Stability and existence of periodic solutions for a time-varying fishing model with delay

In this paper, we study the stability and existence of periodic solutions for a time-varying fishing model with delay Ṅ(t)=N(t)[a(t)1+(N(θ(t))K(t))γ−b(t)], and obtain a necessary and sufficient condition for the existence of periodic solutions and “the best possible” conditions for global attractivity for the above equation. These results improve the existing works in the literature.