Australian Crayfish Research Articles

Effect on Growth, Survival, and Fatty Acid Composition of Australian Red Claw Crayfish Cherax quadricarinatus Fed Practical Diets With and Without Supplemental Lecithin and/or Cholesterol

AbstractRed claw crayfish Cherux quadricarinatus is one of more than a hundred species of Australian freshwater crayfish. However, because of its rapid growth rate, communal and non‐burrowing behavior, ease of spawning, wide temperature and dissolved oxygen tolerance, and no free‐swimming larval stages, red claw may be the best candidate among the Australian crayfishes for semi‐intensive or intensive aquaculture in the United States. The objective of the study was to examine the effects of growth, survival, and fatty acid composition of newly‐hatched red claw when fed four practical diets with or without lecithin and cholesterol. However, little is known of its nutritional requirements or practical diet formulations. An 8‐wk feeding trial was conducted in a recirculating system with newly‐hatched juvenile (mean individual weight, 0.2 g) red claw, each stocked in separate plastic mesh culture units containing their own individual water line. Water was recirculated through biological and mechanical filters. Practical diets were formulated to be isonitrogenous (40% protein) and isocaloric (4 kcal available enerpy/g of diet) and contained menhaden fish meal (25%), soybean meal (35%, except in Diet 4), and shrimp meal (10%, except in Diet 4) as protein sources. Diet 1 had 0.5% lecithin added and 1.0% cholesterol added: Diet 2 contained 0% lecithin and 1.0% cholesterol; Diet 3 contained 0.5% lecithin and 0% cholesterol: and Diet 4 contained 0% lecithin and 0% cholesterol.After 8 wk, juvenile red claw fed diets with 0% supplemental lecithin (Diets 2 and 4) had no significant difference (P >0.05) in final weight and percentage weight gain (5.6 g and 2626%. respectively) compared to red claw fed the control diet (Diet 1) containing 0.5% lecithin. Red claw fed a diet without added cholesterol (Diet 3) had significantly (P 0.05) lower final weight (3.6 g) and percentage weight gain (1,717%) compared to red claw fed the control diet (Diet 1). However, red claw fed Diet 4 (containing 0% added cholesterol and 0% added lecithin) showed no significant (P >0.05) difference in final weight (5.1 g) and percentage weight gain (2254%) compared to red claw fed all other diets. There was no significant difference (P >0.05) among all diets for specific growth rate (SGR) which averaged 5.38%/d. Percentage survival was not significantly different among all treatments and was 76% for red claw fed Diet 1, 64% (Diet 2), 56% (Diet 3), and 80% (Diet 4). These results indicate that red claw fed Diet 4 containing 25% menhaden fish meal, 44.5% soybean meal, 0.5% choline chloride, 2% cod liver oil and 1% corn oil may satisfy the lecithin and cholesterol requirements and that the addition of dietary lecithin and cholesterol may not be necessary for good growth and survival of small (0.2 g) juvenile red claw. This may allow for less expensive diet formulations for use by producers of red claw crayfish.

Trans-Tasman Sea larval transport: Is Australia a source for New Zealand rock lobsters?

Two species of rock lobster (Palinuridae) are commonly found in coastal waters around both New Zealand and Australia. Both species have a relatively long larval phase, which raises the question of how populations can be maintained in regions where the mean flow advects larvae away from the coast. Previous work shows that Jasus edwardsii is genetically indistinguishable between Australia and New Zealand, whereas Sagmariasus verreauxi may be genetically different between the 2 countries. Satellite altimeter data are used here to test the hypothesis that Australia acts as a source of larvae for some New Zealand populations, and to investigate if there is a physical mecha- nism for the apparent lack of gene flow for S. verreauxi. A Lagrangian approach is used in which the western Tasman Sea is seeded with numerical drifters to build up a statistical summary of the likely distribution of larval trajectories. Ignoring biological factors, about 9% of J. edwardsii and about 2% of S. verreauxi larvae might be expected to arrive in New Zealand waters within their respective larval lifetimes. An order-of-magnitude estimate shows that even with extremely high mortality, these rates are high enough for trans-Tasman larval flow to contribute to and possibly maintain some New Zealand populations. Larval flow across the Tasman Sea should be sufficient to maintain trans- Tasman genetic homogeneity in both species. We suggest that 1 reason that S. verreauxi may not be genetically homogenous is that in order to arrive in New Zealand within 1 larval lifetime, they have to cross the Tasman Sea north of the productive Subtropical Front where there is not enough prey to sustain them.

