Hemolymph Glucose Concentration Research Articles

CIRCADIAN MODULATION OF CRUSTACEAN HYPERGLYCEMIC HORMONE IN CRAYFISH EYESTALK AND RETINA

Previous studies suggested the retina could be a putative locus of daily crustacean hyperglycemic hormone (CHH) secretion, as it possesses its own metabolic machinery and is independent of the well-known CHH eyestalk locus responsible for the circadian secretion of this peptide. However, it has been proposed that hemolymph glucose and lactate concentrations play a dual role in the regulation of CHH in crayfish. To elucidate the temporal relationship between these two different CHH production loci and to examine their relationship with glucose regulation, we investigated the expression of CHH daily and circadian rhythms in the eyestalk and retina of crayfish using biochemical methods and time series analysis. We wanted to determine whether (1) putative retina and eyestalk CHH rhythmic expressions are correlated and if the oscillations of the two metabolic products of lactate and glucose in the blood due to CHH action on the target tissue correlate, and (2) retina CHH (RCHH) and the possible retinal substrate glycogen and its product glucose are temporally correlated. We found a negative correlation between daily and circadian changes of relative CHH abundance in the retina and eyestalk. This correlation and the cross-correlation values found between eyestalk CHH and hemolymph and glucose confirm that CHH produced by the X-organ sinus gland complex is under the previously proposed dual feedback control system over the 24 h time period. However, the presence of both glycogen and glucose in the retina, the cross-correlation values found between these parameters and hemolymph lactate and glucose, as well as RCHH and hemolymph and retina metabolic markers suggest RCHH is not under the same temporal metabolic control as eyestalk CHH. Nonetheless, their expression may be linked to common rhythms-generating processes. (Author correspondence: mlfm@hp.fciencias.unam.mx; mfajul@gmail.com)

Physiological condition and intraspecific agonistic behaviour in Carcinus maenas (Crustacea: Decapoda)

This study tested the hypothesis that physiological condition is a key factor in determining the outcome of intraspecific agonistic interactions for food in male shore crabs Carcinus maenas of equal body size . Physiological condition was manipulated by maintaining crabs under different food regimes (using the cockle Cerastoderma edule) in combination with exposure to a sub-lethal concentration (200 µg L − 1 ) of pyrene, a polyaromatic hydrocarbon (PAH). After 14 days, crabs were used in staged agonistic interactions, whereby, an unexposed crab was paired with a pyrene-exposed crab from the same dietary regime, using a whole cockle ( C. edule; 0.35 ± 0.05 g wet weight) as the limited resource. Agonistic behaviour was recorded over 15 min, then crabs were separated and their energetic status was assessed based on haemolymph glucose and lactate concentrations. Fully-fed (fed 2 g of food each day) crabs had significantly higher concentrations of circulating glucose and lactate compared to starved (no food) and diet-restricted crabs (fed 1 g of food on alternate days after an initial starvation period of 3 days). In fully-fed crabs, blood glucose concentrations were lower, on average, in individuals exposed to pyrene. Physiological condition had no significant effect on most behavioural measures used to describe the agonistic behaviour in crabs (e.g. number of fights, number of wrestles, fight duration, wrestle duration, contest duration and contest intensity); however, starved pyrene-exposed individuals had significantly higher resource possession (defined as % time in possession of the resource) and significantly decreased inter-bout intervals (defined as time spent away from an opponent after an agonistic encounter) compared with starved unexposed individuals. Results show that a reduced physiological condition (‘lower’ RHP) in starved contaminant-exposed crabs resulted in an unexpected increased competitive ability over starved unexposed individuals.

