The primary structure and oxygen-binding properties of the single haemoglobin of the high-Antarctic fish Aethotaxis mitopteryx DeWitt

Summary The complete amino acid sequence of the single haemoglobin of the Antarctic fish Aethotaxis mitopteryx DeWitt has been established by automated repetitive Edman degradation on the intact and cleaved (enzymatically and chemically) and chains. A very high sequence identity with other Antarctic fish haemoglobins has been detected. The haemoglobin has a moderate Bohr effect and no Root effect. Organic phosphates and chloride also regulate oxygen binding only to a moderate extent. The lack of Root effect is consistent with the substitution His — Val at the HC3 C-terminal position of the chain. The low overall heat of oxygenation suggests that in this species oxygen transport is an energy-saving process, presumably related to cold adaptation. The comparative analysis of the haemoglobins of Antarctic fishes emphasises some unique features of the oxygen-transport system of A. mitopteryx, which are likely to be related to its also rather unique mode of life.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Carbon relations and competition between woody species in a Central European hedgerow

Summary The CO₂ uptake capacity of leaves of five competing woody species in an undisturbed developing Central European hedgerow was investigated for possible factors determining competitive ability in the field. Light-saturated maximal CO₂ uptake (A _max) showed species-specific seasonal variations in Prunus spinosa, a bushlike pioneer on fallow land, in Crataegusxmacrocarpa and Acer campestre, two treelike species dominating the canopy, in Rubus corylifolius, a pioneer liane, and in Ribes uva-crispa, a shrubby undergrowth species. In fully-expanded sun leaves of Prunus, Crataegus and Acer A _max ranged from 8 to 12 mol m^-2 s^-1 while it ranged from 6 to 15 mol m^-2 s^-1 in Rubus and Ribes. The temperature responses showed no difference among species. Neither leaf photosynthetic capacity nor nutrient use of carbon fixation determined competitive ability. Differences between species in the capacity of leaves to adapt to shade resulted in differences in species' establishment in the understory and demonstrated the importance of growth in order to escape light-limiting conditions. A specific sequence of species was found for the range of A _max in sun leaves. It was highest in an early pioneer of low competitive ability (Rubus), medium in a later pioneer (Prunus) and in successional plants (Crataegus, Acer), and lowest in the climax species of high competitive ability, Fagus silvatica, (3–4 mol m^-2 s^-1; Schulze 1970).     

Comparative haematology of ten species of marine fish from Visakhapatnam Coast

A comparative study has been made of haematological parameters (erythrocyte numbers, leucocyte numbers, haematocrit and haemoglobin), erythrocyte indices (MCV, MCH and MCHC) and cytometric measurements (cell and nucleus) of 10 species of marine fish from the Visakhapatnam Coast, of which six are from harbour waters, three from rock pools and one from inshore waters. It is found that active fish have high values of erythrocyte numbers, haematocrit, haemoglobin and nucleo/cytoplasmic ratio and low values of leucocyte numbers and erythrocyte cytosome measurements. The most active of all is the inshore species Rastrelliger kanagurta depicting the haematological requirements of an active fish with high oxygen demand to meet the requirements of high metabolic rate. The other active fish such as Megalops cyprinoides and Mugil cephalus are intermediate, with the rock pool fish and Caranx carangus with low values of nucleo/cytoplasmic ratio at the other extreme.     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

Oxygenation properties of haemoglobins from the flatfish plaice (Pleuronectes platessa) and flounder (Platichthys flesus)