Effects of moon phase and soak time on catches of Jasus (Sagmariasus) verreauxi recruits on collectors

The hypothesis tested in this study was that catches of recruits (sum of pueruli to early-stage juveniles of the same year class) of Jasus (Sagmariasus) verreauxi on seaweed-type collectors were affected by lunar periodicity and by the soak time of the collectors. Mean numbers of recruits did not differ between phases of the moon, but significantly more recruits were caught on collectors soaked for four weeks than on those soaked for three or two weeks, which in turn were greater than on those soaked for one week. On the basis of these results, it was recommended that collectors should be soaked for four weeks. This information was used in developing a uniform and optimal methodology for full surveys to monitor the relative abundance of recruits of J. verreauxi along the coast of New South Wales.

FUNCTION OF MOUTHPARTS IN FEEDING BEHAVIOR OF PHYLLOSOMA LARVAE OF THE PACKHORSE LOBSTER, JASUS VERREAUXI (DECAPODA: PALINURIDAE)

Stage IV phyllosoma larvae of the packhorse lobster, Jasus verreauxi (H. Milne Edwards, 1851), were observed while feeding to determine the processing ability and involvement of mouthparts. Phyllosomata were presented live brine shrimp, Artemia salina (Linnaeus, 1758), mussel flesh, Perna canaliculus (Gmelin, 1791), and jellyfish, Aurelia sp., and were given chemical or tactile stimulation to induce a feeding response. Larvae were observed tearing their food with maxillipeds 2 and 3, before maceration by maxillipeds 2 and maxillae 1, mastication by mandibles and labrum, and subsequent ingestion of finer particles via a suction action induced by foregut contractions. Phyllosomata became entangled in food material and did not feed when provided soft tissue, such as jellyfish and mussel gonad. Maxilliped action increased when larvae were provided with harder prey, which indicated greater energetic investment required to process the food. Our observations suggest that phyllosomata are capable of processing fleshier prey items than Artemia, which is traditionally used as food in artificial culture. An ideal food source for phyllosomata should not readily break up and foul the water, should be free of microbes, and should be energetically economical to capture and masticate.

Marked depletion of polar lipid and non-essential fatty acids following settlement by post-larvae of the spiny lobster Jasus verreauxi

The development from the non-feeding post-larva (puerulus) to the first instar juvenile of spiny lobsters is highly energetically demanding. These demands may greatly compromise the energy reserves of the lobsters following settlement, leading to reduced growth and survival in the wild, and also in aquaculture. Therefore, the lipid class and fatty acid composition of wild caught pueruli and first instar juveniles of the spiny lobster Jasus verreauxi (H. Milne Edwards, 1851) were analysed by thin layer chromatography-flame ionisation detection and capillary gas chromatography. Pueruli contained substantially more lipid than first instar juveniles (mean difference =3.5 mg, or 41.9%) and most of this difference was due to the presence of greater amounts of polar lipid (mean difference =3.9 mg or 49.2%) in pueruli. First instar juveniles contained significantly more triacylglycerol (mean =0.2 mg), consistent with the polar lipid being converted to a more readily metabolised lipid class in the hepatopancreas. These results indicate that polar lipid is the major energy store during the non-feeding puerulus stage of spiny lobsters from the genus Jasus. Overall, the essential, polyunsaturated linoleic, docosahexaenoic and eicosapentaenoic acids did not show a significant decrease between the two developmental stages, despite the absence of feeding. However, significant reductions in the abundance of both saturated and monounsaturated fatty acids between the two stages were identified (decrease of 811 and 783 μg per individual, respectively). This suggested that selective depletion of non-essential fatty acids may be occurring, with resultant sparing of the essential fatty acids. Supplying diets rich in these depleted fatty acids, and in particular the essential fatty acids, preferably in polar lipid, is likely to result in increased survival and growth of J. verreauxi and other spiny lobsters from first instar juveniles in aquaculture.

