Answer:
the dissolved oxygen of the water decreases.
the fish need the oxygen for respiration, breathing through their gills.
Explanation:
The salinity decreasing doesn't affect the pickerel, because it's a freshwater fish. no salt needed.
more light penetrating the water just means that more aquatic weed or grasses would grow, giving the pickerel more area to spawn their eggs.
temperature increase in the summer has no affect on the fish, since the spawning happens in late winter.
Dominant' traits will actually disappear faster if they are disadvantageous.
Think about it: if everyone who has even a single copy of a particular allele is at a disadvantage (manifests the phenotype, in this case six fingers), then even single copies are selected against.
In the case of recessive traits, selection occurs only against homozygous carriers, who may be very rare if the allele itself is rare.
A concrete example would be something like Tay-Sachs disease. If the allele that causes this were dominant, every carrier would die before adulthood, and it would occur only as a very rare de novo mutation. But because it is recessive, it persists for now; heterozygous carriers have no disadvantage.
First one is correct. ...remeber my teacher telling us enzymes never get used