Recovery by the Norway lobster Nephrops norvegicus (L.) from the physiological stresses of trawling: Influence of season and live-storage position

Live Norway lobsters ( Nephrops norvegicus L.) were trawled at depths of 30 to 55 m off the coast of Jutland (Denmark) in late winter (March) and in summer (August) in 2006. Water temperatures at the bottom and surface of the sea were 7 °C and 2 °C during the winter, and 12 °C and 21 °C in the summer, respectively. The recovery of specific physiological and metabolic variables from the intense stresses associated with capture (trawling and air-exposure during sorting) was followed in seawater at 5 °C in winter or 18 °C in summer. Recovery was compared in lobsters held individually in two different live-storage positions, either resting vertically on the tail or sitting horizontally. In winter, many animals were alive when brought on board and approximately 86% were still alive at the end of experimentation (96 h). In summer very few animals were alive when brought on board and, of these, approximately 95% were dead at 24 h. When compared with values measured in laboratory controls, the stresses of capture elicited very high haemolymph lactate contents in both seasons, although levels recovered within 24 h. Trawling also caused very high haemolymph glucose concentrations, which differed with season. In winter, haemolymph glucose was elevated for 24 h to levels significantly higher than in summer. In summer, glucose had returned to control levels by 4 h. At 4 h after trawling, haemolymph O 2 status was not markedly influenced in either season, but there were significant disturbances of acid-base status. In winter, a potential metabolic lactic acidosis was compensated by a marked respiratory alkalosis, with significantly increased haemolymph pH and decreased CO 2 total content and partial pressure. These effects disappeared gradually over 96 h. Summer lobsters showed combined metabolic and respiratory acidosis at 4 h, although this had recovered to control values in the small number of survivors sampled at 24 h. The capture stresses elicited very high haemolymph crustacean hyperglycaemic hormone (CHH) titres, significantly higher in summer than in winter. In winter, CHH titre had declined significantly at 24 h, whereas it exhibited a further significant increase at 24 h in summer. Live-storage position had no significant effect on survival or recovery from capture stresses in either season. The results demonstrate that Nephrops were much more stressed by trawling at high summer temperatures and had difficulty recovering from this, with pronounced negative effects on their survival, irrespective of their live-storage position.

Identification of digestible carbohydrate sources for inclusion in formulated diets for juvenile spiny lobsters, Jasus edwardsii

Carbohydrates are a key ingredient in crustacean formulated diets because of their potential to greatly improve production efficiency. For the culture of spiny lobsters where daily food intake is limited, carbohydrates have the potential for delivering a low cost source of energy that could spare protein for growth. Therefore, the digestibility of different carbohydrate sources including refined sugars, mussel glycogen, algal polysaccharides, carboxymethyl cellulose (CMC) and starches (i.e., native, dextrinised, gelatinised) were assessed in juvenile spiny lobster (30–60 g). This was done by measuring the rate of carbohydrate hydrolysis in vitro using enzyme homogenates and postprandial haemolymph glucose concentrations following ingestion of semi-purified diets containing different carbohydrate levels and sources. Fresh mussel gonads and a practical formulated diet were also included for comparison. Storage polysaccharides (i.e., gelatinised starches, dextrin, mussel glycogen) and the structural polysaccharide CMC were the best digested carbohydrate sources in vitro. CMC was more digestible than the algal polysaccharides, agar and alginate, and therefore may have potential as a binding agent in formulated diets for J. edwardsii. The poor hydrolysis of sucrose and trehalose suggests that their use as an energy source might be limited in J. edwardsii. Native wheat starch was the best digested among the various plant starches tested. Gelatinisation of starches markedly improved their digestibility suggesting that pre-treatment of the dietary starch source would have a beneficial influence on the digestibility of diets for J. edwardsii. Consumption of the semi-purified diets (i.e., 1% BW) containing the digestible starch sources (i.e., 27% dry weight), as well as the practical diet, resulted in high haemolymph glucose concentrations (> 5 mmol l − 1 ) and a prolonged hyperglycaemic response (> 24 h) suggesting that these carbohydrate sources are well digested and absorbed, but possibly poorly utilised. In contrast, the fresh mussel gonad diet (i.e., 27% glycogen by dry weight) appeared to be better utilised (reduced glycaemia after 12 h). A lower inclusion level (i.e., 7%) of gelatinised maize starch reduced the peak (1.87 mmol l − 1 ) and extent (12 h) of the glycaemic response. Using lower inclusion levels (< 27%) of the rapidly digested starches (i.e., gelatinised, dextrinised) identified in this study, or incorporating digestible carbohydrate sources resulting in slower appearance of haemolymph glucose (i.e., native wheat starch, CMC), in formulated diets may have the potential to improve their utilisation for growth of juvenile spiny lobsters.

