Comparison of fin ray sampling methods on white sturgeon Acipenser transmontanus growth and swimming performance

Effects of two fin‐ray sampling methods on swimming performance, growth and survival were evaluated for hatchery‐reared sub‐adult white sturgeon Acipenser transmontanus. Fish were subjected to either a notch removal treatment in which a small section was removed from an anterior marginal pectoral‐fin ray, or a full removal treatment in which an entire marginal pectoral‐fin ray was removed. Control fish did not have fin rays removed, but they were subjected to a sham operation. A modified 3230 l Brett‐type swim tunnel was used to evaluate 10 min critical station‐holding speeds (S_CSH) of A. transmontanus, immediately after the fin ray biopsies were obtained with each method. Survival and growth were evaluated over a 6 month period for a separate group of fish subjected to the same biopsy methods. Mean ± s.e . 10 min S_CSH were 108·0 ± 2·3, 110·0 ± 2·6 and 115·0 ± 3·5 cm s^?1 for the notch removal group, full removal group and control group, respectively, and were not significantly different among treatments. Behavioural characteristics including tail‐beat frequency and time spent hunkering were also not significantly different among treatment groups swimming at the same speeds. There were no mortalities and relative growth was similar among treatment groups. Average biopsy time for the notch removal method was lower and the wounds appeared to heal more quickly compared with the full removal method.     

Effects of administration of somatostatin-14 and immunoneutralization of somatostatin on endocrine and growth responses in rainbow trout

Injection of somatostatin‐14 (SS‐14) at 5 ng g^?1 body mass (BM) into rainbow trout Oncorhynchus mykiss decreased (P < 0·05, cubic, r² = 0·54) levels of growth hormone (GH) (1·5 ± 0·9 ng ml^?1v. 6·6 ± 0·6 ng ml^?1) over time when compared to controls. Somatostatin‐14 at 50 ng g^?1 BM also decreased (P = 0·064, quadratic; r² = 0·30) levels of GH (3·6 ± 2·1 ng ml^?1v. 6·6 ± 0·6 ng ml^?1) over time compared to controls. In a second study, passive immunization against SS‐14 (1 : 25 dose) increased (P = 0·10, cubic, r² = 0·12) levels of GH (11·0 ± 4·8 ng ml^?1v. 5·2 ± 1·4 ng ml^?1) over time. Passively immunizing against SS‐14 (1 : 50 dose) increased (P < 0·05, cubic, r² = 0·10) levels of GH (8·2 ± 2·3 ng ml^?1v. 5·2 ± 1·4 ng ml^?1) over time compared to controls. Overall, in the active immunization study there was no difference (P > 0·10) in specific growth rate (G) or feed conversion ratio (FCR) between the three treatment groups during the 9 weeks of the study. Only four of the fish immunized against SS‐14, however, developed antibody titres against SS. Compared to controls, these fish exhibited a G of 0·89 ± 0·09 v. 0·56 ± 0·09% per 3 weeks and FCR of 0·80 ± 0·04 v. 1·20 ± 0·05 g g^?1. In SS‐14 immunized fish, levels of GH decreased (P < 0·05) by day 63 while levels of insulin like growth factor‐I (IGF‐I) increased (P < 0·05) by day 42 and 63. These results indicate the hypothalamic hormone SS‐14 regulates GH secretion similarly in rainbow trout as it does in mammals. Active immunization against SS‐14 could improve growth performance in rainbow trout but enhanced G and FCR is dependent upon generation of antibody titres.     

