THE EFFECT OF SUBLETHAL CONCENTRATIONS OF NATURAL SUSPENDED SILT ON ROUTINE OXYGEN CONSUMPTION BY MOZAMBIQUE TILAPIA (OREOCHROMIS MOSSAMBICUS)

Summary

Exposure of adult Oreochromismossambicusto sublethal concentrations (5 to 20 g silt ?^?1) of natural silt from the Phalaborwa Barrage altered routine oxygen consumption by causing increased rates of oxygen consumption. This indicates that sublethal levels of suspended silt result in a significant (p<0.05) increase in oxygen consumption by the exposed fish due to an increase in metabolic rate associated with increased activity and stress. Any species unable to compensate for this increase in energy expenditure over time would not be able to sustain itself.     

Toxic effects of zinc and iron on the routine oxygen consumption of Tilapia sparrmanii (Cichlidae)

1. The routine oxygen consumption of Tilapia sparrmanii without the addition of any toxicants over a 72 hr period showed a decrease for the first 48 hr, but stabilised thereafter.2. Addition of zinc (98 mg l⁻¹) resulted in a drastic decrease of oxygen consumption for 3 hr. The routine oxygen consumption showed a significant decrease for the first 24 hr, while the second and third 24 hr revealed significant differences with great individual variance.3. The decrease in oxygen consumption observed after exposure to zinc, could be caused by gill damage as well as the internal action of zinc.4. An increase in oxygen consumption was noted for almost 3 hr after addition of iron (88mg l⁻¹). During the first-, second- and third 24 hr the oxygen consumption increased significantly, compared to the control values.5. The increase in routine oxygen consumption of T. sparrmanii when compared to control values after exposure to iron, could be attributed to stress and possible gill changes.6. The study revealed that after acute (72 hr) exposure to sublethal concentrations of zinc and iron, the routine oxygen consumption of T. sparrmanii was altered.     

Intraspecific variation in the growth and survival of juvenile fish exposed to Eucalyptus leachate

Whilst changes in freshwater assemblages along gradients of environmental stress have been relatively well studied, we know far less about intraspecific variation to these same stressors. A stressor common in fresh waters worldwide is leachates from terrestrial plants. Leachates alter the physiochemical environment of fresh waters by lowering pH and dissolved oxygen and also releasing toxic compounds such as polyphenols and tannins, all of which can be detrimental to aquatic organisms. We investigated how chronic exposure to Eucalyptus leaf leachate affected the growth and survival of juvenile southern pygmy perch (Nannoperca australis) collected from three populations with different litter inputs, hydrology and observed leachate concentrations. Chronic exposure to elevated leachate levels negatively impacted growth and survival, but the magnitude of these lethal and sublethal responses was conditional on body size and source population. Bigger fish had increased survival at high leachate levels but overall slower growth rates. Body size also varied among populations and fish from the population exposed to the lowest natural leachate concentrations had the highest average stress tolerance. Significant intraspecific variation in both growth and survival caused by Eucalyptus leachate exposure indicates that the magnitude (but not direction) of these stress responses varies across the landscape. This raises the potential for leachate‐induced selection to operate at an among‐population scale. The importance of body size demonstrates that the timing of leachate exposure during ontogeny is central in determining the magnitude of biological response, with early life stages being most vulnerable. Overall, we demonstrate that Eucalyptus leachates are prevalent and potent selective agents that can trigger important sublethal impacts, beyond those associated with more familiar fish kills, and reiterate that dissolved organic carbon is more than just an energy source in aquatic environments.     

Interactions of temperature and sublethal environmental copper exposure on the energy metabolism of bluegill, Lepomis macrochirus Rafinesque

Copper (0.21 mgl⁻¹) caused a decrease in whole body oxygen consumption in bluegills exposed for 32 days, but no changes occurred during days 3, 4 or 9 of copper exposure. In vitro oxygen consumption of gill and brain, were not significantly altered, whereas liver Q O₂, was slightly elevated which suggests that copper is acting to decrease oxygen consumption of the whole animal at a higher level of integration than these individual tissues. In fish subjected to an increase in temperature as well as sublethal copper exposure, whole body oxygen consumption was higher than controls 5 days after the temperature was increased, indicating a delay in temperature acclimation in the copper exposed fish. This difference was reflected in higher in vitro oxygen consumption in the liver and gill of these fish suggesting the metal was delaying the process of temperature acclimation by at least in part acting directly on the tissues.     