Catch me in winter! Seasonal variation in air temperature severely enhances physiological stress and mortality of species subjected to sorting operations and discarded during annual fishing activities

Several studies have considered the direct and indirect effects of demersal trawling on discarded species in terms of sublethal damages, survival, and stress due to the fishing processes. Nevertheless the effects of air temperature on the physiological stress and the survival of species during sorting operations were only marginally explored. This factor could be particularly important in the context of sustainable fisheries at temperate latitudes where the seasonal variation of air temperature can be particularly pronounced. In this study the seasonal effects of rapido trawling on the non-target species Liocarcinus depurator (Portunidae) in the Northern Adriatic Sea (Mediterranean Sea) have been compared by applying survival tests and considering the unbalance in metabolites’ concentration as indicators of physiological stress. Results showed consistently higher mortalities during exposure to air in summer (temperature: 28°C), which reached about 96% in 20 min, compared to winter (temperature: 9°C) when only 2% of individuals died. Furthermore trawled and emersed crabs showed significant increase of hemolymph ammonia, lactate, and glucose concentrations as effects of extreme exercise and suffocation, which was more prominent during summer, suggesting that air temperature can play an important role in determining non-target species survival.

Haemolymph glucose concentrations of juvenile rock lobsters, Jasus edwardsii, feeding on different carbohydrate diets

Postprandial changes in haemolymph glucose concentration ([Glc] H) were measured in 4-day-fasted juvenile intermoult spiny lobsters, Jasus edwardsii, provided with meals composed of glycogen, maltose, sucrose, glucose, or fructose in a gelatine base, or with gels of the algal glycans agar, alginate and carrageenan. Baseline [Glc] H was 0.61±0.02 mmol L −1. After consumption of glycogen, maltose or sucrose, [Glc] H approximately doubled, peaked after 3 h and returned to baseline between 12 and 24 h. Glucose and fructose meals were followed by periods of sustained hyperglycaemia lasting more than 24 h (peaking at ∼2.5 times baseline at 6 and 3 h respectively). Suggested explanations for augmented hyperglycaemic responses to glucose and fructose are: 1) these monosaccharides by-passed contact digestion and absorption in the R-cells of the digestive gland, directing them away from storage and toward transepithelial scavenging routes; or 2) glucose and fructose directly elicited release of crustacean hyperglycaemic hormone via a chemosensory reflex. Agar and alginate induced significant postprandial glycaemic responses, consistent with reports of carbohydrases in this species and indicating their potential for inclusion in artificial diets as both binders and energy sources. Carrageenan, a highly sulphated galactan, did not produce a glycaemic response. The measurement of glycaemic responses is a quick method of obtaining nutritional information on carbohydrates considered for inclusion in formulated diets prior to lengthy growth trials.

Reference ranges for hemolymph chemistries from Elliptio complanata of North Carolina

Hemolymph chemistries may be useful nonlethal measures of bivalve health. The prognostic value of hemolymph, however, depends on a comparison of chemistry results to reference ranges from healthy individuals. Currently, knowledge of expected hemolymph values in healthy and unhealthy freshwater mussels is extremely limited. The purpose of this study was to develop a set of reference ranges for clinical evaluation of hemolymph from a freshwater mussel species common to southeastern USA. We collected hemolymph from 380 Elliptio complanata from 19 apparently healthy populations from northwest of Raleigh, North Carolina, during May through July 2001. We present reference ranges for hemolymph parameters ammonia, glucose, calcium, magnesium, phosphorus, aspartate aminotransferase (AST), bicarbonate, protein and cell count, and for tissue glycogen. We compare the subpopulations of mussels from regions with an agricultural riparian buffer to those surrounded predominantly by forested lands. We further present correlations noted between hemolymph chemistries and physical or physiologic parameters. The only statistically significant differences between populations contiguous to agricultural and forested lands were in hemolymph calcium and glucose concentrations. Other statistically significant correlations identified were between gravidity and hemolymph protein concentration and tissue glycogen content, as well as between gravidity and parasite burden, and between shell length and hemolymph glucose, AST, calcium and bicarbonate concentrations. The results of this study will aid the interpretation of health measures from populations of E. complanata of similar geographic and seasonal origin.

