Re: Do all fish have fins? Which ones do not?

Kathy! You have produced the classic fish question because everybody wonders about fins, limbs and the animals that have them. The answer is that all fish with jaws have fins. The simpler fish that haven’t reached the bigger head adaptations of others often have suckers and can be without any fins at all. For example, the snake-like lampreys and hagfish have no real fins. A simple skin or vein-like extension on the back acts a little like a fin in some species, but doesn’t contain any structures a fish fin would have. These animals have been around since the first known vertebrates, so we think fins must have evolved since they appeared, or in species descended from them. Sadly, we only have fossils of many examples of jawless fish that do seem to have fins. Modern bony fish and others have paired fins, just the same as we have paired limbs. The extinct jawless fish do seem to have needed the stability and locomotion that fins can provide. They may have moved a lot more than modern jawless fish, with lifestyles just like normal fish, except for the JAWS of course! So finally, all of these fish drawn here http://www.nature.com/hdy/journal/v94/n3/fig_tab/6800635f1.html have fins. The coelacanths and sharks have “proper” fins but the two earliest vertebrates haven’t. Look at the the spectacular dance of the Siamese Fighter, Betta spendens to see how breeding can produce bigger fins than even those you have on more normal fish. The diagram shows the beautiful variation you have in each fish’s fins. jawless lampreys aren’t eaten or studied much, so you can take the answer as---- “Yes, but---“.