Respiratory responses and blood sugar level of the crab, Barytelphusa cunicularis (Westwood), exposed to mercury, copper and zinc.

Barytelphusa cunicularis (Westwood), a freshwater crab was exposed to mercuric chloride, copper sulphate and zinc sulphate from 0 to 12 hr and the oxygen consumption of the animal was measured in order to study the stress caused by these heavy metals. Normal oxygen consumption was affected by the three heavy metals. Similarly, crabs exposed to sublethal concentrations of the same pollutants for 24, 48, 72 and 96 hr showed an elevation in the blood sugar level with a maximum increase at 48 hr. The results indicate a switch towards glycolysis in order to overcome the anaerobic stress caused by the heavy metals.     

Impact of chronic phosalone toxicity on erythropoietic activity of fish, Oreochromis mossambicus.

Effect of multiple sublethal concentrations of Phosalone on whole animal and kidney oxygen consumption, haematological indices and serum enzymes of freshwater fish, Oreochromis mossambicus, were carried out over a 90 day exposure period. Significant changes were observed which have been indicating that the presence of hypoxic condition in the biosystem, gradual increase in the rate of synthesis of haemoglobin and disruption of liver function during the toxicity of phosalone.     

Laboratory studies on the oxygen consumption of the marine teleost,Lichia amia (Linnaeus, 1758)

• 1.1. The oxygen consumption of the marine teleost, Lichia amia was investigated under controlled laboratory conditions.
• 2.2. The routine oxygen consumption showed a strong circadian rhythm with the fish being mainly active during the light period.
• 3.3. The specific mass exponent (dimension: μg O₂/g/hr) is temperature independent and ranges from 0.27–0.29.
• 4.4. Starving the fish results in a mean decrease in active, routine and standard oxygen consumption of 21%, 24% and 20%, respectively.
• 5.5. Feecling led to an increase in the oxygen consumption of the teleosts, with the mean metabolic rate over the 24 hr that followed, being 58% and 50% higher for fish that had been starved for 162hr and 40 hr, respectively.
• 6.6. Apparent SDA showed some variation and ranged from 6.0 to 35.5%.
• 7.7. The results obtained are generally in agreement with those recorded for other teleosts.

     

Oxygen consumption,ammonia excretion,and filtration rate of the marine bivalve Mytilus edulis exposed to methamidophos and omethoate

In this study, the oxygen consumption, ammonia excretion, and filtration rate were monitored in Mytilus edulis in response to administration of the two pesticides, methamidophos and omethoate. Five sublethal concentrations (1, 10, 50, 100, and 200 µgL^?1) were administered over 96 h. Oxygen consumption rates increased following administration of all concentrations of methamidophos for 96 h and to the lower concentrations of omethoate (1, 10, and 50 µg L^?1) from 6 to 24 h. Over 24 h, oxygen consumption decreased significantly. Ammonia excretion rates were higher than the control after 36 h of exposure to methamidophos, while reduction was observed when M. edulis was exposed to omethoate. The O:N ratios increased when the animals were first exposed to these two pesticides and then decreased at all the concentrations. At the concentrations of 100 and 200 µgL^?1, the O:N ratio was below 30 after 72 h. The filtration rate of M. edulis decreased with the increasing concentration of pesticide exposure.     

Effect of sublethal doses of copper sulphate and bayluscide on survival and oxygen consumption of the snail biomphalaria alexandrina

The survival rate and oxygen consumption of Biomphalaria alexandrina snails exposed to sublethal concentrations of copper sulphate and Bayluscide were investigated. Prolonged exposure periods to the sublethal concentrations increased the percentage mortality among the exposed snails. Although the snails exposed to lower concentrations of the sublethal doses, were apparently normal, their oxygen consumption was markedly lower than the control ones. The rate of reduction of oxygen consumption by the experimental snails increased significantly at higher concentrations. The reduction of oxygen consumption was also presistent at prolonged exposure periods.     