Summary The oxygen binding properties and some haematological data of haemoglobins of plaice (Pleuronectes platessa) and flounder (Platichthys flesus) were measured and compared, with the view of discerning their adaptations to the benthic habitat.Compared to plaice, flounders posses higher haematocrit and haemoglobin levels, and their haemoglobin has a higher oxygen affinity, smaller Bohr and Root effects and appears to have a greater ATP sensitivity. At pH 7.6, the half-saturation oxygen tensions,P ₅₀, of stripped plaice and flounder haemoglobins amount to about 5.9 and 4.2 torr, and the Bohr shifts (logP ₅₀/ pH) to –0.51 and –0.34, respectively. The species differences in the oxygen binding patterns occur after stripping the haemoglobin in solution, from dissolved ions and thus appear to be inherent in the pigment molecules. The differences suggest that the haemoglobin of flounder is better adapted to hypoxic and hypercarbic environments than plaice haemoglobin, in accordance with the more inshore occurrence of the former species.The molar ratios of ATP to haemoglobin tetramers are low in plaice and flounder (about 1.6); in plaice this ratio corresponds to that where the cofactor effect is most pronounced. In contrast to previous evidence for an adaptive reduction in the temperature dependence of the haemoglobin of flounder but not of plaice from the Baltic Sea (Friedrich, 1935), the same temperature effects were found in representatives of the two species both from the Dutch North Sea and the Danish Kattegat.     

Stress response in two Antarctic teleosts (Notothenia coriiceps Richardson andChaenocephalus aceratus Lönnberg) following capture and surgery

Blood chemistry and haematological parameters have been determined in two Antarctic teleosts,Notothenia coriiceps Richardson andChaenocephalus aceratus Lönnberg, held at around 1°C.Notothenia coriiceps has a low haemoglobin content compared to tem-perate-zone species, whereasC. aceratus apparently lacks respiratory pigments. Blood samples were obtained by cardiac puncture following landing or using chronically implanted post-branchial arterial cannulae. Although both species showed a similar acidosis on capture (arterial pH as low as 7.5 versus the final recovery value of around 7.9),C. aceratus took 48 h to reestablish baseline values whileN. coriiceps recovered within 12 h, despite initially showing a greater degree of hypercapnic hypoxia. Surgery led to a more severe disturbance of acid-base regulation inN. coriiceps thanC. aceratus (arterial pH of 7.5 versus 7.8) but needed only half as long for recovery. A progressive decrease in arterial oxygen tension and increase in arterial carbon dioxide tension (both more pronounced inN. coriiceps) with level of acidosis was observed down to arteria pH 7.2 InC. aceratus this was accompanied by a rise in blood lactate (up to 10 mmol·1^-1 in some individuals), whileN. coriiceps showed only a modest and transient lactacidosis. Stress inN. coriiceps therefore induces primarily a respiratory, rather than a metabolic acidosis, whereas inC. aceratus both components are present. A differential response to stress is also indicated by an elevated, though low noradrenaline titre inN. coriiceps following surgery and capture, whileC. aceratus was little affected by surgery. However, both species show an unusually weak catecholamine response to induced stress.Abbreviations pH/T °C thermal sensitivity of pH - Ad adrenaline - bw body weight - C.CO₂ total carbon dioxide content - C.O₂ total oxygen content - ED ₅₀ Median effective dose - EDTA ethylenediaminetertra-acetic acid - Hb haemoglobin - Hct haematocrit - HPLC high-performance liquid chromatography - lac lactate - MCH mean corpuscular haemoglobin content - MCHC mean corpuscular haemoglobin concentration - MCV mean cell volume - MS222 tricaine methane sulphonate - NAd noradrenaline - P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen tension - pHa arterial blood pH - RBCC red blood cell count - SW sea water - T _a ambient air temperature - VO₂ oxygen consumption     

Sipuncula of the southeastern Weddell Sea (Antarctica)

Sipunculans collected during the EPOS (European Polarstern Study) leg 3 cruise (13.1.89–10.3.89) to the Weddell Sea shelf area from depths ranging from 186 to 2037 m are recorded. Seven species in three genera are recognized; Nephasoma capilleforme and Phascolion convestitum have not been recorded hitherto in Antarctica. Significant morphological characters as shown by light (LM) and electron (SEM) photographs are described and illustrated. Antarctic distribution maps of the species collected and a checklist of the sipunculan species south of the Antarctic Convergence with depths and bibliographic references are included.     

