Early development of milkfish: effects of salinity on embryonic and larval metabolism, yolk absorption and growth

During embryogenesis of Chanos chanos , more than half of the yolk was consumed and the majority of it was converted into larval tissue. Salinity affected both yolk absorption and embryonic and larval growth. Larvae hatched in 20% had larger yolk reserves but were smaller and grew more slowly than larvae in 35 and 50%. Larvae hatched in 35 and 50% had equal amounts of yolk but those from 35% were larger. Oxygen consumption rates increased during development (from 0.06 ± 0.01 μl O₂ egg^–1 h^–1 by blastulae to 0.37 ± 0-01 μl O₂ egg^–1 h^–1 by prehatch embryos and 0–43 ± 0–03 μl O₂ larva ^–1 h ^–1 by newly-hatched larvae) and were significantly affected by salinity. Eggs and yolk-sac larvae incubated in 35% consumed more oxygen than those in the low and high salinities. Salinity affected both the rate and pattern of yolk utilization but salinity-related differences in metabolism, yolk absorption, and growth were not related directly to the osmotic gradient. Low salinity retarded yolk absorption while high salinity reduced yolk utilization efficiencies. Differences in oxygen consumption rates were probably related to variations in the relative amounts of metabolically active embryonic and larval tissue and/or higher activity levels rather than differential osmoregulatory costs. 35% is probably the most suitable salinity for incubation and larval rearing of milkfish.     

Effects of development, temperature and salinity on metabolism in eggs and yolk-sac larvae of milkfish, Chanos chanos (Forsskål)

Oxygen uptake rates and yolk-inclusive dry weiGhts were measured during the egg and yolk-sac larval stages of milkfish, Chanos chanos (Forsskal). Oxygen uptake by eggs and yolk-sac larvae was measured to assess the effects of four salinities (20,25,30,35 ppt) at 28°C. The effects of three temperatures (23,28,33°C) on oxygen uptake by yolk-sac larvae were determined at a salinity of 35 ppt. Dry weights were measured throughout embryonic development at 28°C and the yolk-sac stage at 23.28 and 33°C.
Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07±0.03 to 0.40 ± 03 μl O₂ egg ⁻¹ h ⁻¹;blastula to prehatch stage). Larval oxygen uptake did not change with age but was affected by rearing temperature (0.33 ± 0.08, 0.44 ± 0.07 and 0.63 ± 0.13 μl O₂ larva ⁻¹ h⁻¹ at 23, 28 and 33°C, respectively; Q₁₀= 1.93). Acute temperature changes from 28 to 33°C caused significant increases in oxygen uptake by embryos (Q ₁₀= 1.69–3.58) and yolk-sac larvae (Q ₁₀=2.55). Salinity did not affect metabolic rates.
Dry weight of eggs incubated at 28°C decreased 13% from fertilization to hatching. Incubation temperatures from 23–33°C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q ₁₀= 2.25).     

Development of bile salt-dependent lipase in larval turbot

Pancreatic bile salt-dependent lipase (BSDL) was present with 0·5 μg BSDL larva⁻¹ from hatching in turbot larvae. The enzyme content increased during the yolk sac phase to 1·1 μg BSDL larva⁻¹. This suggests that larval turbot are able to digest lipids from the start of exogenous feeding. The BSDL synthesis was stimulated first by food about 5 days after the onset of first feeding. The content per larva increased exponentially in fed larvae to 20 μg BSDL larva⁻¹ on day 23 after hatching and decreased in starved larvae. In contrast, the specific content decreased during the first feeding phase, meaning that smaller larvae had a higher content of enzyme related to their biomass than did bigger larvae.     

Ascorbic acid and α-tocopherol levels in larvae of Atlantic halibut before and after exogenous feeding

Ascorbic acid (AA) and α-tocopherol (α-TOH) levels in whole Atlantic halibut larvae were constant during the yolk sac stage at 170 and 131 ng individual⁻¹, respectively. At hatching c . 80% of the AA and 97% of the α-TOH were contained within the yolk-sac compartment. With development, AA and α-TOH levels in the yolk decreased, at different rates. At first feeding (at 200 day degrees post hatch, D°PH)>95% of AA but <30% of α-TOH in the yolk at hatching had been transferred to the larval body. Transfer of α-TOH was completed at 360 D°PH, when the yolk was completely absorbed. The plankton offered to the larvae at first feeding (chiefly Temora longicornis ) contained 756 μg g⁻¹ AA and 120 μg g⁻¹α-TOH (dry weight). The AA content increased to 472 ng individual⁻¹ within one week after first feeding, while it declined slightly in unfed larvae. In fed larvae the AA content reached c . 3500 ng individual⁻¹ at 580 D)PH. The α-TOH content increased only slightly in the first week of feeding (206 to 431 D°PH), but then increased to > 800 ng individual⁻¹ at 483 D°PH.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

