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1.
The California horn shark (Heterodontus francisci), instrumented with a pericardial catheter and a ventral-aortic flow probe, was studied to determine the effect of complete pericardial chamber evacuation on the time course for restitution of pericardial fluid-volume and pressure, and the effects of both fluid removal and its restitution on cardiac output. Prior to evacuation, pericardial pressure was –0.02±0.02 kPa, and cardiac output was 18±2 ml min–1 kg–1. Evacuation reduced pericardial pressure to –0.73±0.14 kPa, and increased cardiac output to 23±4 ml min–1 kg–1. The time course for restoration of post-evacuation pressure is described by a non-linear asymptotic function. A large percentage of the pericardial pressure and volume recovery occurred within the first hour, while, complete restoration of pre-withdrawal conditions required about 11 h. Pericardial pressure-volume relationships, determined by incremental infusion of small volumes of elasmobranch saline into the pericardium, confirm previous findings that the operating pericardial pressure in the horn shark is at or near ambient pressure and that both pericardial fluid volume and cardiac stroke volume influence horn shark pericardial pressure.  相似文献   

2.
The pericardial and peritoneal spaces of elasmobranch fishes are connected by the pericardioperitoneal canal (PPC), which allows pericardial fluid to escape when pressures exceed 0.1–0.3 kPA. Using the horn shark (Heterodontus francisci), we tested the hypothesis that the PPC functions to increase cardiac stroke volume by lowering pericardial pressure during activity. We also assessed the role of the PPC during coughing, feeding, or burst swimming and examined the effects of PPC occlusion. Increases in heart size were not prevented following augmented venous return in sharks with undisturbed or occluded PCP, evidence that argues that pericardial fluid loss through the PPC is a cause of increased cardiac stroke volume and not the result. Coughs, feeding, and burst swimming led to discharge of pericardial fluid. Chronic PPC occlusion resulted in an increased pericardial pressure, fluid volume, and frequency of coughing, and a decreased survival time compared to shams. Thus, in the horn shark the PPC likely compensates for constraints that may be imposed by the pericardium, provides a route for pericardial drainage, and regulates cardiac stroke volume during periods of activity.  相似文献   

3.
The importance of negative pericardial pressure to heart function in clasmobranchs has been questioned due to the discovery of positive pericardial pressures in healthy horn sharks (Heterodontus francisci). We therefore implanted electromagnetic flow probes on the ventral aorta of horn sharks and blue sharks (Prionace glauca) and assessed stroke volume and pericardial pressure as pericardial fluid volume (PFV) was varied to test the hypothesis that elasmobranchs are capable of maintaining a relatively large stroke volume at pericardial pressures near and above ambient. Stroke volume was maximum between zero and 25% maximum PFV (maximum PFV: the volume of pericardial fluid required to open the pericardioperitoneal canal), where pericardial pressure was most negative. At 50% maximum PFV (pericardial pressure near or slightly above ambient) stroke volume was 70% and 98% of its maximum in horn sharks and blue sharks, respectively. At a larger PFV, stroke volume declined drastically, reaching zero where both PFV and pericardial pressure were maximum. Thus, at a pericardial pressure apparently associated with resting or mild activity, stroke volume is a relatively large proportion of the apparent maximum. Increased circulatory demands associated with strenuous activity may induce ejection of pericardial fluid through the perieardioperitoneal canal, which then lowers pericardial pressure. The lowered pericardial pressure causes an increase in stroke volume, indicating that control is in part effected by changing pericardial pressure.  相似文献   

4.
The maximum power output of isolated perfused ventricles of the hafish (Eptatretus cirrhatus) averaged 0.367±0.031 mW g–1 (n=9), considerably high than estimates for the heart of the Atlantic hagfish (Myxine glutinosa). Maximal minute volumes averaged 21.55±1.28 ml min–1kg–1, with a mean stroke volume of 0.71±0.14 ml kg–1 body weight, values which are similar to those reported for many teleost and elasmobranch hearts.Ventricular output showed the characteristic dependence upon atrial filling pressure up to an optimum filling pressure ofc. 4 mm Hg. At output pressures exceeding 14 mm Hg the stroke volume and power output fell sharply. At these afterloads, the ventral aorta remained distended following semilunar valve closure and so the volume of fluid ejected on ventricular systole was reduced. There was little change in the frequency of the heart as either input or output pressures were varied.  相似文献   