Thermostability of haemoglobins from Antarctic fish

Summary Proteins from Antarctic fish are less stable at high temperatures than those from fish from lower latitudes. Investigations into the thermostability of haemoglobins from a range of Antarctic teleosts have been carried out for comparison with data from temperate species. Haemoglobin concentrations following periods of heating at 50°C were analysed spectrophotometrically and the time taken for 50% denaturation (t_50%) determined. The effects of pH and salt concentrations were also examined. With the exception of that of Rhigophila dearborni, the haemoglobins were found to be relatively unstable with t_50% values ranging from 7.7 to 29.9 min at pH 7. All haemoglobins became less stable on addition of KCl but the effect of pH was variable. Freezing had no effect on the stability of haemoglobin from Dissostichus mawsoni. The thermostability of haemoglobin from a temperate nototheniid, Notothenia angustata, was within the range displayed by its antarctic relatives and it would seem that in general the differences between genera are as great as those between Antarctic and temperate species as a whole.     

Haematological and serum biochemical reference values of snow trout,Schizothorax labiatus habiting in river Sindh of Indian Himalayan region

Haematological and serum biochemical parameters are a valuable tool in determining the wellbeing status of different fish species and response in close association to various biological and environmental factors, therefore the aim of the present study was to establish sex-wise reference values of haemato-biochemical parameters of S. labiatus. The haematological parameters such as haemoglobin (Hb) concentration, total erythrocyte count (RBC), total leucocyte count (WBC), packed cell volume (PCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), mean corpuscular volume (MCV) and serum biochemical parameters such as glucose, cholesterol, urea, total protein, albumin and globulin were analysed. The results revealed that the haematological parameters, i.e., Hb, RBC, WBC and PCV showed significant (P < 0.05) differences with respect to sex. Significantly (P < 0.05) higher values of Hb content (11.18 g dl⁻¹), RBC count (1.88 × 10⁶ mm⁻³) and PCV (36.15%) were noted in male fish than females throughout the study period, while significantly (P < 0.05) higher WBC count was noted in females (20.38 × 10³ mm⁻³) compared to males. However, no significant (P > 0.05) difference was observed in erythrocyte indices like MCH, MCHC and MCV between sexes. The serum biochemical parameters, i.e., glucose, cholesterol and urea, also showed significant (P < 0.05) difference between the sexes, but no significant (P > 0.05) difference was noticed in total protein, albumin and globulin. Significantly (P < 0.05) highest values of glucose (116.76 mg dl⁻¹) and urea (9.01 mg dl⁻¹) were recorded in male S. labiatus, while highest value of cholesterol (223.53 mg dl⁻¹) was noted in females. The information generated in the present study gives the basic reference values of haematological and serum biochemical parameters of S. labiatus which will be useful in monitoring the wellbeing status of fish populations. Moreover, the data will also be helpful to ascertain the occurrence of different clinical and subclinical diseases, which may in turn help to boost the overall production of this species.     

Adaptation of intestinal cell membrane enzymes to low temperatures in the Antarctic teleost Pagothenia bernacchii

The enzymatic activity (expressed as milliunits per milligram total proteins) of three intestinal brush-border membrane enzymes, leucine aminopeptidase, alkaline phosphatase and maltase, measured over a range of temperatures between 1.5 and 37 °C, has been found to be much higher in the Antarctic fish Pagothenia bernacchii than in the temperate fish Anguilla anguilla. To explain this experimental observation the apparent Michaelis-Menten constant, the maximal velocity, the activation energy values and the thermal stability of these three enzymes were measured. The apparent Michaelis-Menten constant values of leucine amino peptidase and alkaline phosphatase were different in the intestine mucosal homogenate of the two fish at each measured temperature (from a minimum of 2.5 to a maximum of 37 °C). However, the values found at 2.5 °C for the Antarctic species and 15 °C for the eel where comparable. Furthermore, its value was unchanged in eel intestine apical membranes, both in the presence and without enzyme lipid microenvironment. While the maximal enzymatic activities of the leucine aminopeptidase and maltase did not decrease without their enzyme lipid microenvironment, produced by treatment with Triton X-100, the impairment of alkaline phosphatase maximal activity cannot be significantly differentiated from a non-specific inhibitory effect of the detergent. The activation energy values of leucine amino peptidase, alkaline phosphatase and maltase were lower in the Antarctic fish (11.7, 5.6 and 11.8 kcal·mol^-1, respectively) than in the eel (13.6, 7.6 and 13.1 kcal·mol^-1, respectively). The thermal stability of alkaline phosphatase and maltase is different in Pagothenia bernacchii and Anguilla anguilla intestinal homogenate.Abbreviations BBM brush border membrane - E _a activation energy - EGTA ethyleneglycol-bis-(-amino ethylether)N, N-tetraacetic acid - HEPES 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethane sulphonic acid - Km_app apparent Michaelis-Menten constant - PMSF phenylmethyl-sulphonyl fluoride - TRIS TRIS (hydroxymethyl)-aminomethane     