The effect of light intensity and spectrum on the incidence of first feeding by larval haddock

Under full–spectrum white light, feeding success of haddock Melanogrammus aeglefinus first feeding larvae, as measured both by proportion of larvae feeding and mean prey consumed, peaked at 1·7-18 μmol s^-1 m^-2. Feeding was significantly reduced at lower and higher intensities. A similar result was observed for larvae feeding under blue (470 nm) light, with significantly greater feeding success at intermediate light intensity (1·8 μmol s^-1 m^-2). When different light qualities were compared, larvae had significantly greater feeding success when exposed to blue (470 nm) light than either full-spectrum white or green (530 nm) light. Haddock larvae were capable of prey capture under all light treatments tested, indicating a necessary degree of adaptive flexibility in feeding response. The results are consistent with predisposition of haddock larvae to optimal feeding in a visual environment comparable with open ocean nursery grounds. Information on the impact of light on haddock first feeding can be incorporated into models of larval growth, survival, year-class strength and recruitment, and assist in developing husbandry protocols to maximize larval survival in aquaculture.     

Effects of cadmium chloride on the development of rainbow trout Oncorhynchus mykiss early life stages

The sub-chronic (28–56 days) effects of exposure to low concentrations of cadmium (Cd; 0·05, 0·25, 0·50 and 2·50 μg l⁻¹) shortly following fertilization on embryos, larvae and juvenile rainbow trout Oncorhynchus mykiss were examined. Premature hatching occurred at lower concentrations (0·05 and 0·25 μg l⁻¹ Cd), however, delayed hatching was seen in the 2·50 μg l⁻¹ Cd group, with >90% of hatching occurring on the last day of the hatching period. Larval growth was negatively affected by Cd exposure in a concentration-dependent manner. Larvae exposed to 2·50 μg l⁻¹ Cd were 13·9 ± 0·8% shorter in total length ( L _T) and weighed 22·4 ± 3·5% (mean ± s . e .) less than controls at the end of the exposure period. Plasma sex steroid concentrations (oestradiol in juvenile females and 11-ketotestosterone in juvenile males) were elevated (four- to 10-fold over controls) in exposed fish in both males and females, following 28 days of exposure to 0·05, 0·25 and 0·50 μg l⁻¹ Cd, respectively. These results suggest that environmentally realistic concentrations (in the μg l⁻¹ range) of Cd can affect the development of O. mykiss impacting embryos, larvae and juvenile fish.     

Quantitative Ultrastructural Investigations on Synaptogenesis in the Cerebellum and the Optic Tectum of Light-Reared and Dark-Reared Rainbow Trout (Salmo gairdneri Rich.)

The morphogenetic differentiation of synapses in the cerebellum and the optic tectum of darkand light- reared rainbow trout was investigated at critical stages of development. During normal differentiation the cerebellum is characterized by the appearance of 'indented', spinelike synapses. This type of synapses increases with age and prevails from day 60 on. At the same time the number of 'flat' synapses decreases. In the cerebellum the highest synaptic density (123 ± 12 synapses/1,000 μm²) is reached 30 days after hatching when the larvae begin to swim. The optic tectum is characterized by a preponderance of flat synapses in early postnatal and adult life; maximal synaptic density (66 ± 5 synapses/1,000 μm²) is reached 60 days after hatching when the larvae have reached optimal visual acuity.
Light deprivation causes a considerable and significant reduction in the number of synapses per unit area in the cerebellum and the optic tectum. The length of synaptic contacts do not change. If light-deprived, the density of synaptic vesicles decreases significantly in the optic tectum of a 25-day-old trout (74 ± 3 instead of 132 ± 7 vesicles/μm²). In the cerebellum this effect is absent.     

