**6.4 Discussion**

Ventilation was characterized by alternating positive and negative pressure pulses whose amplitude and frequency were very constant when activity and temperature were stable. Positive pulses were always associated with opening of the mouth and negative pressure with closing of the mouth. Amplitude of these rhythmic pulses generally ranged from 50 to 100 pascals for all lake sturgeon. We also observed that all fish periodically made rapid mouth movements that resulted in considerably larger pressure pulses (800 pascals) compared to the rhythmic ventilations pulses described previously. These pulses were caused by the sudden projection of the jaw approximately 3-4 cm outward form the mouth. Pressure amplitude was often an order of magnitude greater when compared to ventilation pulse pressure. This is interpreted as instances of feeding or feeding attempts. Temperature influences all variables as integral and max-min pressure and frequency of ventilation on pulses increased with temperature. As well, amplitude and period of feeding pulses increased with temperature.

Although we did not measure MO2 (oxygen consumption) directly the data on integration of branchial pressure and an AC waveform indicates that integration and amplitude can be used to predict MO2 (energy budgets) sturgeon in nature. This information could be combined with temperature and feeding data to predict seasonal growth rates, etc.

We have developed a specialized feeding tag for lake sturgeon that functions under laboratory conditions. Inserting the cannula through the cartilage above the pectoral fins had a minimal affect on the fish; however, we have yet to find a satisfactory method to hold the tag securely to the fish for more than 12 days. Internal placement of the tag is not an option as the wires would then have to come from the tag through the body wall to the sensor. The prototype tag weighed 46 gm in air and the next stage of development will be to reduce the weight of the tag size considerably (we are already using depth tags that have a much lower weight than the V16s). Even the prototype tag can be attached to large lake sturgeon (over 25 kg) and the preferred attachment site will likely be the pectoral fin. The next tags will have to weigh less than 15 gm in air, be more streamed lined to reduce resistance and mode of attaching to the boney fins rays will need to accommodate self tightening strap.
