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1.
Soft water acclimated (Ca2+ 0.02 mM; Na+ 0.03 mM; K+ 0.01 mM; pH 7.0), cannulated brown trout (Salmo trutta) were exposed to various pH and aluminium (Al) regimes (pH 7.0, pH 5.0, pH 5.0 plus Al: 50, 25, and 12.5 g l–1) for up to 5 days in order to determine (i) the sublethal concentration of Al at pH 5.0 for this species (ii) their ionoregulatory and respiratory status. No mortality or physiological disturbances were evident at pH 7.0 or pH 5.0. All trout died within 48 h at pH 5.0 in the presence of Al at 50 g l–1 and 67% died over the 5 day period at pH 5.0 in the presence of Al at 25 g l–1. Fish at these lethal Al concentrations showed significant decreases in arterial blood oxygen content (CaO2) but no changes in plasma osmolarity or the concentrations of plasma Na+, K+ and Cl–. Physiological disturbance was more marked at the 50 g l–1 Al concentration. The surviving fish at 25 g l–1 showed few signs of physiological recovery while continually exposed to this regime. No fish died during the exposure to water of pH 5.0 containing 12.5 g l–1 Al, but physiological disturbance was still apparent. These sublethally-stressed trout showed a transient decline in the plasma concentrations of Na+ and Cl–1. Although CaO2 decreased, recovery was evident. The data suggest that in the brown trout, environmental Al concentration is as important as pH and calcium concentration in determining the physiological status of the fish.  相似文献   

2.
The objective of this study was to determine the potential sites of maximal growth limitation in Atlantic cod (Gadus morhua). Forty cod were reared in ten sea water tanks. Fish were randomly divided into 5 groups, a control group (injected with saline solution) and 4 experimental groups that received different levels of recombinant bovine somatotropin (rbST: 1.0, 2.0, 4.0 and 10.0 g g fish–1 2 weeks–1) by injection in the abdominal cavity. Fish were fed ad libitum 3 times a week during four weeks. We measured individual body mass, growth rate, food intake and food conversion efficiency. At the end of the experiment, we measured the activity of acid proteases in the stomach; trypsin and chymotrypsin in the pyloric caeca; alkaline phosphatase (ALP) and glutamyltransferase (GGT) in the intestine. No significant differences were observed in growth rate, food intake or food conversion efficiency among the five groups. Trypsin, chymotrypsin, ALP and GGT activities when expressed in U g fish–1 were correlated with growth rate. These enzymes were also correlated with food ingestion except for trypsin when expressed in U mg protein–1. Trypsin was the only enzyme that showed a significant correlation with food conversion efficiency. Our conclusion is that, at the level of digestion, trypsin is the only enzyme measured that could be suspected to potentially limit growth rate in cod.  相似文献   

3.
Intestinal fluid was collected from 11 marine teleost fish from the Baltic sea and the Pacific ocean. The anterior, mid and posterior segments of the intestine contained 33–110 mM of HCO3 – equivalents (with exception of the Atlantic cod which contained only 5–15 mM). Considering literature values of transepithelial potentials and concentration gradients, these high levels of HCO3 – equivalents are probably the result of active HCO3 – transport. Possible HCO3 – transport mechanisms were studied in the Pacific sanddab (Citharichthys sordidus) in vitro. Measurements of net secretion of HCO3 – equivalents across the intestinal epithelium revealed mucosal DIDS sensitivity (10–4 M) and Cl–-dependence of the HCO3 – equivalent net flux, but no serosal DIDS (10–4 M) sensitivity. Net Na+ uptake was abolished in the absence of Cl–, but some Cl– uptake persisted in the absence of Na+, at a rate similar to that of net HCO3 – secretion. Anterior, mid and posterior segments of the intestine performed similarly. These observations support the presence of an apical rather than a basolateral Cl–/HCO3 – exchanger and thus contrast the currently accepted model for intestinal HCO3 – secretion. This apical Cl–/HCO3 – exchanger alone, however, is not sufficient for maintaining the observed HCO3 – equivalents gradient in vivo. We suggest a coupling of cytosolic carbonic anhydrase, a basolateral proton pump and the apical Cl–/HCO3 – exchanger to explain the intestinal HCO3 – transport.  相似文献   