Heart rate as an indicator of metabolic rate and activity in adult Atlantic salmon, Salmo salar

Telemetered heart rate (f_H) was examined as an indicator of activity and oxygen consumption rate (VO₂) in adult, cultivated, Atlantic salmon, Salmo salar L. Heart rate was measured during sustained swimming in a flume for six fish at 10° C [mean weight, 1114 g; mean fork length (f. l.), 50·6 cm] and seven fish at 15° C (mean weight, 1119 g; mean f. l., 50·7 cm) at speeds of up to 2·2 body lengths/s. Semi–logarithmic relationships between heart rate and swimming speed were obtained at both temperatures. Spontaneously swimming fish in still water exhibited characteristic heart rate increases associated with activity. Heart rate and Vo₂ were monitored simultaneously in a 575–1 circular respirometer for six fish (three male, three female) at 4° C (mean weight, 1804 g; mean F. L., 62· cm) and six fish (three male, three female) at 10° C (mean weight, 2045 g; mean f. l., 63·2 cm) during spontaneous but unquantified activity. Linear regressions were obtained by transforming data for both f_H and Vo₂ to log values. At each temperature, slopes of the regressions between f_H and Vo₂ for individual fishes were not significantly different, but in some cases elevations were. All differences in elevation were between male and female fish. There were no significant differences in regression slope or elevation for fish of the same sex at the two temperatures and so regressions were calculated for the sexes, pooling data from 4 and 10° C. There was no significant difference in the mean ± S. D. Vo₂ between the sexes at 4° C (male, 66·0 ± 59·6 mgO₂ kg^?1 h^?1; female, 88·0 ± 60·1 mgO₂ kg^?1 h^?1) or 10° C (male, 166·2 ± 115·4 mgO₂ kg^?1 h^?1; female, 169·2 ± 111–1 mgO₂ kg^?1h^?1). Resting Vo₂ (x?± s. d.) at 4°C was 36·7 ± 8.4 mgO₂ kg^?1 h^?1, and 10° C was 72·8 ± 11·9 mgO₂ kg^?1 h^?1. Maximum Vo₂ (x?± S. D.) at 4° C was 250·6 ± 40·2 mgO₂ kg^?1 h^?1, and at 10° C was 423·6 ± 25·2 mgO₂ kg^?1 h^?1. Heart rate appears to be a useful indicator of metabolic rate over the temperature range examined, for the cultivated fish studied, but it is possible that the relationship for wild fish may differ.     

Kocuria SM1 controls vibriosis in rainbow trout (Oncorhynchus mykiss,Walbaum)

Aims: To develop probiotics for the control of vibriosis caused by Vibrio anguillarum and Vibrio ordalii in finfish. Methods and Results: Kocuria SM1, isolated from the digestive tract of rainbow trout, was administered orally to rainbow trout (Oncorhynchus mykiss) for 2 weeks at a dose equivalent to c. 10⁸ cells per g of feed and then challenged intraperitoneally with V. anguillarum and V. ordalii. Use of SM1 led to a reduction in mortalities to 15–20% compared to 74–80% mortalities in the controls. SM1 stimulated both cellular and humoral immune responses in rainbow trout, by elevation of leucocytes (5·5 ± 0·8 × 10⁶ ml^?1 from 3·7 ± 0·8 × 10⁶ ml^?1), erythrocytes (1·2 ± 0·1 × 10⁸ ml^?1 from 0·8 ± 0·1 × 10⁸ ml^?1), protein (23 ± 4·4 mg ml^?1 from 16 ± 1·3 mg ml^?1), globulin (15·7 ± 0·2 mg ml^?1 from 9·9 ± 0·1 mg ml^?1) and albumin (7·3 ± 0·2 mg ml^?1 from 6·1 ± 0·1 mg ml^?1) levels, upregulation of respiratory burst (0·05 ± 0·01 from 0·02 ± 0·01), complement (56 ± 7·2 units ml^?1 from 40 ± 8·0 units ml^?1), lysozyme (920 ± 128·8 units ml^?1 from 760 ± 115·3 units ml^?1) and bacterial killing activities. Conclusions: Kocuria SM1 successfully controlled vibriosis in rainbow trout, and the mode of action reflected stimulation of the host innate immune system. Significance and Impact of the Study: Probiotics can contribute a significant role in fish disease control strategies, and their use may replace some of the inhibitory chemicals currently used in fish farms.     

