What fraction of the energy from one trophic level carries up to the next trophic level?

One-tenth .

Explanation:

Energy flow in an ecosystem is is determined by two basic laws of thermodynamics; the first law of thermodynamics and second law of thermodynamics.According to the second law of thermodynamics, there is a gradual decrease in energy at successive trophic levels.It is so because at each transfer, about 80-90% of energy available at lower trophic level is used to overcome its entropy and to perform metabolic activities.Only one-tenth (10%) of the total energy is carried up to the next trophic level.The law governing the retaining of only 10% of chemical energy at each trophic level is called ten percent law.

In the above case we can understand that,

If the pH of the water increases the population of Minnows decreases.Minnows population can be determined by the acidity of the lake water.Minnows cannot survive in basic water.