On day five of creation God created fish and bird. This is described in Genesis 1:20-23 as follows.
20 Then God said, “Let the waters abound with an abundance of living creatures. Let birds fly above the earth across the face of the firmament of the heavens.” 21 So God created great sea creatures and every living thing that moves, with which the waters abounded, according to their kind, and every winged bird according to its kind. And God saw that it was good. 22 And God blessed them, saying, “Be fruitful and multiply, and fill the waters in the seas, and let birds multiply on the earth.” 23 So the evening and the morning were the fifth day. NKJV
On day three of creation, God created plant life. Plant life is stationary and does not change location under its own propulsion. On day four, He created the Sun, the Moon and the Stars to light the earth and provide the seasons. With all of this now in place, God created every living thing that moves within water and air. The Hebrew word for “move” in this passage means to glide, creep, crawl or move. Thus, the fish and bird all move under their own propulsion.
Everything that moves within water includes everything from the simplest one cell organism to the massive sea creatures. This can be summarized as follows: “Marine life consists of the tiniest single-celled plankton to the blue whale, which is the largest animal on Earth”…“Phytoplankton and algae form the bases of aquatic food webs. They are eaten by primary consumers like zooplankton, small fish, and crustaceans. Primary consumers are in turn eaten by fish, small sharks, corals, and baleen whales. Top ocean predators include large sharks, billfish, dolphins, toothed whales, and large seals. Humans consume aquatic life from every section of this food web.” https://www.noaa.gov/education/resource-collections/marine-life .
After day five of creation, the waters “abound” with the “abundance” of living creatures. And, our oceans certainly abound with the abundance of living creatures today. Just look at videos of schools of fishes on the internet. The amount of fish in these schools is massive. The following examples demonstrate just how abundant is marine life. The Grey Grouper lays up to 340 million eggs in one spawn. similarly, the Mola lays up to 300 million eggs. And, the Bluefin Tuna lays up to 10 million eggs. Thus, the oceans are so plentiful with life it is highly unlikely consumption could ever deplete life in the oceans.
Every winged bird on earth could include anything that moves through the air on wings, including birds, dinosaurs, insects, etc. It can be translated as every flying creature. However, most English translations, translate this as “birds.” ScienceDaily.com estimates living species of birds on earth to be between 9,000 and 20,000. https://www.sciencedaily.com/releases/2016/12/161212133645.htm .
Taxonomists (those who classify and name species) estimate the total number of species on earth to be between 3 million and 100 million. One model-based prediction estimates there are 8.74 million species of single and multi-celled organisms containing DNA (Eucaryotes) on earth. The same model estimates 2.21 million of these exist in the world’s oceans. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3160336/ .
According to the Catalogue of Life 2021, over 2 million species on Earth have been identified so far. This includes 1.9 million species living and 1 million species extinct. https://www.catalogueoflife.org/2021/07/29/release . Also, over 50% of the named living species on earth are insects. And, some scientists estimate that over 90% of the species on Earth have not yet been identified.
Once again, God commanded the fish and bird to reproduce according to their own kind. Consistent with this command, each living thing within water and all the birds are of distinct species. No evidence exists to suggest any new species have spontaneously generated except in the original creation under God’s command. Said another way, a horse and a donkey, which is similar in class can breed. But because they are different species, the resulting mule is sterile, infertile and unable to reproduce as a new species. No observable evidence of cross-speciation exists. And, the fossil record does not support a theory of cross-speciation either. In short, fish and bird remain fish and bird.
With the first five days of creation complete, the earth existed in a fully habitable state. God finishes His creation on day six with the creation of land animals and humans.