Carbohydrate metabolism in the central nervous system of the megalobulimus oblongus snail during anoxia exposure and post‐anoxia recovery

The effects of anoxic exposure and the post-anoxia aerobic recovery period on carbohydrate metabolism in the central nervous system (CNS) of the land snail Megalobulimus oblongus, an anoxia-tolerant land gastropod, were studied. The snails were exposed to anoxia for periods of 1.5, 3, 6, 12, 18, or 24 hr. In order to study the post-anoxia recovery phase, snails exposed to a 3-hr period of anoxia were returned to aerobic conditions for 1.5, 3, 6, or 15 hr. Glycogen and glucose concentrations in the CNS, hemolymph glucose concentration, and glycogen phosphorylase (active form, GPa) activity in the CNS were analyzed. Anoxia does not significantly affect the concentration of CNS glucose but induces hyperglycemia and a reduction of CNS GPa activity. The glycogen concentration was decreased at 12 hr of anoxia; however, by 18 and 24 hr in anoxia, the glycogen content was not significantly different from basal control values. During the post-anoxia period, the reduction in GPa activity and the increased hemolymph glucose concentration induced by anoxia returned to control values. These results suggest that the CNS of M. oblongus may use hemolymph glucose to fulfill the metabolic demands during anoxia. However, the hypothesis of tissue metabolic arrest cannot be excluded.

Effects of starvation on haemolymphatic glucose levels, glycogen contents and nucleotidase activities in different tissues of Helix aspersa (Müller, 1774) (mollusca, gastropoda)

In the present study, the glucose concentration in the haemolymph and glycogen levels were determined in the various body parts of the Helix aspersa snail after feeding lettuce ad libitum and after various periods of starvation. To characterize the effect of starvation on nucleotidase activity, enzyme assays were performed on membranes of the nervous ganglia and digestive gland. Results demonstrated the maintenance of the haemolymph glucose concentration for up to 30 days of starvation, probably due to the consumption of glycogen from the mantle. In the nervous ganglia, depletion of glycogen occurs progressively during the different periods of starvation. No significant changes were observed on ATP and ADP hydrolysis in the membranes of nervous ganglia and no alterations in Ca2+ -ATPase and Mg2+ -ATPase occurred in the membranes of the digestive gland of H. aspersa during the different periods of starvation. Although there were no changes in the enzyme activities during starvation, they could be modulated by effectors in situ with concomitant changes in products/reactants during starvation.

The impact of bleaching on the metabolic contribution of dinoflagellate symbionts to their giant clam host

ABSTRACTBleaching (loss of symbiotic dinoflagellates) is known to significantly decrease the fitness of symbiotic marine invertebrates resulting in reduced growth, fecundity and survival. This report is the first to quantify the effects of bleaching on inorganic carbon (Ci) and ammonium flux, fixation and export of photosynthate to the host, in this case the giant clam Tridacna gigas. The 1998 bleaching event was found to decrease the zooxanthellae population 30‐fold when comparing bleached to non‐bleached clams. This resulted in significant increases in haemolymph Ci and decreases in haemolymph pH and glucose concentration, the predominant photosynthate exported from zooxanthellae in this symbiosis. There was also a decrease in the expression levels of host carbonic anhydrase, an enzyme involved in Ci transport to the zooxanthellae, and although host glutamine synthase levels were unaffected, the clams ability to assimilate ammonium was eliminated in bleached individuals, suggesting that photosynthate from the zooxanthellae is required for ammonium assimilation. In an artificial bleaching experiment haemolymph Ci (r2 = 0.97), pH (r2 = 0.94) and glucose levels (r2 = 0.95) were correlated to zooxanthellae numbers during both bleaching and recovery. Recovery of the zooxanthellae population, was enhanced four‐fold by the addition of organic and inorganic nutrients, as were related haemolymph characteristics. These results highlight the profound physiological changes that occur in symbiotic organisms during and after a bleaching event.

