How is a fish slice different than a spatula?
Table of contents
What is a Spatula?
First, what is a spatula? A lot of the kitchen utensils that we call spatulas are also known as turners. Check it out:

Both of the items in the photo above are commonly referred to as spatulas. The top left item is also called a turner, and, in this case, a slotted turner. Slotted turners are typically used to flip food in a pan or skillet, especially greasy foods such as hamburgers, fatty fish like salmon, and fish with skin.
For a detailed discussion about the terms spatula and turner, read this: Spatula vs Turner.
In other words, a slotted turner IS a fish slice. And, depending on which terminology you are using, a slotted turner is a fish slice is a spatula.
What is a Fish Slice Kitchen Tool?
A modern fish slice is the same item as a modern slotted turner. Take a look at this antique fish slice:

Fish Slice is an Outdated Term
If you are shopping for a fish slice and not having any luck, instead try shopping for a slotted turner or a fish turner. Fish turners are longer slotted turners that may help with handling fragile fish fillets.
For a detailed discussion on utensils like these, check out this article.

Is a Fish Slice a Good Kitchen Tool
Yes, a fish slice is a good kitchen tool. In fact, you probably already have one if you have a slotted turner, which may also be called a spatula. If you have a slotted turner/spatula, there is no need to buy a special “fish turner”; your slotted turner works in the exact same manner.
Summary
Fish slices are great, you probably already own one but don’t know it because you call it something else (maybe a turner or a spatula), they work really well, and any slotted turner will work perfectly as a fish slice. No need to buy a special “fish” turner.