Imagine that millions of years ago, there was a population of fish that could live in shallow water in a region with many shallow lakes. The lakes often reduced to a tiny puddle of mud in the summers. Many of the fish died in the summers. The only individuals that survived each year were those that were able to breathe in the muddy water, and also forage for food better than the others in the highly competitive environment. One day, a baby fish was born that was able to breathe air due to a genetic mutation. This fish reproduced and passed on its air-breathing genes to future generations. Soon, in the summers, more and more fish were surviving because the air-breathing fish were able to live on land and forage on land, and not have to compete with the water-living fish. What is the mechanism by which these air-breathing fish are increasing in numbers over the years

The mechanism is natural selection.

Explanation:

Natural selection is the mechanism that these air-breathing fishes have gone through to survive. This mechanism allows species to survive and reproduce due to differences in the phenotypes of every individual in the specie, throughout the time the heritable traits that every individual inherits changes according to the environment and the characteristics of its ancestors.

the mecanism is the selection natural

Explanation:

The mechanism of natural selection is based on the fact that the individual that survives is the one that is considered the most suitable for the environment, the adaptations of the most suitable species are through genetic mutations that generate new phenotypic expressions so as not to become extinct. In this case, the mutation that allowed the fish to breathe air and be able to transmit it to that gene through its parents is a genetic acquisition that expresses a favorable phenotype.

i don't know. if i were you, i would search it up online : d