"You learn something new every day." Today's lesson: Swai.

I was visiting with my grandmother, and we were watching "Chopped", a game show on the food network that she likes.  They were cooking with char, and she asked me a two-word question: "What's that?"

Now, this, I actually already knew.  During Lent this year, I had purchased whatever fish happened to be cheapest.  At our local grocery store, that included char.  I told her that it tasted very good.  It was pink, like salmon, but that it tasted more like trout.

Then came the three-word question: "Can fish cross-breed?"  This time, I had no idea. I told Granner that I would go down to the grocery store, and see if they still had Char in stock.  They did not.  They did have swai, which I purchased and cooked for her. She asked me to use my research skills and find out, for our discussion tomorrow, if fish could cross-breed.

(Posting the answer here will not spoil the surprise in any way, since Granner doesn't use the internet.)

So, swai is also known as the Iridescent Shark, although it is actually a catfish that lives in the rivers of Southeast Asia.  Char, also called Arctic Char, is found in freshwater northern lakes, including Loch Ness. It is a memeber of the family Salmonidae, which includes whitefish, salmon, and trout.  I felt rather proud of my unofficial, uneducated comment that it was "between a salmon and a trout", after I found out that, yeah, it pretty much is.

So although Char is considered its own fish, the answer is a surprising yes: breeds within the same species are capable of cross-breeding.  The reason that we don't see much cross-breeding in the wild is because the offspring don't always survive.  Even when they do, they would almost always be so outnumbered by the "normal" fish that they aren't often discovered. If, for example, a whitefish and a trout cross-breed, and 20 of the eggs survive and grow to adulthood, in a lake system with hundreds of purebred whitefish and purebred trout, chances are slim that one of these 20 is caught by a fisherman who doesn't just call it a trout. 

In aquariums, fish within the same species will often interbreed.  The result is goldfish with a remarkable range of colorings.

One traveler of the information highway put it this way: "If you want to know if two fish can inter-breed, look at the Latin name of each.  If the first word in the Latin name is the same, then cross-breeding is possible."  Surprisingly, Wikipedia notes that Swai, the "Iridescent Shark", may not actually be a separate species of catfish, but may, in fact, be a sub-species, the result of cross-breeding from two different types of catfish.

So, I have an answer for my grandmother, and I have learned something new today.  Fish can cross-breed, but it is not extremely common.