4.
The effects of severe experimental anaemia on red blood cell HCO3 – dehydrationin vitro were examined in rainbow trout,Oncorhynchus mykiss. After 5 days of anaemia (haematocrit=4.9±1.1%) induced by intraperitoneal injection of phenylhydrazine hydrochloride, fish displayed elevated arterial CO2 tensions (anaemic PaCO2=3.19±0.42 torrvs. control PaCO2=1.35±0.17 torr) and a significant acidosis (anaemic pHa=7.73±0.04vs. control pHa=7.99±0.04). However, after 15–20 days of anaemia (hct=6.6±0.8%) induced by blood withdrawal, the arterial CO2 tension was significantly lower than the control value, suggesting that physiological adjustments occurred within this time period to compensate for the lowered haematocrit. Compensation probably did not involve alterations in ventilation, which was unaffected by 5 days of anaemia (anaemic ;w=786±187 ml min–1 kg–1 vs. control ;w=945±175 min–1 kg–1), based on indirect Fick principle measurements.Potential adaptations to longer term anaemia at the level of the red blood cells were investigated using a radioisotopic HCO3 – dehydration assay. Owing to the difference in haematocrits, the HCO3 – dehydration rate for blood from anaemic fish was significantly lower than that for control fish following equilibration at the same CO2 tension. This difference was eliminated when HCO3 – dehydration rates were measured on blood samples adjusted to the same haematocrit, a result which implies that the intrinsic rate of CO2 excretion at the level of the red blood cell was not up-regulated during anaemia. The difference was also eliminated by equilibrating the blood samples with CO2 tensions appropriate for the group from which the sample was obtained,i.e., PCO2=1.4 torr for control samples and PCO2=3.2 torr for anaemic samples; each at the appropriate haematocrit. It is concluded that the elevated PaCO2 helps to reset CO2 excretion to the control level, but that some additional physiological adjustment occurs to lower the PaCO2 after 15–20 days of anaemia.  相似文献   

5.
Fast and slow muscle fibers were isolated from the myotomes of atlantic cod (Gadus morhua L.) and sculpin (Myoxocephalus scorpius L.). Epinephrine was found to have no effect on twitch or sub-tetanic contractions in fast muscle fibres. Isoprenaline (10–6M) had no effect on the contractility of slow muscle fibres. In contrast, epinephrine elicited a dose-dependent decrease in the half-time for twitch relaxation (t1/2r), and in most cases a decrease in twitch amplitude. The maximum decrease in t1/2r was around 5–20% of control values (at 10–6M epinephrine), with a half maximal response at about 30 nmol l–1. Responses to epinephrine were unaffected by propranolol and reversed by phentolamine, consistent with the stimulation of -adrenoreceptors. 10–6M epinephrine produced a rise in cAMP levels from 1.8 to 3.1 pmol mg dry wt–1 in cod slow fibres. However, the cellular mechanism underlying the action of epinephrine is unclear since forskolin, a potent activator of adenylate cyclase activity, where it has been investigated, was found to increase not decrease twitch duration and amplitude. The responses of fast and slow fibres to epinephrine and its antagonists were similar in summer (13°C) and winter acclimatized (5–6°C) sculpin.It is suggested that epinephrine may act to modulate the active state of slow muscle fibres at high cruising speeds and thereby increase swimming performance.  相似文献   

6.
Doppler flow probes were fitted around the ventral aorta of rainbow trout, which were exposed to combinations of pH and aluminum (pH 5.1–6.2, Al 0–80 g l–1) for 60 h. Fish accumulated Al at the gill and exhibited decreased blood Na+, Cl–, and Ca2+ concentrations, and increased K+, hematocrit, hemoglobin, glucose, and lactate, indicating increasing ionoregulatory disturbance with increasing Al concentration. Fish exposed to ambient water (6.2) or low-pH (5.3) water without Al exhibited slight reductions in heart rates, as well as increased stroke volume, resulting in little variation in cardiac output. In the presence of Al (20 to 40 g l–1) at low pH (5.1–5.3), fish increased their heart rate slightly and generally maintained their stroke volume, resulting in increased cardiac output in the first two days of exposure. At the highest Al concentration (80 g l–1, pH 5.1), tachycardia was observed, concomitant with a decrease in stroke volume. The ionoregulatory imbalance and resulting increased blood viscosity explain these increases in heart rate rather than stroke volume in fish exposed to high concentrations of Al.  相似文献   

