Respirometry

Scientific context

Scientific context

« Blazka » type respirometerA swimming chamber enables us to measure the effects of low oxygen levels on metabolism and swimming activity of cod. Its design and the possibilities it offers make this instrument very interesting for our work.

Work on oxygen, metabolism and swimming date back many years. After experimenting with static systems where oxygen uptake was measured at rest in closed systems, the next step was to do similar measurements during activity. Blazka type respirometer; This approach is not new and various types of instruments have been used which are adapted to various fish species, from the very small (sticklebacks) to the very large (tunas). After an extensive literature review and after consulting with other laboratories, a Blaza-type system was chosen and adapted for use with cod up to 50 cm in length.The instrument used at the MLI enables us to film the fish while it is swimming at different speeds and to detect changes in swimming pattern Water velocity and hence swimming velocity can also be controlled. Thus we can subject fish to a controlled swimming exercise under different experimental treatments. The system also enables us to measure the oxygen uptake (metabolic rate) of a resting or swimming fish. It is therefore possible to measure how a variable, such as temperature, affects the metabolic rate and the swimming capacity of a fish. All these measurements can be made in a closed or open system. It is also possible to vary the oxygen concentration to simulate the various underwater environments of the Gulf and estuary. Coupled with the automatic data capture system and video system, this instrument is highly versatile.

Experiment

When environmental conditions degrade and food resources become scarce, cod mobilize energy reserves stored as fat in their liver and as protein in the axial muscle (some 60% of body mass). Cod are adapted to this situation which takes place during winter and peaks in the spring when reproduction occurs. Cod may use their energy stores to a considerable extent and this is considered to have negative consequences in terms of their physiological capacities. During the summer however, cod feed intensively and rebuild their energy reserves preparing for a new cycle of fasting and sexual maturation. The following experiment was conducted to learn about the impacts of seasonal changes in energetic condition on the physiological capacities of cod.

Cod were either food deprived or fed capelin, one of their favourite preys, to obtain fish with low or high condition factor values. The fish were then put into a static respirometer where their basal metabolic rate was determined. The basal metabolic rate is defined as the minimal rate of oxygen consumption of a resting, unfed fish. The cod were then transferred to a Blazka-type respirometer and subjected to stepwise increases in current velocities which forced the fish to swim progressively faster. Their oxygen consumption was measured at each current velocity. Fish have a limited swimming capacity and eventually stop swimming at higher speeds. he oxygen consumption measured at the highest sustained swimming speed is the maximum consumption. The aerobic scope of cod is defined by these minimal and maximum values.

Example of a typical work day

Results

Although individual condition differs markedly between starved and fed cod (condition indices of 0.68 and 0.92, respectively), oxygen consumption at rest (weight specific) does not differ between the two groups. However, oxygen consumption during exercise (weight specific) shows a greater increase for the starved fish. When the data are not expressed on a weight specific basis, the two groups of fish show a similar increase.

However, the swimming capacity of fish with a lower condition index is clearly less, which suggests that fish in poor energetic condition are less efficient. This may result in a higher vulnerability to predation and to trawlers as well, and a reduced feeding success on moving preys.

Starved fish Fed fish
Condition index : 0.68 Condition index : 0.92
Length (mm) : 442 Length (mm) :464
Mass (g) : 580 Mass (g) : 924

Consumption at rest and during exercise (mg O2 / hour)

  per kg per fish
  rest exercise rest exercise
Starved fish : 42.3 251.3 24.6 145.8
Fed fish : 43.8 182.8 40.5 168.9

Net consumption due to exercice

Starved fish : 121.2 mg O2 / h / fish
Fed fish : 128.4 mg O2 / h / fish

Effect of fasting on endurance and swimming

Effect of fasting on endurance and swimming

Effect of exercise on oxygen concentration

Effect of exercise on oxygen concentration

Oxygen uptake vs swimming speed

Oxygen uptake vs swimming speed