The effects of environmental salinity on the growth and physiology of totoaba Totoaba macdonaldi and shortfin corvina Cynoscion parvipinnis

Totoaba Totoaba macdonaldi and shortfin corvina Cynoscion parvipinnis, were acclimated and reared together at salinities of 0, 2, 5, 10, 20 and 35 for 56 days. Initial overall mean ± s.d . body masses of 67·6 ± 7·1 g T. macdonaldi and 37·3 ± 3·1 g C. parvipinnis increased to final overall masses of 217·4 ± 30·3 and 96·5 ± 16·5 g, respectively, at the end of the study. Totoaba macdonaldi was not able to tolerate salinities of 0 and 2 and C. parvipinnis of 0. In contrast, both species had 100% survival at salinities ≥ 10. Somatic growth was highest not at natural seawater salinity of 35, but at 10. Plasma osmolality ranged from 172·5 to 417·0 mOsmol kg^?1 for T. macdonaldi and from 207·0 to 439·5 mOsmol kg^?1 for C. parvipinnis and varied in direct proportion to salinity. The estimated isosmotic salinities of T. macdonaldi and C. parvipinnis were 12·3 and 13·4, respectively. Cynoscion parvipinnis reared at two had significantly lower plasma lysozyme activity (95·0 Units ml^?1) than fish held at salinities from 5 to 35 (ranging from 215·0 to 355·0 Units ml^?1), but without clear trends over this range. Blood neutrophil oxidative radical production (NBT) (ranging from 3·9 to 6·7 mg ml^?1) had some significant differences among salinities, but these did not follow a clear pattern. For T. macdonaldi, neither lysozyme activity nor NBT was affected by salinity. Ash content of whole fishes varied directly and moisture content inversely, with salinity for both species.     

Zinc and salinity effects on membrane transport in Chara connivens

Pressure-probe measurements showed that the pressure relaxation of internodal cells of the freshwater alga Chara connivens slowed considerably when 1–5 mol m^?3 Zn²⁺, or more especially Zn²⁺ and 75 mol m^?3 NaCl, were present in the medium for periods of 1 h or longer. These results indicate that the water permeability of the Chara membrane is decreased by Zn²⁺, and that this effect is enhanced by 75 mol m^?3 NaCl. Specific values taken after 375 min exposure were: 5 mol m^?3 Zn²⁺ and 75 mol m^?3 NaCl caused the half-time for bulk water movement to increase from 7·8±2·3 to 79·5±5·4s, corresponding to a decrease in the hydraulic conductivity (Lp) from (13·0±3·3) × 10^?7 m s^?1 mPa^?1 to (1·25±0·23) × 10^?7 m s^?1 MPa^?1 (mean±S.D., n= 10). These changes are not seen in the presence of NaCl alone, and to a reduced extent in the presence of 5 mol m^?3Zn²⁺ alone (after 375 min, Lp was (2·4±0·1) × 10^?7 m s^?1 MPa^?1, mean±S.D., n = 6). Ca²⁺ cannot substitute for Zn²⁺, but seems to competitively inhibit Zn²⁺. There was another, kinetically distinct effect of Zn²⁺: the ingress of Na⁺ within 15 min of exposure to 75 mol m^?3 NaCl is halved by the presence of 1–5 mol m^?3 Zn²⁺, although internal osmolality is little changed by Zn²⁺. In spite of this, Zn²⁺ does not exert the long-term protection against NaCl that has been reported for Ca²⁺. Depending on the concentration of Zn²⁺ and the duration of the exposure, the effects on water permeability were fully or partly reversible within 24–48 h. The mechanism of these changes is difficult to identify. One possibility is a zinc-induced restriction of trans-membrane channels to give single-file channels which can be blocked by salt.     

Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding dissolved inorganic nitrate uptake in Saccharina latissima and Laminaria digitata (Phaeophyceae)

Uptake rates of dissolved inorganic phosphorus and dissolved inorganic nitrogen under unsaturated and saturated conditions were studied in young sporophytes of the seaweeds Saccharina latissima and Laminaria digitata (Phaeophyceae) using a “pulse‐and‐chase” assay under fully controlled laboratory conditions. In a subsequent second “pulse‐and‐chase” assay, internal storage capacity (ISC) was calculated based on V_M and the parameter for photosynthetic efficiency F_v/F_m. Sporophytes of S. latissima showed a V_S of 0.80 ± 0.03 μmol · cm^?2 · d^?1 and a V_M of 0.30 ± 0.09 μmol · cm^?2 · d^?1 for dissolved inorganic phosphate (DIP), whereas V_S for DIN was 11.26 ± 0.56 μmol · cm^?2 · d^?1 and V_M was 3.94 ± 0.67 μmol · cm^?2 · d^?1. In L. digitata, uptake kinetics for DIP and DIN were substantially lower: V_S for DIP did not exceed 0.38 ± 0.03 μmol · cm^?2 · d^?1 while V_M for DIP was 0.22 ± 0.01 μmol · cm^?2 · d^?1. V_S for DIN was 3.92 ± 0.08 μmol · cm^?2 · d^?1 and the V_M for DIN was 1.81 ± 0.38 μmol · cm^?2 · d^?1. Accordingly, S. latissima exhibited a larger ISC for DIP (27 μmol · cm^?2) than L. digitata (10 μmol · cm^?2), and was able to maintain high growth rates for a longer period under limiting DIP conditions. Our standardized data add to the physiological understanding of S. latissima and L. digitata, thus helping to identify potential locations for their cultivation. This could further contribute to the development and modification of applications in a bio‐based economy, for example, in evaluating the potential for bioremediation in integrated multitrophic aquacultures that produce biomass simultaneously for use in the food, feed, and energy industries.     

Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding N:P dynamics in Ulva lactuca (Chlorophyta)

Dissolved inorganic phosphorus (DIP ) is an essential macronutrient for maintaining metabolism and growth in autotrophs. Little is known about DIP uptake kinetics and internal P‐storage capacity in seaweeds, such as Ulva lactuca (Chlorophyta). Ulva lactuca is a promising candidate for biofiltration purposes and mass commercial cultivation. We exposed U. lactuca to a wide range of DIP concentrations (1–50 μmol · L^?1) and a nonlimiting concentration of dissolved inorganic nitrogen (DIN ; 5,000 μmol · L^?1) under fully controlled laboratory conditions in a “pulse‐and‐chase” assay over 10 d. Uptake kinetics were standardized per surface area of U. lactuca fronds. Two phases of responses to DIP ‐pulses were measured: (i) a surge uptake (V_S ) of 0.67 ± 0.10 μmol · cm^?2 · d^?1 and (ii) a steady state uptake (V_M ) of 0.07 ± 0.03 μmol · cm^?2 · d^?1. Mean internal storage capacity (ISC_P ) of 0.73 ± 0.13 μmol · cm^?2 was calculated for DIP . DIP uptake did not affect DIN uptake. Parameters of DIN uptake were also calculated: V_S  = 12.54 ± 1.90 μmol · cm^?2 · d^?1, V_M  = 2.26 ± 0.86 μmol · cm^?2 · d^?1, and ISC_N  = 22.90 ± 6.99 μmol · cm^?2. Combining ISC and V_M values of P and N, nutrient storage capacity of U. lactuca was estimated to be sufficient for ~10 d. Both P and N storage capacities were filled within 2 d when exposed to saturating nutrient concentrations, and uptake rates declined thereafter at 90% for DIP and at 80% for DIN . Our results contribute to understanding the ecological aspects of nutrient uptake kinetics in U. lactuca and quantitatively evaluating its potential for bioremediation and/or biomass production for food, feed, and energy.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Dietary analysis of the herbivorous hemiramphid Hyporhamphus regularis ardelio: an isotopic approach