Effect of temperature on hemolymph lactate and glucose concentrations in spiny lobster Panulirus interruptus during progressive hypoxia

Some metabolic fuels in hemolymph samples from the sinuses at the base of the third walking leg (pre-branchial blood) and from the cardiac sinus (post-branchial blood) in the red lobster, Panulirus interruptus, were evaluated during normoxia, hypoxia, and at the critical oxygen point ( P cr) at two temperatures of acclimatization. Three-way ANOVA indicated a significant effect of oxygen saturation R(6140)=19.84 in metabolic fuel concentrations. Lactate varied from 0.01 to 0.29 mg/ml at 20 °C, from 0.02 to 0.29 mg/ml at 27 °C, and increased significantly during hypoxia ( P<0.05). Glucose varied from 0.10 to 0.27 mg/ml at 20 °C, from 0.13 to 0.33 mg/ml at 27 °C, and increased with temperature. Proteins varied from 80.78 to 119.99 mg/ml at 20 °C and from 82.99 to 130.30 mg/ml at 27 °C.

Carbohydrate metabolism during anoxia and post-anoxia recovery in Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets

We assessed the effects of anoxia exposure and recovery on glycogen synthesis and mobilization, glucose uptake, and on the enzymes that control carbohydrate metabolism in the hepatopancreas of Chasmagnathusgranulata crabs receiving either a carbohydrate-rich (HC) or a high-protein diet (HP). In both dietary groups, anoxia led to a reduction in glucose uptake and in glycogen synthesis, and to an increase in hepatopancreas glycogen mobilization and in hemolymph glucose concentration. During the first 4 h of exposure to anoxia, total glycogen phosphorylase (GPT) and a form activity increased in HP and HC crabs, leading to a decrease in hepatopancreas glycogen concentration. During recovery, HP and HC crabs rapidly restored the hemolymph glucose levels to pre-anoxia concentrations. In HC crabs, incorporation of 14C from glucose into glycogen increased gradually after 12 h in normoxia, leading to restoration of glycogen concentration. Also during recovery, the ratio of glycogen synthase I (GSI) to glycogen phosphorylase a (GPa) increased in the HC group. In turn, recovering HP crabs had two peaks of glycogen synthesis, related with two peaks in the ratio of GSI to GPa. Consequently, no mobilization of 14C-glycogen occurred in recovering HP animals. Anoxia in C.granulata induces a marked decrease in the synthesis of carbohydrate reserves that is accompanied by an increase in glycogen mobilization and in circulating glucose levels. During the recovery period, there is an activation of endergonic processes which cause a decrease in hemolymph glucose levels. In C.granulata, glycogen metabolism seems to be controlled by the ratio of the GSI form to the GPa form. In field conditions, theses changes in the metabolic pattern may result from environmental PO2 availability. In the winter, C.granulata stays in its holes, where environmental PO2 falls to zero. The carbohydrate or protein content of the diets administrated to the crabs seem to induce different metabolic adjustments during anoxia and recovery.

