Changes in vision and olfaction during sexual maturation in the European eel Anguilla anguilla (L.)

Retinal structure was examined in sexually immature and artificially matured female Anguilla anguilla . Inner nuclear layer cell numbers decreased from 600 mm⁻¹ retinal cross-section to 300 mm^−I and ganglion cells from 60 to 30 mm⁻¹ cross-section, during sexual maturation. Most of the decrease occurred prior to the stage of maturation at which migration begins. Electroretinograms were recorded from the intact eyes of immature and maturing eels. There was no change in scotopic sensitivities to light of wavelengths 480 and 520 nm, with increasing sexual maturity. Olfactory organs were examined in female eels of a similar range of maturity states and were found to atrophy in artificially matured eels of advanced development. The density of mucous cells in olfactory lamellae decreased from a maximum of 443 mm⁻² in sexually immature eels to as low as 19 mm⁻² in sexually maturing eels. The changes in vision and olfaction were thought to indicate a change in the relative importance of the two sensory modalities with sexual maturation.     

Resting spore formation of aphid-pathogenic fungus Pandora nouryi depends on the concentration of infective inoculum

Resting spore formation of some aphid-pathogenic Entomophthorales is important for the seasonal pattern of their prevalence and survival but this process is poorly understood. To explore the possible mechanism involved in the process, Pandora nouryi (obligate aphid pathogen) interacted with green peach aphid Myzus persicae on cabbage leaves under favourable conditions. Host nymphs showered with primary conidia of an isolate (LC₅₀: 0.9–6.7 conidia mm⁻² 4–7 days post shower) from air captures in the low-latitude plateau of China produced resting spores (azygospores), primary conidia or both spore types. Surprisingly, the proportion of mycosed cadavers forming resting spores ( P _cfrs ) increased sharply within the concentrations ( C ) of 28–240 conidia mm⁻², retained high levels at 240–1760, but was zero or extremely low at 0.3–16. The P _cfrs – C relationship fit well the logistic equation P _cfrs  = 0.6774/[1 + exp(3.1229–0.0270 C )] ( r ² = 0.975). This clarified for the first time the dependence of in vivo resting spore formation of P. nouryi upon the concentration of infective inoculum. A hypothesis is thus proposed that some sort of biochemical signals may exist in the host–pathogen interaction so that the fungal pathogen perceives the signals for prompt response to forthcoming host-density changes by either producing conidia for infecting available hosts or forming resting spores for surviving host absence in situ .     

The role of life history in the relationship between population dynamics and environmental variability in two Mediterranean stream fishes

Chub Squalius torgalensis and nase Chondrostoma lusitanicum , in a Mediterranean stream, showed important differences in life-history traits and population dynamics. Both species reached mean maturity at age 2 years. Chub lived up to age 5 years, spawned in March to June, grew at a maximum rate of 0·59 mm mm⁻¹ year⁻¹ and showed a low reproductive allocation, with fecundity and egg size increasing with body size. Nase lived up to age 4 years, spawned in January to April, grew at a maximum rate of 0·46 mm mm⁻¹ year⁻¹ and showed a high reproductive allocation, with egg size independent of body size. Both chub and nase showed moderate fluctuations in population size during 1991–1998, but differed in factors driving density at age. Density of age 1 year juvenile chub decreased following severe summer droughts and proportionate survival prevailed thereafter. Density of age 2 year adult nase decreased following severe spring floods, but neither environmental nor parental stock effects were detected for juveniles and older fishes. The results illustrated the interplay between life history and environmental variability in driving fish population dynamics, with impacts of both summer droughts and spring floods being contingent on species-specific patterns of spawning and reproductive investment.     

Somatolactin mRNA expression during the parr–smolt transformation in hatchery-reared Atlantic salmon Salmo salar smolts

Expression of somatolactin (SL) mRNA was quantified during smoltification at 2 week intervals during January and February and weekly during March, April and May 2004 in a line-bred ranching stock of Atlantic salmon Salmo salar . Gene expression of SL (and a splice variant termed SL₁₈₀) was lower in fish sampled in the later weeks of smoltification than in those at the beginning, a pattern opposite to that of gill Na⁺ K⁺-ATPase activity.     