5.
A new technique combining oesophageal intubation, dorsal aorta cannulation, and urinary catheterization was developed to monitor concentration of nutrients in the blood circulation and their metabolites in the urine of 1–2 kg white sturgeon, Acipenser transmontanus. Three experiments were conducted to assess the technique based on: (1) quantitative delivery of nutrients; (2) stress levels post-operation; and (3) monitoring of nutrients in the blood and metabolites in the urine. In Experiment 1, recovery of intubated Cr2O3 was 105±5% (mean ± SEM, n=3) 3 h after intubation. In Experiment 2, plasma cortisol and glucose concentrations returned to respective basal levels of 8.2±1.8 ng ml–1 and 74± mg dl–1 (n=9) 48 h post-operation. In Experiment 3, sturgeon intubated with 1 g kg–1 body weight of glucose or dextrin at 48 h post-operation showed a significantly different (p<0.05) peak plasma glucose level of 139±4 and 100±5 mg dl–1 (n=5), respectively, at 4 h. Urinary glucose excretion was 1.8±0.9 mg kg–1 h–1 (n=5) 4–8 h after intubation with glucose. Our results show that the new technique allows quantitative delivery of nutrients, repeated sampling of blood, and continuous collection of urine in white sturgeon with minimum stress.  相似文献   

6.
The incidental capture by marine fisheries as bycatch poses a global threat to pelagic sharks and rays. In large, industrialized fisheries that often operate in areas beyond national jurisdiction, at least 22 threatened species of pelagic elasmobranchs are caught as bycatch, representing the majority of megafauna bycatch in tuna fisheries. Here, we investigate (1) the efficacy of the current policies of the five tuna-related Regional Fisheries Management Organizations (tRFMOs) in mitigating elasmobranch bycatch, (2) data needed to better assess the amount and impact of elasmobranch bycatch and (3) the research necessary for the adoption of new policies. We found that tRFMOs have adopted 34 active policies that address pelagic elasmobranch bycatch. However, most policies (~76%, n = 26) are unlikely to avoid or minimize elasmobranch bycatch. Instead, most policies focus on mitigating post-capture mortality via remediation and requiring or encouraging research and data collection. Despite the emphasis on research mandates, we find that the existence of research was not related to policy adoption, suggesting that lack of research has not historically prohibited policymaking. Overall, we suggest that current research and data transparency, though perhaps not necessary for policy adoption, are not sufficient to adequately evaluate the population-level impacts of bycatch on many elasmobranch species in tRFMO-managed fisheries. Given these results, we recommend a precautionary approach that involves reforms in tRFMO voting processes to facilitate the adoption of binding requirements for elasmobranch catch limits, bycatch avoidance, pre- and post-capture handling and release modifications and protection of areas important to threatened pelagic elasmobranchs.  相似文献   

