Getting further, getting harder?

Is it just me or once you get closer to 400 fish you find it nearly impossible to find more new fish or being able to create w/what you have to get what you need? I really am captivated by this game, find it harder than the 1st Fish Tycoon but my 70 yr. old brain was way younger then. The most difficult at the moment, or the past wk. is more like it is finding the Spined Foxface, or for that matter anything Spined or Silky. Would appreciate any suggestions for your lessons of experience you might share or even "hint" at. Many Thanks!