The metabolic rates associated with resting, and with the performance of agonistic, submissive and digging behaviours in the cichlid fish Neolamprologus pulcher (Pisces: Cichlidae)

We measured the metabolic rates as a direct estimate of energy expenditure of individual Neolamprologus pulcher, a cooperatively breeding cichlid fish, when resting and when performing agonistic, submissive or digging behaviours in a respirometer. Standard and routine metabolic rates increased linearly with body mass (range 0.9–8.4 g) when plotted on a doubly logarithmic scale (linear regression equations: standard metabolic rate: log individual oxygen consumption rate = 0.65 + 0.86 log body mass; routine metabolic rate: log individual oxygen consumption rate = 0.75 + 0.86 log body mass). Routine metabolic rates were, on average, 30% higher than standard metabolic rates. Submissive and agonistic behaviours raised routine metabolic rates by factors of 3.3 and 3.9, respectively. Digging resulted in a 6.1-fold increase of routine metabolic rates. Differences in metabolic rates between active and resting rates were statistically significant. However, those between the three behaviours were not. Mean opercular beat frequencies correlated significantly with routine metabolic rates and with metabolic rates when performing specific behaviours, which offers methodological prospects for field measurements. In N. pulcher, the high energy expenditure for submissive behaviour may indicate that this is a reliable signal. The considerable energy expenditure involved in territory defence suggests that these costs should be considered in addition to risk in cost-benefit analyses. This is the first study in which the energy expenditures of specific social and territory maintenance behaviours of individual fish were measured directly by respirometry and within the usual social setting of the fish. Accepted: 20 February 1998     

Adaptation to sea level rise: does local adaptation influence the demography of coastal fish populations?

This study compared the growth of two western mosquitofish Gambusia affinis populations that were previously demonstrated to have genetic adaptations that increased survival under lethal salinity exposures. The objective was to evaluate how genetic adaptations to lethal salinity stress affect population demography when exposed to sublethal salinity stress. Results indicate that chronic salinity exposure had a generally negative impact on population size, but fish originating from one of the two populations established with fish from a brackish site exhibited an increase in population size. Saltwater intrusion seems to result in reduced population size for most populations. Some populations inhabiting more saline sites, however, may develop localized adaptations, mitigating the consequences of increased salinity on population productivity.     

Ventilation and metabolic rate of young rainbow trout (Salmo gairdneri) exposed to sublethal environmental pH.

Differences between ventilatory response and metabolic rates of young rainbow trout tested within the sublethal range of pH 6 to pH 9 were observed using a flowing water respirometer. The oxygen consumption was monitored at swimming speeds of 12 cm/sec and 24 cm/sec. The oxygen consumption rates at 24 cm/sec and pH 6 (423 mg/kg-hr) and pH 9 (367 mg/kg-hr) were considerably higher than those determined near neutrality (328 mg/kg-hr). Ventilation rate increased to either side of neutrality, but significantly fewer respiratory reversals, or "coughs," were observed at pH 6 and a greater number at pH 9 than occurred at pH 7 and 8 or in untested fish. The respiratory-cough response is shown to be pH-dependent in rainbow trout and may therefore not be as reliable an indication of pollutant-caused stress in studies where the experimental pH has not been specified or controlled.     

Effects of environmental salinity and 17alpha-methyltestosterone on growth and oxygen consumption in the tilapia, Oreochromis mossambicus

Effects of environmental salinity and 17α-methyltestosterone (MT) on growth and oxygen consumption were examined in the tilapia, Oreochromis mossambicus. Yolk-sac fry were collected from brood stock in fresh water (FW). After yolk-sac absorption, they were assigned randomly to one of four groups: FW, MT treatment in FW, seawater (SW) and MT treatment in SW. All treatment groups were fed to satiation three times daily. The fish reared in SW (both control and MT-treated groups) grew significantly larger than either group in FW from day 43 throughout the experiment (195 days). The fish fed with MT added to their feed grew significantly larger than their respective controls from day 85 in FW and in SW until the end of the experiment. The routine metabolic rate (RMR) was determined monthly from month 2 (day 62) to month 5 (day 155). A significant negative correlation was seen between RMR and body mass in all treatment groups. Among fish of the same age, the SW-reared tilapia had significantly lower RMRs than the FW-reared fish. The MT-treated fish in SW showed significantly lower RMRs than the SW control group at months 3–5, whereas MT treatment in FW significantly increased the RMR at month 3. Comparison of regression lines between RMR and body mass indicates that MT treatment in FW caused a significant increase in oxygen consumption at a given mass of the fish, whereas MT treatment was without effect on RMR in SW-reared fish. These results clearly indicate that SW-rearing and MT treatment accelerate growth of tilapia, and that RMR decreases as fish size increased. It is also likely that the increased RMR and growth in MT-treated tilapia in FW may be due to the metabolic actions of MT, although the reason for the absence of MT treatment in SW is unclear.     