7.
The mudskipperB. boddaerti, was able to survive in waters of intermediate salinities (4–27). Fish submerged in dechlorinated tap water suffered 60% mortality by the fifth day while 60% of those in 100% sea-water (sw) died after the third day of exposure. After being submerged in 50% or 80% sw for 7 days, the plasma osmolality, plasma Na+ and Cl– concentrations and the branchial Na+ and K+ activated adenosine triphosphatase (Na+,K+-ATPase) activity were significantly higher than those of fish submerged in 10% sw for the same period. However, the activities of the branchial HCO3 – and Cl– stimulated adenosine triphosphatase (HCO3 –,Cl–-ATPase) and carbonic anhydrase of the latter fish were significantly greater than those of the former. Such correlation suggests that Na+,K+-ATPase is important for hyperosmotic adaptation in this fish while HCO3 –-Cl–-ATPase and carbonic anhydrase may be involved in hypoosmotic survival.  相似文献   

8.
Similar to gas secretion into the swimbladder, some teleosts also exhibit ocular gas secretion to supply their thick and avascular retina with oxygen. The process in the eye, however, is complicated by the fact that the retina is supplied with arterial blood only indirectly through the pseudobranch, a reduced gill arch of still unknown function. Approaches for closer analysis of the physiological implications of this serial blood supply arrangement and the associated process of O2 release include complete unilateral vascular isolation of eye and/or pseudobranch while maintaining normal blood flow characteristics for undisturbed operation of the counter-current rete mirabile.Blood flow velocity in the afferent pseudobranchial artery (aPA; essentially equal to ophthalmic artery flow) of rainbow trout was measured by application of ultrasonic Doppler techniques. Accurate determination of flow rate in the untouched vessel was facilitated by mounting the Doppler crystal with a custom-made holder on the bone of the jaw and raw signal analysis by Fast Fourier Transformation for improved signal/noise ratio. Normal unilateral aPA blood flow was 746 l min–1 kg–1 body weight, (1.6% of cardiac output), the tissue-weight-specific blood flow was 3.6 ml min–1 g–1 for pseudobranch and 2.3 ml min–1 g–1 for the retina. Only about 28% of the oxygen potentially available with maximal activation of the Root effect is actually consumed in pseudobranch and retina. This generous supply of blood and the implicit safety margin may serve minimization of pH disturbances of retinal tissues, but may also come suitable during unilateral occlusion of supplying arteries for continued oxygen supply to the retinae. During contralateral occlusion, flow through the ipsilateral aPA increased to 136%. According to the normally low O2 extraction, a minimal flow of 36% through bilateral anastomosis and contralateral ophthalmic artery may maintain complete contralateral oxygen supply.  相似文献   

9.
The changes in proximate composition, amino acid (total and free) and fatty acid content of artificially propagated trout cod, Maccullochella macquariensis larvae from five mothers hatched, weaned and reared separately, each in two groups, one fed with Artemia naupli and the other starved, for 15 days (after yolk resorption), are presented. There was no significant change in the proximate composition of fed larvae with devlopment, but in starved larvae the protein (linearly) and lipid (curvi-linearly) content decreased significantly as starvation progressed. The essential amino acids (EAA) and non- essential amino acids (NEAA) found in highest amounts in trout cod larvae were lysine, leucine, threonine and arginine, and alanine, serine and glutamic acid, respectively. In fed larvae the total amino acid (TAA), TEAA and TNEAA content did not vary significantly as development progressed. In starved larvae the TAA, EAA and NEAA content, as well as all the individual amino acids decreased significantly (P<0.05) from the levels in day of hatch and/or yolk-sac resorbed larvae. The greatest decrease occurred in the TEAA content (7.38±0.76 at day of hatch to 1.96±0.09 15 day starved in moles larva–1; approximately a 74% decrease), whereas the decrease in TNEAA was about 38%. Unlike in the case of TAA distinct changes in the free amino acid (FAA) pool were discernible, from day of hatch and onwards, in both fed and starved trout cod larvae. In both groups of larvae the most noticeable being the decrease of % FEAA in TFAA, but not the % FAA in TAA. Four fatty acids together, accounted for more than 50% of the total in each of the major fatty acid categories in all larvae sampled; 16: 0, 18:1n-9, 22: 6n-3 and 20: 4n-6, amongst saturates, monoenes, n-3 PUFA and n-6 PUFA, respectively. Twelve fatty acids either decreased (14: 0, 16: 1n-7, 20: 1n-9, 20: 4n-6, 20: 5n-3, 22: 5n-3 and 22: 6n-3) or increased (18: 2n-6, 18: 3n-3, 18: 3n-6, 18: 4n-3 and 20: 3n-3) in quantity, after 15 days of feeding, from the base level in day of hatch and/ or yolk- sac resorbed larvae. The greatest increase occurred in 18: 3n-3 from 6.4±0.1 to 106.2±13.1 g mg lipid–1 larva–1, and the greatest decrease occurred in 22: 6n-3 (181.2±12.4 to 81.4±6.2 g mg lipid–1 larva–1). In starved larvae, at the end of 15 days, all the fatty acids, except 18: 0, 20: 3n-3 and 20: 4n-6, decreased significantly (P<0.05) from the levels in day of hatch and/or yolk- sac resorbed larvae.  相似文献   