Hydrogen cyanide release during feeding of generalist and specialist lepidopteran larvae on a cyanogenic plant, Passiflora capsularis

Abstract.  The hydrogen cyanide-based interaction of a strongly cyanogenic plant, Passiflora capsularis , and larvae of two insect herbivores, a generalist ( Spodoptera frugiperda ) and a specialist ( Heliconius erato ), is examined in terms of the combined kinetics of the feeding process and the simultaneous hydrogen cyanide (HCN) liberation, as compared with the natural kinetics of hydrogen cyanide evolution by plant-leaf tissue. There are marked differences in acceptance of P. capsularis by third-instar larvae of specialist and generalist species. The former, H. erato , display a parsimonious ingestion rate of 0.74 ± 0.15 mg (fresh weight) min⁻¹ comprising 18% active feeding time, whereas S. frugiperda larvae show a more erratic and restrained feeding involving 4% of the time at 0.45 ± 0.14 mg min⁻¹. These S. frugiperda larvae ingest 124.4 ± 8.3 mg (fw) of the non-cyanogeneic Spinacia oleracea leaves in 24 h compared with only 74.7 ± 20.1 mg of P. capsularis in the same period. The total hydrogen cyanide released naturally from wild specimens of P. capsularis plants is in the range 326–3901 μg g⁻¹. Hydrogen cyanide evolution from macerated P. capsularis leaves takes place along a hyperbolic function with time and initial velocities of cyanide evolution are a linear function of total hydrogen cyanide. When feeding on P. capsularis leaves, H. erato releases only a minor fraction relative to total hydrogen cyanide (0.09%) and to the anticipated cyanide from the initial velocity (7%). By contrast, S. frugiperda evokes 5.8-fold more than the anticipated hydrogen cyanide release from the plant. The findings are interpreted as diverging strategies by generalist and specialist insects in the utilization of hydrogen cyanide in cyanogenic plants.     

The effects of temperature, body mass and feeding on metabolic rate in the tsetse fly Glossina morsitans centralis

Abstract.  Metabolic rate variation with temperature, body mass, gender and feeding status is documented for Glossina morsitans centralis . Metabolic rate [mean ± SE; VCO₂= 19.78 ± 3.11 μL CO₂ h⁻¹ in males (mean mass = 22.72 ± 1.41 mg) and 27.34 ± 3.86 μL CO₂ h⁻¹ in females (mean mass = 29.28 ± 1.96 mg) at 24 °C in fasted individuals] is strongly influenced by temperature, body mass and feeding status, but not by gender once the effects of body mass have been accounted for. A significant interaction between gender and feeding status is seen, similar to patterns of metabolic rate variation documented in Glossina morsitans morsitans . Synthesis of metabolic rate-temperature relationships in G. m. centralis , G. m. morsitans and Glossina pallidipes indicate that biting frequency as well as mortality risks associated with foraging will probably increase with temperature as a consequence of increasing metabolic demands, although there is little evidence for variation among species at present. Furthermore, metabolic rate–body mass relationships appear to be similarly invariant among these species. These data provide important physiological information for bottom-up modelling of tsetse fly population dynamics.     

Cutaneous taste buds in cod

The distribution of cutaneous taste buds was determined quantitatively in larvae, juveniles and young adults of cod, using scanning electron microscopy. Changes in these distributions associated with development were followed in laboratory reared fish. Taste buds were first seen on the snout and lips of cod at a total length of 8 mm, and on the barbel at a length of 22 mm. The highest taste bud densities were seen at a length of around 90 mm, and subsequently declined on the barbel and pelvic fins with further growth. In these late 0-group fish, mean taste bud densities over much of the head, e.g. throat, dentary and sides of the snout were <100 mm⁻². On the tip of the snout and the lips, mean densities were in the region of 350–400 mm⁻², while on projecting parts of the fish, especially the barbel, anterior naris flap and extremities of the fins, spot densities occasionally exceeded 1000 mm⁻² at some sites. Mean taste bud diameter increased rapidly from 2.23μ± 0.35 μm (S.D.) at a length of 22 mm to 7.19 ± 0.23 μm at 90 mm length, with a much slower increase to about 8 μm associated with a further doubling in body length. These changes indicate a phase of rapid proliferation and growth in size of cutaneous taste buds in the period preceding the adoption of a benthic habit in their first summer. The presence of high taste bud densities on the barbel and pelvic fins in particular appears to correlate with the known feeding behaviour of cod.     