Function of Mouthparts in Feeding Behavior of Phyllosoma Larvae of the Packhorse Lobster, Jasus Verreauxi (Decapoda: Palinuridae)

Stage IV phyllosoma larvae of the packhorse lobster, Jasus verreauxi (H. Milne Edwards, 1851), were observed while feeding to determine the processing ability and involvement of mouthparts. Phyllosomata were presented live brine shrimp, Artemia salina (Linnaeus, 1758), mussel flesh, Perna canaliculus (Gmelin, 1791), and jellyfish, Aurelia sp., and were given chemical or tactile stimulation to induce a feeding response. Larvae were observed tearing their food with maxillipeds 2 and 3, before maceration by maxillipeds 2 and maxillae 1, mastication by mandibles and labrum, and subsequent ingestion of finer particles via a suction action induced by foregut contractions. Phyllosomata became entangled in food material and did not feed when provided soft tissue, such as jellyfish and mussel gonad. Maxilliped action increased when larvae were provided with harder prey, which indicated greater energetic investment required to process the food. Our observations suggest that phyllosomata are capable of processing fleshier prey items than Artemia, which is traditionally used as food in artificial culture. An ideal food source for phyllosomata should not readily break up and foul the water, should be free of microbes, and should be energetically economical to capture and masticate.

Effect of temperature and food ration on the growth and survival of early and mid-stage phyllosomas of the spiny lobster Jasus verreauxi

Instar 1, 3, 5, and 7 phyllosomas of the spiny lobsterJasus verreauxi were reared individually at one of four temperatures (18, 21, 24, and 27C) and fed low, medium, or high rations of 2- to 3-mm Artemia salina. An increase in the temperature reduced the intermoult period for all instars tested, but only the instar 5 phyllosomas showed any significant differences in postmoult size with temperature; those at 18C were smaller. Phyllosomas reared at 18C ate fewer Artemia each day than did those at the higher temperatures, but instars 3 and 5 at 18C consumed more in total over the intermoult period. Survival for all instars tested was lowest at 18C. Increasing the food rations affected the growth and survival of instar 5 and 7 phyllosomas; those fed at the lower rations took longer to moult and had a smaller growth increment. For all instars tested, the feeding rate and total consumption increased with food ration.

Effects of nearness to reef and exposure to sea-swell on estimates of relative abundance of Jasus verreauxi (H. Milne Edwards, 1851) recruits on collectors.

The hypothesis tested was that catches of J. verreauxi recruits (numbers of pueruli to early juveniles) on sea-weed-type collectors were affected by the nearness of the collectors to vegetated reef and relative exposure of the collectors to sea-swell. Numbers of recruits on collectors set far from reef were greater than on collectors near reef. Collectors far from reef may be the first, preferred type of habitat encountered by recruits as they move across the Continental Shelf. Alternatively, fewer recruits may inhabit collectors set near reef because of the nearness of natural, vegetated reef. A cost-benefit analysis determined that the optimal sampling strategy for surveys of the abundance of recruits at one location and time, would be three replicate collectors at each of three sites. Sampling once with this strategy at one location would give a standard error of around 20% of the mean. This information was used in developing a uniform and optimal methodology for full surveys to monitor the relative abundance of J. verreauxi recruits along the coast of New South Wales.

The structure and growth of the statocyst in the Australian crayfish Cherax destructor.

The morphology of the statocyst of the Australian crayfish Cherax destructor was examined using scanning electron microscopy. It resembles in general structure, size, and position the statocysts of crayfish described previously, and the size and distribution of the fields of setae on the floor of the capsule are similar but not the same. Over the size range examined, the relationship between the carapace length, the length of the basal antennular segment, the diameter of the statocyst capsule, and the total number of setae are all linear. The number and position of setae on the floor of the statocyst capsule were mapped for animals in two size classes (small, ca. 20 mm; large, ca. 50 mm) to test for changes in their arrangement during growth. The change in the ratio of setal number to statocyst size between the two size classes was about three times greater for the anterior setal field than for the other fields. We propose that differential development of the setal fields may be related to changes in the force-monitoring requirements of the animals as they increase in size, but this remains to be experimentally tested.

Respiratory, acid–base and metabolic responses of the freshwater crayfish Cherax destructor to lead contamination