A study of some factors affecting rates of oxygen consumption of plaice, Pleuronectes platessa L.

Oxygen uptake by plaice, Pleuronectes platessa L ., was measured using both 'closed' and 'flow-through' respirometers. Oxygen consumption was found to be influenced by oxygen concentrations below a critical level of 45–60 mmHg. Rates of oxygen uptake were also affected by fish size, temperature and nutritional status. The problems involved in using values of oxygen consumption, determined in the laboratory, for estimating energy requirements of wild fish are discussed.     

Physiological adaptation to hypoxia of a neotropical characoid fish Colossoma macropomum,Serrasalmidae

Synopsis Investigations of seasonal changes in the hematological parameters of Colossoma macropomum revealed that during times of the year when they are exposed to low oxygen concentrations (< 0.5 mg 1^–1), there is an increase in the hemoglobin content of the blood and the erythrocyte count. Experiments to determine the influence of oxygen content on the routine oxygen consumption showed that the critical concentration is 2 mg 1^–1 at 30°C. At concentrations below 0.5 mg O₂ 1^–1, surface water is used for aquatic respiration. Above the critical concentration, short-term fluctuations in oxygen availability are compensated for by adjustment in the ventilation rate. Gas exchange is facilitated by the unusually large gill surface area (349 mm²g^–1 for a 200 g fish).     

Measurements of oxygen consumption in Mytilus edulis during exposure to, and recovery from, high sublethal concentrations of formaldehyde, benzene and phenol.

1. The rate of oxygen consumption has been monitored continuously in M. edulis during acute exposure to high sublethal concentrations of formaldehyde, phenol and benzene and subsequent recovery periods of 96 hr. 2. The results are discussed in relation to changes in the electrochemical potential difference of sodium, the content of ATP and the tissue concentration of strombine. 3. After exposure to benzene and phenol, an increase in the rate of oxygen consumption that could not be explained by oxygen debt from the exposure period was observed. 4. Depression of the rate of oxygen consumption after exposure to formaldehyde may be explained by a reduced ability to extract oxygen from the water. 5. The pattern of oxygen consumption and behavioural responses, as well as the combined changes in the biochemical markers, were distinctly different in the three cases.     

Metabolic Rate and Natural History of Ozark Cavefish, Amblyopsis Rosae, in Logan Cave, Arkansas

We investigated the effects of mass, season, and activity on oxygen consumption of the federally threatened Ozark cavefish, Amblyopsis rosae, at Logan Cave National Wildlife Refuge, Benton County, Arkansas. We used an acclimatization protocol to measure in-situ metabolic rates. There was a significant effect of mass on the metabolic rate of Ozark cavefish and this relationship differed significantly among seasons. We observed a positive relationship between mass and oxygen consumption during summer and autumn but a negative relationship for winter and spring. There was a 1°C water temperature change between summer/autumn sampling and winter/spring sampling, but it is not likely temperature alone accounted for seasonal variation in mass-oxygen consumption relationships. Activity in the respirometer did not vary significantly among seasons and was not correlated with fish mass or time of day. Seasonal relationships between mass and oxygen consumption may therefore reflect alterations in environmental conditions (i.e. food availability, ambient dissolved oxygen), condition, changes in susceptibility to handling stress, or may reflect low numbers of fish tested. Natural history observations were made throughout the study. Four females were seen in late August with ova visible in the body cavity. On 20 June 1996 we first observed five small cavefish (approximately 10 mm TL) in a pool just upstream of the sinkhole entrance that were likely less than a month old. One large adult (55 mm TL) was seen in the same pool with the young fish for six weeks, until two small fish were displaced by a storm event. Although this does not provide a clear sign of parental care, it does suggest that cannibalism is not always the rule for this species as previously suggested.     

