The 6 tagged fish among the 80 caught reflects the proportion of tagged fish to the lake population.

For instance, we'd expect about 3 in 40 to be tagged, or 12 in 160 based on that.

Hence the ratios ought be approximately equal.

By catching a number of fish initially and tagging them,

a certain proportion or percentage of tagged fish to the entire fish population of the lake has been established.

Then, the number of fish caught that have tags afterwards should about reflect that proportion.

The group ratio ought to approximately reflect the population ratio "on average".