Effects of Galaxias maculatus on Nutrient Dynamics and Phytoplankton Biomass in a North Patagonian Oligotrophic Lake

In this study we analysed the effects of Galaxias maculatus, a landlocked small fish species, on nutrient dynamics, and the consequent effects on phytoplankton biomass of an oligotrophic North Patagonian lake. We performed field and laboratory experiments in order to explore nutrient release by G. maculatus with increasing fish biomass and body size, and the resulting phytoplankton responses. Our results showed that phytoplankton biomass was strongly enhanced in the presence of fish, and that enhancement was greater with increasing fish biomass. These algal increments were associated with higher nutrient concentrations, due to the excretion/egestion processes of fish. In our two laboratory experiments we did not observe phytoplankton increase, probably due to light conditions, but we did observe significant effects of fish on nutrient concentrations. As was expected, mass-specific nutrient release rates were higher in smaller fish than in larger ones. So, the amount of nutrients supplied to phytoplankton would be influenced by the size structure of fish population. As a consequence of different N and P release rates, an increase in the :P_TDP ratio was observed in the presence of fish. The fact that G. maculatus is a species that moves in schools would determine spatial heterogeneity in nutrient release, with important effects of reducing nutrient limitation and shifting :P_TDP ratios.     

An Arctic teleost fish with a noticeably high body fluid osmolality: a note on the navaga,Eleginus navaga (Pallas 1811), from the White Sea

Navaga (Eleginus navaga), an Arctic gadoid fish, were sampled in the White Sea in spring and body fluid osmolality analysed. At the time of capture the water in the White Sea was close to freezing ( -1°C) and salinity was about 20 ppt. Navaga serum was found to be isosmotic (approximately 590 mosmol/l) with that of the surrounding water. Thus, the osmotic concentration in the body fluids of navaga is one of the highest reported for teleost fish and is comparable to that of the strictly marine Nototheniids from the Antarctic     

In situ localization of two haemoglobin gene clusters in the chromosomes of 13 species of Chironomus

Two haemoglobin (Hb) gene clusters cloned from the genomic DNA of Chironomus thummi were localized in the polytene chromosomes of 13 Chironomus species. The haemoglobin gene cluster containing the genes for the monomeric haemoglobin proteins III and IV (CttG1) hybridized in all species to the end of chromosome arm E. The haemoglobin gene cluster containing the genes for the dimeric HbVIIB proteins (piHb1) could be localized to chromosome arm D. The chromosomal position of the haemoglobin genes was always found in morphologically specified groups of bands and is in agreement with cytological data, which have been used to establish the evolutionary relationships between the species of the genus Chironomus.     

Subtle relationships: freshwater fishes and water chemistry in southern South America