10.
The pattern of changes of activity of the urea cycle enzymes and the rate of urea-N excretion were studied in the perfused liver of an Indian air-breathing ureogenic walking catfish, Clarias batrachus. The liver was perfused with different concentrations of NH4Cl for a period of 60 min to determine the role of ammonia for stimulation of hepatic ureogenesis and the threshold level of ammonia loading needed to cause such stimulation. Both the urea-N excretion and the ammonia uptake by the perfused liver were found to be a saturable process. Ammonia accumulated significantly in the liver infused with 1.25 moles g liver –1 min–1 of NH4Cl, followed by a maximum accumulation of about 28.5 moles g wet wt–1 with the infusion of 5.08 moles g liver–1 min–1. The Vmax of the urea-N excretion (0.47 mol g liver–1 min–1) was obtained with the addition of 5.08 moles g liver–1 min–1 of NH4Cl. Both the tissue and the specific activity of the urea cycle enzymes, except ornithine transcarbamylase and arginase, were stimulated significantly with the infusion of either 1.25 or 5.08 moles g liver–1 min–1 of NH4Cl. Maximum stimulation of tissue activity of carbamoyl phosphate synthetase (about 120%) was seen with the infusion of 5.08 mol g liver–1 min–1, and for argininosuccinate synthetase (about 135%), and argininosuccinate lyase (about 50%) with the infusion of 10.81 mol g liver–1 min–1 of NH4Cl. Higher accumulation of ammonia of about 10–15 mol g wet wt–1 from the physiological level in the perfused liver while infusing with NH4Cl was suggested to be one of the major causes of stimulation of ureogenesis. The presence of such physiological adaptive strategy is probably necessary in this unique group of air-breathing walking catfish to survive under hyper-ammonia stress in their normal habitat or while living outside water or while burrowing inside mud.  相似文献   

11.
An alkaline deoxyribonuclease (DNase) from cod pancreatic tissue has been characterized. The enzyme is a DNase I type endonuclease and hydrolyzes effectively both native and denatured DNA. Monomeric actin inhibits the enzyme reaction. The enzyme obeys Michaelis-Menten kinetics and the apparent Km value for native linear duplex DNA is 33 µg/ml. The cod DNase opens supercoiled plasmid DNA, by introducing adjacent nicks in both strands, possibly separated by 5–10 nucleotides. DNA hydrolyzed by cod DNase functions as substrates both for DNA polymerase and ligase, and the nicks therefore contain 5-phosphoryl and 3-hydroxyl groups. Optimum concentrations of divalent cations are 5 mM Mg2+, 0.63 mM Mn2+ and 0.075 mM Ca2+. However, Ca2+ is apparently not essential for the enzymatic functions. The enzyme has a narrow temperature optimum at 42°C and is thermolabile above 50°C; however, Mn2+ shifts the optimum slightly to 45°C by causing increased temperature stability. The cod DNase reaction is inhibited by the DNA intercalating compounds actinomycin D and ethidium bromide. Histidine-modifying reagents such as tosyl phenylalanyl chloromethylketone and diethyl pyrocarbonate inhibit the enzyme activity, but the cod DNase is insensitive to disulfide-reducing agents.  相似文献   