7.
  1. Many shark and ray (elasmobranch) species are threatened with extinction, due to overfishing and commercial trade
  2. Sarawak is situated in Malaysian Borneo in the Coral Triangle: a global priority region for elasmobranch conservation. Malaysia is the world’s eighth largest elasmobranch fishing nation, and Sarawak is one of Malaysia’s largest fishing states, yet there are limited species-specific data on catch and trade of elasmobranchs to support conservation and fisheries management decisions.
  3. This study presents landing site and market survey data, collected in Sarawak from January 2017 to December 2019. Geographical, temporal and operational trends in volumes of catch and trade are explored; the total volume, value and species composition of Sarawak's local elasmobranch markets is estimated; and simple size-based indicators are used to assess the sustainability of elasmobranch utilization for several conservation-priority and frequently traded species, including Critically Endangered and CITES-listed scalloped hammerhead sharks (Sphyrna lewini) and bottlenose wedgefish (Rhynchobatus australiae).
  4. The results conservatively estimate that >26,500 elasmobranchs (~90,000 kg) are locally traded in Sarawak annually, worth ~US$125,000 per year at the market level.
  5. Trade is dominated by small to medium-sized coastal requiem sharks (Carcharhinidae) and stingrays (Dasyatidae), with endangered and CITES-listed species making up 26% and 32% of total landings and trade, respectively.
  6. High proportions of immature individuals were recorded, with evidence of overfishing for several species, based on simple size-based indicators.
  7. Several options are outlined for improving management of elasmobranch fishing and trade in the future, including spatio-temporal closures and live release protocols, which could help to reduce the mortality of critically endangered species and implement CITES. Such measures could have large conservation impacts with limited socio-economic cost, since these species make up <5% of the total value of the elasmobranch market. However, management plans need to be co-designed with full participation of affected coastal communities in order to be ethical and effective.
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8.
Secondary effects of capture and handling stress in the Atlantic sharpnose shark, Rhizoprionodon terraenovae, were investigated in this study. Twenty-four sharks were serially bled and changes in several hematological parameters were monitored over a 1-h time period, following capture by hook-and-line. Blood samples were obtained from each shark at 0, 15, 30, 45 and 60 min. All 0-min (initial) blood samples were obtained within 3 min of capture. Blood glucose (9.2–13.1 mmol l–1), lactate (1.5–28.9 mmol l–1), and plasma osmolality (871–929 mOsm kg–1) all increased after capture, whereas blood pH (6.86–6.78) declined. Hematocrit values (initial = 25.1%) remained unchanged throughout the 1-h stress period. Due to the short amount of time it took to obtain the initial sample and the lack of a significant relationship between the initial time and the initial parameter levels, all initial samples are considered the best approximation of the predisturbance resting levels. The use of repeated measures in this study enables us to describe the dynamics of the secondary stress response in the Atlantic sharpnose shark.  相似文献   

9.
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   

10.
The impact of feeding, fish size (body weight from 18.5 to 56.5 g) and water temperature (20 and 23 °C) on oxygen consumption (OC, mg O2 kg–1 h–1) and ammonia excretion (AE, mg TAN kg–1 h–1) was studied in Eurasian perch held in recirculation systems. OC for both fed and feed-deprived (3 days) fish was higher at 23 °C (278.5 and 150.1 mg O2 kg–1 h–1) than at 20 °C (249.3 and 135.0 mg O2 kg–1 h–1; P < 0.01). AEs for both fed and feed-deprived fish were also significantly higher at 23 °C than at 20 °C (P < 0.001). Water temperature and fish size had a significant impact on the oxygen:feed ratio (OFR, kg O2 kg–1 feed fed day–1) and ammonia:feed ratio (AFR, kg TAN kg–1 feed fed day–1; P < 0.001). Their average values at temperatures of 20 and 23 °C were 0.17 and 0.19 kg O2 kg–1 feed fed day–1 and 0.009 and 0.011 kg TAN kg–1 feed fed day–1, respectively.  相似文献   

11.
  • 1. 309 Great Barrier Reef Marine Park recreational fishers were surveyed to examine recreational catch and harvest of elasmobranchs and to explore recreational fishers' handling behaviour and attitudes.
  • 2. Elasmobranchs represented 6% of fishers' total catch of all fish (including released individuals), and 0.8% of fishers' total harvest (i.e. retained individuals) across all survey days. The majority of elasmobranchs caught by fishers were released, primarily because they were perceived as being inedible.
  • 3. Recreational fishers' self‐reported handling and release behaviour for elasmobranchs is largely consistent with ‘best practice’ guidelines except that fishers had low use of circle hooks and barbless hooks, and a significant proportion (33%) reported using stainless steel hooks.
  • 4. Most fishers had positive attitudes towards elasmobranchs, placing high importance on releasing sharks and rays in good condition (86%), high value on their existence (84%), and low value on catching them (63%).
  • 5. Results indicate that post‐release mortality is probably the largest source of recreational fishing mortality of elasmobranchs in the Great Barrier Reef. Future research should be targeted at obtaining better estimates of species‐specific post‐release mortality levels, understanding how post‐release survival can be increased by changing fishing techniques or fisher behaviour, and developing more effective methods of engaging fishers in elasmobranch conservation. Copyright © 2009 John Wiley & Sons, Ltd.
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12.
Changes in ionic composition as Na+,K+, Ca2+ and Mg2+, osmolality inseminal fluid, percentage of motile spermatozoaand velocity were investigated in response toCPP and different dosage of LHRHa. The lowestvelocity of sperm was observed after use CPPtreatment. The velocity of spermatozoa,significant main effect of the treatment(P < 0.0001) and the time of sperm collection(P < 0.0104) were evaluated. The osmolality ofseminal fluid was different betweenexperimental groups of LHRHa (48.0–62.7mOsmol.kg–1) and CPP (33.0–46.3mOsmol.kg–1) treatments. The osmolalitywas significantly higher on the first day andone-half, then declined on day three, rangingfrom 33.0 to 62.7 mOsmol.kg–1. Analysisof variance showed significant main effects ofthe treatment (P < 0.0001) and the time ofsperm collection (P < 0.0002) on the osmolalityof seminal fluid. The level of Na+ andK+ ion was different between experimentalgroups of LHRHa and CPP treatment. The highestconcentration of 11.11 mmol.l–1 wasobserved at Na+ ion. Then theconcentrations declined on the level 1.56, 0.52and 0.36 mmol.l–1 for K+, Ca2+and Mg2+ ions, respectively. There werehighly positive correlations between osmolalityof seminal fluid and dosage of LHRHa treatment(r = 0.84), velocity of spermatozoa andosmolality of seminal fluid (r = 0.57) andosmolality of seminal fluid and Na+concentration at seminal fluid (r = 0.70).Injection with LHRHa increased quality of spermas velocity of sperm, level of Na+,K+ and osmolality at seminal fluidcompared to CPP treatments.  相似文献   