μ-Opioid Receptor Stimulation of Inositol (1,4,5)Trisphosphate Formation via a Pertussis Toxin-Sensitive G Protein

Abstract: The cellular mechanisms underlying opioid action remain to be fully determined, although there is now growing indirect evidence that some opioid receptors may be coupled to phospholipase C. Using SH-SY5Y human neuroblastoma cells (expressing both μ-and δ-opioid receptors), we demonstrated that fentanyl, a μ-preferring opioid, caused a dose-dependent (EC₅₀= 16 n M ) monophasic increase in inositol (1,4,5)trisphosphate mass formation that peaked at 15 s and returned to basal within 1–2 min. This response was of similar magnitude (25.4 ± 0.8 pmol/mg of protein for 0.1 μ M fentanyl) to that found in the plateau phase (5 min) following stimulation with 1 m M carbachol (18.3 ± 1.4 pmol/mg of protein), and was naloxone-, but not naltrindole-(a δ antagonist), reversible. Further studies using [ d -Ala², MePhe⁴, Gly(ol)⁵]enkephalin and [ d -Pen^2,5]enkephalin confirmed that the response was specific for the μ receptor. Incubation with Ni²⁺ (2.5 m M ) or in Ca²⁺-free buffer abolished the response, as did pretreatment (100 ng/ml for 24 h) with pertussis toxin (control plus 0.1 μ M fentanyl, 26.9 ± 1.5 pmol/mg of protein; pertussis-treated plus 0.1 μ M fentanyl, 5.1 ± 1.3 pmol/mg of protein). In summary, we have demonstrated a μ-opioid receptor-mediated activation of phospholipase C, via a pertussis toxin-sensitive G protein, that is Ca²⁺-dependent. This stimulatory effect of opioids on phospholipase C, and the potential inositol (1,4,5)trisphosphate-mediated rises in intracellular Ca²⁺, could play a part in the cellular mechanisms of opioid action.     

Relationships between biovolume and carbon and nitrogen content of bacterioplankton

Abstract Cell volume, carbon and nitrogen content were determined for bacteria grown in batch cultures in water samples collected at five localities in western Florida, USA. Cultures were set up by inoculating 0.2 μm filtered water with 2.5 to 7.0% of 1.0 μm filtered water. Biovolumes of the bacteria were measured by epifluorescence photomicrography. Bacterial carbon and nitrogen contents were determined with a CHN analyser. During incubations, bacterial volumes doubled from 0.070±0.037 μ m³(mean ± S.E.) to 0.153 ± 0.036 μ m³ at early stationary phase. Bacterial C:N ratios ranged between 2.8 and 10.3, with a mean of 6.5, and were inversely correlated with cell volumes. Conversion factors for volume to carbon and nitrogen content were relatively high and variable, ranging from 0.21 to 161 pg C μm⁻³ (mean: 0.72 pg C μm⁻³) and from 0.05 to 0.25 pg N μm⁻³ (mean: 0.12 pg N μm⁻³). Small cells contained more C and N per unit volume than did large cells. The data suggested that biovolume to biomass conversion factors may be higher than previously thought and may be highly variable both temporally and geographically.     

Oxygen consumption in Oreochromis niloticus (L.) in relation to development, salinity, temperature and time of day

Oxygen consumption of Oreochromis niloticus at different stages of development was studied in relation to salinity, temperature and time of day, using a Warburg apparatus. The oxygen consumption of newly hatched (0–14 h) larvae was 3.40 μl O₂ larva⁻¹ h⁻¹, of older yolk sac larvae 10.09 μl O₂ larva⁻¹ h⁻¹, and of one-month-old fry 32.99 μl O₂ larva⁻¹ h⁻¹. The QO₂ values showed a decrease with development and growth, ranging from 21.2–26.0 μl O₂ mg⁻¹ h⁻¹ in newly hatched larvae to 2.97 μl mg⁻¹ h⁻¹ in one-month-old fry. Changes in oxygen consumption occurred with salinity, the highest being at 17%o. Active larvae (12-24 mm T.L.) showed a doubling of consumption with a 10° C rise in temperature, and their Q₁₀ factor increased from 2.25 to 3.43 with increasing size. Day-old yolk-sac larvae, late yolk-sac larvae (5 days old) and fry of 12 14 mm length all showed a depression in oxygen consumption at midnight followed by a dawn rise.     

Carbon dioxide-induced changes in beech foliage cause female beech weevil larvae to feed in a compensatory manner

The phenology of Fagus sylvatica was unaffected by exposure to an atmosphere of elevated CO₂ (600 μL L^-1) after two years of fumigation. Non-significant changes in nitrogen and phenolic content of the leaves decreased the nutritional status of beech for female larvae in elevated CO₂ such that they responded by eating in a compensatory manner; males were unaffected. Rates of development, mortality and adult biomass of Rhynchaenus fagi were no different from those in ambient CO₂ concentrations (355 μL L ^-1). It is possible that, with the changes in leaf chemistry affecting the females, fecundity will be altered, with important consequences for populations of beech weevil.     