We investigated the relationships between water chemistry and the occurrence, distribution, physiology, and morphology of fish faunas. We examined 34 species (ca. 10% of the Argentinean freshwater fish fauna) from 120 localities (5 areas) situated between 26°15 S (Trancas, Tucumán) and 38°30 S (Sierra de la Ventana, Buenos Aires). Fourteen chemical features are described by: conductivity, total dissolved solids, temperature, pH, CO ₃ ^2– , CO₃H^–, Cl^–, SO ₄ ^2– Ca²⁺, K⁺, Mg²⁺, Na⁺, Mg/Ca, Mg+Ca/Na+K. Three Basic Data Matrices considering the mean, maximum and minimum values of each variable for each fish species were used in a Cluster and Principal Component Analysis. Groups of species clustered in similar ways to particular water chemistries. Similarity was the common occurrence of species in a defined area and preference for a common range of the factors considered. Groups of species so defined showed patterns of distribution related to climate, environment, trophic state and hydrographic complexity. Each cluster included some eurytopic species which appeared together at extreme chemical and geographic characteristics. Twenty four species had ranges of tolerance for the 14 variables and evidence of a grouping according to these ranges. Eighteen species which occurred at maximum or minimum absolute values for more than one factor were ordered along an eurytopy — stenotopy axis. We support the statement that species with a larger tolerance range for most factors have a higher probability of being widely distributed. Astyanax fasciatus and A. bimaculatus tolerated the highest number of maximum and minimum values, followed by Jenynsia l. lineata, A. eigenmanniorum and Trichomycterus corduvensis. Groups of species based on chemical factors showed differences in the relative number of basic morphological types.This paper was submitted at the symposium Fish Ecology in Latin America during the 1993 meeting of the ASIH at Austin.Consejo Nacional de Investigaciones CientíficasInstituto de Limnología de La PlataFacultad de Medicina, Universidad Nacional de La Plata     

Haematological parameters in a neotropical fish, Corydoras paleatus (Jenyns, 1842) (Pisces, Callichthyidae), captured from pristine and polluted water

We report normal ranges of haematological indices in healthy Corydoras paleatus from an unpolluted area. Haematological parameters studied include: erythrocyte counts (Er), haematocrit (Ht), haemoglobin concentration (Hb), mean cell volume (MCV), mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC). Normal red blood parameters did not change according to maturation stages, sex or seasons. Then, we compared them with those coming from fish captured in a site polluted by sewage. Fish exposed to pollution presented significantly higher values of Er, Ht, Hb, MCH and MCHC than those captured in an unpolluted area. Discriminant analysis showed that Hb is a key parameter to point out differences between populations exposed to different environmental conditions. We suggest that haematological values of C. paleatus, registered during this study, could be used as biomarkers in future works evaluating the incidence of environmental stress on fish as well as pointing out changes in the water quality.     

Identification and quantification of prostaglandins in Antarctic krill (Euphausia superba Dana)

Summary The amount and types of prostaglandins present in Antarctic krill (Euphausia superba Dana.) were estimated. Samples of fresh krill were collected during III Antarctic Cruise of RV Polarstern in November 1984. Prostaglandins were extracted, separated by column and thin-layer chromatography and identified as PGA₂, PGB₂, PGE₂, PGF₂. Quantitative measurements were made by a biological method (Vane cascade), concentrations of the most abundant prostaglandins PGE₂ and PGF₂ being 1.6 and 4 ng/1 g of fresh tissue, respectively. Such low level of prostaglandin would not be harmful when using krill as a food supplement.     

Visual and lenticular pigments in the eyes of demersal deep-sea fishes

We report on the lens pigmentation and visual pigments of 52 species of demersal deep-sea fishes caught at depths ranging from 480 m to 4110 m in the Porcupine Seabight and Goban Spur area of the North-eastern Atlantic. Only one species, caught between 480 and 840 m, had a lens with large amounts of pigment, consistent with the hypothesis that heavily pigmented lenses in deep-sea fish serve to enhance the contrast of bioluminescent signals by removing much of the background radiance, which is only visible to fish living shallower than 1000 m. Low concentrations of lens pigmentation were also observed in a further two species (Rouleina attrita and Micromesisteus poutassou). The retinae of all species except five, contained only a single visual pigment, as determined by microspectrophotometry of individual rods, and/or spectrophotometry of retinal wholemounts and retinal extracts. Those fishes caught between 500 m and 1100 m had wavelengths of peak sensitivity (_max) ranging from 476 nm to 494 nm, while most fish living below 1100 m tended to be more conservative with (_max) values ranging from 475 nm to 485 nm. The only exceptions to this were three deep-living species caught between 1600 m and 2000 m whose retinae contain abnormally short-wave sensitive visual pigments (Cataetyx laticeps — _max 468 nm; Alepocephalus bairdii — _max 467 nm; Narcetes stomias _max 472 nm), suggesting adaptation for the detection of short-wave bioluminescence.     