Fat body fructose-2,6-bisphosphate content and phosphorylase activity correlate with changes in hemolymph glucose concentration during fasting and re-feeding in larval Manduca sexta

Fasting of second-day fifth instar larval Manduca sexta leads to a rapid decrease in hemolymph glucose concentration from 3.39±0.29 to 0.33±0.06 mM in 1 h, along with a decrease in the fructose-2,6-bisphosphate content in the fat body (from 5.92±0.31 to 2.80±0.47 nmol fructose-2,6-bisphosphate/g fat body in 3 h) and activation of fat body glycogen phosphorylase (from 16% to 55–65% phosphorylase a). During re-feeding an increase in the glucose level in the hemolymph was observed (from 0.36±0.05 to 3.91±0.36 mM in 3 h), along with an increase in the fructose-2,6-bisphosphate level in the fat body (from 2.88±0.47 to 6.66±0.42 nmol fructose-2,6-bisphosphate/g fat body in 3 h) and inactivation of fat body glycogen phosphorylase (from 56% to 16% phosphorylase a). These data are consistent with the hypothesis that a decrease in hemolymph glucose both activates fat body glycogen phosphorylase and causes a decrease in fat body fructose-2,6-bisphosphate content. Both of these changes would favor conversion of stored glucose to trehalose in the fat body. When second-day larvae were decapitated, the changes in hemolymph glucose and fat body fructose-2,6-bisphosphate were very similar to those observed in fasting whole insects. These data are consistent with a direct role for glucose in controlling carbohydrate metabolism in Manduca sexta.

Osmoregulatory capacity according to nutritional status, molt stage and body weight in Penaeus stylirostris

Hypo-osmoregulatory capacity (or hypo-OC, i.e., the difference between the osmolality of the haemolymph and that of sea water), haemolymph glycemia and haemolymph sodium and chloride concentrations of Penaeus stylirostris were studied in experimental tanks according to the size, the molt stage and the nutritional status of the shrimp. Osmolality and haemolymph glycemia of fed and starved P. stylirostris were also studied in earthen ponds in fluctuating sea water according to time. In experimental tanks, the absolute hypo-OC of shrimp decreased linearly with increasing wet weight for each molt stage considered. For specimens weighing 16.6±1.7 g, the absolute hypo-OC was maximum in stage C (217±17 mosm kg −1) and significantly lower in stages B (165±16 mosm kg −1), D 0 (181±18 mosm kg −1), D 1 (146±20 mosm kg −1) and D 2 (135±13 mosm kg −1). The hypo-OC and haemolymph glucose concentration varied significantly after the food supply. No variations in haemolymph sodium and chloride concentrations were observed. In earthen ponds, haemolymph osmolality and haemolymph glucose concentration of molt stage C shrimp increased shortly after the food supply. When shrimp were kept starved for 24 and 48 h, haemolymph osmolality remained constant and haemolymph glucose concentration varied only slightly according to time. In light of these results, the use of shrimp hypo-OC (and/or haemolymph osmolality) and haemolymph glycemia in aquaculture as potential physiological indicators of disturbance in the aquatic environment is discussed.

D-glucose-sensitive neurosecretory cells of the crab Cancer borealis and negative feedback regulation of blood glucose level.

We studied the effects of glucose on cultured X-organ neurons of the crab Cancer borealis using single-electrode current- and voltage-clamp techniques. A subpopulation of the cells responded to D-glucose with a hyperpolarization. These cells, but not glucose-insensitive cells, showed immunoreactivity to crustacean hyperglycemic hormone (CHH), the hormone responsible for the elevation of blood glucose levels in crustaceans. Glucose-sensitive cells were also inhibited by serotonin and gamma-aminobutyric acid but were not affected by dopamine and Leu-enkephalin. The response was specific for D-glucose, with an EC50 of 0.25 mmoll-1. No response was seen to L-glucose, sucrose, galactose, mannose or fructose. The glucose response persisted in the absence of extracellular Na+ and in low-Ca2+/Mn2+ saline. In voltage-clamp experiments, D-glucose evoked a small current with a reversal potential close to that of voltage-dependent K+ currents. We conclude that D-glucose activates a K+ current in CHH-immunoreactive cells that, in normal saline, induces a hyperpolarization. We propose that this enables glucose to regulate directly the release of CHH into the hemolymph, thus constituting a negative feedback mechanism regulating hemolymph glucose concentration.

