Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ± s . e . fork length, L _F, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method ( C _m). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature ( I _U) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C². In a separate experiment, the I _U of large age 2+ year fish (34·4 ± 0·5 cm L _F) was 1·2 and 0·6° C lower ( P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm L _F) at acclimation temperatures of 16 and 23° C. Using the C _m, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.     

Differential survival of juvenile sockeye and coho salmon exposed to low dissolved oxygen during winter

Juvenile sockeye salmon (43–78 mm) survived 100% for 24 h in cages in ice–covered Black Lake, Alaska at oxygen saturations >65% (9 mg l^–1), but only 45% at 24% saturation (3·0–3·3 mg l^–1) and none at <17% saturation (2·3 mg l^–1). All juvenile coho (50–120 mm) survived 100% for 24 h down to 21% oxygen saturation (3·1 mg l^–1), and all 50 coho survived 4–5 days at 23–24% saturation (3·2–3·3 mg l^–1).     

Thermal dependence of swimming endurance in juvenile brown trout

The maximum swimming stamina of hatchery reared juvenile brown trout Salmo trutta , swimming against a fixed-velocity water flow of 36·6 cm s^-1 (6·97 L s^-1), was achieved at 16·1° C, and a 90% performance level occurred over a breadth of 7·7° C (12·2–19·9° C). The wide range of temperatures at which swimming performance is close to the maximal capacity could be a consequence of the implications for survival of this function.     

Cardiorespiratory status of triploid brown trout during swimming at two acclimation temperatures

At 14° C, standard metabolic rate (75·1 mg O₂ h⁻¹ kg⁻¹), routine metabolic rate (108.8 mg O₂ h⁻¹ kg⁻¹), active metabolic rate ( c . 380 mg O₂ h⁻¹ kg⁻¹), critical swimming speed (U_crit 1·7 BL s⁻¹), heart rate 47 min⁻¹), dorsal aortic pressure (3·2 kPa) and ventilation frequency (63 min⁻¹) for triploid brown trout Salmo trutta were within the ranges reported for diploid brown trout and other salmonids at the same temperature. During prolonged swimming ( c . 80% U _crit), cardiac output increased by 2·3-fold due to increases in heart rate (1·8-fold) and stroke volume (1·2-fold). At 18° C, although standard and routine metabolic rates, as well as resting heart rate and ventilation frequency increased significantly, active metabolic rate and certain cardiorespiratory variables during exercise did not differ from those values for fish acclimated to 14° C. As a result, factorial metabolic scope was reduced (2·93-fold at 18° C v . 5·13-fold at 14° C). Therefore, it is concluded that cardiorespiratory performance in triploid brown trout was not unusual at 18° C, but that reduced factorial metabolic scope may be a contributing factor to the mortality observed in triploid brown trout at temperatures near 18° C.     

Radio-transmitted electromyogram signals as indicators of swimming speed in lake trout and brown trout

Swimming speed and average electromyogram (EMG) pulse intervals were highly correlated in individual lake trout Salvelinus namaycush ( r ²=0·52–0·89) and brown trout Salmo trutta ( r ²=0·45–0·96). High correlations were found also for pooled data in both lake trout ( r ²=0·90) and brown trout of the Emå stock ( r ²=0·96) and Lærdal stock ( r ²=0·96). The linear relationship between swimming speed and average EMG pulse intervals differed significantly among lake trout and the brown trout stocks. This successful calibration of EMGs to swimming speed opens the possibility of recording swimming speed of free swimming lake trout and brown trout in situ . EMGs can also be calibrated to oxygen consumption to record energy expenditure.     

Tolerance of parr of Arctic charr, Salvelinus alpinus, to reduced dissolved oxygen concentrations

One year old pan Item Windermere (north west England) tolerated lower incipient lethal levels of oxygen [18 20 mg 1 ¹: 15 17% air saturation value (ASV)] at lower (5, 10°C) than at higher (15, 20°C) an elimation temperatures (2·2 2·4 mg 1 ¹ 22 25% ASV). Values were not significantly different for two races of charr in the lake and are amongst the lowest recorded for salmenid species.     

Reproductive migration of brown trout in a small Norwegian river studied by telemetry

The movement of 34 large (39–73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m³ s⁻¹) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m³ s⁻¹) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low ( c . 6° C), but not at high ( c . 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2–51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day⁻¹, respectively. All tagged brown trout that survived spawning returned to the lake after spawning.     

Physiological stress effects of continuous- and pulsed-DC electroshock on juvenile bull trout

Juvenile bull trout Salvelinus confluentus exposed to continuous- or pulsed-DC electroshock exhibited rapid elevations in plasma cortisol and glucose, but plasma chloride did not change. In a 1-h experiment using 240 V at 1·4 A of 60-Hz pulsed DC (voltage gradient 0·81 V cm⁻¹), which proved lethal, plasma cortisol and glucose rose significantly within 15 min of a 10-s electroshock. Plasma cortisol reached a peak level of 156 ± 18 ng ml⁻¹ at 45 min and then decreased, whereas plasma glucose reached its highest level of 179 ± 7·5mg dl⁻¹ at 1 h. In a 24-h experiment using lower dosages, plasma cortisol increased from 6·1-16 ng ml⁻¹ to peak levels of 155–161 ng ml⁻¹ in 1 h in response to a 10-s electroshock of continuous (130 V, 0·5 A, 1·45 V cm⁻¹) or pulsed (120 V, 0·5 A, 60 Hz, 0·55 V cm⁻¹) DC. Although plasma concentrations declined thereafter, levels remained above control values at 24 h. Plasma glucose was elevated from 60–65 to 120–134 mg dl⁻¹ after 1h by both electroshock treatments and remained near or above those levels for the 24-h duration. Plasma cortisol and glucose levels were much higher in electroshocked bull trout at 1 h compared with those in fish 1 h after receiving a 30-s handling stressor (cortisol, 90 ± 12 ng ml⁻¹; glucose, 82 ± 6·1 mg dl⁻¹). The results indicate that both continuous and pulsed DC were more stressful to juvenile bull trout than handling and that recovery, at least for pulsed DC, may take longer than 24 h.     

The critical thermal limits for juvenile Arctic charr Salvelinus alpinus

The chief objective was to determine the critical thermal limits for alevins, fry and parr of Arctic charr, Salvelinus alpinus , (L.) from four races living in Windermere (northwest England). The experimental fish were reared in a hatchery but were the progeny of wild parents. As comparisons between tethal temperatures at four acclimation temperatures (5, 10, 15, 20° C) revealed few significant racial differences, the data were pooled to estimate the lethal values for survival over 7 days (incipient lethal temperature) and over only 10 min (ultimate lethal temperature) for each life stage. Upper lethal values increased with acclimation temperatures for alevins but this effect was negligible for fry and parr, Alevins were generally less tolerant than fry and parr at lower, but not higher, acclimation temperatures; e.g. after acclimation at 5° C, mean upper ultimate values were 23·3, 25·1 and 25·7° C and mean upper incipient values were 18·7, 21·5 and 21·5° C for alevins, fry and parr respectively; after acclimation at 20° C, mean upper ultimate and incipient values were 26·2, 26·1 and 26·6° C and 20·8, 20·8 and 21·6° C for alevins, fry and parr respectively. The area of the temperature tolerance polygon (expressed as ° C²) for juvenile Arctic charr is amongst the lowest recorded for salmonids; being 409, 439 and 461° C² for alevins, fry and parr respectively. These low values are due to lower upper tolerance limits, not high lower tolerance limits; the latter being close to 0° C (<1°C for parr and fry, <0·3° C for alevins) at all acclimation temperatures. Arctic charr are therefore amongst the least resistant of salmonids to high temperatures but probably the most resistant to low temperatures.     

The immunoglobulin of the brown trout, Salmo trutta and its concentration in the serum of antigen-stimulated and non-stimulated fish

Immunoglobulin production in the primary and secondary immune response of brown trout to keyhole limpet haemocyanin has been investigated including the effect of dose size, route and number of injections, and the use of adjuvant. Antibody activity was found in the first fraction from Sephadex G200 and in the second from Sepharose 6B. Trout immunoglobulin had β₂—Γ₁ electrophoretic mobility, and S_app of 16·7 and an approximate molecular weight of 670 000 daltons. It was sensitive to dithiothreitol and stable at 56°C for 30 min. Immunoglobulin concentrations were measured by single radial immunodiffusion with a specific rabbit antiserum. Sera from non-injected trout had a mean immunoglobulin level of 7·3 ± 0·3 mg ml⁻¹ which accounted for 10% of the total serum protein. Phosphate buffered saline-injected controls contained 6·7 ± 0·2. In fish given a single injection the mean concentration ranged from 7·5 to 12·9 and in those given more than one injection from 12·6 to 16·8. The use of adjuvant resulted in higher immunoglobulin concentrations. Neither dose nor route had any significant effect on the primary response. However, in the secondary response the intramuscular route resulted in significantly increased immunoglobulin production.     

Feeding behaviour of yearling and older hybrid grass carp

Hybrid grass carp resulting from the cross of a female grass carp, Ctenopharyngodon idella (Val.), and a male bighead carp, Hypophthalmichthys ( Aristichthys ) nobilis Rich., 12–18 months old ( c . 300 mm T.L.) were studied in a two-part experiment to determine feeding preference and total daily consumption fish^-1 on selected species of aquatic plants. Fish were maintained in circular pools with 6840·8 1 of water inside a temperature-controlled greenhouse. Preference tests were conducted at three temperature ranges; 25–28° C, 17–20° C and 12–15° C. Based on the time to complete consumption or the relative quantity consumed, the most preferred plant was Lemna gibba when in combination with six other species. Chara sp., Najas guadalupensis and Potamogeton peciinatus were readily consumed and considered to be of about equal preference. Ceratophyllum demersum and Myriophyllum brasiliense were least preferred. Hybrid grass carp generally consumed as much plant material species^-1 and in the same order of preference at the 12–15°C range as they did at 25–28° C. In the second part, mean daily consumption (g) fish^-1 at 25·7–31·0° C for five plant species tested separately was as follows: Chara sp. 369·8; Lemna gibba 178·2; Najas guadalupensis 172·6; Hydrilla verticillata 106·4 and Ceratophyllum demersum 8·8.     

Changes in movement, range and habitat preferences of adult grayling from late summer to early winter

Radio‐tagged adult grayling Thymallus thymallus ( n  = 22), monitored from mid August to mid December 1999 in the River Kuusinkijoki, Finland, shifted by the end of September (water temperature 10·0–14·5° C) from riffle sites to deeper and slower pool sites 0·7–1·6 km up‐ or downstream. In early winter ( c . 0° C water temperature), eight of 13 fish still under study made a further shift into new pool sites, possibly triggered by ice formation. The summer range of grayling in the riffles was smaller (mean ±  s . d . length: 75 ± 146 m) than the autumn range (99 ± 46 m) in the pools, but gross daily movements were equally short in both the seasons (18 ± 34 m and 15 ± 7 m, respectively). In late summer, adult grayling preferred water depths 80–120 cm and mean velocities >40 cm s⁻¹. In autumn, the preferred ranges were 100–240 cm and <30 cm s⁻¹, respectively. Substratum was mainly boulders in the summer sites, and gravel or pebbles in the autumn sites.     

The relative abundance of brown trout in acidic softwater lakes in relation to water quality in tributary streams

The influence of the water quality of tributary streams on the relative abundance in benthic gillnet catches (catch per unit effort, cpue) of allopatric brown Salmo trutta was assessed in associated acidic, softwater lakes. The study was carried out over 6 years (1989–1994) in 15 lakes located at altitudes between 230–715 m a.s.l. in two Norwegian catchments. The water quality of the main inlets and outlets varied little, as indicated by their of pH range (4·93–5·51) and calcium concentrations (0·19–0·44 mg 1⁻¹), but varied more with respect to concentrations of inorganic, monomeric aluminium (7·0–41·0 μg l⁻¹). Most of the lakes were also fed by secondary streams with better water quality: a maximum pH of 6·56, calcium levels of up to 0·74mg 1⁻¹, and inorganic aluminium levels as low as l·0 μg 1⁻¹. The cpue was inversely correlated with lake altitude ( r ²=0·50), and thus was adjusted to a mean altitude. The calcium concentration in the richest secondary stream to each lake, its richness judged on the basis of its acid-neutralizing capacity, had the highest predictive power of the variability in cpue ( r ² = 0·49).The calcium content in the other secondary streams or in the main inlets and outlets did not correlate with cpue. Alkalinity in the main outlets correlated to some extent with cpue ( r ² = 0·27). It is suggested that secondary streams with good water quality provide important refuges for the recruitment of brown trout in acidic softwater lakes.     

Is tilting behaviour at low swimming speeds unique to negatively buoyant fish? Observations on steelhead trout,Oncorhynchus mykiss,and bluegill,Lepomis macrochirus

When swimming at low speeds, steelhead trout and bluegill sunfish tilted the body at an angle to the mean swimming direction. Trout swam using continuous body/caudal fin undulation, with a positive (head-up) tilt angle ( 0 , degrees) that decreased with swimming speed ( u , cm s⁻¹) according to: 0 =(164±96).u^{(−1.14±0.41)} (regression coefficients; mean±2 s.e. ). Bluegill swimming gaits were more diverse and negative (head down) tilt angles were usual. Tilt angle was −3·0 ± 0.9° in pectoral fin swimming at speeds of approximately 0.2–1.7 body length s⁻¹ (Ls⁻¹; 3–24 cm s⁻¹), −4.5 ±2.6° during pectoral fin plus body/caudal fin swimming at 1·2–1·7 L s⁻¹ (17–24cm s⁻¹), and −5.0± 1.0° during continuous body/caudal fin swimming at 1.6 and 2.5 L s⁻¹ (22 and 35cm s⁻¹). At higher speeds, bluegill used burst-and-coast swimming for which the tilt angle was 0.1±0.6°. These observations suggest that tilting is a general phenomenon of low speed swimming at which stabilizers lose their effectiveness. Tilting is interpreted as an active compensatory mechanism associated with increased drag and concomitant increased propulsor velocities to provide better stabilizing forces. Increased drag associated with trimming also explains the well-known observation that the relationship between tail-beat frequency and swimming speed does not pass through the origin. Energy dissipated because of the drag increases at low swimming speeds is presumably smaller than that which would occur with unstable swimming.     

Oxygen requirements of larvae of the smallmouth bass, Micropterus dolomieui Lacépède

Smallmouth bass larvae became highly sensitive to oxygen deficiency on the second day after hatching and continued so to the 10th day. During this period they could not survive exposure to 1 mg O₂ l^–1 for 3 h at 20° C, and many were killed within 1 h. At 2 mg O₂ l^–1 half the larvae survived 3 h at 20° C; at 2.5 mg l^–1 most survived, and at 3.5 mg l^–1 all survived. Resistance to oxygen deficiency was regained by the 11th day, the majority of the larvae withstanding a 3-h exposure at 1 mg O₂ l^–1. At 25° C the effects of low oxygen concentration were intensified. At 3 and 4 mg O₂ l^–1 and 20° C the normally quiescent larvae became very active, even swimming to the surface 5 or 6 cm above the substrate. Increasing the temperature increased this response. Smallmouth larvae were more sensitive than large-mouth bass larvae to oxygen deficiency.     

The population dynamics of young trout (Salmo trutta L.) in a Danish brook

The population size, dispersal of fry, growth of fry in relation to density, mortality and production of young trout ( Salmo trutta L.) were studied in a Danish brook during 1970–1972. In the first few months after emergence downstream emigration of fry took place both in 1971 and 1972, after which the trout became stationary. Growth was inversely density dependent and mortality was density dependent in the months just after emergence. Later mortality was constant and independent of density. Trout production varied between 10 g/m² and 18.6 g/m² in the 2 years.     

Body composition and energy allocation in life-history stages of brown trout

Energy contents of immature parr and smolts, and mature resident and anadromous brown trout Salmo trutta sampled from a small stream in southern Norway were estimated from lipid, protein and carbohydrate concentrations. In immatures the lipid concentrations were highest in parr in the autumn. Mean lipid concentrations increased significantly with age in parr sampled in autumn (1·3% in age 0+ to 3·4% in age 3+), whereas they did not in smolts. The lipid concentrations of parr in spring were not significantly different from those of similarly aged smolts. By contrast, the relative water content (%) decreased with age in parr in the autumn and increased with age in smolts, mean values being slightly higher in smolts (78%) than in parr (77%). Protein and carbohydrate concentrations did not vary with age in the immature fish, mean protein concentrations being 18·0, 17·5 and 16·8% in parr in the autumn and spring, and in smolts, respectively. In residents, the concentrations of lipids were lower and of water higher, in age group 1 than in older fish, whereas there was no significant variation with age amongst anadromous trout. The energy concentration of 2+ smolts (349 kJ 100 g^-1) was similar to that of 0+ parr in the autumn. Mean somatic energy density in autumn was 1·1 times higher in freshwater residents than in parr at age 1+ (407 and 387 kJ 100 g^-1) and marginally different at age 2+ (462 and 426 kJ 100 g^-1, respectively). The energy contents per unit mass of residents were 1·3–1·6 times that of similar aged smolts. Mean somatic energy density of anadromous trout (504 kJ 100 g^-1) was higher than that of residents (455 kJ 100 g^-1). Somatic energy, lipid and protein concentrations were correlated highly with water contents of all life stages, age and sex groups.     

The effect of temperature fluctuations on oxygen consumption and ammonia excretion of underyearling Lake Inari Arctic charr

Underyearling Lake Inari Arctic charr Salvelinus alpinus were acclimated to 11·0) C for 3 weeks, and then one group was maintained at 11·0) C and others were exposed to 14·4) Cconst, 17·7) C_const or a diel fluctuating temperature of 14·3° C ± 1° C (14·3° C_fluc). Routine rates of oxygen consumption and ammonia excretion were measured over 10 days before the temperature change and over 31 days following the change. Measurements were made on fish that were feeding and growing. The temperature increase produced an immediate increase in oxygen consumption. There was then a decline over the next few days, suggesting that thermal acclimation was rapid. For groups exposed to constant temperature there was an increase in oxygen consumption ( M _accl, mg kg⁻¹ h⁻¹) with increasing temperature ( T ), the relationship being approximated by an exponential model: M _accl= 46·53e0·^{086 T} . At 14·3° C_fluc oxygen consumption declined during the 3–4 days following the temperature shift, but remained higher than at 14·4° C_const. This indicates that small temperature fluctuations have some additional influences that increase metabolic rate. Ammonia excretion rates showed diel variations. Excretion was lower at 11° C_const than at other temperatures, and increases in temperature had a significant effect on ammonia excretion rate. Fluctuating (14·3° C_fluc) temperature did not influence ammonia excretion relative to constant temperature (14·4° C_const).     

The growth of brown trout (Salmo trutta) in mild winters and summer droughts in upland Wales

SUMMARY. 1. We compared the observed annual growth of 0- and I-group trout in nine Welsh upland streams, with growth predicted from temperature assuming that this was the only limiting factor.
2. Autumn weights of second year fish were 51–67% of predicted ( G _max) values in 1988, but only 30–40% in 1989 and 1990 when drought occurred. Though initial weights of fry were unknown, simulations suggested that first year growth was also less than G _max, but with no obvious effect of drought.
3. To evaluate the possible effects of future climate change, we simulated stream temperature regimes 1.5–4.5°C above those of a recent year with temperatures similar to the long-term average. Growth was set at 60% G _max for both 0- and I-group, or at 40% for I-group to represent the effect of drought. As winter temperature increased, time to hatching and emergence decreased, for example by 56 and 49 days respectively for a rise of 3°C. 0-group growth was slightly enhanced at up to + 3°C but retarded at + 4.5°C. Simulations of I-group growth suggested that warmer winters could enhance trout growth while warmer summers would only increase growth if there were no adverse effects of drought.
4. We discuss many uncertainties in these simulations, which nevertheless suggest the magnitude of possible effects of climate change.     

Phytase activity of Selenomonas ruminantium: a preliminary characterization

Obligately anaerobic ruminal bacteria have been found to possess phytase activity, in particular, Selenomonas ruminantium . The phytase activity of S. ruminantium JY35 was produced late in growth and required neither phytate for induction nor phosphate limitation for derepression. The activity was completely cell-associated with a significant fraction extractable by a magnesium chloride solution. Zymogram analysis suggested that the activity was the result of a single gene product of a monomeric nature and approximately 46 kDa in size. The phytase had a temperature optimum of 50–55 °C, but activity dropped off sharply at 60 °C. Phytase activity was optimal over the pH range of 4·0–5·5, and dependent on the nature of the buffer used. Activity was inhibited by citric acid buffer and by the addition of 5 mmol l⁻¹ Fe²⁺, Fe³⁺, Cu²⁺, Zn²⁺ and Hg²⁺. The addition of 5 mmol l^–1 Pb²⁺ to the enzyme assay appeared to enhance activity of the enzyme.