The stable isotope values for a range of size classes of Hyporhamphus regularis ardelio from Moreton Bay, south‐east Australia were determined. There was a positive linear relationship between δ¹³C and standard length (L_S)(δ¹³C = 0·034 L_S ? 16·23; r² = 0·78). δ¹³C ranged from ?8·48 to ?17·29‰ with the smallest size class (50 mm L_S) being on average 1·04‰ enriched with respect to that of zooplankton (Temora turbinata) and 7·97‰ depleted compared to Zostera capricorni. δ¹³C was positively correlated with L_S(P < 0·01)(more enriched with increasing L_S) with those fish of the largest size class (225 mm L_S) being 9·86 and 0·84‰ enriched than T. turbinata and Z. capricorni, respectively. There was no detectable trend in δ¹⁵N values with L_S(P > 0·01) with δ¹⁵N, ranging from 9·18 to 11·00‰. Fish of all size classes were on average 2·32 and 7·63‰ more enriched than zooplankton and seagrass, respectively. Carbon isotope data indicate that H. r. ardelio commence life as carnivores and change to a diet in which seagrass is the primary carbon source. The dependence on animal matter, however, is always present. Due to the low percentage of nitrogen in Z. capricorni(2·5%) compared to zooplankton (9·1%) it appears that nitrogen from zooplankton is necessary throughout their life history with the carbon requirements for these fish coming chiefly from Z. capricorni.     

The influence of irradiance,photoperiod and temperature on the growth kinetics of three planktonic diatoms

The influence of irradiance, photoperiod and temperature was determined for the growth kinetics of the diatoms Aulacoseira subarctica, Stephanodiscus astraea and Stephanodiscus hantzschii and the results compared with those of cyanobacteria. Irradiance and photoperiod relationships were qualitatively similar to those for cyanobacteria in that: (1) growth rate (K) was proportionally greater under short photoperiods, with ratios of K under continuous light to K under 3:21 light:dark (LD) cycles of 1·50, 1·80 and 2·96 for A. subarctica, S. astraea and S. hantzschii respectively; (2) at subsaturating irradiances, K was proportional to irradiance and independent of temperature with a negligible predicted maintenance growth rate requirement. Apparent growth efficiencies (GE) at subsaturating irradiances were 0·26±0·03, 0·42±0·03 and 0·50±0·03 divisions mol^-1m² for A. subarctica, S. astraea and S. hantzschii with the values for Stephanodiscus species comparable to values for Oscillatoria species. Under a 3:21 LD cycle at 4 °C, light-saturated growth rates were 0·066±0·004, 0·197±0·033 and 0·285±0·018 divisions day^-1 for A. subarctica, S. astraea and S. hantzschii. S. hantzschii growth rate at 4 °C exceeded maximum Oscillatoria growth rates at 23 °C and the S. astraea growth rate at 4 °C was equivalent to O. agardhii growth rate at 20 °C. Temperature increases above 4 °C gave Q₁₀ values between 4 °C and 12 °C of 3·68, 2·39 and 1·92 for A. subarctica, S. astraea and S. hantzschii, but higher temperatures resulted in minor increases in K. S. astraea growth rate peaked at 16 °C, declining sharply at higher temperatures. February to March in situ growth rates in Lough Neagh, mean temperature 4·3 °C, showed that the A. subarctica in situ K of 0·058 divisions day^-1 was close to the laboratory K at 4 °C, but that S. astraea in situ K of 0·101 divisions day^-1 was lower than the laboratory K at 4 °C.     

Using the robust design framework and relative abundance to predict the population size of pallid sturgeon Scaphirhynchus albus in the lower Missouri River

Several population viability models were constructed to aid recovery in endangered Scaphirhynchus albus, but these models are dependent upon accurate and precise input parameters that are not provided with standard catch per unit effort (CPUE) indices. Nine years of sampling efforts, under the robust design framework, provided 1223 unique captures with an 18·3% recapture rate. The annual population estimates varied from 4·0–7·3 fish rkm^?1 for wild and 8·4–18·4 fish rkm^?1 for hatchery‐reared S. albus. The relationship between abundance (N) and annual trot‐line CPUE indices (x = 70.726y + 2·533, R² = 0·91, P < 0·001) was used to predict an abundance of 13 616 ± 7142 s.e. S. albus in the lower Missouri River. The use of small‐scale intensive sampling to develop a relationship with relative abundance indices reported here, may provide a framework for other fisheries management applications where large‐scale intensive sampling is not feasible, but catch data are available.     

