The Complete Beginner’s Guide to Seahorse Evolution

Just how did seahorses make the leap from ordinary fish to extraordinary oddity? Damselfish photo by Klaus Stiefel When you look at a seahorse, it’s easy to wonder how such a bizarre creature could come to be. The seahorse’s behavior and appearance is so radically different from most other fish that one can’t help but ponder how they evolved into what we see today. With it’s unusual horse-like head, chameleon eyes, monkey tail, kangaroo pouch and insect-like armor; how did did it evolve to be so strange? To understand that, we need to look at some of the seahorses relatives. One issue we face with discovering how seahorses evolved is the lack of fossils. There are a few fossils that show some early seahorses, but like most sea-dwelling creatures, it’s a very limited number. Fortunately for us, many of it’s living relatives give us a glimpse at the seahorse’s evolutionary path. While these relatives aren’t exactly what seahorses evolved from, they give a pretty clear picture of how changes over time go from subtle to extreme to become seahorses. First, we start out with the seahorse’s more normal but distant relatives. These are scorpion fish, a large group of ray finned fish. Some are elaborately ornate, like the lionfish. Photo by Christian Mehlführer Others are camouflaged to match their surroundings. Marbled Rock Fish. Photo by Nemo’s Great Uncle. Many though, look just like normal fish. Kelp Rockfish. Photo by Brian Gratwicke The next interesting ancestor analog is the stickleback. Many sticklebacks look like a pretty normal fish by all accounts. But their is something new starting. Sticklebacks are starting to develop the armored skeleton for protection, and lacks scales. But it’s still overall very fish-like. The male protects the eggs in a bubble nest he creates. The Three Spine Stickleback Gasterosteus aculeatus pictured below still looks overall fish-like. Three Spine Stickleback. Photo by Jack Wolf Then we come to the Fifteen Spine Stickleback Spinachia spinachia. Its mouth is elongated, its body stretched out; it’s starting to look less like your common fish. In sticklebacks, the parental care is done by the male. This also is not uncommon in fish, with many males taking on the role of primary caregiver. Fifteen Spine Stickleback. Photo by Mark Thomas Now we come to the middle of the journey. Here we have trumpetfish, Aulostomus spp. Still fishlike, still swimming like a fish, but the mouth of a seahorse is clearly evident. It’s an open water spawner, with no parental care. We don’t know where it diverged from it’s common ancestors or why it’s a broadcast spawner, but other traits, such as the elongated body, and suction like mouth are similar to seahorses. Trumpetfish. Photo by Vlad Karpinskiy It’s body is still fish like, and it swims like most common fish; it shares a similar mouth shape to seahorses, but less refined. Trumpetfish head detail. Photo by Noodlefish An ancestor similar to the cornetfish Fistularia spp. probably came next. Also known as flutemouths, these elongated fish still swims mid water, but has reduced fins and a very long snout. They are probably the largest of the fish we’ll be looking at, with some species growing up to 6′ (~180cm). Blue Spotted Cornetfish. Photo by Kevin Bryant Next in line is the ghost pipefish, which grows only to a maximum of 6″ (~15cm). They are probably a branch off of a common ancestor that shared many of the traits seahorses do, but with some differences. These fish have started to move to caring for their eggs on their body, like most close seahorse relatives. However, it’s the female that carries the eggs, clutching them in her pelvic fins. Ornate Ghost Pipefish. Photo by Doug Anderson Flagtail pipefish are the next on this evolutionary ride. Care of the eggs is once again the realm of the males. Chances are it never left, but it’s not clear why some living relatives like the trumpetfish and ghost pipefish developed different reproductive strategies. It’s pretty clear this is the beginning of what we think of as the paternal care common in these fish. The male carries eggs laid by the female in an intricate dance along his belly. Dunckerocampus spp. carries the eggs on their bellies completely exposed, while Doryrhamphus spp. has a flap of skin that helps protect the eggs. Flagtail pipefish swim midwater much like the fish listed above. Banded Pipefish, a type of Flagtail Pipefish that swims mid-water. Photo by Lakshmi Sawitri From there we go to pipefish that carry the eggs at the base of their tails, some in partial pouches, later with pouches that almost entirely encase the eggs. Most still have a tail fin, but it is getting smaller. They slither close to surfaces, using their bodies as anchors. Many use their bodies and even their tails to help grip on to rocks, seagrass, or floating algae. Dragonface Pipefish. Photo by Philippe Guillaume There are at least 200 species of pipefish, with a dizzying array of body types and behaviors. Some live in seagrass beds, others on coral reefs. Some are only 2″ (~5cm) long, but the biggest species grows to over 2′ (~60cm). The photo below shows a literal handful of different species found off the coast of North America. Several pipefish of different species found off the coast of North America. Photo by Roger Shaw Now we start to see an amazing transformation. Pygmy pipehorses are the next in this evolutionary march. These tiny fish are all 2.5″ (~65cm) or smaller in length. They hitch just like seahorses and lack a tail fin, and their body is starting to take the angular shape that seahorses have, but their heads are still overall in alignment with their long bodies. Interestingly, males prefer to keep their body vertically, but females perch more upright, similar to seahorses. West Atlantic Pygmy Pipehorse Amphelikturus dendriticus. Photo by Stig Thormodsrud Pygmy pipehorses are loosely grouped as pipefish-like pygmy pipehorses and seahorse-like pygmy pipehorses because of how similar they are to one or the other. The first of which is the pipefish-like pygmy pipehorses. They do not have a tail fin, instead using their prehensile tails to grasp onto algae and wait for food to swim by. They are frequently misidentified as pipefish or missed all together because of their diminutive size. Short Pouch Pygmy Pipehorse Acentronura-tentaculata Photo by Nick Hobgood The seahorse-like pygmy pipehorses could almost be mistaken for seahorses. One beautiful example is the Sydney Pygmy Pipehorse Idiotropiscis lumnitzeri. They look much closer to that of a true seahorse, and even have some of the head structures that seahorses have. Pregnant male Sydney Pygmy Pipehorse. Notice the round area between his body and tail. Photo by Michael McKnight  The head is distinct from the body, the male has a full brood pouch at the base of the tail. The head can bend, but is usually held in alignment with the body. They don’t chase down prey; instead waiting for it to drift past their holdfast. Sydney Pygmy Pipehorse. Photo by Steve Gillespie And finally we get to seahorses, the strangest fish of them all. They’ve made the leap to standing upright most of the time, the bent head allowing for a longer reach to snap up prey. But like their distant ancestors, still relies on camouflage to hunt and gulps their prey whole; only this time through a straw. Pot Belly Seahorse hitched to sponge. Photo by Doug Anderson. I hope you enjoyed this look into seahorse evolution. As mentioned earlier, this is a rough map based on living relatives, not the exact ancestors of seahorses. Taxonomy, the study of how animals are related and categorized is always changing so we may find new information about these relationships as time goes on. But hopefully these examples will make it easier to understand how the seahorse became what it is today. Evolutionary Tree This entry was posted on Friday, January 10th, 2014 at 8:42 pm and is filed under Biology. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

