If an organism has high biological fitness in one environment, does that mean that it would also have high biological fitness in another environment? Why or why not?

The answer is no, high biological fitness in one environment doesn't have to be high in another environment. Biological fitness is a term used in evolutionary biology and it is the quantitative representation of how a genotype (or phenotype) is successful (reproductively) in a certain environment. The biological fitness of an organism is dependent on its ability to survive and reproduce in a given environment. If different traits or alleles increase the fitness of an organism, those alleles will consequently increase in the gene pool, and that trait will increase in the population.

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-Dream