate. Three different carbon substrates were used for inoculum preparation – 1,2-dichloroethane, tri-sodium citrate and a nutrient broth. The fastest growth on monochloroacetate occurred for 1,2- dichloroethane-grown inoculum. The assays of haloacid dehalogenase in crude extract indicated that the bacteria grown on 1,2-dichloroethane possessed higher level of the enzyme. The response of the GJ10 culture towards spikes of 20mM monochloroacetate was tested in 2.5-l continuously stirred tank fermentor. The substrate was readily utilized within 7–8h. Continuous degradation of monochloroacetate in the fermentor was demonstrated for monochloroacetate concentration of 20mM and dilution rate 0.016 h^–1. Quantitative agreement between the amount of monochloroacetate introduced and chloride released was found. The results demonstrated that the strain X. autotrophicus GJ10 might be suitable for biodegradation of monochloroacetate contaminated media.     

Softening response of banana fruit treated with 1-methylcyclopropene to high temperature exposure

Elevated temperatures experienced by harvested fruit can modulate theirripening. Moreover, heat treatments can be applied to reduce susceptibility tolow temperature disorders and to help control pests and diseases. Theethylene-binding inhibitor 1-methylcyclopropene (1-MCP) was used to investigatethe ethylene-mediated softening response of banana fruit exposed to elevatedtemperatures. A preliminary experiment was conducted to determine levels ofhightemperature (30–50°C) imposed for a short periodof time that did not cause skin scald. The softening response of Williamsbananafruit treated with 1-MCP at various temperatures and durations wascharacterisedin subsequent experiments. Exposure of fruit to hot air for 60 minat 45°C or for 30 min at50°Ccaused 30–40% peel scald. The peel was not visibly damaged forfruit treated at 40°C for up to 60 min.Softening of fruit treated with 1-MCP for 12 h at25°Cand then held for 7 days at 30, 35 or 40°C wasinhibited in proportion to increasing concentration over the range 0.01–1l/l 1-MCP. However, softening was progressively enhanced withincreasing holding temperatures from 30–40°Cand/or time from 1–7 days, although fruit treated with the higher 1-MCPconcentrations of 1 and 10 l/l were comparatively lessresponsive to heat. Although banana fruit held at30–40°Cdid not de-green, their increased softening at elevated temperatures andinhibition of this response by 1-MCP suggest that heat enhances synthesis ofnewethylene sites which mediated banana fruit softening.     

Developmental morphology of the cyprinid fish Horadandia atukorali

Embryonic, larval, and juvenile development of a small Indian cyprinid, Horadandia atukorali, is described from laboratory-reared specimens. The eggs, measuring 0.7–0.8mm in diameter, were demersal, almost spherical in shape, transparent and unpigmented, with a pale yellow yolk without oil globules. Hatching occurred 47–54h after fertilization at 26.3–27.5°C. The newly hatched larvae, measuring 2.3–2.6mm in body length (BL) with 16+13=29 myomeres, had no melanophores, except on the eye, a single melanophore occurring on the lower margin, and xanthophores surrounding the pupil. The yolk was completely absorbed at 3.0mm BL. Notochord flexion was initiated at 4.0mm BL and finished at 4.4mm BL. Aggregate numbers of all fin rays were completed at 8.0mm BL. Squamation was initiated at 6.4mm BL and completed at 9.5mm BL. Although the eggs of Horadandia atukorali resembled those of other small danionin species, including Aphyocypris chinensis, Chela dadiburjori, Danio rerio, Devario malabaricus, and Hemigrammocypris rasborella, they differed from those of Danio rerio and Devario malabaricus in having a narrower perivitelline space. The larvae and juveniles of Horadandia atukorali were also similar to those of the latter five species in general morphology, especially in the presence of a melanophore on the lower margin of the eye at hatching, as in C. dadiburjori. However, the early life stage morphology of Horadandia atukorali differed from the other danionin species in having a conical yolk sac at hatching, no cement organ on the forehead in the yolk-sac larval stage, a divided gas bladder in the flexion larval stage, two dark lateral streaks on the head and chevron-like melanophores on the ventral body surface from the preflexion to postflexion larval stages, and xanthophores on the eyes at hatching.     

Reproduction of the Endangered Killifish Aphanius iberus at Different Salinities

Adult fish of a freshwater population of the Iberian endangered cyprinodontid Aphanius iberus, were induced to reproduce at salinities of 5, 15, 30, 45 and 60ppt. For each salinity five 30l aquaria were used, each one including a male and two females. Maturity and spawning outside the natural season, were obtained at conditions of 22 to 28°C and a photoperiod of 14L:10D. The larvae were fed with rotifers Brachionus plicatilis and Synchaeta cecilia valentina. Experiment lasted 40 days. The first spawning occurred on the 17th day at 45ppt of salinity and the first embryos hatched on the 34th day at 5 and 15ppt salinity. The final average number of larvae per aquarium ranged from 5.2 (45ppt salinity) to 10.8 (15ppt salinity). No significant differences were found between the average values at different salinities (p<0.01).     

Temporal–spatial distributions of high nitrogen concentrations in headwater areas of regions with low precipitation

Temporal–spatial distributions of nitrogen in the low-precipitation headwater areas of the Sanuki Mountain Range, Kagawa Prefecture, Japan, was studied to clarify the natural loading from forests to rivers as basic knowledge for elucidating the eutrophication in dead-water regions downstream. The survey to clarify temporal variations was carried out once every two weeks at the headwaters of five rivers in the Sanuki Mountain Range and the Shikoku Mountains on Shikoku Island, Japan, between May 6, 2002, and April 22, 2003. The survey to clarify the spatial distribution was carried out at 23 stations on the headwaters of the Sanuki Mountain Range between August 13 and 15, 2002. In the Kazuratani and Tarobei Rivers, which originate in the Sanuki Mountain Range, where precipitation is scarce, total N was consistently high – greater than 1mgl^–1 throughout the year. The maximum value of total N was 3.2mgl^–1 in the Kazuratani River. The spatial distribution of total N in the headwater areas was 0.47–3.8mgl^–1. High concentrations over 1mgl^–1 were found in the central region of the Sanuki Mountain Range and the maximum value was 3.8mgl^–1. From these results, it became clear that nitrogen concentrations in headwater areas of the Sanuki Mountain Range are high compared with those in other regions. Various factors were considered in relation to low precipitation and drying as the causes of the high nitrogen concentrations. Furthermore, It was noted that the majority of the regions with the highest NO₃ ^–-N concentrations in our study were composed of granitic rock.     

Seasonal variation of denitrification rate in Lake Suwa sediment

The seasonal variation of denitrification rate in sediments in the central station of Lake Suwa, Japan, was estimated by the acetylene-inhibition technique from March 20 to December 10, 1994. The denitrification rate ranged from 0 to 1800µmolNm^–2day^–1 and showed a distinct seasonal trend, i.e., relatively high rates in spring and winter, and low or negligible rates in summer. The denitrification rate was well correlated with NO^–₃ concentration in overlying water, suggesting that NO^–₃ in overlying water was the primary controlling factor for denitrification. The annual rate of denitrification was 0.15molNm^–2year^–1. Denitrification removed 5% of the annual nitrogen load from the lake, and this fraction was relatively small compared to the values reported for a variety of aquatic environments. In Lake Suwa, NO^–₃ in the water column was depleted during summer, and this suppressed effective removal of nitrogen from the lake by denitrification.