The role of leaf and canopy-level gas exchange in the replacement of Quercus virginiana (Fagaceae) by Juniperus ashei (Cupressaceae) in semiarid savannas

Photosynthesis, transpiration, and leaf area distribution were sampled in mature Quercus virginiana and Juniperus ashei trees to determine the impact of leaf position on canopy-level gas exchange, and how gas exchange patterns may affect the successful invasion of Quercus communities by J. ashei. Sampling was conducted monthly over a 2-yr period in 12 canopy locations (three canopy layers and four cardinal directions). Photosynthetic and transpiration rates of both species were greatest in the upper canopy and decreased with canopy depth. Leaf photosynthetic and transpiration rates were significantly higher for Q. virginiana (4.1–6.7 μmol CO₂·m⁻²·s⁻¹ and 1.1–2.1 mmol H₂O·m⁻²·s⁻¹) than for J. ashei (2.1–2.8 μmol CO₂·m⁻²·s⁻¹ and 0.7–1.0 mmol H₂O·m⁻²·s⁻¹) in every canopy level and direction. Leaves on the south and east sides of both species had higher gas exchange rates than leaves on the north and west sides. Although Quercus had a greater mean canopy diameter than Juniperus (31.3 vs. 27.7 m²), J. ashei had significantly greater leaf area (142 vs. 58 m²/tree). A simple model combining leaf area and gas exchange rates for different leaf positions demonstrated a significantly greater total canopy carbon dioxide uptake for J. ashei compared to Q. virginiana (831 vs. 612 g CO₂·tree⁻¹·d⁻¹, respectively). Total daily water loss was also greater for Juniperus (125 vs. 73 Ltree⁻¹·d⁻¹). Differences in leaf gas exchange rates were poor predictors of the relationship between the invasive J. ashei and the codominant Q. virginiana. Leaf area and leaf area distribution coupled with leaf gas exchange rates were necessary to demonstrate the higher overall competitive potential of J. ashei.     

Abscisic acid introduced into the transpiration stream accumulates in the guard-cell apoplast and causes stomatal closure

Petioles of water‐sufficient intact Vicia faba L. plants were infused with 1 µm abscisic acid (ABA) to simulate the import of root‐source ABA. This protocol permitted quantitative ABA delivery, up to 300 pmol ABA over 60 min, to the leaf without ambiguities associated with perturbations in plant–water status. The ABA concentrations in whole‐leaf samples and in apoplastic sap increased with the amount infused; ABA degradation was not detected. The ABA concentration in apoplastic sap was consistent with uptake of imported ABA into the leaf symplast, but this interpretation is qualified. Our focus was quantitative cellular compartmentation of imported ABA in guard cells. Unlike when leaves are stressed, the guard‐cell symplast ABA content did not increase because of ABA infusion (P = 0·48; 3·0 ± 0·5 versus 4·0 ± 1·2 fg guard‐cell‐pair^?1). However, the guard‐cell apoplast ABA content increased linearly (R² = 0·98) from ?0·2 ± 0·5 to 3·1 ± 1·3 fg guard‐cell‐pair^?1 (≈ 3·1 µm ) and was inversely related to leaf conductance (R² = 0·82). Apparently, xylem ABA accumulates in the guard‐cell wall as a result of evaporation of the apoplast solution. This mechanism provides for integrating transpiration rate and ABA concentration in the xylem solution.     

