This is not complicated as others suggest Mark. Blocks similar to the following snippet should work. The snipped has to be adapted to your programming.
is produced with code like this
Click on a green runtime Marker, the customMarker appears and a larger sized image. Both images display for 20 seconds using a Clock initially in a TimerEnabled state of false and a TimeInterval of 20000 ms (20 seconds). Clicking the green icon displays the images for 20 seconds. A delay procedure is not required.
You have to photograph and catch your fish yourself. Provide appropriate code to make a reduced size image of your fish (for your customMarker). The customMarker image wont scale, you have to provide a copy of the image right sized. Perhaps display a 'full' size image if you want as shown in the example. The images in my example are stored in Media.
Experiment and try some Blocks. What you do depends on how you handle your List of image components (called newMarker in this simple example). If you have issues, share your Blocks and someone might have advice.
This approach works with design time Markers. The same effect is easier to achieve using runtime markers.