12.
Use of egg custard augmented with cod liver oil (CLO) fed during the day, and of an overnight feed with Moina micrura, were evaluated in terms of its effects on production of freshwater prawn (Macrobrachium rosenbergii) postlarvae (PL). Four levels of CLO (0, 1,3 and 5%) were tested. Significantly higher mean (sd) productions, ranging from 11.27 (1.16) to 13.02 (1.70) PL l–1, were obtained for larvae fed egg custard enriched with CLO compared with that of 7.83 (1.58) PLl–1 for larvae fed egg custard without CLO. The development and survival of larval stages were also higher for the CLO diets. The -3 highly unsaturated fatty acid (HUFA) in egg custard increased with increasing CLO level (0–5%). The fatty acid composition of postlarvae reflected the composition of the diet.  相似文献   

13.
A recombinant carp growth hormone (rcGH) was used to develop for a GH radioreceptor binding assay in the goldfish (Carassius auratus). Specific binding of125I-rcGH to goldfish liver membranes was a pH, time, temperature, and membrane protein dependent process. Scatchard and LIGAND analysis indicated a single class of high affinity and low capacity binding site, with an association constant (Ka) of 1.9×1010 M–1 and a maximum binding capacity (Bmax) of 9 fmol mg–1 protein. Liver tissue displayed the highest125I-rcGH binding of all the tissues examined. Displacement of125I-rcGH with various unlabeled teleost and mammalian GHs and prolactins revealed that the goldfish hepatic binding site was highly specific for teleost GH. Intraperitoneal administration of 0.1, 1.0, and 10 g rcGH g–1 body weight to hypophysectomized goldfish resulted in a 27, 52, and 68% decrease in total binding sites, respectively. Injection of a high dose of rat prolactin (rPRL) (5 g rPRL g–1 body weight) also resulted in a 32% decrease in total binding sites. These results suggest that endogenous GH may have a role in the regulation of its own receptors in the goldfish.  相似文献   

14.
To specifically study the functional ontogeny of the digestive tract, larvae of Japanese flounder at various developmental stages were injected with liquid solutions using tube feeding in vivo. The survival in the stages tested was on average 93%. The injected solutions were almost completely transferred from the presumptive stomach, or stomach to the midgut within 10 min of injection. The passage to the hindgut in some cases started 10 min after injection and over 90% of the solution had passed from the midgut to the hindgut after 1 h. In most cases the hindgut seemed to be completely empty after 3 h.Two different mixtures of pH indicators with sensitivities in the alkaline (7.5 to 9) and acid (4 to 6) ranges respectively were used for assessment of pH in the various gut segments. The pH of the stomach remained alkaline during the larval period, but had fallen close to 4 during late metamorphosis, an indication of active HCl secretion and progressive stomach differentiation. In mid and late metamorphosing fish a rapid colour change in the pH indicator was observed once it had passed the pyloric sphincter. This demonstrates that there was also active secretion of alkaline fluid, most likely HCO3 –, from the pancreas into the pylorus lumen.A single injection of liquid solution of 14C-FAA showed that assimilation of FAA was high in all stages tested (79.5 ± 7.1%; SD; n=91). The presently reported data for Japanese flounder support earlier studies that FAA are absorbed with a high efficiency in the early stages of marine fish.  相似文献   

