I promise you that I'll try to keep this as informative and exciting as possible! Please keep in mind that I did take college level courses in Anatomy and Physiology and Molecular Biology; therefore, I do have an idea of what I am talking about here. Heh.
So...you got the bite and set the hook! Fish on!!! If it's a big one, soon the drag starts to scream, meaning that the fish is trying its best to swim away from you. You pump it up; start gaining ground, and soon the fish is at your disposition -- ready to be scooped up. This is exactly what I remember from all those Rapala fishing video games. As a matter of fact, most old school fishing games had a little "energy bar" for the fish at the top. Ultimately, the objective of the game would be to "tire the fish" by depleting its "energy bar," so you could bring in your catch.
If you think about it, reeling in a fish is the same thing as giving it plenty of exercise! From a video game perspective, the fish starts with 100% of its available energy (full bar). The main difference between the video game scenario and real life catching lies in the fact that by the end of the real life fight, the fish's remaining energy will actually depend on how long the fish fought for! In other words, the fish's energy doesn't necessary have to be totally depleted for the angler to land the fish (having a net always helps in this case).
Now, let's convert this video game scenario to proper Biology! It's well known in the body of C&R research that angling duration is directly proportional to physiological disturbance. Therefore, the longer you play the fish, more exercise it will have to do. More exercise results in more physiological changes, such as increased heart ratio and depletion of energy stores. The main question here, however, is "what type" of exercise are we talking about. In the field of Biology, there are two types of exercises: aerobic and anaerobic.
Aerobic exercises are "light" exercises where the organism can use its oxygen as a source of fuel/energy. From a human being point of view, that would be the same as walking or jogging at a pace. Your heart ratio and your breathing spikes; however, oxygen can still be carried from your breath to your muscles, empowering your cells to sustain the strain. From a fish's perspective, that would be a fish swimming in the Lake at a constant velocity. For aerobic exercises, lactic acid is not produced and built up in muscles. In other words, the organism doesn't really get "sore" the next day.
Anaerobic exercises are "heavy" exercises where the organism can no longer use oxygen as a source of fuel/energy. From a human being point of view, that would be the same as sprinting -- running at full speed for a short amount of time. At this point, oxygen alone is not enough to provide the organism the energy it needs. Therefore, glycogen -- the "storage form" of glucose -- gets used instead. From a fish's perspective, that would be a fish giving short swimming bursts in pursuit of its prey. For anaerobic exercises, lactic acid is formed as a product of glycogen depletion. Since glycogen is mainly stored in the muscles, its byproduct builds up over time. The lactic acid is actually what is responsible for the "soreness" and "fatigue" that happens the next day.
For those who are more visual, here is a nice diagram of the Glycogen-Lactic Acid cycle:
Thus, you should know by now that those "swimming bursts" that fish do when we play them are an example of anaerobic exercise. In other words, oxygen alone is no longer enough to sustain all the strain from the exercise. The fish's swimming bursts are driven by their white muscles, resulting in the depletion of their energy storage. Every time a fish pulls your drag or bents your rod, a little bit of its Phosphocreatines -- the fish's version of glycogen/energy storage -- and ATP are depleted. The fish also suffers from lactic acid build up in their muscles. Therefore, the longer you play them, more "sore" and "fatigued" they will get afterwards.
--- Fish Anatomy and Physiology: What Happens after the release? ---
Now you already know exactly what happens to a fish when you are playing it. Summarizing it, the fish goes through a stage of intense anaerobic exercise. It uses its energy storage (i.e. phosphocreatines and ATP) for short swimming bursts, which in consequences causes lactic acid build up in their muscles. In the Glycogen-Lactic Acid cycle diagram, that would be exactly what is happening on the right side of it.
Then, as one would expect, the left side of the diagram would be the "recovery time" for the fish: when the lactic acid gets transported from the muscles to the liver and something similar to gluconeogenesis happens (in fish, the lactic acid would be transformed once again into phosphocreatines in their liver). It's also at this stage that the fish takes its time to rest and recharge its energy storage. As bad as it may sound, this "healing stage" is really the same as having a crippled fish with low immune system during the amount of time that it takes to heal.
Since the fish is released with almost all of its storage depleted and a high amount of stress, the same doesn't really have the necessary energy to even feed after release. Can you imagine then if it were spawning season or migration season for the fish that you caught? Then, as mentioned in (E) way above, that would be extremely damaging for its offspring: in terms of migration, it would get delayed for that specific fish; in terms of protecting a nest during spawning season, the fish wouldn't even have the strength to chase away predators. If we were talking specifically about a bedding Largemouth Bass, the Sunfish would be all over its eggs and daddy wouldn't be able to do a thing until after a while.