Respiratory, Acid-Base, and Metabolic Responses of the Christmas Island Blue Crab, Cardisoma hirtipes (Dana), during Simulated Environmental Conditions

The dependency of the Christmas Island blue crab, Cardisoma hirtipes, on fresh water for respiratory gas exchange and transport was investigated in laboratory simulations. The gas exchange rates of air-breathing C. hirtipes were similar to those of other land crabs but decreased to 20% in submerged crabs. Crabs with access to air maintained arterial and pulmonary O2 content (CO2) and partial pressure (PO2), while in submerged crabs the PO2 and CO2 rapidly decreased (by 50%). There was no anaerobiosis, but haemolymph glucose concentration and cardiac output decreased when crabs were submersed, which suggests a hypometabolic state. Submersion induced a metabolic rather than a respiratory alkalosis, and since respiratory gas exchange was low, CO2 excretion to water was unimportant. Cardisoma hirtipes haemocyanin (Hc) has high O2 affinity but low pH sensitivity, which facilitates O2 uptake from hypoxic environments. The high Hc-O2 affinity supports O2 loading but may prevent access to a venous O2 reserve. Calcium, magnesium, and urate, but not L-lactate, were effectors of Hc-O2 affinity. In submerged crabs increased circulating urate maintained haemolymph O2 content. The CO2 capacitance and nonbicarbonate buffering of the haemolymph were relatively low. A significant Haldane effect seemed important for CO2 excretion but would require CO2 and O2 exchange to occur at the same organ (gills or lungs). Submersion interferes with respiration and is not needed for haemolymph acid-base balance; thus; C. hirtipes is an air-breathing crab.

Haemolymph chemistry of tropical rock lobsters (Panulirus ornatus) brought onto a mother ship from a catching dinghy in Torres Strait

For export of live Panulirus ornatus from northern Queensland, divers catch the lobsters by hand and keep them in small tanks on dinghies before draining the tanks and returning at speed to a mother ship that has a larger storage tank. The lobsters are sometimes too weak for export. The physiological state of lobsters stored in a tank on the mother ship was studied by measuring the concentrations of L-lactate, D-glucose and ammonia in the haemolymph. Oxygen levels in the dinghy tanks were normally acceptable but fell rapidly below 50% saturation when flow was stopped and the tank was draining. The concentration of lactate in the haemolymph of lobsters arriving from the dinghy was 16.4 ± 5.7 mmol L-1 (mean ± s.d.,n = 9); this fell during storage on the mother ship. On the mother ship, serum concentrations of calcium, potassium and magnesium ions all increased, haemolymph glucose concentration increased slightly and then decreased, and ammonia concentration did not change. Future work may identify which aspects of prior handling are responsible for the elevated lactate concentrations in captive lobsters, but improvements could be made meanwhile to water flow through the dinghy tanks.

Seasonal Changes in Calcium and Glucose Concentrations in Different Body Fluids of Anodonta Anatina (L.) (Bivalvia: Unionidae)

Samples of haemolymph, extrapallial fluid and mantle cavity fluid for calcium and glucose analyses were taken in different seasons immediately after mussel collection in the field in order to see whether the calcium and glucose concentrations varied seasonally. Peak calcium concentrations in the haemolymph and extrapallial fluid (between 5 and 6 mmol/l) were found in summer when the water temperature was highest, and were lower (about 4.1-4.6 mmol/l) at other times. They only differed from each other in March, when the extrapallial fluid contained less calcium (about 3.5 mmol/l). Calcium concentration in the mantle cavity fluid was clearly higher than in the surrounding water but, during the whole year, significantly lower than in the haemolymph (about 3-4.5 mmol/l). The haemolymph glucose concentration was at its highest (about 110-125 μmol/l) in late spring and late summer, and the lowest value (50 μmol/l) was detected at midsummer between the two aforementioned peaks. During this time, mussels are releasing their gametes and rapid shell growth has begun. In the extrapallial fluid, glucose concentration was at its lowest (about 100-140 μmol/l) in summer, and from autumn to early summer it was significantly higher than in the haemolymph (140-220 μmol/l). In the mantle cavity fluid, glucose concentration was as high, or nearly as high, as in the haemolymph. The mantle cavity thus serves as a pre-blood chamber in the exchange of electrolytes and metabolites between the animal and the environment.