Water velocity, growth-form and diffusion resistances to photosynthetic CO2 uptake in aquatic bryophytes

Abstract. Boundary-layer resistances of aquatic bryophytes for CO₂ diffusion in water were estimated from wind tunnel measurements of evaporation of aniline in air, using the principle of dynamic similarity. The results indicated resistances at water velocities between 0.02 and 0.2 m s ⁻¹ ranging from about 35 to 5 s mm⁻¹ and 70 to 9 s mm⁻¹, respectively, for the mat-forming liverworts Nardia compressa and Scapania undulata , measured on a projected area (canopy) basis. Over a range of velocities from 0.01 to 0.2 m s⁻¹ the estimated CO₂ boundary-layer resistance of the streamer-like shoots of the moss Fontinalis antipyretica is between about 180 and 15 s mm⁻¹. Comparison with experiments on photosynthetic ¹⁴CO₂-uptake at a range of water velocities suggests that boundary-layer resistance limits photosynthesis at velocities below about 0.01 m s^−l in Fontinalis and below about 0.1 m s⁻¹ in the mat-forming species. It is suggested that high leaf-area index allows the mat growth form more effectively to exploit the low boundary-layer resistance at high velocities while remaining relatively invulnerable to drag. By contrast, the streamer form allows Fontinalis to maximize surface area under conditions where boundary-layer resistance is limiting.     

Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

Early-season river entry of adult Atlantic salmon: its dependency on environmental factors

River entry of adult Atlantic salmon Salmo salar into the River Tornionjoki, monitored during three migration seasons (1997–1999) by horizontal split-beam hydroacoustics, started early in June when water temperature was c . 9° C and when the discharge varied between 1700 and 2000 m³ s⁻¹. In 1997 and 1999, migration peaked during the latter half of June, 17 days after the peak flood, at water temperatures ranging from 11· 5 to 18·2° C. Few statistically significant correlations were observed between river entry and six measured environmental factors and those that were significant were not persistent over the years. The strongest correlation (  r  = −0·60) was between the number of upstream migrants and seawater level, with a time lag of 1 day in 1998. In 1998 and 1999, no clear diurnal migration pattern was observed, although in 1997 the intensity of midday migration was higher than that of the midnight migration. It is concluded that environmental factors have little effect on river entry of Atlantic salmon in a large pristine river located at high latitude.     

Early growth and juvenile population structure of lemon sharks Negaprion brevirostris in the Atol das Rocas Biological Reserve, off north‐east Brazil

Lemon sharks Negaprion brevirostris were sampled in the Atol das Rocas, a nursery area, on nine occasions from March 1999 to October 2003, during which 157 individuals were tagged and 35 were recaptured. The male : female sex ratio of captured individuals was 1 : 1·12. Mean ±  s . d . growth rates were 24·7 ± 3·4 cm year⁻¹ in total length ( L _T), 20·7 ± 3·2 cm year⁻¹ in fork length, and 19·5 ± 2·7 cm year⁻¹ in precaudal length. There was no significant difference in growth rates between males and females. Mean ±  s . d . increase in mass was 2565 ± 762 g year⁻¹. The von Bertalanffy growth parameters estimated by the Fabens method based on L _T were: k  = 0·077, L _∞ = 399·9 cm and t ₀ = −2·16. Despite the large variation of environmental conditions, particularly of tidal range and currents, and the lack of protective mangrove cover in the nursery area at Atol das Rocas, juvenile lemon sharks grew relatively faster than at other nurseries. Such rapid growth could be a response to abundant food availability or high risk of predation by adults that enter the nursery area.     

River flow and fish abundance in a South African estuary

The ichthyofauna of the Thukela Estuary, a small (55 ha), shallow (<1·5 m) system on the KwaZulu-Natal coast (mean annual river runoff of 3865 × 10⁶ m³, from a large catchment of 29 000 km², is seasonal: peak inputs occurring between November and March), was dominated by the juveniles of marine taxa that used the estuary as a nursery area. A striking feature of the above community was the decline in fish abundance with increasing river input, with flow values >100 m³ s⁻¹ leading to increased loss of species from the system. This decline was linked to the lack of saline intrusion into the estuary and increased freshwater flooding through the system.     