13.
Lepeophtheirus acutus Heegaard, 1943 (Caligidae, Siphonostomatoida, Copepoda), was collected from or observed on four of six elasmobranch species held at Burgers’ Zoo (Arnhem, The Netherlands). Circumstantial evidence suggested that a zebra shark, Stegostoma fasciatum (Hermann), from the wild carried the infection into the facility, where copepods reproduced and colonized additional hosts. Copepods typically attached on and about the eyes, in the mouth and occasionally about the cloaca and on the claspers. Severe ocular lesions were associated with infections on zebra sharks, a grey reef shark, Carcharhinus amblyrhynchos (Bleeker), whitetip reef sharks, Triaenodon obesus (Rüppell), and giant shovelnose ray, Rhinobatos typus Bennett, while blacktip reef sharks, Carcharhinus melanopterus (Quoy & Gaimard), and blacktip sharks, Carcharhinus limbatus (Valenciennes), living in infested aquaria showed no sign of infection. Water treatments using trichlorfon were considered primarily responsible for the eradication of copepods from hosts and infested aquaria. This case is the first report of a copepod infection being closely associated with disease and death of an aquarium‐held elasmobranch. Given its ability to infect a wide variety of elasmobranchs and promote life‐threatening lesions on some hosts, L. acutus should be considered a dangerous pathogen of captive elasmobranchs.  相似文献   

14.
The presumptive Na+/H+ exchange sites of trout and eel erythrocytes were quantified using amiloride-displaceable 5-(N-methyl-N-[3H]isobutyl)-amiloride (3H-MIA) equilibrium binding to further evaluate the mechanisms of i) hypoxia-mediated modifications in the trout erythrocyte -adrenergic signal transduction system and ii) the marked differences in the catecholamine responsiveness of this system between the trout and eel. MIA was a more potent inhibitor of both trout apparent erythrocyte proton extrusion (IC50 = 20.1 ± 1.1 mol l–1, N = 6) activity (as evaluated by measuring plasma pH changes after addition of catecholamine in vitro) and specific 3H-MIA binding (IC50 = 257 ± 8.2 nmol l–1, N = 3) than amiloride, which possessed a proton extrusion IC50 of 26.1 ± 1.6 mol l–1 (N = 6) and a binding IC50 of 891 ± 113 nmol l–1 (N = 3). The specific Na+ channel blocker phenamil was without effect on adrenergic proton extrusion activity or specific 3H-MIA binding. Trout erythrocytes suspended in Na+-free saline and maintained under normoxic conditions possessed 37,675 ± 6,678 (N = 6) amiloride-displaceable 3H-MIA binding sites per cell (Bmax, presumptive Na+/H+ antiporters) with an apparent dissociation constant (KD) of 244 ± 29 nmol l–1 (N = 6). Acute hypoxia (PO2 = 1.2 kPa; 30 min) did not affect the KD, yet resulted in a 65% increase in the number of presumptive Na+/H+ antiporters. Normoxic eel erythrocytes, similarly suspended in Na+-free saline, possessed only 17,133 ± 3,716 presumptive Na+/H+ antiporters (N = 6), 45% of that of trout erythrocytes, with a similar KD (246 ± 41 nmol l–1, N = 6). These findings suggest that inter- and intra-specific differences in the responsiveness of the teleost erythrocyte -adrenergic signal transduction system can be explained, in part, by differences in the numbers of Na+/H+ exchange sites.  相似文献   