Role of Digestive Gland in the Energetic Metabolism of Penaeus setiferus.

We determined the role of the digestive gland in the respiratory metabolism of Penaeus setiferus adult males as a step toward proposing a feeding schedule based on the cycle of activity in the digestive gland. We measured pre- and postprandial values for oxygen consumption rate and hemolymph glucose concentrations in live animals, and oxygen consumption rate and glycogen concentration in excised digestive gland. After the animals were fed, which enhanced general metabolic activity, these indices changed. There was a high correlation between the oxygen consumption rate of the animal and the glucose concentration in the hemolymph, and between the oxygen consumption rate by the digestive gland and the glycogen concentration in the digestive gland, all in relation to time after feeding. Correlations support the hypothesis that the energy demand depends upon the metabolic substrate concentration. In this theory, glucose sustains muscle activity (during ingestion of food) and glycogen is the product of the digestive gland during food assimilation. Our observations of metabolic dynamics during the feeding period allowed us to examine the feeding process. The metabolic activity of the digestive gland was highest 6 h after feeding. This could mean that assimilation, having started 2 h after food intake, peaked 6 h after feeding. Eight hours after feeding, the oxygen consumption rate of the digestive gland decreased and fell to values similar to those recorded for animals subjected to 72 h of fasting.

Effects of extreme pH on the physiology of the Australian 'yabby' Cherax destructor: acute and chronic changes in haemolymph oxygen levels, oxygen consumption and metabolic levels

Respiration and metabolism of the freshwater crayfish Cherax destructor were investigated with respect to the acidification and alkalization of its environment. Crayfish were exposed for up to 504 h (21 days) to pH 4.5, pH 7.1 (control) or pH 8.0 water and oxygen consumption rate, haemolymph oxygen transport and haemolymph glucose and lactate concentrations were determined. The effect of reducing environmental [Ca2+] in acid water from 500 to 50 &micro;mol l-1 was also examined. In acid water (500 &micro;mol l-1 Ca2+), oxygen uptake by Cherax was reduced by 79 % after 504 h (21 days) compared with 'control' animals (pH 7.1, 500 &micro;mol l-1 Ca2+). Haemolymph lactate concentration (mean 0.6 mmol l-1) remained constant, indicating that anaerobiosis was not important, while glucose concentrations were regulated within the range of control values (0.32&plusmn;0.01 mmol l-1). The arterial-venous CO2 difference of Cherax haemolymph decreased after 288 h and PaO2 increased from 11.1&plusmn;0.5 mmHg to 42.4&plusmn;1.0 mmHg between 96 h and 288 h. Decreased oxygen uptake and delivery without compensatory increases in anaerobiosis or glucose levels describe a hypometabolic response to low pH. The hypometabolic response of Cherax was greater in alkaline water as shown by a 53 % reduction in O2 uptake rate compared with a 44 % reduction in acid-exposed (500 &micro;mol l-1 Ca2+) animals after 96 h. This decrease in M(dot)O2 of alkaline-exposed animals was correlated with decreased haemolymph glucose levels (from 0.32&plusmn;0.01 at 0 h to 0.06&plusmn;0.01 mmol l-1 at 96 h). Lowering the [Ca2+] of the water both increased the magnitude of the effects of acid exposure and elicited further changes in haemolymph oxygen transport. The maintenance of high haemolymph PO2 during pH stress appears to reduce the involvement of haemocyanin, since this promotes decreased a&shy;v CO2. Hypometabolism probably permits Cherax to conserve resources that might otherwise be used, however, for growth and reproduction. The implications for the fitness of the animal are discussed.