15.
Studies of the enzyme fructose-1,6-bisphosphatase (FBPase) of rainbow trout (Oncorhynchus mykiss) have been undertaken in order to illuminate aspects of skeletal muscle gluconeogenesis in these animals. Maximal activities in crude homogenates of several organs suggest that the liver possesses the greatest FBPase activity on a unit g–1 tissue basis but that the white muscle, owing to its bulk, contributes substantially to whole body FBPase activity. Studies of fructose-6-phosphate-1-kinase (PFK) and FBPase in crude homogenates of several organs suggests an important role for intracellular pH in regulating the relative carbon flux through the FBPase/PFK locus in vivo. Furthermore, a three-step purification scheme is described for trout white muscle FBPase by which a stable and homogeneous (by SDS PAGE) enzyme preparation (isoelectric point = 7.2; molecular weight = 37.6 kd) was obtained. Kinetic studies of the purified enzyme were undertaken at 20°C under conditions reflective of "rest" and "exercise/recovery" intramuscular pH in vivo. Affinity for substrate (F-1,6-P2) was increased (Km = 6.88 versus 2.44 mol 1-–1 as was enzyme activity when pH was lowered from 7.0 to 6.5. Various inhibitor metabolites are identified including F-2,6-P2 (mixed-type inhibitor, Ki = 0.201 mol 1–1, pH 7.0) and AMP (non-competitive inhibitor, Ki = 0.438 mol 1–1, pH 7.0). Inhibition by F-2,6-P2 was strongly alleviated by a reduction in pH from 7.0 to 6.5 (I50 increased from 0.14 to 0.32 mol 1–1). AMP on the other hand was a more potent inhibitor at pH 6.5 but this inhibition was totally reversed under conditions of citrate, NH4 + and AMP typical of muscle during recovery from exercise in vivo. In purified white muscle enzyme preparations, FBPase demonstrated maximal activity at pH 6.5 whereas the optimal pH of PFK was 7.0 or greater. Indeed, it appears from these in vitro data that regulation by metabolite levels as well as pH are required for net FBPase flux in vivo. It is concluded, therefore that trout white muscle FBPase demonstrates the potential to play an important enzymatic role in the control of intramuscular gluconeogenesis in these animals. The results are discussed in relation to present knowledge regarding the metabolic responses of trout white muscle to, and its subsequent recovery from, exhaustive exercise.  相似文献   

16.
Gonad and plasma samples were taken from blue cod captured throughout the reproductive cycle, gonad condition was assessed, and plasma levels of 17-hydroxyprogesterone (17OHP), 17,20-dihydroxy-4-pregnen-3-one (17,20P), testosterone (T), 17-estradiol (E2) and estrone (E1) were measured by radioimmunoassay. It was confirmed that spawning occurred over an extended period in late winter and spring, with individual fish being involved in multiple spawning events. Plasma levels of T were bimodal in both sexes with peaks (maximum of 6.0 ng.ml–1) occurring 2 months prior to, and also during the early part of the spawning period. 17,20P was elevated in males (2.1 ng.ml–1) in mid-spermatogenesis coinciding with the first T peak (4.9 ng.m.–1). 17,20P was detectable but not significantly elevated (0.6–1.2 ng.ml–1) at any sample time in females. E2 was elevated in mature females (1.0 ng.ml–1) early in the spawning period but remained at assay detection limits (0.3 ng.ml–1) at all other sample times. Neither 17OHP nor E1 were detectable in the plasma of either sex. It is suggested that bimodal increases in sex steroids prior to spawning may be a feature of species with rapid recrudescence.  相似文献   

17.
The rate of oxygen consumption of minced whole body was determined volumetrically, as an indication of metabolic rate in vitro (M in vitro ), at 20°C in porgy Pagrus major ranging from 0.0002 g (just after hatch) to 2.9 g (67 days old) in body mass. A triphasic relationship was found between M in vitro of individual fish (l.min–1) and wet body mass W (g). During the prolarval stage accompanied with the transitional period to the postlarval stage (0.00020–0.00023 g, 0–6 days old), the mass-specific metabolic rate in vitro (M in vitro /W in l.g–1.min–1) increased with age (D in days) as expressed by an equation M in vitro /W = 3.88 + 0.74/D. During the postlarval stage (0.00031–0.003 g, 8–22 days old), M in vitro /W remained almost constant, independent of body mass following an equation M in vitro /W = 5.24 W–0.085. During the juvenile and adolescent stages (0.0047–2.9 g, 30–67 days old), M in vitro /W decreased with increasing body mass following an equation M in vitro /W = 1.66 W–0.235. These results correspond with the triphasic relationship between metabolism in vivo and body mass observed in intact porgy of 0.0002–270 g (Oikawa et al. 1991). It is concluded, therefore, that the dependence of mass-specific metabolic rate on body size exists in vitro as well as in vivo, during the early stages in the porgy. Based on these results, factors controlling the metabolism-size relationship are discussed.  相似文献   