Interactions between gnathiid isopods,cleaner fish and other fishes on Lizard Island,Great Barrier Reef

The rate of emergence of micropredatory gnathiid isopods from the benthos, the proportion of emerging gnathiids potentially eaten by Labroides dimidiatus, and the volume of blood that gnathiids potentially remove from fishes (using gnathiid gut volume) were determined. The abundance (mean ±s.e .) of emerging gnathiids was 41·7 ± 6·9 m^?2 day^?1 and 4552 ± 2632 reef^?1 day^?1 (reefs 91–125 m²). The abundance of emerging gnathiids per fish on the reef was 4·9 ± 0·8 day^?1; but excluding the rarely infested pomacentrid fishes, it was 20·9 ± 3·8 day^?1. The abundance of emerging gnathiids per patch reef was 66 ± 17% of the number of gnathiids that all adult L. dimidiatus per reef eat daily while engaged in cleaning behaviour. If all infesting gnathiids subsequently fed on fish blood, their total gut volume per reef area would be 17·4 ± 5·6 mm³ m^?2 day^?1; and per fish on the reefs, it would be 2·3 ± 0·5 mm^?3 fish^?1 day^?1 and 10·3 ± 3·1 mm³ fish^?1 day^?1 (excluding pomacentrids). The total gut volume of gnathiids infesting caged (137 mm standard length, L_S) and removed from wild (100–150 mm L_S) Hemigymnus melapterus by L. dimidiatus was 26·4 ± 24·6 mm³ day^?1 and 53·0 ± 9·6 mm³ day^?1, respectively. Using H. melapterus (137 mm L_S, 83 g) as a model, gnathiids had the potential to remove, 0·07, 0·32, 0·82 and 1·63% of the total blood volume per day of each fish, excluding pomacentrids, caged H. melapterus and wild H. melapterus, respectively. In contrast, emerging gnathiids had the potential of removing 155% of the total blood volume of Acanthochromis polyacanthus (10·7 mm L_S, 0·038 g) juveniles. That L. dimidiatus eat more gnathiids per reef daily than were sampled with emergence traps suggests that cleaner fishes are an important source of mortality for gnathiids. Although the proportion of the total blood volume of fishes potentially removed by blood‐feeding gnathiids on a daily basis appeared to be low for fishes weighing 83 g, the cumulative effects of repeated infections on the health of such fish remains unknown; attacks on small juvenile fishes, may result in possibly lethal levels of blood loss.     

Seagrass feeding choices and digestive strategies of the herbivorous fish Sarpa salpa

This is the first study investigating the plant–herbivore interaction between Sarpa salpa, which has overgrazed seagrass transplants in Portugal, and the seagrasses Cymodocea nodosa, Zostera marina and Zostera noltii, which have been considered for restoration. When offered the choice between the three seagrasses in outdoor tanks, adult S. salpa clearly preferred Z. noltii. Testing the seagrasses separately, mean ± s.d. feeding rates ranged from 21 ± 11 g seagrass fresh mass kg^?1 fish mass day^?1 for Z. marina to 32 ± 9 g seagrass fresh mass kg^?1 fish mass day^?1 for C. nodosa and 40 ± 11 g seagrass fresh mass kg^?1 fish mass day^?1 for Z. noltii (temperature = 16° C). Food‐processing rate in S. salpa did not differ between seagrasses, and there was no evidence of a regulation of processing rate according to food intake. Seagrasses differed substantially in nitrogen content and C:N, with C. nodosa containing the highest nitrogen content and lowest C:N (2·5 ± 0·1% and 14·0 ± 1·0), followed by Z. noltii (2·1 ± 0·1% and 17·0 ± 1·0) and Z. marina (1·4 ± 0·1% and 26·0 ± 2·0). Food‐processing rate in S. salpa and the nutritional value of the seagrasses were not correlated with the observed feeding preference and rate. The study suggests that C. nodosa and Z. marina are less at risk of overgrazing by S. salpa and might thus be preferable to Z. noltii for seagrass restoration in areas with noticeable abundances of this fish.     

