IGFA Hall of Fame Captain, Peter B. Wright, shares his skepticism on how long fish can sustain reported speeds.
I seriously question the speeds often given for any fish, especially when Wikipedia and some reputable encyclopedias claim that Sailfish are supposed to be the fastest fish known to hit 60 miles per hour.
Searching several references and online sites looking for Orca speeds, I found a range of speeds anywhere from 25 to 35 miles per hour (mph) on these publications and websites. None of these were anywhere near as fast as some of the speeds some fish can supposedly attain.
Since Orcas can swim down, catch and feast on Bluefin Tuna, I question any of the old unsubstantiated references of speeds that fish can travel. I believe fishing writers grossly exaggerate at how fast most fish can be. It's not often a reader can get excited when reading about a Bonefish tearing line off a reel at 15 mph, which is slower than many humans can run. In my youth, I could run down a beach in shallow water fast enough to avoid losing line to even a big Bone.
Being a long time big game fishing guide and part-time Biological Oceanographer with decades of personal experience (otherwise known as anecdotal evidence by scientists), I am positive no marine fish can exceed about 25 mph. I often chase large marine fish (Tuna and Marlin) with a boat and quickly catch them at 20 mph.
In addition, if a fish jumped straight up at 60 mph (88 ft/sec), simple math shows that after one sec the force of gravity (32 ft/sec) would have slowed the fish to 38 mph (88 ft/sec - 32 ft/sec = 56 ft/sec which is 38 mph). The height of the fish at the end of that one second would be 72 ft and it would still be going up at 38 mph. Height equals AVERAGE velocity times one second. Average V would be 88 + 56 divided by 2 giving a height of 72 feet.
Last but not least, there is the study AFTCO did decades ago which showed how much frictional drag there was on given lengths of line being pulled through the water. If any fish could go even 30 mph, they would break off before any crew could clear the lines and merely backing up would not make enough difference to avoid breaking the line.
Big fish eat little fish and the biggest predatory fish are the fastest. I doubt very much any fish can go 30 mph — it is too easy for Orcas to catch them for fish to obtain that kind of speed and no one says Orcas can hit 60 mph!