The territorial system of the kob antelope (Kobus kob kob) in the Comoé National Park, Côte d'Ivoire

The territorial system of kob antelopes in the Comoé National Park, Côte d'Ivoire, was studied from March 1993 until April 1997. Whereas size and shape of territories remained constant between 1993 and 1994, the number of territories decreased from 1994 onwards. A decline of the population density probably led to the decline in territory numbers and also to variations in size and shape of the remaining territories. The decline of kob numbers is the result of heavy poaching in the study area. Whereas a lekking system was present in the study area prior to 1975 when the population density was approximately 14.4 kobs/km², males switched to the resource defence territorial system present today after the population density decreased to 12.5/km² in 1993 and finally to 2.3/km² in 1997. Compared to other research areas with higher population densities, territories in the Comoé National Park are larger, almost all adult males are capable to defend a territory, fights over territories are rare and loss of territory tenureship is almost exclusively due to the death of the territorial male. We suggest that those differences can all be related to the low population density in the study area.     

Physiological impact of sea lice on swimming performance of Atlantic salmon

Atlantic salmon Salmo salar were infected with two levels of sea lice Lepeophtheirus salmonis (0·13 ± 0·02 and 0·02 ± 0·00 sea lice g⁻¹). Once sea lice became adults, the ventral aorta of each fish was fitted with a Doppler cuff to measure cardiac output ( ̇ ), heart rate ( f _H) and stroke volume ( V _S) during swimming. Critical swimming speeds ( U _crit) of fish with higher sea lice numbers [2·1 ± 0·1 BL (body lengths) s⁻¹] were significantly lower ( P  < 0·05) than fish with lower numbers (2·4 ± 0·1 BL s⁻¹) and controls (sham infected, 2·6 ± 0·1 BL s⁻¹). After swimming, chloride levels in fish with higher sea lice numbers (184·4 ± 11·3 mmol l⁻¹) increased significantly (54%) from levels at rest and were significantly higher than fish with fewer lice (142·0 ± 3·7 mmol l⁻¹) or control fish (159·5 ± 3·5 mmol l⁻¹). The f _H of fish with more lice was 9% slower than the other two groups at U _crit. This decrease resulted in ̇ not increasing from resting levels. Sublethal infection by sea lice compromised the overall fitness of Atlantic salmon. The level of sea lice infection used in the present study was lower than has previously been reported to be detrimental to wild Atlantic salmon.     

Photosystem I acceptor side limitation is a prerequisite for the reversible decrease in the maximum extent of P700 oxidation after short-term chilling in the light in four plant species with different chilling sensitivities

Changes in the extent of P700 oxidation (P700⁺) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1 h under light with various photon flux densities. At 50 µmol photons m⁻² s⁻¹, the decrease in P700⁺ was observed only in cucumber, but at 150 µmol photons m⁻² s⁻¹, it was found in all plants except barley, revealing their expected chilling sensitivities. However, the decrease in P700⁺ by this short-term chilling was reversible in the presence of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or methyl viologen, and it did not show any causal relationship with the decrease in the electron transfer rate nor with the down-regulation of photosystem II through the accumulation of zeaxanthin and the development of non-photochemical quenching. These results led to the suggestion that photosystem I (PSI) acceptor side limitation is a prerequisite for the decrease of P700⁺. Furthermore, PSI acceptor side limitation could be mainly due to limitation of electron-sink pathways such as CO₂ assimilation and ascorbate–glutathione cycle, because treatment with glycolaldehyde which inhibits the former pathway, and with KCN which inhibits both pathways, decreased P700⁺ by 20–30% in barley leaves after chilling in the light.     