15.
Estimated declines in shark and ray populations worldwide have raised major, widespread concern about the impacts of global fisheries on elasmobranchs. The mechanisms causing elasmobranch mortality during fisheries’ capture are not fully understood, but we must gain greater clarity on this topic for fisheries managers to develop effective conservation plans to mitigate further population declines. To evaluate how two important factors, respiratory mode and fishing gear type, impact elasmobranch survival, we compiled publicly available data sources on the immediate mortality percentages of 83 species and post‐release mortality percentages of 40 species. Using Bayesian models, we found that sharks and rays captured in longlines had significantly lower immediate mortality than those caught in trawls or gillnets. Our models also predicted the mean total discard mortality (combined immediate and post‐release mortality) percentages of obligate ram‐ventilating elasmobranchs caught in longline, gillnet and trawl gear types to be 49.8, 79.0 and 84.2%, respectively. In contrast, total discard mortality percentages of stationary‐respiring species were significantly lower (longline capture mean = 7.2%, gillnet capture mean = 25.3%, trawl capture mean = 41.9%). Our global meta‐analysis provides the first quantified demonstration of how mortality is affected by these two factors across a broad range of species. Our results and approach can be applied to data‐deficient elasmobranchs and fisheries to identify species that are likely to experience high rates of mortality due to respiratory mode and/or fishing methods used, so that appropriate mitigation measures can be prioritized and investigated.  相似文献   

16.
Rainbow trout (Oncorhynchus mykiss) with a mean (sd) weight of 120 (2) g were fed diets supplemented with astaxanthin extracted from the yeast Phaffia rhodozyma (OY1 = 50 mg carotenoids kg–1 feed, OY2 = 100 mg carotenoids kg–1 feed), astaxanthin (AX = 100 mg astaxanthin kg–1 feed) and canthaxanthin (CX = 100 mg canthaxanthin kg–1 feed) for 4 weeks. Muscle analyses at the end of the experiment indicated a significantly higher carotenoid concentration in the AX group, while CX and OY1 groups were similar in spite of the differences in dietary concentration. The measure of total muscle colour difference (E* ab) between initial samples and 4 week ones was higher for the AX fish group but showed no significant difference between OY1, OY2, and CX. The hue and the reflectance ratio (R650:R510) of fish muscle increased in proportion to carotenoid intake. Digestibility (ADC) of yeast astaxanthin in OY1 and OY2 groups was significantly higher than that in the AX group. Canthaxanthin ADC was about one sixth of that of astaxanthin (AX group). Carotenoid retention in the muscle, expressed as a percentage of carotenoid intake, was higher for the AX group than that recorded for OY1 and OY2. According to ADC, carotenoid retention showed a marked lower value for the CX group. Muscle retentions were similar for astaxanthins from both sources.  相似文献   

17.
A study was conducted to examine the effect of dietary cation-anion difference (CAD, Na++K+-Cl–, mEq kg –1) on acid-base balance, food consumption and growth of juvenile African catfish, Clarias gariepinus. Four dietary CAD levels (-100, 100, 500, 700 mEq kg–1) were established by altering levels of NaHCO3, CaCl2 and NH4Cl in the diets. The group fed the diet of excess anions (CAD: -100 mEq kg–1) had low food consumption and growth rate. Food consumption and growth increased linearly with an increase in dietary CAD within the range -100 to 700 meq. kg–1. Blood pH was not significantly influenced by dietary CAD. A quadratic relationship between Na+, Cl– and CAD level in plasma and dietary CAD was found. Body composition of fish and nitrogen/energy utilisation efficiency differed between dietary CAD treatments. The results suggest that dietary CAD influence acid-base regulation and thus the energy costs for maintaining homeostasis. The increased food intake and growth performance of C. gariepinus at higher CAD levels may be related to a reduced maintenance costs for homeostasis.  相似文献   

