At slower rates of dilution (0.031 0/00 salinity/hour), however, the fish stopped swimming at 20.3 0/00 salinity. McCairns and Bernatchez (2010) studied freshwater and marine sticklebacks and found that freshwater populations can survive in saltwater conditions, albeit at lower survival rates. The reverse was also true with marine populations in freshwater habitats. Second, it is a well-known fact that saltwater and freshwater can form layers on top of one another. The mixing of freshwater and saltwater in places was not complete. Pockets of water of varying salinity can exist next to one another. For example, MacGinitie (1939) reported layers of freshwater persisting atop layers of saltwater for several days. Fish with different salinity tolerance levels could have survived the Flood in these layers of varying salinity (Oard 1984). Lastly, aquatic organisms can tolerate varying levels of salinity, even within the same species, genus, or family. Similarly, it could also be possible that different species within the same kind (baramin) of fish exhibit differing levels of tolerance towards adverse levels of salinity. In other words, both freshwater and saltwater fish species could be part of the same kind (Whitcomb and Morris 1961, p. 387). Woodmorappe lists several examples of euryhaline organisms, namely animals that can not only tolerate both saltwater and freshwater but have been observed living in these environments. These include the roofed turtle (Kachuga sp.), the diamondback terrapin (Malaclemys sp.), the American crocodile (Crocodylus acutus), the cichlid fish Tilapia grahami, and the crab species Telphusa sp. (Woodmorappe 1996, p. 144). Adaptation to varying saltwater concentrations is a trait that is not exclusive to fish alone. This also implies that certain changes in gene regulation allow for rapid physiological changes in response to a challenge in salinity in fish. These changes can involve hundreds or even thousands of genes. Similar regulatory changes in genes exist in microorganisms that allow them to adapt to adverse environmental factors. For example, the green alga Chlamydomonas reinhardtii can accumulate carbon in response to low CO2 levels (Brueggeman et al. 2012) as well as form multicellular clusters in the presence of predators (Cserhati 2019). Although this is an example only from a species of algae, this could possibly be true in the case of vertebrate animals, as seen in various cases of sexual dimorphism that are due to genetic differences. These pre-existing gene repertoires appear to constitute a divinely engineered regulatory circuitry that may be activated during adaptation to a water environment differing in salinity, such as a landlocked environment (an environment that is permanently closed to influx of external saltwater). These gene repertoires may have allowed for the post-Flood adaptation of fish to new environments due to the receding Flood waters (Genesis 8:13–14). These changes in the regulatory machinery would have allowed fish not only to survive during the Flood but also to adapt to new environments that arose after the Flood, such as lakes, ponds, rivers, inland seas, and estuaries. Landlocking is a process whereby diadromous fish (species that migrate between saltwater and freshwater environments during their lifetime) lose their capability of adapting to saltwater and permanently end up in a landlocked lacustrine environment, and therefore cannot migrate back to a marine environment. Species that migrate as adults from saltwater to freshwater to spawn, after which juveniles swim back to the ocean are called anadromous species. Conversely, species that migrate from freshwater to saltwater to spawn, after which juveniles migrate back to freshwater are called catadromous species. Amphidromous fish migrate between freshwater and saltwater for purposes other than spawning. Such species are born in freshwater, then float out into the sea then return to freshwater as adults to spawn (McDowall 2007). See Figure 1 for the differences between these migratory lifestyles, along with several examples of species that belong to these groups. Actinopterygian (ray-finned) fish make up 96% of all fish species. In this clade, there are 15,150 freshwater and 14,740 (roughly 50%– 50%) marine species, even though oceans make up 90–99% of the Earth’s surface volume. When we look at non-fish species, Dawson (2012) estimates that there are around 4,000 marine gastropods versus 30,000 freshwater ones and 40 marine hydrozoans versus 3,500 found in freshwater habitats. Clearly, due to greater species richness, freshwater habitats are the scenes for rapid speciation, although freshwater fish can also acclimatize to saltwater conditions. Genesis 1:20 describes the waters as abounding with living creatures, which would naturally include fish. As such, we can be sure that fish had high numbers at Creation Week. As of February 2022, the FishBase database has described 34,800 species of fish (Froese and Pauly 2022). Fish are the most abundant and diverse group of vertebrates (Magurran et al. 2011). As to whether the created diversity in a particular fish kind was low or high would classify it as a type 2b or type 3b Carter baramin (Carter 2021). Within the same family of fish that inhabit both freshwater and saltwater, the more closely related species differ in their level of salt tolerance in many cases (Huyse et al. 2004). Carrete Vega and Wiens (2012) claim that species from the clade Percomorpha repeatedly invaded freshwater habitats, along with cichlids, percids, and peociliids in several minor and major radiations. Although only 4% of extant actinopterygians are found in both freshwater and saltwater, many freshwater species have direct sister species in marine habitats (Seehausen and Wagner 2014), such as in the fish faunas of Iceland, New Zealand, Madagascar and Australia (Lévêque et al. 2008). Furthermore, freshwater sub-species may arise from the same marine species several times, as in the case of the threespine stickleback (Gasterosteus aculeatus) species complex (Jones et al. 2012). In this paper, I shall examine the scientific literature to see what kinds of biological factors influence the adaptation of fish to new environments, such as the landlocking process. These could include things such as changes in water salinity, presence of pathogen or predator species (Choi et al. 2013; Perry et al. 2022), changes in lifestyle, geographical location (mainland or island populations), epigenetic factors, and sex-based differences (for example the disproportionate dispersal of one sex due to mating) (Hutchings and Gerber 2002). Furthermore, molecular baraminological analyses will be performed to verify whether freshwater and saltwater species exist within the same kind. This will be done by calculating the sequence similarity between the mitochondrial genome sequences of various fish species within a selected group. Then, clusters will be formed based on these sequence similarities. Species membership of these putative baramins will be checked against ecological annotation from FishBase to see the distribution of species that live in freshwater, brackish water, and saltwater. CSERHATI Molecular baraminology of fish 2023 ICC 182
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