Antioxidative Activity of Arbutin in a Solution and Liposomal Suspension

Chattonella marina, a raphidophycean flagellate, is one of the most toxic red tide phytoplankton and causes severe damage to fish farming. Recent studies demonstrated that Chattonella sp. generates superoxide (), hydrogen peroxide (H₂ O₂), and hydroxyl radicals (·OH), which may be responsible for the toxicity of C. marina. In this study, we found that other raphidophycean flagellates such as Hetevosigma akashiwo, Otisthodiscus luteus, and Fihrocapsa japonica also produce and H₂O₂ under normal growth condition. Among the flagellate species tested, Chattonella has the highest rates of production of and H₂O₂ as compared on the basis of cell number. This seems to be partly due to differences in their cell sizes, since Chattonella is larger than other flagellate species. The generation of by these flagellate species was also confirmed by a chemiluminescence assay by using 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[l,2-a]pyrazin-3-one (MCLA). All these raphidophycean flagellates inhibited the proliferation of a marine bacterium, Vibrio alginolyticus, in a flagellates/bacteria co-culture system, and their toxic effects were suppressed by the addition of superoxide dismutase (SOD) or catalase. Our results suggest that the generation of reactive oxygen species is a common feature of raphidophycean flagellates.     

Annual net production and life span of floating leaves in Nymphaea tetragona Georgi: a comparison with other floating-leaved macrophytes

Fredericella sultana (Blumenbach, 1779) has long been considered one of the few freshwater bryozoan species with a truly cosmopolitan distribution. However, chromosome spreads from European material show 2n = 16 compared to 2n = 14 in North American specimens. In laboratory rearing the two forms are morphologically indistinguishable except for the surface texture of their statoblasts. Smooth statoblasts of European colonies match early illustrations of the species, while the densely pitted statoblasts of the North American form resemble those of F. indica Annandale 1909. On the basis of these observations we tentatively designate the North American F. sultana as F. indica. The only known American species with smooth statoblasts is F. australiensis Goddard 1909, in which the 2n = 16 karyotype is similar or identical to European F. sultana; however, despite this karyotypic similarity the two species retain their distinguishing morphology when reared together in the laboratory. Two enzymes from a single specimen of European F. sultana were electrophoretically distinct from the corresponding enzymes present in samples of both F. australiensis and North American F. sultana. Four phosphoglucose isomerase alleles were present in North American F. aultana from four geographically separated collection sites, although only one genotype for this locus was observed in material from any one site. These genetic findings are consistent with a relatively short-range dispersal potential in this species as compared to Plumatella species.     

Molecular mechanisms of temperature adaptation in fish myofibrillar adenosine triphosphatases

Summary Studies have been carried out on the Mg²⁺ Ca²⁺-myofibrillar ATPase from the muscles of fish adapted to different environmental temperatures. The thermal stability of the ATPase is strongly correlated with mean habitat temperature. Activities of Antarctic fish ATPases are significantly higher at low temperatures than those of temperate and tropical water species. The effects of ionic strength on ATPase activity have also been studied. The Gibbs free energy of activation (G ^#) was found to increase and enzyme activity decrease with increasing ionic strength within the physiological temperature range of each species. Significantly lower values of G ^#, of around 1 Kcal/mole, are obtained for the ATPase of cold-adapted compared to tropical fish. Enthalpic and entropic activation energies were also reduced in the cold adapted ATPases. It is postulated that the reduction of the enthalpic activation term in the cold adapted enzyme confers the advantage of reducing the temperature sensitivity of the rate limiting step thus partly compensating for the low heat content of the cellular environment. Possible molecular mechanisms of temperature compensation in fish myofibrillar ATPase are discussed.