18.
Arctic charr,Salvelinus alpinus L. were fed five test diets containing 0% or 1% of different polyunsaturated fatty acids (PUFA) for 93 days. The fish were injected intraperitoneally with (1–14C)–18:2(n–6) or (1–14C)–18:3(n–3), and the bioconversion to longer chain PUFA studied. The conversion rate in neutral lipids was slow, with most label found as the fatty acid injected, while extensive modification took place prior to or during incorporation into polar lipids. Linolenic acid was preferred over linoleic acid as substrate for elongation and desaturation regardless of diet. In polar lipids, the predominant products of (1–14C)–18:2(n–6) metabolism were generally 20:3(n–6) and 20:4(n–6), while 18:4(n–3), 20:5(n–3) and 22:6(n–3) were the major products of (1–14C)–18:3(n–3) metabolism. The lack of radioactivity in 22:5(n–6) suggests that 4 desaturation is specific for (n–3) PUFA. Feeding the PUFA deficient diet reduced the 5 desaturation compared to fish maintained on PUFA supplemented diets. The 6 desaturation was only reduced in fish fed C18 PUFA and injected with (1–14C)–18:3(n–3). Longer chain C20 and C22 PUFA, particularly those of the (n–3) family, exerted some inhibition on the elongation and desaturation of injected fatty acids compared to those fed C18 PUFA. The incorporation of radiolabelled fatty acids into polar lipids of fish fed a commercial diet was very low, and the desaturation neglectible in both polar and neutral lipids, showing that Arctic charr under culture conditions do not convert short chain PUFA to longer chain metabolites.  相似文献   

19.
The endemic, anadromous cyprinidChalcalburnus tarichi is the only fish species known to occur in alkaline Lake Van (Eastern Anatolia, Turkey). EightC. tarichi were maintained individually in Lake Van water (17 – 19°C; pH 9.8; 153 mEq·I–1 total alkalinity; 22 total salinity) and tank water samples analyzed for 24 h in 2 to 4 h intervals. At zero time, < 1µM ammonia was present and urea was undetectable in the tank water; at 24 h, total ammonia and urea made up 114±32 and 35±25µM, respectively. Over the experimental period, ammonia-N and urea-N excretion averaged 1041±494 and 607±169moles·kg–1 fish·h–1, respectively. The extent of urea excretion was highly variable between specimens. Uric acid excretion was not detectable.Urea was present at high concentrations in all tissues and plasma (25 – 35moles·g–1·ml–1) of freshly caughtC. tarichi; total ammonia content of the tissues was by a factor of 1.9 (liver) to 3.0 (brain) lower. High arginase activity (2.4±0.2 U·min–1·g–1) was detected in the liver ofC. tarichi but ornithine carbamoylphosphate transferase, a key enzyme of the ornithine-urea-cycle, was absent. Ureagenesis is likely through degradation of arginine and/or uricolysis. High glutamine synthetase activity (11±0.6 U·min–1·g–1) and low ammonia content in brain suggest that, like other teleosts,C. tarichi has an efficient ammonia detoxification in the brain, but in no other tissue.Nitrogenous waste excretion at alkaline pH is discussed. The ability ofC. tarichi to excrete high levels of ammonia at extremely alkaline pH is unique among teleosts studied so far. The mechanism of ammonia excretion under Lake Van conditions remains to be elucidated.  相似文献   

20.
Gill Na+-K+ ATPase and carbonic anhydrase activities were measured, on a fortnightly basis, from February to July, in 0+ age Atlantic salmon (Salmo solar), hatched and reared in a freshwater experimental station in Covas, northern Portugal. Plasma osmolarity and ionic composition were also measured. Gill Na+-K+ ATPase activity increased slowly until April (15–19 moles Pi mg prot–1 h–1). From April to late May there was a great increase in activity (19–32 moles Pi mg prot–1 h–1) followed by a sharp decline in June (15 moles Pi mg prot–1 h–1). In contrast, carbonic anhydrase activity decreased significantly from early April to early June (170-70 moles p-nitrophenol mg prot–1 h–1) and increased in late June, suggesting the existence of a compensatory mechanism for the changes in Na+-K+ ATPase activity. Plasma osmolarity and sodium concentration showed lower levels during the period of high ATPase activity. On the other hand, plasma calcium concentrations showed an increase during the same period (3.47–5.98 mm1–1 of plasma). A transitory decrease in osmolarity and plasma sodium and chlorine concentrations occurred in March, prior to the surge in Na+-K+ ATPase activity, suggesting that the physiological changes, characteristic of parr-smolt transformation can be a consequence of this loss of freshwater osmoregulatory capacity.  相似文献   

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