There are a couple of ways to make a fish exercise to exhaustion. One is to use a swim tunnel, in which a current is generated by an impeller. Trout will naturally swim against the current. The current velocity can be increased until the fish exhaust and is no longer able to maintain its position in the swim tunnel. This method works well for small (<20 g) fish, but you need a really BIG tunnel to exhaust bigger fish.

A second method, somewhat cruder but just as effective, is to place fish in a circular swim tank and manually chase them around the tank for about 5 min.

At this point, the fish is exhausted (not to mention the hard-working student!) . This has become a very common method used to exercise fish to exhaustion.

Well, that depends upon the question asked. Typically, we want to assess physiological changes within the fish. The simplest way to do this is to sample blood and measure parameters of interest (e.g. levels of hormones, and/or metabolites). A common and useful method for obtaining blood samples from fish is to surgically implant a catheter in a blood vessel while the fish is anaesthetized. This technique is quick (~15 min), the fish survives and it allows us to obtain several blood samples from a individual fish with minimal disturbance to the fish. After surgery, the fish are placed in individual boxes and allowed to recover. We can then exercise them and measure several parameters in the blood.