The effects of lead contamination on respiratory, acid–base and metabolic status were investigated in the freshwater Australian crayfish, Cherax destructor. Lead has been found to perturb sodium balance in C. destructor and it seemed likely, given the link between ion regulation and gas exchange in aquatic crustaceans, that respiration and acid–base balance would be compromised. Exposure of C. destructor to either 100 or 0.5 mg l −1 Pb in the water caused a reduction in oxygen consumption ( M ̇ O 2 ) of at least 50% within 24 h, and after 21 days M ̇ O 2 was only 30% of pre-exposure levels. The reduced M ̇ O 2 was accompanied by a decrease in heart rate from 66±9 to 29±6 beats min −1 in the initial 24 h but ventilation rate remained unchanged (23±5 beats min −1). Concomitantly there was a marked reduction of the oxygen transfer factor ( TO 2) across the gills from 2.69×10 −2 μmol Pa −1, typical of crustaceans, to 1.08×10 −2 μmol Pa −1 in impacted crayfish after 21 days exposure. Despite the reduced M ̇ O 2 and TO 2, there was almost no change in the acid–base status of Pb impacted crayfish in comparison to controls. While part of the normal response of C. destructor to hypoxia is a hyperventilation leading to lowered M ̇ O 2 , the apparent hypoxia caused by Pb impact did not elicit any increase in ventilation and thereby no attempt was made to maintain a ‘normoxic’ M ̇ O 2 . Metabolism was not supplemented by anaerobiosis and thus overall energetic demand must have been lowered. This response strongly suggests that Pb promotes a hypometabolic state as well as an elevation of the threshold PO 2 at which anaerobiosis would be initiated. Lead contamination would therefore exclude C. destructor from waters prone to hypoxia.

Accumulation of lead and its effects on Na balance in the freshwater crayfishCherax destructor

The accumulation of lead in tissues of the freshwater Australian crayfish Cherax destructor and its effect on ion and osmoregulation were investigated. Crayfish were exposed to two different lead concentrations for up to 21 days, either 100 mg · 1–1 or a sublethal concentration of 0.5 mg · 1–1, to determine the distribution of lead in exposed crayfish. The gills were the primary site of lead accumulation at both concentrations, with crayfish exposed to 100 mg · 1–1 accumulating 46.4 mg Pb2+ · g–1 wet weight. However, there was a marked difference in the distribution of lead at the two concentrations. C. destructor exposed to sublethal lead levels maintained osmotic pressure and the haemolymph ion concentrations of Na, K, Mg, and Cl. However, there was a 37% decrease in haemolymph Ca concentration in Pb-exposed crayfish after 21 days. While Na homeostasis was maintained, there was a 50% decrease in unidirectional sodium influx in long-term-exposed crayfish, which correlated with a 40% inhibition of Na+/K+-ATPase activity in gill homogenates from long-term-exposed C. destructor. The ability of Pb-exposed crayfish to activate Na transport was also reduced by 70% as determined from the maximum rate of net Na uptake. Thus the accumulation of large lead burdens in the gills and the reductions in Na flux rates will effectively restrict the distribution of C. destructor into soft water bodies. The ability of C. destructor to rapidly accumulate and tolerate the effects of lead indicate that this species is a suitable candidate as a bioindicator of freshwater lead contamination. J. Exp. Zool. 281:270–279, 1998. © 1998 Wiley-Liss, Inc.

The result of evolutionary limb loss on the complement of motor neurons in a crayfish limb nerve revealed by serial homology

Many macruran decapod crustaceans show sexual dimorphism of abdominal appendages adapted for use as secondary reproductive organs. Not only does the Australian crayfish, Cherax destructor, show no external, abdominal dimorphism, but both males and females have lost the pleopods of the first abdominal segment entirely. The first nerves of the abdominal ganglia of crayfish and lobsters carry the axons of the pleopod motor neurons. We used intracellular cobalt infusion into the first nerves of the first and second abdominal ganglia to reveal the motor neuron complement of these ganglia in males and females. The first nerves of the second abdominal ganglia of both males and females have approximately 37 motor neurons associated with them. The homologous nerves in the first abdominal segment, where there are no pleopods, have only 8 or 9 motor neurons associated with them. The evolutionary implications of this difference are discussed.

Culture of larval spiny lobsters: a review of work done in northern Japan

The method developed over the past decade in northern Japan to culture phyllosoma larvae of five species of principally cool-temperate spiny lobsters combines the features of upwelling water, co- cultured microalgae, and use of mussel gonad as food. The feeding behaviour of the phyllosomas shows that they are primarily predators with the pereiopods and secondarily plankton feeders with the maxillipeds and maxillae. Recent work has shown that contamination of culture water by microorganisms such as the fouling protozoans Vorticellaspp. can greatly reduce phyllosoma survival. The significance of co-cultures of microalgae in maintaining water quality is not yet fully understood. Newly hatched lavae of sailfin sandfish (Arctoscopus japonicus) is an excellent food for late-stage phyllosomas of Jasus verreauxi. About 5% of J. verreauxi phyllosomas metamorphosed into pueruli. Mortality during the puerulus stage was reduced by increasing the capacity of the culture tanks from 30 L to 100 L. A single Palinurus elephas phyllosoma raised in co-culture with diatoms and fed mussel gonad and A. japonicus larvae metamorphosed into a puerulus in 65 days after seven moults.

