Mouthbrooding fish are not common. Perhaps the most well known are some of the cichlids found in central Africa, though there are other examples as well. Most fish, however, are more apt to eat their young than care for them in any way once the eggs are laid. However, recently, a species of deep-sea fish known as the parazen was found to have eggs of its own species in its mouth. This accidental discovery has propelled a discussion of the evolution of mouthbrooding.
The parazen is a several inch long fish found in the deep ocean. It ranges from a depth of around 500 to around 1600 feet and has roughly a worldwide distribution in tropical waters, with the exception of the eastern Pacific and Atlantic. Very little information exists about this fish outside of highly technical papers and, in fact, the original purpose of the study that made this discovery was to determine how many species there are in genus Parazen. The process of examining a preserved specimen from Taiwan revealed that the female in question had a mass of eggs in her mouth. Originally, the researchers were unsure what the eggs were and thought that the eggs were possibly something the parazen had eaten before being captured. However, the researcher discovered that there were special tendrils attached to the back of the fish’s mouth which appeared to be holding the mass of eggs in place. This seemed to indicate they were not being ingested by the fish. Instead, they appear to have been held there for incubation. The researchers removed the eggs and viewed them through a CT scan. They discovered around five-hundred thirty eggs that contained developing embryos.
The researchers proposed that the parazen, which has been observed sifting sand as part of its feeding behavior, has evolved a specialized structure, known as a pharyngeal lobe. This pharyngeal lobe, which is found in other sand sifting species across both salt and freshwater habitats, is supposed to help filter sand, as well as prevent any hatchlings in the parent’s mouth from being injured by the teeth or gills, as well as swallowed. The researchers hypothesize that this pharyngeal lobe and sand sifting were evolutionary predecessors of mouthbrooding.
This hypothesis seems very weak, particularly since mouthbrooding does not require sand sifting as a lifestyle. Members of the genus Betta, the well known Siamese fighting fish, are mouthbrooders and they do not sift sand as part of their normal diet. In fact, evolutionists themselves acknowledge the mouthbrooding cichlids have evolved ten separate times. This does not even include the popular salt-water tropical creatures, jawfish, and cardinalfish, both of which mouth brood their young in at least some species. Other types of fish also mouth brood their eggs or young Mouthbrooding appears to be a difficult problem for evolution since numerous different lines of fish all possess it.
Mouthbrooding is a very interesting behavior. It requires some very specific things to occur. The female (or in some cases male) must be able to recognize her own eggs. Further, she must be aware of whether they are fertilized or not in at least some cases. She must also be able to pick up the eggs without harming them in a mouth designed to prepare food for digestion. She then must be able to hold these eggs until they hatch, and sometimes beyond that as the larvae develop in her mouth. The sheer complexity of this system, with all the fail-safe mechanisms that have to go into it, is astounding. If even one part of the mechanism does not work the first time around, the organism will be unable to reproduce. Since reproduction is king in the neo-Darwinian paradigm, this inability to successfully reproduce would result in the extinction of the organism and any new adaptations lost.
From a creationist perspective, mouthbrooding is incredibly exciting to consider. The behavior is found across multiple groups, as well as its incredible complexity points strongly to an original creator. While the behavior has been lost in some instances or has been modified in some ways, the behavior itself is likely a built-in artifact of creation. Finding a deep-sea fish that is a mouthbrooder, while somewhat surprising, is not something that in any way challenges a young earth creationist view.
https://www.nature.com/articles/s41598-020-60534-0
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