An Aquarist’s Notes: Turbulence in Hawaii

Butterflyfishes on the west coast of the Big Island of Hawaii where aquarium collectors are active. Image by Eric Sorensen, WSU. An Aquarist’s Notes: Turbulence in Hawaii I first went to Hawaii on assignment for CORAL Magazine in 2010, and for the better part of four years I have covered that state’s aquarium fishery. I expected to find a fishery full of complicated regulations and even more complicated conflict. I found the latter in spades, but the former, to my surprise, didn’t really exist. Regulations were relatively few and far between—no total allowable catches (TACs), no quotas, no bag limits, no limited entry. I was, quite frankly, shocked that a commercial fishery in U.S. waters would be so unregulated. The fishers I interviewed, especially on Big Island, didn’t view it that way. Many felt they were being unfairly targeted and that veils of regulation were being drawn around them like the barrier nets they use to catch aquarium fishes. Some felt they had consistently given ground, made concessions in the face of anti-trade activism. Some were ready to make a stand, saying they couldn’t—wouldn’t—give any more. Some of these fishers opposed the rules package just signed by the governor. A few of them still oppose it, although they are not willing to say so on the record. Those fishers who stand in opposition to the new rules have some strange bedfellows. There are the anti-trade activists who say the rules don’t go far enough; the most extreme will not be satisfied with anything short of a fishery closure. Then there are mainland aquarists who are lukewarm on the new rules. They worry that a White List will make it more difficult to acquire some species with which they want to work in the short term. They anticipate a slippery slope that will lead to fewer and fewer species remaining available to trade in the long run. Personally, I was pleased to see the governor sign the rules package. I’m pleased because I see it as a step forward for aquarium fisheries in general. I see an opportunity to manage the fishery based on real data. The data really does matter, and rather than less, we need more. This rules package takes a relatively small swath of ocean—a shoreline of less than 150 miles—and says we’re going to manage it based on something more than anecdote and emotion. I look forward to reporting on the progress and talking about how this may be a model viable for export to other aquarium fisheries in far worse shape than Hawaii’s. Hawaii is on a path of good, data-based, adaptive management of its aquarium fishery. This type of management can protect the fishery in terms of both environmental sustainability and economic value. It replaces a messy form of conflict resolution with a multi-stakeholder, community-based approach, and now that the new rules are law, I think we all owe it to the people, the process, and the potential to get behind them.