Tagging eastern rock lobsters Jasus verreauxi: effectiveness of several types of tag

An experiment was done in the laboratory over 147 weeks to assess tag loss (tag-induced mortality plus tag shedding) in tagged or marked eastern rock lobsters, Jasus verreauxi. The incidence of tag-induced mortality, tag shedding or tag loss did not generally differ among tag types (toggle, T-anchor, dart tags), mark, or untagged lobsters. The exceptions were that more untagged lobsters died between weeks 86 and 147 than lobsters tagged with T-anchor or dart tags. The percentages of lobsters that died were 51, 45, 43, 47, and 62 for toggle, T-anchor, dart, marked, and untagged treatments, respectively. An additional 18%, 22% and 23% of lobsters tagged with either toggle, T-anchor or dart tags, respectively, shed their tag. None of the marked lobsters lost their marks. We conclude that no one type of tag used in the experiment was more suited to tagging J. verreauxi than another. Marking was discounted as a technique to use in long-term experiments because, although the mark was still evident after 147 weeks, only trained observers could recognise it, making the technique inappropriate for the general public.

Weight Gain and Survival of Juvenile Australian Crayfish Cherax quadricarinatus Fed Formulated Feeds

Abstract.— Weight gain and survival were examined in newly‐hatched juvenile Australian crayfish Cherax quadricarinatus fed formulated crustacean feeds. Crayfish cultured using several Argent specialty feeds, including brine shrimp flakes, freeze‐dried krill, powdered spirulina, and hatchfry encapsulon, exhibited high mortality (>90%) and little or no weight gain. After ten weeks of culture, crayfish fed AB crayfish feed (AB) exhibited the highest weight gain with nearly 100% survival. Weight gain of crayfish fed other formulated feeds, such as Zeigler post‐larval feed (ZPL), Zeigler shrimp grower (ZSG), Burris Mill crayfish feed (BM), Rangen shrimp grower (RSG), and a formulated CNStacean feed (CRUS) were significantly lower. Survival of crayfish cultured using these feeds was also significantly lower, ranging from 40% (CRUS) to 72% (BM). Mortalities associated with these feeds occurred both during the intermolt period and during the molt. Recovered biomass was approximately half of that observed for crayfish cultured using AB feed, further indicating the inadequacy of these formulated feeds for use in crayfish cultures. These data suggest that many commercially available feeds do not provide the nutritional requirements for juvenile Australian crayfish.

Chromosomes of Temnocephala minor, an ectosymbiotic turbellarian on Australian crayfish found in Kagoshima Prefecture, with karyological notes on exotic turbellarians found in Japan

Records of exotic turbellarian species found in Japan are reviewed from taxonomic and karyological viewpoints. Temnocephala minor Haswell, 1888, an ectocommensal on a freshwater crayfish of Australia, was found from culture ponds of Cherax tenuimanus (introduced from W. Australia) in Kagoshima Prefecture. T. minor had the chromosome number of 2x = 18 (2sm + 2m + 2m + 2sm + 2m + 2m + 2m + 2sm + 2m). The following 3 species of exotic freshwater triclads were recorded from tanks and ponds used for tropical fish culture: Dugesia austroasiatica Kawakatsu, 1985 (2x = 16), Dugesia tigrina (Girard, 1850) (2x = 16) and Rhodax? sp. (3x = 24; 3x = 24 & 3x + 1LB + 1SB = 25 + 1SB). The following 3 species of exotic terrestrial triclads were recorded: Bipalium nobile Kawakatsu et Makino, 1982 (2x = 10), Bipalium kewense Moseley, 1878 (2x = 18), and Platydemus manokwari de Beauchamp, 1962 (n = 6, 2x = 12). An extensive occurrence of P. manokwari in the Southwest Islands of Japan may be due to an unexpected introduction of the animal in very recent years.

Patterns in Landings and Size Composition of Jasus Verreauxi (H. Milne Edwards, 1851) (Decapoda, Palinuridae), in Waters Off New South Wales, Australia

Available information suggests that the relative abundance of the New South Wales' spiny lobster stock, exploited since at least 1873, has declined over the past 20 years. Annual landings fluctuated until 1948-49 but have fallen in most years since. Data on fishing effort and CPUE were available only for years from 1969-70 onwards. Fishing effort was stable over most years to 1978-79 but has continued to rise since then. CPUE declined over the period for which data were available; this was attributed to a fall in the abundance of Jasus verreauxi, since this species comprises around 97% of the commercial catches of lobsters in New South Wales. The lengths of J. uerreauxi in catches from commercial vessels between 1986 and 1988 varied between locations. The spatial pattern in annual distributions of lengths suggests that this species may move along-shore. When data from all sites were combined, only 10% of the J. verreauxi sampled were longer than the smallest length at which 50% of females carry eggs (166.5 mm CL). Although the optimum level of fishing effort could not be determined from the available data, the patterns in landings, effort, and CPUE suggest that measures are necessary to conserve this resource until estimates of maximum sustainable yield and optimum fishing effort can be determined.

