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In my world are fish-like animals that breathe air through their gills. These gills have an operculum, like bony fish, and a pair of mammalian ears replacing their spiracles. Their face is piscine, with the nostrils lacking internal openings

These animals are mostly amphibious, but some species are more adapted for deeper water

Are there any blowhole analogues, that would be useful for inhaling air from in the water?

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  • $\begingroup$ I'm not sure what you're really looking for. If you want there to be, your ancestral amphibians had a developmental gene duplication, with doubled lungs. One set of organs became classical "fish" gills with operculum, while the others followed the classical amphibian gills-to-lungs path, and there's no reason that those lungs couldn't simply have a blow-hole to assist in shallow surfacing. Heck, use a periscope-type breathing tube if you want. Why not? $\endgroup$
    – DWKraus
    Dec 18, 2021 at 18:59
  • $\begingroup$ Most amphibians don't need to breathe surface air unless they lose the ability to breathe underwater as adults (and that doesn't sound like the case here). Some can breathe underwater exclusively the skin (like the lungless salamander who has neither lungs nor gills). Many CAN breathe surface air if they leave water. What's the function of the breathing hole? Do your amphibians breathe air more efficiently than water? $\endgroup$
    – DWKraus
    Dec 18, 2021 at 19:20
  • $\begingroup$ @DWKraus The fish are obligate air breathers, and breathe solely through their gills $\endgroup$ Dec 18, 2021 at 19:21
  • $\begingroup$ So...they exclusively breathe surface air, but use gills to do so? Aren't they called lungs at that point? I can find lungs that can breathe water, but not gills that breathe air. $\endgroup$
    – DWKraus
    Dec 18, 2021 at 19:26
  • $\begingroup$ @DWKraus There are fish that use their gills to breathe air. In fact, it is more efficient as gills tend to have a higher surface area than lungs $\endgroup$ Dec 18, 2021 at 19:31

3 Answers 3

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If you want a blowhole and gills you just need one thing different than earth vertebrates, your aliens evolved to breath air from something other than their digestive system. if their respiratory system is separated from the digestive system a blowhole is fine, they are not breathing through their mouth. Air contains far more oxygen than water which is why air breathing evolved in fish. Your creature pulls air into a lung through the blowhole and not the mouth. Maybe their air harvesting system evolved from a reproductive organ or some excretory organ, mybe it is an inverted amphibian like gill sysem only used in the young that then becomes an air breathing organ in adults when their adult gills grow in.

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Stomach Breathing Fish

The ancestors of these gill-breathing fishes evolved a rather unique form of air respiration: the blowhole.

This blowhole arises from an archaic partial duplication of the gastric invagination that developped into the alimentary canal. However, rather than opening through the (primary) mouth, this secondary os opens posterior to the mouth, and anterior to the brain.

The blowhole's external appearance is a mound of labial tissue, fitted with sphincter muscles. The windway passes just below the brain, where it has separated and pushed aside the bony structures of the mid-face & eyes. It continues, dorsally & most often slightly offset to the left of the esophagus, to the blind invagination known as the air stomach. Curiously, a number of examples of this fish have been found with a vestigial duodenal invagination.

The muscular action of the air stomach draws in fresh air from the surface; and, once distended, pushes the fresh air back out through the gill fistulas, which connect the air stomach to the bilateral gill structures.

The respiratory cycle is mediated by the sphincters: the external labia that surround the blowhole open upon surfacing for inhalation, but close tightly when the fish submerges. The midline windway sphincter closes once the air stomach is full; and the bilateral analogues of the sphincter of Oddi, sending the fresh air through branching vessicles that terminate in the gills. Thence, the air is expelled through the "bubbler", a system of tubules that run along the ventro-lateral surfaces of the abdomen, terminating in pores that release bubbles of gas through the skin.

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Suck-Hole

There is no blowhole. There is a suck-hole that takes in air while the creature swims along the surface. The air goes along a tube inside the animal to the gills where it bubbles out from the inside. The gills absorb oxygen from the bubbles.

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  • $\begingroup$ But what is this suckhole? What structure is it derived from? $\endgroup$ Sep 3, 2022 at 12:41
  • $\begingroup$ It is a hole on the top part of the creature that sucks air inside the body and down a tube. The other end of the tube is the gills. $\endgroup$
    – Daron
    Sep 3, 2022 at 13:28
  • $\begingroup$ @IchthysKing I don't understand the structure question. $\endgroup$
    – Daron
    Sep 3, 2022 at 13:29
  • $\begingroup$ I'm asking what anatomical structures (like nostrils or ears) this suckhole would have evolved from $\endgroup$ Sep 3, 2022 at 14:37
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    $\begingroup$ @IchthysKing It didn't evolve from something else. The suckhole is its own thing. $\endgroup$
    – Daron
    Sep 3, 2022 at 15:34

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