Fish-Community Response To Protective Liming in Thrush Lake, Minnesota

A protective limestone treatment was applied to an acid-sensitive lake in northeastern Minnesota as part of the Acid Precipitation Mitigation Program. This 6–year study evaluated the impact of that treatment on lakes in the upper Midwest that experience episodes of acid stress but have not lost basic species integrity and community structure. Several changes in the fish community can be directly or indirectly attributed to the addition of 4.6 tonnes of calcium carbonate early in the third year of the study. An almost 30–fold increase in the population of Pimephales promelas(fathead minnow) a year after liming, based on mark-recapture estimates from trap netting and snorkeling, was attributed to a pH increase and a three-fold increase in the calcium concentration of the epilimnion. After the initial increase, the abundance of fathead minnows declined in subsequent years, as did the elevated pH and calcium concentrations. The Salvelimis fontinalis(brook trout) population also increased in the lake following application of limestone, but this was due in part to closing the lake to fishing. An increase in survival of stocked brook trout to age 1+ and an increase in growth of older brook trout after liming were attributed to the increased forage that the fathead minnows provided. Fathead minnows may have also reduced predation pressure on young brook trout by older brook trout. This study demonstrated that liming of a slightly acidic lake did not adversely affect the integrity of the fish community, and in fact may have increased the abundance and biomass of the forage fish community and indirectly increased the survival, abundance, and growth of brook trout.     

Oxygen consumption of active rainbow trout, Salmo gairdneri Richardson, derived from electromyograms obtained by radiotelemetry

A radiotelemetry apparatus is described for sensing and transmitting electromyograms (EMGs) from free-swimming fish. EMGs are recorded from the epaxial muscles of adult rainbow trout during periods in spontaneous (= routine) activity, and forced-swim, respirometers. When such EMG records are integrated, subjected to spectral analysis, and computer-averaged, the EMG values (in μV) are highly correlated with the fish oxygen consumption during the activity periods. However, there is a marked difference between the regression slopes for oxygen v . EMG value for the data from the spontaneous, and forced-swim, respirometers; the former slope is the steeper. The probable explanation of this phenomenon is that whereas in forced swims the epaxial myomeres are responsible for most of the activity of the fish, in spontaneous activity other muscle systems (e.g. of the lateral, dorsal and ventral fins) come to account for a greater relative proportion of body movement. The difference in slope, although great, is evidently a regular phenomenon. The shift from one regression to the other occurs at a fairly precise epaxial EMG value ( c . 5 μV). This suggests that the laboratory calibration of EMG value in terms of oxygen consumption can be utilized in the wild so that EMG records from free-swimming fish, fitted with telemetry packages can be used to deduce oxygen consumption attributable to activity. It also appears that such records can be used as a guide to the type of activity of the fish, i.e. desultory movements or free cruising.     

Metabolic response of juvenile gray snapper (Lutjanus griseus) to temperature and salinity: Physiological cost of different environments

Juvenile gray snapper (Lutjanus griseus) occupy a wide range of estuarine and nearshore habitats that differ in physico-chemical properties. To quantify the energetic cost of inhabiting these different habitats, routine metabolism of individual gray snapper was measured in the laboratory at 20 combinations of temperature (18, 23, 28, and 33 °C) and salinity (5, 15, 25, 35, and 45 psu). An open, flow-through respirometer was used, enabling trials to be run for long periods (∼16 h), while maintaining water quality (dissolved O₂>70% saturation), and providing fish sufficient time to habituate to the chambers undisturbed. Video recordings of fish in the respirometer chambers were analyzed to quantify the spontaneous activity rate of individuals. Analysis of covariance, using fish weight and mean activity rate as covariates, indicated significant temperature and salinity effects on oxygen consumption. Oxygen consumption was significantly higher at high salinities, and the salinity effect was temperature dependent. A polynomial equation describing oxygen consumption as a function of temperature and salinity indicated the increase due to salinity from 5 to 45 psu at high temperatures (30-33 °C) was equivalent to a 3 °C increase in temperature. At intermediate temperatures (24-26 °C), the increase due to salinity from 5 to 45 psu was less dramatic, equivalent to a 2 °C increase in temperature. At the lowest temperatures (18 °C), salinity did not have a significant effect on oxygen consumption. The increased metabolic costs in high salinities (∼7% at the high temperature) represent a significant energy cost for juveniles, that would need to be balanced by lower predation risk or greater food availability to result in similar juvenile production compared to lower salinity environments.