Patterns in Landings and Size Composition of Jasus Verreauxi (H. Milne Edwards, 1851) (Decapoda, Palinuridae), in Waters Off New South Wales, Australia

Available information suggests that the relative abundance of the New South Wales' spiny lobster stock, exploited since at least 1873, has declined over the past 20 years. Annual landings fluctuated until 1948-49 but have fallen in most years since. Data on fishing effort and CPUE were available only for years from 1969-70 onwards. Fishing effort was stable over most years to 1978-79 but has continued to rise since then. CPUE declined over the period for which data were available; this was attributed to a fall in the abundance of Jasus verreauxi, since this species comprises around 97% of the commercial catches of lobsters in New South Wales. The lengths of J. uerreauxi in catches from commercial vessels between 1986 and 1988 varied between locations. The spatial pattern in annual distributions of lengths suggests that this species may move along-shore. When data from all sites were combined, only 10% of the J. verreauxi sampled were longer than the smallest length at which 50% of females carry eggs (166.5 mm CL). Although the optimum level of fishing effort could not be determined from the available data, the patterns in landings, effort, and CPUE suggest that measures are necessary to conserve this resource until estimates of maximum sustainable yield and optimum fishing effort can be determined.

Freshwater crayfish aquaculture in North America, Europe, and Australia: families Astacidae, Cambaridae, and Parastacidae

ContentsIntroduction * I. Cultivation of Freshwater Crayfishes in North America * Freshwater Crayfish Culture * Freshwater Crayfish Processing * Diseases of Louisiana Crayfish * II. Cultivation of Freshwater Crayfishes in Europe * Introduction * The Crayfish and Crayfish Production in Europe * Crayfish Culture * III. Cultivation of Freshwater Crayfishes in Australia * Introduction * Phylogeny * Distribution of Parastacids in Australia and Their Suitability for Aquaculture * The Yabbie, Cherax destructor * The Marron, Cherax tenuimanus * Redclaw, Cherax quadricarinatus * Economics * Marketing * Status of Australian Crayfish Culture, 1989?90 Season * Index

Heat and oxygen flux as a function of environmental po2 in juvenile Australian crayfish, Cherax quadricarinatus

AbstractOxygen and heat flux of the juvenile Australian red claw crayfish, Cherax quadricarinatus, were measured in parallel respirometry and calorimetry systems at 28°C at varying levels of environmental po2. Juvenile crayfish maintained an average oxygen flux of 5.0 ± 0.4 (SEM) pmol O2/(s*mg fresh weight) over the po2 range from 20.7 to 5 kPa. At approximately 4 kPa po2, oxygen flux decreased, conforming to decreasing oxygen tensions. Juvenile crayfish maintained an average heat flux of −2.2 ± 0.2 μW/mg fresh weight when exposed to 100 and 50% air saturated conditions (18.1 to 20.7 and 7.8 to 10.4kPa po2, respectively). The ratio of the amount of heat dissipated per oxygen consumed, called the calorimetric/respirometric (CR) ratio, at 100 and 50% air saturated conditions averaged −440 kJ/mol O2. When crayfish were exposed to 25% air saturated conditions (2.5 to 5.2 kPa po2), heat flux decreased initially to −1.1 ± 0.4 μW/mg fresh weight. Within 4 hr, however, heat flux returned to normoxic values. When crayfish were exposed to anoxic conditions, heat flux decreased to zero. Most juvenile crayfish did not survive short‐term (1–2 hr) anoxic stress. These data suggest that juvenile C. quadricarinatus are excellent oxygen regulators over a wide range of environmental po2. These data indicate also that juvenile C. quadricarinatus can compensate metabolically, possibly via aerobic and/or anaerobic adjustments, in order to maintain metabolic rate at critically low po2. Last, this crayfish appears limited in its ability to utilize anaerobic pathways to maintain metabolic rate in anoxic environments. © Wiley‐Liss, Inc.