To tell the difference between many different varieties of fish.
At the market:
Take your book to the fish market and try to find the distinguishing feature of each type of trout, salmon, or cod that is available.
Write down their proper Latin names.
See if you can find any fish that are mislabeled in the market.
If you go fishing:
Try to identify everything you catch. Keep track of the size and number of fish you catch. Write down the depth, water temperature and time of day.
Keeping records like this is not only scientific, it will help you catch more fish because you’ll be able to check your records and know where and how to catch more fish the next time you go to a particular spot.