毛白杨细胞质抗坏血酸过氧化物酶基因的克隆及表达分析

利用同源克隆技术得到1个毛白杨细胞质抗坏血酸过氧化物酶基因,命名为PcAPX。该基因编码249个氨基酸残基,预测分子量为33.01kD。采用原核表达技术在大肠杆菌中表达并纯化该蛋白并进行酶活性分析,结果表明:重组PcAPX蛋白对抗坏血酸(AsA)和过氧化氢(H2O2)有很高的活性,其对抗坏血酸的米氏常数(Km)和最大反应速度(Vmax)分别为(0.71±0.03)mmol·L-1和(0.41±0.02)mmol·L-1·min-1·mg-1;对过氧化氢的Km和Vmax分别为(0.60±0.21)mmol·L-1和(0.35±0.12)mmol·L-1·min-1·mg-1,表明PcAPX对AsA和H2O2拥有较高的催化底物的能力和催化效率。利用实时定量RT-PCR分析毛白杨PcAPX基因的表达模式,结果表明其在老叶中表达量高于新叶、韧皮部、形成层和根部。该研究结果将进一步促进毛白杨APX基因家族成员参与植物生长调控的研究。     

Australian mulga ecosystems –13C and 15N natural abundances of biota components and their ecophysiological significance

Samples of recently produced shoot material collected in winter/spring from common plant species of mulga vegetation in eastern and Western Australia were assayed for ¹³C and ¹⁵N natural abundance. ¹³C analyses showed only three of the 88 test species to exhibit C₄ metabolism and only one of seven succulent species to be in CAM mode. Non-succulent winter ephemeral C₃ species showed significantly lower mean δ¹³C values (– 28·0‰) than corresponding C₃-type herbaceous perennials, woody shrubs or trees (– 26·9, – 25·7 and – 26·2‰, respectively), suggesting lower water stress and poorer water use efficiency in carbon acquisition by the former than latter groups of taxa. Corresponding values for δ¹⁵N of the above growth and life forms lay within the range 7·5–15·5‰. δ¹⁵N of soil NH₄⁺ (mean 19·6‰) at a soft mulga site in Western Australia was considerably higher than that of NO₃^– (4·3‰). Shoot dry matter of Acacia spp. exhibited mean δ¹⁵N values (9·10 ± 0·6‰) identical to those of 37 companion non-N₂-fixing woody shrubs and trees (9·06 ± 0·5‰). These data, with no evidence of nodulation, suggested little or no input of fixed N₂ by the legumes in question. However, two acacias and two papilionoid legumes from a dune of wind-blown, heavily leached sand bordering a lake in mulga in Western Australia recorded δ¹⁵N values in the range 2·0–3·0‰ versus 6·4–10·7‰ for associated non-N₂-fixing taxa. These differences in δ¹⁵N, and prolific nodulation of the legumes, indicated symbiotic inputs of fixed N in this unusual situation. δ¹⁵N signals of lichens, termites, ants and grasshoppers from mulga of Western Australia provided evidence of N₂ fixation in certain termite colonies and by a cyanobacteria-containing species of lichen. Data are discussed in relation to earlier evidence of nitrophily and water availability constraints on nitrate utilization by mulga vegetation.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.     

Ventilatory and behavioural responses of the marbled sole Pseudopleuronectes yokohamae to progressive hypoxia

This study identified ventilatory and behavioural responses in the marbled sole Pseudopleuronectes yokohamae under experimentally induced progressive decreases in dissolved oxygen (DO) levels. Ventilation frequency showed an increase with decreasing DO levels from normoxia to 2·75 mg O₂ l^?1, followed by a decrease in ventilation frequency at decreased DO levels from 2·00 to 0·75 mg O₂ l^?1. At DO levels below 2·00 mg l^?1, behaviours at the bottom were suppressed, whereas avoidance behaviours increased. A decrease in avoidance behaviours was observed from 1·00 to 0·75 mg O₂ l^?1. Upside‐down reversal and incapacitation at DO levels of 1·00–0·75 mg O₂ l^?1 suggested that sublethal effects on P. yokohamae were induced. The responses observed before the sublethal DO level could be interpreted as an effort to maintain oxygen uptake, reduce routine activities and facilitate avoidance. The observed DO level thresholds that induce behavioural responses, in addition to sublethal effects, indicate hypoxia‐tolerance that is important for understanding the effects of hypoxia on coastal ecosystems.