Sangeetha Pulapaka

Since there are no equations given to choose from, the equation which would best describe this will be,

p = 3000 \cdot\Big( \frac{1}{10}\Big)^{t} where p is the population of the fish, and t is the number of years.

This is an exponential decay function as you can see, with a decay factor of \frac{1}{10}.