Seasonal variation in egg production and batch fecundity of European hake Merluccius merluccius (L.) in the Bay of Biscay

Sexually mature female hake Merluccius merluccius with hydrated ovaries were sampled on a monthly basis in the Bay of Biscay, from May 1996 to October 1997 and from March to April 1998. The batch fecundity was positively related to total length. The relative batch fecundity ( F _Brel) varied significantly among months and years, but not between areas, i.e. International Council for the Exploration of the Sea Divisions VIIIa and VIIIb within the Bay of Biscay. Two levels of F _Brel were found in 1997: the highest between January and April (mean ± s . e . 167 ± 5 eggs g⁻¹) and the lowest from May to October (112 ± 3 eggs g⁻¹). Population condition factor and gonado-somatic indices ( I _G) followed the expected trend in relation to the monthly changes in F _Brel during 1997. The F _Brel variation between years was 9% for 1996–1997 and 28% for 1997–1998, and the difference of the I _G was c. 14 and 36%, respectively. Population relative egg production varied from a high value in January to March (985 eggs g⁻¹) to a low egg production between April and October 1997 (445 eggs g⁻¹).     

Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L^–1), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m^–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus .
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m^–2, although peaking as high as 9000 ind. m^–2. Average annual biomass ranged from 102 to 721 mg m^–2, and reached >2000 mg m^–2 at one site in autumn.
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.     

Differences in temperature conditions and somatic growth rate of larval and early juvenile spring-spawned herring from the Vistula Lagoon, Baltic Sea manifested in the otolith to fish size relationship

Larval and juvenile herring Clupea harengus collected in the Polish part of the Vistula Lagoon in May-July 1997 had hatched between 17 April and 9 June and originated from three cohorts. The spawning season began on 1 March at 3·8° C and was completed on 3 June at 12·7° C. Mortality among larvae was high in the first 2 weeks of April, probably associated with significant temperature decrease at the beginning of the spawning season. The growth of 10–48 mm L _S herring was linear, highest for larvae and juveniles from the first cohort (0·58 mm mm^-1 day^-1), slower for the second cohort (0·55 mm mm^-1 day^-1) and the slowest for the third cohort (0·45 mm mm day^-1). Temperature effects on the growth were inconclusive and potentially unfavourable feeding conditions in June might have been responsible for the relatively slow growth of third cohort larvae and juveniles.
Relationships between otolith size (perimeter, length, width, area, and weight) and fish size ( L _S) differed among the three cohorts, related mostly to the positive temperature effect on otolith growth, individuals growing in warmer water had larger otoliths. Although a negative growth rate effect was observed as well, it was less significant.     

Anaerobic sulfur oxidation in the absence of nitrate dominates microbial chemoautotrophy beneath the pelagic chemocline of the eastern Gotland Basin, Baltic Sea

Oxic–anoxic interfaces harbor significant numbers and activity of chemolithoautotrophic microorganisms, known to oxidize reduced sulfur or nitrogen species. However, measurements of in situ distribution of bulk carbon dioxide (CO₂) assimilation rates and active autotrophic microorganisms have challenged the common concept that aerobic and denitrifying sulfur oxidizers are the predominant autotrophs in pelagic oxic–anoxic interfaces. Here, we provide a comparative investigation of nutrient, sulfur, and manganese chemistry, microbial biomass distribution, as well as CO₂ fixation at the pelagic redoxcline of the eastern Gotland Basin, Baltic Sea. Opposing gradients of oxygen, nitrate, and sulfide approached the detection limits at the chemocline at 204 m water depth. No overlap of oxygen or nitrate with sulfide was observed, whereas particulate manganese was detected down to 220 m. More than 70% of the bulk dark CO₂ assimilation, totaling 9.3 mmol C m⁻² day⁻¹, was found in the absence of oxygen, nitrite, and nitrate and could not be stimulated by their addition. Maximum fixation rates of up to 1.1 μmol C L⁻¹ day⁻¹ were surprisingly susceptible to altered redox potential or sulfide concentration. These results suggest that novel redox-sensitive pathways of microbial sulfide oxidation could account for a significant fraction of chemolithoautotrophic growth beneath pelagic chemoclines. A mechanism of coupled activity of sulfur-oxidizing and sulfur-reducing microorganisms is proposed.     

