That's not actually a fish, but your point is well taken. We often hear the question of why are there no transitional species, but to me most species are transitional species, intergrade between something more advanced and something more primitive. Thus we have egg-laying mammals such as the platypus among the nominally viviparous but also live-bearing ovoviviporous species such as the garter snakes among the nominally oviparous reptiles. And it's why we see the mudskipper (undeniably a fish) able to spend long periods outside of the water while a hellbender (undeniably an amphibian) unable to do the same. Most everything is on its way to becoming something else to adapt to a constantly changing environment, exploit a new food source, or foil a predator, to the point that the truly ancient creatures such as turtles or coelacanths are notable for their relative immutability.
Among individual features the same progression within the seemingly random variability can be seen. We often hear the eye cited as proof on intelligent design, and I do have some skepticism that such intricate organs could evolve purely on the basis of chance and natural selection, at least on a scale necessary to provide a viable new species, but the eye is not so singular as some might think. We see everything from the simplest eye spots in flat worms, recording only the absence or presence of light, to the incredibly evolved and intricate eyes of geckos and cuttlefish. We also know from observation that many of the proteins required to build such a complicated are quite similar to other proteins - in fact, the same genes which create the required proteins can create completely different proteins given slightly different environmental stimuli. Evolution is an ongoing, well-documented, and wondrous process.