18.
  1. The illegal sale of endangered elasmobranchs has been recorded in a number of different Brazilian states, where sharks and rays are being marketed primarily as ‘cação’ or ‘viola’. Brazil is ranked among the top 10 nations worldwide that harvest most sharks, causing an immeasurable impact on the local elasmobranch populations.
  2. The present study applied the DNA barcoding technique, based on the cytochrome C oxidase subunit I gene, for the molecular identification of the elasmobranch species sold as processed products under the generic names of ‘cação’, ‘mangona’, ‘azul’, ‘cambeva’, ‘fiuso’ and ‘lombo preto’, in the fish market of the city of Florianópolis, capital of the state of Santa Catarina, Brazil.
  3. Nine elasmobranch species were identified in the 56 samples analysed, including six sharks and three rays, representing six families, the Carcharhinidae, Sphyrnidae, Squatinidae, Arhynchobatidae, Myliobatidae and Gymnuridae. Prionace glauca, identified in more than half (56%) of the samples analysed, is listed as Near Threatened by the International Union for the Conservation of Nature.
  4. Six species identified in the present study, Sphyrna zygaena, Sphyrna lewini, Squatina guggenheim, Carcharhinus signatus, Gymnura altavela and Rioraja agassizii, are under some level of risk of extinction, while two others (Rhizoprionodon lalandii and Myliobatis goodei) are listed as Data Deficient.
  5. Our results indicate that the commercial exploitation of endemic sharks and rays at risk of extinction is commonplace in southern Brazil. This reinforces the need for more systematic monitoring of the trade in fishery products and more effective application of the environmental legislation and conservation programmes.
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19.
The effects of feeding frequency (1, 2, 3, or 15 times daily) on oxygen consumption (OC, mg O2 kg−1 h−1) and ammonia excretion, (AE, mg TAN kg−1 h−1) of walleye (Stizostedion vitreum) are described. Walleye were reared at a practical culture density of 35·4 kg m−3 in a single-pass system at 23·2°C. Diurnal variation in metabolic rates were related to feeding, not to photoperiod. Minimum OC rates occurred 30 min before the first feeding of the day, which was the longest average time since the last feeding. Metabolic rates increased immediately after feeding. The maximum rates for OC were 36–49% higher than the minimum rates, and 14–22% higher than the 24-h mean rate. Maximum rates for AE were 137–409% higher than the minimum rates, and 39–87% higher than the mean rates. There was a highly significant difference in the mean metabolic rates related to feeding frequency. The mean OC rate for 1 feeding day−1 (222·0 mg O2 kg−1 h−1) was greater than the mean rates for 2, 3 and 15 feedings day−1. The OC rate for 1 feeding day−1 was 50·6% greater than the rate for 15 feedings day−1 (147·4 mg O2 kg−1 h−1), the lowest mean rate. Mean and maximum oxygen/feed ratio (OFR, kg O2 kg−1 feed fed day−1), varied inversely with feeding frequency. The mean ammonia/feed ratio (AFR) was similar for all but the 3 feedings day−1 treatment, but the maximum AFRs for 2 and 15 feedings day−1 were lower than the AFRs for 1 and 3 feedings day−1. AE was directly proportional to OC; the regression equations were highly significant, but specific for feeding frequency.  相似文献   

20.
Pikeperch were induced to spawn 3 months prior to the natural spawning period through photothermal and hormonal stimulation. Females (five specimens in each group) were stimulated with injection of human chorionic gonadotropin (hCG) once (200 IU kg–1), twice (200 IU kg–1, second dose after 48 h–400 IU kg–1) or three times (200 IU kg–1, after 24 h–200 IU kg–1 and after another 24 h–200 IU kg–1). The control group was injected once with 0.9% NaCl. The males were stimulated with a single hormone dose of 200 IU kg–1. Eggs were obtained from all the hormonally treated fish. None of the control group females, which were only stimulated photothermally, ovulated any eggs. The time of ovulation was 66–71 h following the first injection, and the eggs viability until the eyed stage (from 71.5 to 77.5%) did not depend on the number of hormone doses (P > 0.05). The out-of-season spawning method described in this paper could be used to provide pikeperch larvae for intensive culture systems (recirculating water systems) before natural spawning season and to produce larger-sized pikeperch fingerlings for stocking.  相似文献   

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