Population dynamics and production of Jesogammarus annandalei, an endemic amphipod, in Lake Biwa, Japan

SUMMARY 1. Population dynamics and production of Jesogammarus annandalei , an endemic amphipod in Lake Biwa, were examined from April 1997 to June 1998. The life cycle of this species was 1 year with the new generation beginning in early autumn. They preferred low temperature (<12 °C) and their spatial distribution varied seasonally and accordingly.
2. In deep water, the abundance of J. annandalei ranged from 200 to 63 000 m⁻² and decreased towards summer and the biomass (0.01∼3.6 g C m⁻²) was on average comparable that of zooplankton. The density was much higher than that recorded by a study conducted 35 years ago.
3. Individual growth rate of this amphipod was high in winter and spring but decreased in summer. Annual production of J. annandalei (6.2 g C m⁻² year⁻¹) was only 2% of primary production but was at the higher end of the range reported for amphipods in oligo- and mesotrophic lakes.
4. These results are consistent with the view that Lake Biwa is becoming more eutrophic, with a consequent decrease in the abundance of predatory fish in the profundal zone.     

The use of a surface adhesion immunofluorescent (SAIF) method for the rapid detection of Yersinia enterocolitica serotype O:3 in meat

This study examined the attachment kinetics of Yersinia enterocolitica serotype O:3 to determine the optimum conditions for its isolation from meat enrichment systems using a novel surface adhesion technique. Minced beef was inoculated with Y. enterocolitica at an initial level of 10 cfu g⁻¹ and incubated at 25 °C in an enrichment broth. Yersinia was recovered from enriched samples on polycarbonate membranes by surface adhesion and enumerated using immunofluorescence microscopy. The surface adhesion immunofluorescence technique (SAIF) had a minimum detection limit of approximately 4·0–4·5 log₁₀ cfu ml⁻¹ and provided good correlation between the estimation of the numbers of Yersinia in the enrichment broth derived from plate counts on Yersinia Selective agar (CIN) and those determined by SAIF ( r ² ₌ 0·94; rsd ₌ ± 0·21). A derived regression equation of the SAIF count vs plate counts was used to predict Y. enterocolitica numbers in spiked meat samples stored at 0 °C for up to 20 d. The numbers as predicted by the SAIF method showed good correlation with counts derived by plating techniques ( r ² ₌ 0·78; rsd ₌ ± 0·42). The application of the SAIF technique for the rapid detection of Y. enterocolitica serotype O:3 from meat is discussed.     

Longevity of the freshwater anostracan Streptocephalus mackini (Crustacean: Anostraca) in relation to food (Chlorella vulgaris) concentration

SUMMARY 1. Temporary ponds are inhabited by a variety of invertebrates, of which anostracans are an important group. We studied the lifetables of male and female anostracan Streptocephalus mackini at 3 algal concentrations (0.5 × 10⁶, 1.0 × 10⁶ and 1.5 × 10⁶ cells mL⁻¹).
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 10⁶ cells mL⁻¹.
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 10⁶ cells mL⁻¹, was more than three times that at 1.5 × 10⁶ cells mL⁻¹.
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 10⁶ cells mL⁻¹) and intermediate (1.0 × 10⁶ cells mL⁻¹) food levels. The r -value at low food level (0.5 × 10⁶ cells mL⁻¹ of Chlorella ) was 0.20 ± 0.01 per day.     

Electrical signalling and cytokinins mediate effects of light and root cutting on ion uptake in intact plants

Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1–2 min) effects on net K⁺ and H⁺ transport at the root surface. H⁺ efflux decreased (from −18 to −12 nmol m⁻² s⁻¹) and K⁺ uptake (∼2 nmol m⁻² s⁻¹) reverted to efflux (∼−3 nmol m⁻² s⁻¹). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a ∼3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H⁺ efflux and stopped K⁺ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 m m NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (−50 nmol m⁻² s⁻¹). Kinetin (2–4  µ m ), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed.