Effects of temperature, hypoxia and activity on the metabolism of juvenile Atlantic cod

Standard metabolic rate (SMR), active metabolic rate (AMR) and critical oxygen saturation ( S_crit ) were measured in Atlantic cod Gadus morhua at 5, 10 and 15° C. The SMR was 35.5, 57.0 and 78.2 mg O₂ kg⁻¹ h⁻¹ and S_crit was 16.5, 23.2 and 30.3%, at 5, 10 and 15° C, respectively. Previously reported SMR for Atlantic cod from arctic waters at 4° C was twice that measured at 5° C in the present study. A possible intraspecific latitudinal difference in the SMR is discussed. The AMR was 146.6, 197.9 and 200.4 mg O₂ kg⁻¹ h⁻¹ and the critical swimming speed ( U_crit ) was 1 6, 1.7 and 1.9 at 5, 10 and 15° C, respectively. The maximum oxygen consumption was found to be associated with exercise, rather than recovery from exercise as previously reported in another Study of Cod metabolism.     

Inter‐individual differences in rates of routine energy loss and growth in young‐of‐the‐year juvenile Atlantic cod

Inter‐individual differences in rates of routine (non‐feeding) metabolism and growth were evaluated in young‐of‐the‐year (YOY) juvenile Atlantic cod Gadus morhua . Rates of O₂ consumption, CO₂ production and ammonia (TAN) excretion were measured in 64, 25–43 mm standard length ( L _S) YOY growing at different rates (0·27–0·47 mm day⁻¹) in a common rearing tank. Parameter rates ( y ) increased allometrically ( y = a·M^b ) with increasing body mass ( M ) with b ‐values for O₂ production, CO₂ consumption and TAN excretion equal to 0·81, 0·89 and 0·56, respectively. In some cases, residuals from these regressions were significantly negatively correlated to fish growth rate. In no cases did residuals of parameter rates increase with increasing growth rate. These data suggest that, during unfed periods, relatively fast‐growing fish were more metabolically efficient than slower‐growing fish from the same cohort. The fish condition factor, derived from     , also significantly decreased with increasing growth rate. Results indicated differences in both the rates of routine energy loss and the patterns of growth allocation among YOY Atlantic cod. Since these physiological attributes were positively correlated with growth rate, they may be indicative of 'survivors' in field populations.     

Reduced growth of Atlantic cod in non-lethal hypoxic conditions

Growth in length and mass, improvements in condition, as well as final condition of c. 700 g Atlantic cod Gadus morhua were significantly less at 45% and 56% O₂ saturation than at 65%, 75%, 84% and 93% O₂ saturation. Hypoxia decreased food consumption. In turn, food consumption explained 97% of the variation in growth. Conversion efficiency varied slightly, but significantly, with level of dissolved O₂, except that the group reared at 93% O₂ had a lower than expected conversion efficiency. Slow growth in low O₂ was not due to increased activity, because activity decreased in hypoxia. In the Gulf of St Lawrence, waters deeper than 200 m usually are <65% saturated in O₂, and thus should impact negatively on cod growth.     

The effects of body mass and feeding on metabolic rate in small juvenile Atlantic cod

Apparent specific dynamic action (SDA) amplitude in young juvenile Atlantic cod Gadus morhua (1 to 8 g wet mass), fed a standardized meal and then exercised in a circular swimming respirometer at a constant swimming speed of 0·5 ± 0·3 body lengths s^-1, occurred within l h after feeding in all juveniles. SDA amplitude were 1·4 to 1·8 times higher in fed fish compared to unfed fish, and rates of oxygen consumption decreased as body mass increased. SDA duration had a tendency to decrease with increasing body mass and was shortest, at 6 h, in the smallest fish (1–1·5 g), but increased to 10–11 h in the largest fish. Apparent SDA in fed fish ( R _r) scaled with a mass exponent of 0·89, while maximum metabolic rate ( R _max) determined by chasing fish to exhaustion and then measuring oxygen consumption for 12 h, and unfed routine metabolic rate (R_r) scaled with a mass exponent of 0·79 and 0·76 respectively. Relative aerobic scope ( R _max– unfed R _r) did not appear to vary over the 1 to 8 g increase in wet mass. These results show that as body mass increased in young juvenile Atlantic cod: (1) apparent SDA ( R _f) increased more rapidly than R _max, and (2) apparent SDA took up >98% of the relative aerobic scope and that young Atlantic cod allocated most of the energy to growth, and left little for other metabolic activities.     

Oxygen uptake in developing eggs and larvae of the cod, Gadus morhua L.

Unfertilised cod eggs showed a mean oxygen uptake rate at 5°C of 0.089 μl O₂, dry wt.⁻¹ h⁻¹; this gradually rose to 0.768 μl O₂ mg dry wt.⁻¹ h⁻¹ in eggs about to hatch. From hatching to complete yolk absorption larvae respired at 1.6 μl O₂, mg dry wt.⁻¹ h⁻¹. During starvation following yolk absorption, uptake fell significantly to 1.1 μl O₂, mg dry ⁻¹ h⁻¹. Much of this decrease in oxygen consumption was shown to be caused by reduction in activity. Loss of weight during the embryo and larval phases could not easily be reconciled with total oxygen consumption; it is suggested that cod embryos and larvae may not rely solely upon endogenous energy reserves during development.     

Effects of graded hypoxia on Atlantic salmon infected with amoebic gill disease

Atlantic salmon Salmo salar with amoebic gill disease (AGD) were exposed to a graded hypoxia (135–40 mmHg water P O₂) and blood samples analysed for respiratory gases and pH at 119, 79·5 and 40 mmHg water P O₂. There were no differences in the rate of oxygen uptake between infected and control fish. However, arterial P O₂, and pH were significantly lower in the infected fish whereas P CO₂ was significantly higher in infected fish compared with controls prior to hypoxia and at 119 mmHg water P O₂. At 79·5 and 40 mmHg water P O₂ saturation, there were no significant differences in blood P O₂ or pH although blood P CO₂ was elevated in AGD affected fish at 50% hypoxia (79·5 mmHg water P O₂). The elevated levels of P CO₂ in fish affected by AGD resulted in a persistent respiratory acidosis even during hypoxic challenge. These data suggest that even though the fish were severely affected by AGD, the presence of AGD while impairing gas transfer under normoxic conditions, did not contribute to respiratory failure during hypoxia.     

Post-exercise metabolic rate in Atlantic cod and its dependence upon the method of exhaustion

This study tests whether or not post-exercise oxygen consumption rates ( M o₂) in fish are dependent upon how exhaustion is induced. A group of eight Atlantic cod ( Gadus morhua ) were each exercised using (1) a critical swimming speed ( U _crit) protocol, (2) an exercise protocol designed to measure anaerobic capacity of fish ( U _burst), and (3) a protocol in which the fish were chased to exhaustion manually. M o₂ was measured for a 2-h period following exhaustion induced by all three exercise regimes ( U _crit, U _burst and chase). Post-exercise M o₂ following exhaustion from the U _burst and chase protocols were significantly higher than post-exercise M o₂ following the U _crit protocol. Each fish during the U _crit protocol exhibited maximal M o₂ during exercise rather than during recovery, yet 75% of the fish during U _brust recovery and 100% during chase recovery exhibited M o₂ higher than that measured during U _crit exercise. These results, as well as the large interindividual variations in M o₂ among the eight fish, show that post-exhaustion M o₂ is specific to the exercise regime employed, thus, investigators must exercise caution when combining results from different exercise protocols and/or individuals.     

Endurance swimming of European eel

A long‐term swim trial was performed with five female silver eels Anguilla anguilla of 0·8–1·0 kg ( c . 80 cm total length, L _T) swimming at 0·5 body lengths (BL) s⁻¹, corresponding to the mean swimming speed during spawning migration. The design of the Blazka‐type swim tunnel was significantly improved, and for the first time the flow pattern of a swim tunnel for fish was evaluated with the Laser‐Doppler method. The velocity profile over three different cross‐sections was determined. It was observed that 80% of the water velocity drop‐off occurred over a boundary layer of 20 mm. Therefore, swim velocity errors were negligible as the eels always swam outside this layer. The fish were able to swim continuously day and night during a period of 3 months in the swim tunnel through which fresh water at 19° C was passed. The oxygen consumption rates remained stable at 36·9 ± 2·9 mg O₂ kg⁻¹ h⁻¹ over the 3 months swimming period for all tested eels. The mean cost of transportation was 28·2 mg O₂ kg⁻¹ km⁻¹. From the total energy consumption the calculated decline in fat content was 30%. When extrapolating to 6000 km this would have been 60%, leaving only 40% of the total energy reserves for reproduction after arriving at the spawning site. Therefore low cost of transport combined with high fat content are crucial for the capacity of the eel to cross the Atlantic Ocean and reproduce.     

Swimming performance, oxygen consumption and excess post-exercise oxygen consumption in adult transgenic and ocean-ranched coho salmon

Routine oxygen consumption ( M o ₂) was 35% higher in 1 day starved and 21% higher in 4 day starved adult transgenic coho salmon Oncorhynchus kisutch relative to end of migration ocean-ranched coho salmon. Critical swimming speed ( U _crit) and M o ₂ at U _crit ( M o _2max) were significantly lower in 4 day starved transgenic coho salmon (1·25 BL s⁻¹; 8·79 mg O₂ kg⁻¹ min⁻¹) compared to ocean-ranched coho salmon (1·60 BL s⁻¹; 9·87 mg O₂ kg⁻¹ min⁻¹). Transgenic fish swam energetically less efficiently than ocean-ranched fish, as indicated by a poorer swimming economy at U _crit ( M o _2max     ). Although M o _2max was lower in transgenic coho salmon, the excess post-exercise oxygen consumption (EPOC) measured during the first 20 min of recovery was significantly larger in transgenic coho salmon (44·1 mg O₂ kg⁻¹) compared with ocean-ranched coho salmon (34·2 mg O₂ kg⁻¹), which had a faster rate of recovery.     

Respiratory responses of Oreochromis niloticus (Pisces, Cichlidae) to environmental hypoxia under different thermal conditions

The oxygen uptake ( V O₂), breathing frequency ( f _R), breath volume ( V _S.R), gill ventilation ( V G) and oxygen extraction (%) from the ventilatory current of four groups of Oreochromis niloticus during graded hypoxia were measured under the following acclimation temperatures: 20. 25. 30 and 35°C. The critical oxygen tensions ( P O₂), determined from V O₂ v. P O₂ of inspired water at each experimental temperature were, respectively. 19±1±3±1. 18±0±4±9, 29±7± 4±1 and 30±2± 0.6 mmHg. The f _R remained nearly constant during the reductions of O₂ at all the temperatures studied. V G increased discretely from normoxic levels until the P O₂ was reached, below which it assumed extremely high values (17-fold higher or more). The increases observed in V G resulted, at all the acclimation temperatures, in an elevation in V _S.R rather than in f _R. The extraction of O₂ decreased gradually from normoxia until the P O₂ was reached, below which an abrupt reduction of extraction was recorded, except at 35°C when fish showed a gradual reduction in extraction just below the tension of 80 mmHg.     

Evidence that growth hormone-induced elevation in routine metabolism of juvenile Atlantic salmon is a result of increased spontaneous activity

Growth hormone (GH) significantly increased the growth in mass and length of Atlantic salmon parr. It also significantly increased routine oxygen consumption ( M O₂). This change in routine M O₂ could be attributed to an increase in activity, but not resting M O₂. Any elevation in resting M O₂ due to GH treatment is much lower than previously suggested.     

Scaling of oxygen consumption of Lake Magadi tilapia, a fish living at 37°C

Rates of oxygen consumption were measured in the geothermal, hot spring fish, Oreochromis alcalicus grahami by stopped flow respirometry. At 37° C, routine oxygen consumption followed the allometric relationship: V o₂=0.738 M ^0.75, where V o₂ is ml O₂ h ⁻¹ and M is body mass (g). This represents a routine metabolic rate for a 10 g fish at 37° C of 0.415 ml O₂ g⁻¹ h ⁻¹ (16.4 μmol O₂ g ⁻¹ h ⁻¹). Acutely increasing the temperature from 37 to 42° C significantly elevated the rate of O₂ consumption from 0.739 to 0.970 ml O₂ g ⁻¹ h ⁻¹ ( Q ₁₀=l.72). In the field, O. a. grahami was observed to be 'gulping' air from the surface of the water especially in hot springs that exceeded 40° C. O. a. grahami may utilize aerial respiration when O₂ requirements are high.     

The occurrence of aerial respiration in Rhinelepis strigosa during progressive hypoxia

Rhinelepis strigosa did not surface for air breathing in normoxic or moderate hypoxic water. This species initiated air breathing when the P _io₂ in the water reached 22 ± 1 mmHg. Once begun, the air-breathing frequency increased with decreasing P _io₂. Aquatic oxygen consumption was 21·0 ± 1·9ml O₂ kg⁻¹h⁻¹ in normoxic water, and was almost constant during progressive hypoxia until the P _io₂ reached 23·9 mmHg, considered the critical oxygen tension (P_co₂). Gill ventilation increased until close to the P _co₂ (7·9-fold) as a consequence of a greater increase in ventilatory volume than in breathing frequency. Gill oxygen extraction was 42 ± 5% and decreased with hypoxia, but under severe hypoxia returned to values characteristic of normoxic. The critical threshold for air breathing was coincident with the P_co₂ during aquatic respiration. This suggests that the air-breathing response is evoked by the aquatic oxygen tension at which the respiratory mechanisms fail to compensate for environmental hypoxia, and the gill O₂ uptake becomes insufficient to meet O₂ requirements.     

Routine metabolism of juvenile spot, Leiostomus xanthums (Lacépède), as a function of temperature, salinity and weight

Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums , were measured over a range of temperatures, salinities and fish weights. As predicted, Q O₂ increased with temperature and decreased with body weight. However, Q O₂ decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log₁₀ Q O₂ (mg O₂ g⁻¹ h⁻¹) = 0.129 log_lo salinity (%0) + 1.604 log₁₀ temperature (°C)-0.1401og₁₀(g)-2.767.     

Oxygen consumption of East Siberian cod: no support for the metabolic cold adaptation theory

Standard metabolic rate ( R _s) at 2°C of eight East Siberian cod Arctogadus borisovi , caught in West Greenland, body mass of 601.5 ± 147.6 g (mean ± s.D.), was 40.9 ± 5.9 mg O₂ kg^-1 h^-1 and 59.0 ± 6.6mg O₂ kg^-1 h^-1 when extrapolated to a standardized 100 g fish. R _s was compared with three other Gadidae, to test the theory of metabolic cold adaptation (MCA). There was no evidence of MCA in the family.     

Seasonal differences in routine oxygen consumption rates of the bonnethead shark

Routine oxygen consumption rates of bonnethead sharks, Sphyrna tiburo , increased from 141·3±29·7 mg O₂ kg⁻¹ h⁻¹ during autumn to 218·6±64·2 mg O₂ kg⁻¹ h⁻¹ during spring, and 329·7±38·3 mg O₂ kg⁻¹ h⁻¹ during summer. The rate of routine oxygen consumption increased over the entire seasonal temperature range (20–30° C) at a Q ₁₀=2·34.     

Field-based measurements of oxygen uptake and swimming performance with adult Pacific salmon using a mobile respirometer swim tunnel

Novel field measurements of critical swimming speed ( U _crit) and oxygen uptake (  M o₂) in three species of adult Pacific salmon Oncorhynchus spp. up to 3·5 kg in body mass were made using two newly designed, mobile Brett-type swim tunnel respirometers sited at a number of field locations in British Columbia, Canada. Measurements of U _crit, which ranged from 1· 68 to 2·17 body lengths s⁻¹, and maximum M o₂, which ranged from 8·74 to 12·63 mg O₂ kg⁻¹ min⁻¹ depending on the species and field location, were judged to be of similar quality when compared with available data for laboratory-based studies. Therefore high quality respirometry studies were possible in the field using adult wild swimming salmonids. In addition, the recovery of wild adult Pacific salmon from the exhaustive U _crit swim test was sufficiently rapid that swimming performance could be repeated with <1 h of recovery time between the termination of the initial swim test and the start of the second test. Moreover, this repeat swimming performance was possible without routine M o₂ being reestablished. This result suggests that wild adult salmon are capable of carrying a moderate excess post-exercise oxygen consumption without adversely affecting U _crit, maximum M o₂ or swimming economy. Such capabilities may be extremely important for timely migratory passages when salmonids face repetitive hydraulic challenges on their upstream migration.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

Swimming alters responses to hypoxia in the Adriatic sturgeon Acipenser naccarii

When the Adriatic sturgeon Acipenser naccarii was exposed to progressive hypoxia under static conditions, it exhibited a linear decline in O₂ uptake, behaving as an 'oxyconformer'. When, however, it was allowed to swim at a low sustained speed, it could regulate O₂ uptake down to a mean ± s . e . critical ( P _crit) of 4·9 ± 0·5 kPa ( n = 6). At moderate levels of hypoxia, static fish exhibited significant reductions in arterial blood O₂ content, and increases in plasma lactate, which were not observed in swimming animals.     

Seasonal growth of Atlantic cod: effects of temperature, feeding and reproduction

Growth of 2659 Atlantic cod Gadus morhua aged 4 to 9 years examined in Placentia Bay, Newfoundland, peaked in most cases in June and was at a minimum in October or November. Water temperature, partial fullness index ( I _P) and gonado‐somatic index ( I _G) explained between 31 and 52% of the monthly variability in growth. Temperature and I _P of capelin Mallotus villosus had significant effects on growth of all age groups and explained most of the variance for ages 6–8 and 4–5 years, respectively. The I _P of large invertebrates (ages 4 to 7 years), sandlance ( Ammodytes sp. age 6 years) and demersal fishes (age 9 years) had age‐specific effects in the model. Overall, amphipods, decapods and echinoderms dominated the Atlantic cod diet in most seasons, but fish consumption by Atlantic cod was high in June and July, particularly on capelin. The rapid increase in somatic mass during June and July occurred despite cold water temperatures ( < 3° C at 50 m) and moderate to high gonado‐somatic index. The findings of this study suggest that when food was not a limiting factor, growth tended to increase even when Atlantic cod occupied colder waters, but when food was limiting, the opposite may have occured.