Symbiotic N2 fixation in a high Alpine grassland: effects of four growing seasons of elevated CO2

1. Increasing carbon dioxide concentration (E: 680 μl CO₂ litre^–1 vs ambient, A: 355 μl CO₂ litre^–1) around late-successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992–1995) had no detectable effect on symbiotic N₂ fixation in Trifolium alpinum —the sole N₂-fixing plant species in these communities (74 ± 30 mg N m^–2 year^–1, A and E plots pooled).
2. This result is based on data collected in the fourth growing season showing that elevated CO₂ had no effect on Trifolium above-ground biomass (4·4 ± 1·7 g m^–2, A and E plots pooled, n = 24) or N content per unit land area (124 ± 51 mg N m^–2, A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N₂ fixation (%Ndfa: 61·0 ± 4·1 across A and E plots) estimated using the ¹⁵N dilution method.
3. Thus, it appears that N inputs to this ecosystem via symbiotic N₂ fixation will not be dramatically affected in the foreseeable future even as atmospheric CO₂ continues to rise.     

Monoamine oxidase activity in kidney and heart of Piaractus mesopotamicus (Holmberg)

The values of Michaelis–Menten constant (K_M) and maximum velocity (V_MAX) for kidney and heart monoamine oxidase (MAO) from pacu Piaractus mesopotamicus were determined. The mean ± s . e . K_M values were 17·28 ± 2·27 μM for kidney and 15·38 ± 1·86 μM for heart. MAO activities were 111·60 ± 3·25 and 15·12 ± 0·30 nmols min⁻¹ g⁻¹ of wet tissue for kidney and heart, respectively. In addition, MAO inhibitory studies in these two tissues indicate that this enzyme may be a different isoform of MAO.     

THE PROLIFERATION OF LYMPHOID CELLS IN GUINEA-PIG BONE MARROW

A double isotope DNA labelling method has been used to determine the duration of DNA synthesis (S) in bone marrow lymphoid cells classified by their nuclear diameters in smears. Incorporation of ³H-thymidine was confined almost entirely to marrow lymphoid cells of 8·0-15·0 μm nuclear diameter (large lymphoid cells). After exposure to ³H-thymidine in vivo and ¹⁴C-thymidine 40-104 min later in vitro , the proportion of cells labelled with ³H alone to those labelled with ¹⁴C(±³H) in radioautographic smears, plotted against time indicated the efflux from S per hour. Collectively, 28·3 ± 1·1% of all large lymphoid cells were in S and the efflux from S was 15·1% per hour. With decreasing cell size (nuclear diameter) the efflux fell progressively from 28·3% per hour (11·0 μm) to 9·2% per hour (8·0-8·9 μm) and the proportion of cells in S declined from 54·9 ± 2·3% to 14·8 ± 1·6%. Influx into S, measured in vitro by reversing the sequence of isotopes, closely resembled the corresponding efflux values in vivo relative to cell size. Most DNA synthesizing marrow large lymphoid cells belonged to a subgroup with deeply basophilic cytoplasm. The results demonstrate that basophilic large lymphoid cells in the marrow are actively proliferating and have a mean S phase duration of 6·6 hr. The largest marrow lymphoid cells (11·0 μm) proliferate most rapidly (S phase, 3·5 hr; maximum cell cycle time, 6·4 hr) while S duration is prolonged progressively to 10·9 hr for the smaller cells (8·0-8·9 μm).     

Oxygen control prevents denitrifiers and barley plant roots from directly competing for nitrate

Abstract Two denitrifying bacteria ( Pseudomonas chlororaphis and P. aureofaciens ) and a plant (barley, Hordeum vulgare ) were used to study the effect of O₂ concentration on denitrification and NO₃⁻ uptake by roots under well-defined aeration conditions. Bacterial cells in the early stationary phase were kept in a chemostat vessel with vigorous stirring and thus a uniform O₂ concentration in the solution. Both Pseudomonads lacked N₂O reductase and so total denitrification could be directly measured as N₂O production.
Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O₂ saturation (0.14 μM O₂) and was totally inhibited at 0.04% O₂ saturation (0.56 μM O₂). In this well-mixed system denitrification was 10-times more oxygen sensitive than stated in earlier reports. Uptake of nitrate by plants was measured in the same system under light. The NO₃⁻ uptake rate decreased gradually from a maximum in 21% O₂-saturated medium (air saturated) to zero at 1.6% O₂ saturation (22.4 μM O₂). Owing to the very different non-overlapping oxygen requirements of the two processes, direct competition for nitrate between plant roots and denitrifying bacteria cannot occur.