Therefore, ultimately, the main problem lies in the amount of time necessary for this healing process to happen. Most anglers tend to believe that the released fish will recover in a matter of thirty minutes or so and it will be as good as new! Well...it doesn't quite turn out to be that way. As a specific example, a research conducted in 2006 showed that it takes a Largemouth Bass as much as 12 hours after release to go back to its normal resting state, taking in consideration an angling duration of 5 minutes. Now, of course nobody really takes 5 minutes to reel in a Largemouth Bass. Therefore, using mathematics, we can estimate that it takes the fish as much as 2-3 hours to recover for an angling duration of 1 minute! Notice that this data can only be applied for the Largemouth Bass, as the healing time varies from Species to Species.
The healing time not only varies from Species to Species, but also varies according to the different dependent variables that we have mentioned before -- the "trends." In other words, a fish that was exposed to air for a long time, after fighting an intense fight, miss handled, and perhaps dropped on the floor, will heal much slower than a fish that fought for a shorter time and was handled correctly. That's exactly why we want to follow these trends for proper C&R, so that the fish heals as fast as it can. Eventually, that includes reeling in the fish as fast and comfortably as possible, so that its energy storage is not completed depleted after release.
--- To Play or not to Play the Fish ---
After all this Biology talk, everything boils down to our main question: can we actually take our time and "play" the fish and still ensure that it survives after we release it? And the answer is: it depends. Before going deeper in this subject, here is a list of mortality ratios by Species from a research conducted in 1994 by Muoneke and Childress:
Note that this table is not entirely accurate because each data entry was taken from a different research paper. In other words, Muoneke and Childress pretty much compiled a bunch of research papers on hooking mortality in the field of recreational angling. The dependent variables for each individual research were not the same! For example: in one research, they may have used treble hooks. In another research, they may have used j-hooks. In one research, the local water temperature may have been 60F. In another research, water temperatures were around 40F. The usage of live bait was the only dependent variable that was the same for all the data on this table. In conclusion, this table is only useful for us to see how "sensitive" a species of fish is in comparison to another. No other conclusions should be drawn from it.
From the table, we clearly see that some Species are more sensitive than others. A higher mortality ratio indicates more sensitivity. The Trout family, for example, has a natural higher mortality compared to other Species of fish. The lowest mortality ratios were from the Esox family (i.e. Pike, Muskellunge) and the Smallmouth Bass, probably because the researches were conducted in places where water temperature was low (recall: higher water temperatures result in less oxygenated water; therefore, higher stress on the fish). On the other hand, Channel Catfish came up with a pretty high mortality rate, probably because the research took in consideration the amount of fish who swallowed their hooks. Largemouth Bass and Striped Bass got a whooping 56% and 69% mortality ratio, since we were dealing with live bait and not artificial lures (for artificial lures, their mortality ratio decreased drastically).
Summarizing...As one can see, it turns out that it's not as simple as expected when it comes to caring for our fishes' survival. A person can't simply barge in and tell someone that "he is killing the fish for playing it too long." Ultimately, it really depends on what type of fish is being targeted; what type of gear and technique is the person using; what time of the year is he fishing; what is the level of oxygen in the water; if he is following proper C&R procedures; etc. Too many dependent variables!!! So, I hope you folks get the idea when I say that "it depends." Should you play the fish or force-fish it? Does it decrease its mortality rate after you release it? It really depends!
--- Conclusion ---
Different Species of fish have different sensitivity when it comes to different stressors in the field of Catch-and-Release fishing. However, one thing is certain: despite the Species, an angler should reel in the fish as fast and comfortably as possible! In other words, one should always try to minimize angling duration. That doesn't necessarily mean "force-playing" the fish -- it means to land the fish at a first opportunity without wasting any additional time. Fishing accessories such as a net should be used.
Force-playing a fish should definitely be practiced under extreme circumstances or while fishing for smaller Species of fish. For example: fighting a sensitive fish Species (i.e. Walleye) or post-spawn fish during high water temperature levels; or Micro-Fishing in a Creek. That is to prevent too much Lactic Acid build up in their white muscles and depletion of energy sources such as phosphocreatines and ATP, so that the released fish can return to normal functioning as soon as possible. Sensitive fish will be able to have enough oxygen to recover and smaller fishes will have enough energy to run away from predators.
To maximize the survival rate of released fish, a Catch-and-Release angler should also be pro-efficient with the other trends related to safe fish handling: wetting its hands before handling the fish; keeping the fish outside of the water for a limited amount of time; constraining the fish from injuring itself; using gear that prevents the fish from swallowing the hook; etc. A proper revival for bigger and trophy fish should be practiced until the fish has enough energy to swim away on its own (the process may take up to 5 minutes).
If all of these notes are taken, an angler should have absolutely no problem playing a fish comfortably, enjoying the fight and the entertainment that angling provides, all while ensuring the fish's safety after release.
Best of luck for all of us,
Long Days and Pleasant Nights,